NiMh 3x AAA batteries charging circuit - Page 1
Forum section: electronics / beginners

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 06:05:24 pm
content: Hello,kindly check suggested schematic in attachments.I have a device which has clock battery that I need to have this mod board designed for it. it uses ML2032 battery originally but it is not so reliable.it outputs 3~3.1v or so to the point, and has that 3v battery connected to it by about 15 ohms resistor.I made the suggested replacement circuit which removes old battery and 15 ohm resistor and puts all this instead.My points of question are:1- 3x AAA NiMh batteries will be nominal 3.6v which is clearly above 3v, assume charging voltage is 3~3.1v or max of 3.3v... can this be ok to the battery pack? like, the individual battery will be around 1v each or a bit more.2- to make it 3.3v regulated, I added the zener circuit. is it correct? it must protect the device during charge or discharge. I am not sure it tolerates 3.6v. I could make the zener 3.1v if necessary. should I change zener resistor? so that it does not draw much current from the battery.originally I wanted to use one 18650 li-ion battery but it will get complicated to charge\discharge\protect it. then 2x AAA NiMh batteries charged to 3 or 3.1v but this could be dangerous to them right? I mean each battery is going to be 1.5v or up to 1.65v if 3v charging or 3.3v charging voltage respectively.any suggestions?best regards

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 04, 2023, 06:36:30 pm
content: No, this is not a good design.NiMh batteries need to rise to 1.5v or so to be fully charged, so 2 would be better than 3 for this reason.The zener shunt regulator is counter productive and increases current drain from the battery unnecessarily.Post a schematic of the original circuit and maybe we can come up with the proper solution. We really need to know the lower and upper bounds of the voltage that this clock can work at and more details on the power source for charging.

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 06:44:09 pm
content: Quote from: Kim Christensen on March 04, 2023, 06:36:30 pmputting 2 is ok and even better for me.original is dreamcast controller board having what I posted above, ML2032 battery then 15R resistor to the charging\discharging point. this point takes from battery when device is off, and takes power from device's power supply when it is on (and battery get charged).I put 3 so that if 2 were used with nominal voltage, it will be 1.2v each = 2.4v which I think is not enough for clock battery. so I tried to stick to original design of 3v.My first question was about if it is ok not to fully charge the batteries, but rather keep them at about 3v (assuming 3 batteries). i mean in terms of safety first, then charge retain or performance.

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 07:17:35 pm
content: I found original circuit, it is in attachments.it has 3.3v internally, connected to a diode which makes it roughly 3.1v which is the power needed to sustain real-time clock. it is BVCC.so we can assume it will be 3.1v max, but right now the battery is so drained and i am reading about 2.74v at that pin.that pin (via ribbon cable) goes from main motherboard to the controller board which has the battery. from there it is connected to 15R resistor and to the battery in series, very simple.can this really work with 2 NiMh batteries without extra protection\charging circuitry?I mean maximum of 3.1v will be about 1.55v for each battery and assume long time it will retain such high voltages... won't it be destroyed? or in this case isn't 3 in series better?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 04, 2023, 08:04:26 pm
content: Well you can safely trickle charge NiMh forever at 0.05C... So that means that a 800mAh AAA cell can take 40mA (800 * 0.05) continuous charge.Assuming I've understood you correctly, the batteries are attached as I've drawn it in the edited schematic below?That would mean the batteries are charged from the 3.3V supply via R612 (130) D603 and a 15resistor all in series. This would mean that the battery current would be well below 40mA for any battery voltage...

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 08:19:26 pm
content: Quote from: Kim Christensen on March 04, 2023, 08:04:26 pmyour drawing is correct, however now only one ML2032 battery (3v) which I intend of replacing it with 2x AAA NiMH batteries.my understanding was that it gets 3.1v via diode D601, but also the same point is tied to the end of diode D603. could it be that it gets 2 different charging voltages this way?but for us 3.1v is the maximum, so can 2x AAA NiMH work in this situation?I mean charging them with this very slow way could take a lot... of which maybe the device could be shutdown before they reach 1.5v then it would not be enough to power the real-time clock circuit?edit: the series resistor could be 10-11 ohms since my multimeter reads this now. color coding of it shows 13 ohms 5%.

author: Rick Law
author_rank: Super Contributor
timestamp: March 04, 2023, 08:27:15 pm
content: Quote from: VEGETA on March 04, 2023, 06:44:09 pmThat is a problem I come across with NiMH often also - 2 is not enough and 3 is too many. While freshly charged NiMH is >= 1.5v, but depending on make, it drops rather quickly from 1.5V. Most of the energy coming out is delivered at or around 1.2v to 1.3v.I have a device that starts choking at about 2.5v and shuts down under that. Some Energizer "Green" delivers most of it energy at around 1.3v, so voltage was good but it holds less mAH so it doesn't run so long. My TEnergy (Eneloop clone, so they said) acts rather like an Eneloop delivered most of it's energy at around just above 1.2v. So while my TEnergy holds higher mAH even in my own discharge test, I get even less run time from them on this device.It will benefit you a great deal totest howyour NiMHbattery works. Surely you don't have to full-charge a battery. But even if you are to charge to only 3V, it may take higher than 3v to charge it to 3v.Another important factor is -- at 3v, it may hold very little energy. With some batteries, it will drop off like a cliff after the "most energy discharge at" voltage. If yours delivers most of it's energy at (say for example) > 1.3v, you are in rather good shape with just two. If you use 3 of them, since most energy is discharge at our example of 1.3v (3x1.3v=3.9v), your three batteries at 3v may well hold less than what a pair of fully charged hold.Unlike typical Lithium Ion (18650 and some phone batteries), some lithium polymer batteries charges to only 3V. They may work out better. I have not found one that fits the space I got, so form factor could be a problem for you as well.

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 08:38:49 pm
content: Quote from: Rick Law on March 04, 2023, 08:27:15 pmthe point is I need easily found batteries for people to use, since this project will sell very good if it succeeds. Li-Po or so may not be that, NiMH are ok, and 18650 is better but 18650 as mentioned needs more circuitry especially that it should be charged with 3.1v and discharged to 3v... meaning 2 circuits with interlock between them. I can't simply put the cell there with its nominal 3.7v to be used and charged with 3.1v without protection.according to your analysis, if using 3 batteries with nominals of 1.2 will be 3.6v, but with 3.1v charging they will be about 1~1.05v each, I guess this is too little right?if they can hold charge well, then no problem since discharge will be so small because very little current needed.but assuming 2 batteries -> 3.1v will be 1.55v each which could drop to 1.5 or minimum of 1.45... again if it retains this for long time no problem but will it?what do you suggest for using a readily available easily found batteries which won't be a hassle to design circuits for?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 04, 2023, 09:00:48 pm
content: Quote from: VEGETA on March 04, 2023, 08:19:26 pmD601 provides power to the clock circuitry and D603 routes charging current to the battery when the power is on.When the power is off, D602 routes power from the battery to the clock circuitry and D601 & D603 are reverse biased and prevent the battery voltage from back-feeding the 3.3V rail.QuoteAAA cells have way more capacity than needed. The charge current for them would probably be too low. Also, you would have to experiment to see how low a voltage the clock can work with because of NiMh's lower nominal voltage.I doubt this clock circuit takes much power at all, which is why the original ML2032 battery was so small (65mAh). I mean, you could probably just disable the charging circuitry by removing R612 or D603 and two AAA alkaline batteries would power it for years (Probably last as long as their shelf life), or use some non rechargeable Lithium cell which will outlast the equipment itself...

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 09:19:32 pm
content: Quotebut BVCC is at the 2 sides of D602, how does that work here as you explained?Quoteat 1.2v nominal = 2.4v which is too low. and for 3 batteries 1v each is too low per battery.Quoteyes it does not take much at all but 65mA battery was rechargeable and its datasheet or guide says it cannot hold the charge more than 20 days or so, thus you need to use the console regularly.such mods already exists, to use CR2032 battery with a diode to block charging.. here is my recent video about it:however, this solution I need to make is to solve this issue not go around it. alkaline batteries tend to leak which is bad, not very good solution overall, even small cr2032 is better.therefore I found NiMH to be better alternative since they have much capacity and can hold the charge for very long + available easily + do not need special charging and protection circuitry.I could later on try to make 18650 solution but it needs more head usage, now I am very comfortable with using NiMH.if you say charging is the problem then I could either remove the 13 ohm resistor or at least make it something like 3.3R or 4.7R to make charging faster.

author: VEGETA
author_rank: Super Contributor
timestamp: March 04, 2023, 09:47:58 pm
content: as for my complicated circuit for 18650 battery implementation, here is the current idea in attachments.the key is the analog switch which gets activated by external 5v point in the board. this 5v does not work when the system is off, therefore LDO (discharge) circuit is the active one when the system is off. when on, 5v is there and it switches to boost+charger circuit.of course i could put the analog switch before them both, at that node just at the output of the battery to prevent ldo quiescent current... but even if it is like this, the boost+charger will supply more than enough current to charge the battery and cover such low current for LDO when its output is disconnected.what do you think?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 04, 2023, 11:32:59 pm
content: Quote from: VEGETA on March 04, 2023, 09:19:32 pmDon't be misled by the B.VCC label. B.VCC on CN601 isnotthe same point as the B.VCC that you drew a red arrow pointing to. This is just poor labeling by the schematic creator.ie: There isnota short circuit between TP608 and TP619 nor is D602 shorted out.QuoteSo how long does the CR2032 battery last in your modded Dreamcast?QuoteI think your circuit is overly complicated for what it needs to do. Since you also have access to the 5V supply, you could trickle charge a 3 cell NiMH stack and then use an ultra low power LDO to drop the voltage to 3V... (Remove D603 to prevent back feeding the LDO. If you add another diode like you did in the video, you're going to add unnecessary voltage drop)If you wanted to use a 18650 (I'd use a much smaller lithium cell) you could charge it from 5V via a TP4056 Lithium Battery Charger Module (Change current setting resistor as required. 1A might be too much extra load on the Dreamcast's 5V supply).

author: VEGETA
author_rank: Super Contributor
timestamp: March 05, 2023, 03:59:55 am
content: Quotei see your point now. it is bad labeling for sure.QuoteI just installed it some 3 days ago, I'll see how much it stays.Quotewell, using 5v is a good idea. the 5v rail is not used much anyway so I can use it, 100mA charging is very much doable.the idea is to not touch the motherboard, so no removing is required. the users should just solder the mod board in place after desoldering some components and it should work perfectly fine.if I use 5v rail with 3xAAA batteries, shouldn't I use an LDO to lower it down to about 3.6v for the 3 cells? or to how much does it need to be lowered for optimal performance?then I can use an LDO to further regulate the 3.6v down to 3.2v -> then use a schottky diode which will get it to about 3v + prevent charging back the LDO.I think this works right?Quotedoing the same as previous idea but for 18650 is also doable since I did some measurements and I think 18650 can fit there.All components should be on board, no modules or off-the-shelf modules to be used.as for 18650, it does need a charger and protection ICs, so a total of 2 right? or is there 2 in 1 solution for that?using 18650 is easiest since it is very well available to all people, they can find it everywhere which is a requirement for this design. they are even more available than NiMH batteries.so I will redraw the circuit using 5v source, but I need to decide which type of battery to use.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 05, 2023, 06:10:25 am
content: QuoteTo charge 3 NiMh AAA cells from the 5V rail, you could just use a Schottky diode and resistor in series. Assuming 0.3V diode drop and a 18resistor: When the AAAs are fully discharged (1V per cell) then the charge current would be 95mA and when nearly fully charged (1.5V per cell) the current would taper to around 11mA... The voltage doesn't need to be regulated because the battery will do that. That's the simplicity of trickle charging. Worst case failure mode (all 3 cells shorted) would mean 260mA could be drawn from the 5V rail.Then you just need a single LDO to take the variable 3 - 4.5V from the 3 NiMh AAA cells and reduce it to 3V... The LDO may be OK with some back feeding because the current would be limited by R612 on the motherboard. The advantage of not adding a diode after the LDO is that the voltage to the "clock" will not drop below 3V as soon as it would when the AAA cells are nearly discharged. (Remember at a nominal 1.2V per cell, you'll only have 3.6V to work with) So it'll depend on which LDO you choose.QuoteYou could just copy the same basic circuitry that's on those modules. They are pretty standard chips. One of them is the charger IC (TP4056) and the other is a protection IC (DW01A) and there's a dual MOSFET too.https://www.sunrom.com/p/lithum-battery-charger-with-protection-microusb

author: VEGETA
author_rank: Super Contributor
timestamp: March 05, 2023, 06:50:22 am
content: I will surely investigate more on the trickle charging you mentioned, seems simple enough. despite i am concerned on back-feeding the LDO.Quoteinstead, I went and done more research and found these parts:battery protection: BQ29732DSERbattery charger: MCP73812Tdual mosfet: still didn't search but should be very easy.LDO: MIC5365-3.3shottkey diode: still didn't search but should be very easy.here all parts are of high quality proven brands.LDO is 3.3v followed by a shottkey diode of 0.2v~0.3v dropout to be 3~3.1v final result. here the chosen battery is 18650 which will work very well with such very low current consumption.3.3v taken from nominal 3.7 with extremely low current demand is suitable. with this battery charger, i can use 4.7k resistor to set charging current to roughly 212mA which will charge the cell rather quickly to 4.2v maximum. even if play time was 1 hour that would still do good charging, even if i choose 100mA instead of 212mA. DC 5v rail is barely used anyway, people report it is around 500mA or less in total, so it can afford 100-250mA more.what do you think?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 05, 2023, 07:48:01 pm
content: QuoteTook a quick glance at the datasheets.One concern would be that the battery charger IC MCP73812T doesn't implement charge termination which will be hard on the battery. Because of the way this thing will be used, you might be better off with a charger IC that lets you change the constant voltage setting to something a bit lower than 4.2V... Essentially you'll be constantly topping the 18650 up to 100% and that will reduce it's lifespan unnecessarily. But, either way, you really need an IC that implements charge termination.MCP73812T:Quote

author: mariush
author_rank: Super Contributor
timestamp: March 05, 2023, 08:06:56 pm
content: There's smarter charge controllers, like for example MCP7387x series , which has built in charge termination and also system load sharing - if it has input, it passes through the input while charging battery, if the input is gone, it outputs from battery.Chips on digikey :https://www.digikey.com/short/m1j32d0jDatasheet :https://ww1.microchip.com/downloads/en/DeviceDoc/MCP73871-Data-Sheet-20002090E.pdf

author: VEGETA
author_rank: Super Contributor
timestamp: March 05, 2023, 08:15:04 pm
content: if that is a concern then I found this part: MCP73841-410I/UNwhich is maximum charging of 4.1v, but it is 3 times more expensive. I wish I could find one as cheap as previous option.there is also this one from TI: BQ25170DSGR but also not cheap.for you suggestion of better part.I guess I can use a battery monitor protector IC that has lower cuttoff but this will affect the circuit right? I mean if battery is cut, the charger will be just feeding the LDO and could stop working if voltage suddenly fluctuated??I will post my first schematic tomorrow.Quoteseems better and more advanced, but also more pricey. also has that thermistor thing which i don't need nor want to use.i will let you see my suggested schematic tomorrow and then we'll check what is better choice.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 05, 2023, 09:30:39 pm
content: QuoteThat wouldn't be a good idea because it will shut charging off well before the current drops and who knows what charge state the battery will end up with. Better to choose the right charge controller IC.QuoteYou could put an ordinary resistor in place of where the thermistor would go. I guess what it comes down to is price vs availability vs features and only you can determine that.

author: VEGETA
author_rank: Super Contributor
timestamp: March 05, 2023, 09:41:44 pm
content: I have found these new alternative ICs:MCP73830L -> CV\CC charging with charge termination. price-wise is less than other suggestions, and it has as it looks like automatic charge termination once the charge reaches 7.5% or 10% of total defined amount... still can't figure out how to set it but overall won't make much difference for me.

author: VEGETA
author_rank: Super Contributor
timestamp: March 06, 2023, 06:13:23 pm
content: here is my preliminary schematic.I changed charger to MCP73830L for better termination.1.8K ohm PROG resistor means 111mA charging current... very suitable IMO.what do you think?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 07, 2023, 12:12:07 am
content: I've made some notes on your schematic:

author: VEGETA
author_rank: Super Contributor
timestamp: March 07, 2023, 04:21:01 am
content: hello,here are my comments:1- missing connection: what is the missing connection? this is the negative side of the pack and should be ground.2- datasheet says 0.1uF: I will adjust it for sure, unless it allows for bigger value. I will check.3- not sure why you need this resistor: it is irrelevant to this circuit. this resistor and the fuse + C1 are parts on the original board. the mod board to be installed have the replacement parts so the user should remove these 3 and solder the mod board in their place instead.4- not sure about logic here: 47uF is to be removed since not needed much but 10uF ceramic is needed. your point is that it is big but I put it since it does not hurt to be big. I didn't want to add another BOM line for this, so I used the already used part which should not affect the circuit. do you think it will negatively affect the circuit?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 07, 2023, 05:09:02 am
content: QuoteI drew the ground symbol in for you (Connected to Q1 source, R3 & C4). It was missing in your original diagram.QuoteOk, but that's a strange way to draw it because it looks like you areaddingthose parts to the mod board.Quote10uF should be OK. Makes sense to shrink the BOM list.

author: VEGETA
author_rank: Super Contributor
timestamp: March 07, 2023, 05:21:13 am
content: Quotehhh I feel embarrassed xD. you drew the GND to look like it was already there, very nice drawing. I will add GND for sure.Quoteyes i didn't mention it before, but now kindly check the image where I pointed out their placement.Quoteyes, 10uF is nice value and will be same price and footprint anyway.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 07, 2023, 06:19:16 am
content: Quote from: VEGETA on March 07, 2023, 05:21:13 amI see them... I'm not an user of KiCAD but, by putting those parts on your schematic, doesn't that add them to the PCB you'll be making?ie: Aren't those components (resistor and the fuse + C1) going to be staying on the original board?

author: VEGETA
author_rank: Super Contributor
timestamp: March 07, 2023, 06:30:16 am
content: Quote from: Kim Christensen on March 07, 2023, 06:19:16 amnow i know i didn't explain better, so here it is:the user who will buy the mod board must de-solder the existing mentioned components (47uF cap + fuse + 13R resistor + ML2032 battery) then solder the mod board in their place. the mod board will have solder through hole pads perfectly aligned to those components' pads but a little bit larger so that the use aligns the mod board then solder it perfectly in place.now the mod board will have similar old components (47uF cap + 13R resistor + fuse) PLUS the circuit we mentioned here which includes new battery and its charging, protection, and LDO stuff. Now functionality will be the same as before but with longer life battery, significantly better design and components, as well as, final solution to this annoying problem which is better than any other mod available.

author: mariush
author_rank: Super Contributor
timestamp: March 07, 2023, 08:26:27 am
content: How about3v.. 3.3v - > voltage doubler IC to get 5.5-6v - > charger IC for lithium battery (requires 4.5v ... 7v) -> (optional source auto-switch - or controller) -> ldo to 3v to simulate the battery1. 3v...3.3v -> lm2665/alternatives -> 5.5v-6vA cheap voltage doubler IC will do 40mA so it's safe to slowly charge the lithium battery provided you can program the charger ic to slow charge, the MCP73830L can do as little as 20mAFor example LM2665 can do 40mA and only needs a diode and two ceramic capacitors to double the voltage :https://www.digikey.com/en/products/detail/texas-instruments/LM2665M6X-NOPB/3668832. 5.5.. 6v - > mcp73830L charger (optionally add a diode on input to make sure you don't go above 6v, but absolute max voltage is 7v for this charger ic)Set it to 20-40mA (probably less than 40mA if you go with the 40mA lm2665) and it should slowly charge the battery.Instead of a plain LDO, you could use a device likeTPS22293or something simpler (and cheaper) :https://www.digikey.com/en/products/detail/texas-instruments/TPS22933ARSET/3725886This one's $0.85 in quantity so not super expensive.Here's datasheet :https://www.ti.com/lit/ds/symlink/tps22933.pdfIt has 3 input voltages and auto-switches to highest voltage available, so you could have one input the output of the voltage doubler and the second input the lithium battery voltage.If the device is turned on, you get that higher voltage and the battery is not connected to anything and the charger can properly top up the battery and terminate charging (otherwise the linear regulator would take a very low amount of current from battery all the time)The chip also has a fixed 3.6v LDO capable of 50mA, so you'd also save on the LDO part ... just add a diode in series with the output to drop half a volt to get around 3v to fake the ml2032 battery.Something else to consider... the ML2032 can't really source a lot of current anyway, so I think it should be fairly safe to just have the ldo always connected to the lithium battery even when battery is charging

author: VEGETA
author_rank: Super Contributor
timestamp: March 07, 2023, 11:37:13 am
content: QuoteI couldn't fully understand the thing you are trying to achieve instead of what was suggested in schematic above.I mean why get a voltage doubler IC to get 5v where I can get 5v directly from the main board itself?notice that the 3-3.3v source you are using is the same point which needs to be connected to the output of LDO to supply such voltage and power to internal clock circuitry... taking this voltage while console is on then doubling it then feeding it through switch\regulator ic then back again to the same point does not seem ok to me.while my suggestion above uses a different rail and different point as a source... the currently used parts prices seems ok to me. I could still change some and use a similar auto-switch as yours if it reduces the total cost by good amount with same reliability. However, it will take 5v directly from the board itself just like I did above... then feed the charger and switch. so here I will be saving the price of LDO.do based on your suggestion:5v rail -> charger -> battery (which is connected to protection IC) -> auto-switch (+ regulator)5v rail -> auto-switch (+ regulator).auto-switch -> diode (0.5-0.6v so no schottky)correct?what benefit can this do instead of old design?EDIT: i found one potential killer for this idea, which is the LDO is 3.6v while new cells are nominal 3.7v which means the drop is 0.1v. it is too low and requires really nice low dropout LDO which might not be the case with this IC's internal one.

author: mariush
author_rank: Super Contributor
timestamp: March 07, 2023, 01:34:25 pm
content: I didn't read all the previous messages, so I wasn't sure you have 5v available. If that's the case, it's even simpler.The LDO's dropout voltage is 0.11v at 10mA, according to datasheet. So 3.7v required to output stable 3.6v. But, considering you don't really care about how stable it is, because you want in the end some voltage around 3v... and it's not like the regulator will turn itself off, it will just output less voltage.See page 5, the note at the bottom :QuoteYour lithium battery will be for most of its life at around 3.75v, so you won't care if it gets close to 3.6v, you'll just have 3.5v at the output ... drop 0.5v with a diode and you have your 3v.I think you'd need to also have a connection from battery to the enable pin for the ldo through a diode (to protect from 5v from input) and from 5v to enable so that the ldo will always be on.A BAT854 for example would serve both purposes, drop around 0.5v for your output, and for enabling the regulator while protecting battery from input voltagehttps://www.digikey.com/en/products/detail/nexperia-usa-inc/BAT854AW-115/1232136Plain BAT54A would also work and it's like 5 cents in quantity, gets you around 0.4v drop at 20-40mA :https://www.digikey.com/en/products/detail/panjit-international-inc/BAT54A-R1-00001/14660174ps. also you may want to consider the discharge curve of a ml2032 :https://www.maxell.com.tw/images/uploads/2015/05/ML2032_DataSheet_table.pdfThe designers of that product you have for sure have considered that if the device is not used for a few weeks, the cell may discharge and hover at around 2.75v, maybe even 2.5v ... so you don't really need to be that super strict about your circuit output exactly 3v. It could be much less and still work well.So you could probably even use a plain boring 1n400x diode that will drop around 0.6-0.8v at that low current amount.

author: VEGETA
author_rank: Super Contributor
timestamp: March 07, 2023, 03:15:16 pm
content: QuoteI still think previous design is simple enough.Quotethat could work too. but as soon as the battery starts charging it will go above 3.7 which will be fine.QuoteI checked datasheet for TPS22933 and it doesn't need that since it has LOUT which is the "always-on" LDO output while VOUT is the switched output via internal FET. using LOUT is the way to go with this IC.Quotethe biggest con of this design is that you always need it to be on within 2-3 weeks for some time to charge the battery or it will lose charge and you will have to reset the clock everytime...etc.I can afford to use a good diode though with my suggested 3.3v regulator to be 2.9~3.1v which is very good. as you said exact value is not needed.I looked for alternatives for TPS22933 but most of them are pricey and would just replace the LDO. the LDO I use is this:https://www.digikey.com/en/products/detail/microchip-technology/MIC5365-3-3YC5-TR/1868094it is very nice with ultra low dropout at < 0.2$ each...

author: VEGETA
author_rank: Super Contributor
timestamp: March 12, 2023, 06:17:58 am
content: a quick note on MCP73830L: i saw in datasheet that it has automatic recharge or no automatic recharge options available from factory but couldn't find part number specification to ensure I got the automatic recharge one.other possible alternatives:MCP73832T-2DCI/MC-> has charge termination + automatic recharge and very cheap. chosen part number has 4.2v charge, no Preconditioning Current Regulation (Trickle Charge Constant-Current Mode), 7.5% Charge Termination Current Ratio, 96.5% Recharge Voltage Threshold Ratio, and 8-VFDFN Exposed pad package since it has better thermal capabilities. charge status could be put to ground via 10k resistor since i won't need it. it is very cheap! like 0.84$ per single chip.^ this seems to tick all boxes while being cheapest.BQ25170: very famous but more pricey at 1.84$ per one IC.I think going with MCP73832T-2DCI/MC is best choice. do you agree?suggested N-mosfets till now:single:https://www.digikey.com/en/products/detail/nexperia-usa-inc/PMN16XNEX/5981374dual:https://www.digikey.com/en/products/detail/diodes-incorporated/DMG6968UDM-7/2075441

author: VEGETA
author_rank: Super Contributor
timestamp: March 12, 2023, 04:53:59 pm
content: Hello,did some updates:- final schottky diode is RB751V40,115 which has constant 370mV dropout. final voltage will be 3.3-0.37v which is about 2.93v, good.- changed charger to MCP73832T-2DCI/MC as indicated above. cheapest option with all features included especially charge termination and automatic recharge. basically perfect fit. 10k resistor = 100 mA charging current.- used DMG6968UDM-7 dual N-mosfet package for protection.- did many re-arrangements to fit everything nicely. now most stuff will be under the battery as PCB shape has to be this small and ultra compact due to no space inside.please check it out and give me your opinion.BTW, all these KiCAD warning arrows are for connecting power or signal traces to unspecified pin... very annoying despite putting power flag thing.also for 100mA charge current, assume the cell is 3.7v now and it is 3000mAH capacity, how many minutes should pass before its voltage is up by 0.1v? I couldn't find calculators which can do this? this is to know how long will the battery take to be fully charged which helps if the battery itself is lower than required voltage and needs much time. I could increase the charge current but prefer not to exceed 200mA.

author: mariush
author_rank: Super Contributor
timestamp: March 12, 2023, 06:25:33 pm
content: I wouldn't put the charger IC under the battery footprint.It's not a big deal with the low charge currents, but the charger IC is a glorified regulator, so it's gonna make some heat, the battery's gonna warm up as it charges, no reason you should heat up the battery more with the charger IC.You could flip the battery so that battery+ is on the left side. This way battery negative is on the right, and you could position M1 above the battery holder, in the top right corner below the lightning picture. U3 could be shifted somewhere under the three through holes, under "Thunder"U1 could be shifted a bit to the right, andC3 could be to the left of U2, and R2 and R3 could be to the right of U2 ,and everything could be where u1 is , and u1 could be below the two through holes.C1 and F1 could be placed between those through holes , maybe where the "board" in "Advanced controller board" is ... you could shift "Advanced controller board" to the left and align it with the cutout.Something like in the attached picture. Maybe you could even move the "Advanced controller board" under the battery placeholder, and put thundertronics and the lightning logo there. so you have more room for the M1 and U3 in top right corner.With a bunch of vias to the bottom you could have the battery negative on the bottom side only until it goes through M1Don't understand the purpose of R4, if it could be optional maybe consider adding a way to disconnect that resistor? two pads close together so you could put a blob over the pads to enable the resistor?C5 at 47uF seems overkill ... maybe reuse a 10uF ... don't think you need capacitor, diode, capacitorMIC5306-3.0v is available on Digikey for under $1 :https://www.digikey.com/en/products/detail/microchip-technology/MIC5306-3-0YD5-TR/1834782edit: didn't notice F1 is connected directly to those through holes near it, without being inline with other stuff ... so in that case it would be fine positioned in that left top corner. Even less stuff to clutter the other side.

author: VEGETA
author_rank: Super Contributor
timestamp: March 12, 2023, 06:48:25 pm
content: The charger current is 100mA max, hard set by 10k resistor. will it heat the battery significantly though?however, your re-arrangements make sense and doable. I will remove silkscreen stuff and try to fit all electronics away from battery guided by your suggestions.Quoteit is part of the original circuit itself, a 13 ohm resistor to lower the charging current. it should be there and does not hurt really. I placed it between the pads which is the best and easiest way to do it.R4, C1, and F1 all are original parts in the original board and I must replace them with newer parts not remove them completely. I placed them between their respective pads.C1 is the main 5v rail filter cap to the whole board, was elec. cap but I want to replace it with tantalum.Quoteyes but it was very cheap so I thought of putting it... 10uF works fine too.Quoteif I wanted 3v reg I would have chosen the same part but with 3v, much cheaper:https://www.digikey.com/en/products/detail/microchip-technology/MIC5365-3-0YD5-TR/5283844but how about the reverse voltage protection?I mean when the console is on, it outputs about 3~3.1v at the other side of R4 which in previous circuit was the way ML2032 to be charged. Now if I put my 3v LDO there, 2 voltage sources will be shorted together and I don't want to risk anything going bad. what do you think?

author: VEGETA
author_rank: Super Contributor
timestamp: March 13, 2023, 07:22:36 am
content: on another note, should I be using this 47uF tantalum capacitor instead of just using 47uF electrolytic one like the one already installed? I think I can fit it in the board.what is the potential danger of using tantalum here where currents are certainly low (<300mA max)?I wanted to use the tantalum here for saving space (despite this can be managed easily) and to never have the problem of elec. caps leak\degrade overtime.

author: mariush
author_rank: Super Contributor
timestamp: March 13, 2023, 07:43:22 am
content: Ceramics are affected by voltage and temperature so they kinda suck with big values.But no need for tantalum...There's surface mount polymer capacitors available, for example :https://www.digikey.com/en/products/detail/aishi-capacitors/SA10JM470A19R25XXX/16536382Nothing wrong with electrolytic capacitors, there's quite small capacitors these days, you could lay one flat (horizontally) like a crystal /oscillator or even make a cutout in the pcb for the capacitor body if you need to, but you don't need to. At such low capacitance values and not being subjected to a lot of heat, electrolytic capacitors will have decades of life.ex .. 5mm diameter, 12.5mm length :https://www.digikey.com/en/products/detail/w%C3%BCrth-elektronik/860020472006/5727060orhttps://www.digikey.com/en/products/detail/kemet/ESH476M010AC3AA/13176036Oh, I wanted to add... it may be a good idea to add footprint for one of the connectors commonly used with those pouch cells just in case you or someone decides to not solder the battery holder and just use a flat battery attached to your board with some double sided adhesive tape. JST PH seems to be quite common, see for example some models here :https://www.digikey.com/short/q4h8h4w8Those a lot of these have protections built in so not sure if you'd have to disable your protection chips with such batteries or not.

author: VEGETA
author_rank: Super Contributor
timestamp: March 13, 2023, 08:40:46 am
content: I think I will go with elec. caps (smd), here is the one I will use:https://www.lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_Lelon-VES470M1CTR-0505_C134798.htmlLelon seems to be good, cheap too. I don't know if cap brand matters these days, I mean not for this project which is very low power but for more current demanding projects like SMPS.I never used polymer before, don't know their advantages over elec. caps.Quoteall board components will be smt assembled by pcb manufacturer.there is absolutely no room for putting any pouch cells, please see the attached image showing (in Yellow) where the new mod board will be installed.I don't think my battery protection will matter if protected cells were used because it is a matter of which protection circuit gets activated first. I have seen a video designingthis productwhich he used a protection circuit similar to mine and still works with protected and unprotected battery.also there is no need for using anything else besides 18650 battery since it is very common and very cheap with huge capacity especially for such ultra low demand like our circuit here. this mod board will solve a +20 yo problem very well known in the scene.my concern was that I wanted to use this first:https://www.digikey.com/en/products/detail/keystone-electronics/1043/2745669then switched to using 2 of those instead:https://www.digikey.com/en/products/detail/keystone-electronics/54/2254090in the video of Walid Issa explaining the design of that universal battery charger, he mentioned such connectors do not suit protected 18650 since they are noticeably longer... thus he used the clips one. they are sturdy enough even if battery is mounted on bottom side, so this made me change + the fact that they are a lot cheaper.the problem was how to space them? the datasheet drawing specifies 48mm between the 2 parallel vias (out of 3 holes) for unprotected, while it needs 67mm for protected cells.what I did here was to just make them 48mm to suit unprotected cells, and I think (hope) that it can also fit protected cells since the clips are kinda flexible by their nature. do you have any thought on this? it has to accept both protected and unprotected 18650.Looks like you didn't see my comments about putting 3v LDO directly at the point without diode protection. please check it out.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 13, 2023, 03:46:16 pm
content: I don't like your mounting idea for the 18650 cell on that PCB for three reasons:Clips: If the unit is dropped, the cell could fall out of the clips and roll around. You'd need some additional strap system to unsure it stays in place rather than just relying on the clips.Because you are mounting this board as a daughter board and using existing PCB lands as mounting points, you'll be adding undue stress with the 18650's extra mass.(If someone ships or transports a modified unit, those points covered above could be a problem. Not an issue if it's just sitting on a shelf undisturbed the entire time)Also, when you insert/remove an 18650, some of that force will be applied via the existing PCB lands...

author: VEGETA
author_rank: Super Contributor
timestamp: March 13, 2023, 04:27:37 pm
content: well, I don't like the mounting method either but it is the only way. no space is there plus no way to put screws and so on.for strapping, the daughter board has an opening for the ribbon cable to be routed.... anyone could easily get a small plastic ties <0.1$ and firmly secure the battery. I don't think I can provide it with it due to the hassle of it as I plan to make remote shipping.the other more dangerous issue is the stress which was in my mind first moment. if you notice i put lots of pad area for these solder points + many solder points. if the user put much solder on all of these pads which is the intended thing to do, then i guess it will be ok. shipping 18650 is forbidden anyway so a modified unit without battery is totally ok to ship imo.also, i will instruct the user not to desolder previous components but rather cut them off to leave their legs in place... then solder the daughter board along with the legs which should be more firm than mere solder pads.one potential solution I thought of is using astandoffand make a hole for it at the board corner. this way it will rest on the standoff (or 2 of them) rather than the solder joints. then besides the problem of including them in the package (using remote shipping), I will need to figure out the correct spacing....any suggestion?edit:this spacer seems fine:spacerandthis onetoo.length is ok but 3mm hole is too much since it will be under clip to the corner. may touch the clip or so.edit 2: hmmm after thinking i could put the 2 standoff holes under the battery itself which gives more sturdiness and won't affect placement. but I fear the standoff cap will touch the battery if it is long enough.here is the drawing of the clip:https://www.digikey.com/en/htmldatasheets/production/746046/0/0/1/54.html] too.length is ok but 3mm hole is too much since it will be under clip to the corner. may touch the clip or so.edit 2: hmmm after thinking i could put the 2 standoff holes under the battery itself which gives more sturdiness and won't affect placement. but I fear the standoff cap will touch the battery if it is long enough.here is the drawing of the clip:keystone 54how many mms are there between the bottom of the battery and the pcb in this case?

author: mariush
author_rank: Super Contributor
timestamp: March 13, 2023, 05:02:36 pm
content: All the area in the red region could be used for flat pack battery.The area in orange could potentially be used for a battery if some kapton tape or other insulator can be applied over the power supply pcb - there's only low voltage there so no risk for the user.However, on a quick google search i saw another version of dreamcast where the power supply was different and that white power connector a bit more to the right, unless I'm mistaken...Probably the best mod you could do would be to replace even the existing pcb - it's a single layer pcb and a regular end user would only have to desolder the 4 ports / connectors ... looking at 5 pins for each port. A bit more time consuming, but not more difficult as they're already desoldering around 6-8 pins already.The board could be extended to go all the way to the cd mechanism (where the fan ends) and you could also have small changes like moving the fan connector all the way in the bottom corner to the right of that screw for example, to make more room for battery.Even better, you could have a right angle connector for the flexstrip that's pointing in the other direction, towards the buttons. This way, the flex strip could be curved and inserted into the connector on the bottom of the pcb and then you screw down the pcb - the metal seems to have that depression in just the right place for such flexstrip header.

author: VEGETA
author_rank: Super Contributor
timestamp: March 13, 2023, 05:27:20 pm
content: Quoteyes, PAL version has the PSU extend a bit while other versions the psu does not have that extra area. this mod board with its current dimensions will fit both nicely.Quotethis could be a version 2 of it in the future. I think it needs a lot of work to trace all signals and so on.. not a straightforward job really. right now I and many others will be happy with my current solution.you could check my previous post about standoffs if you have a comment or advise, also on the LDO stuff you mentioned above and my comments about them.

author: VEGETA
author_rank: Super Contributor
timestamp: March 13, 2023, 05:38:07 pm
content: or I could extend the pcb itself as in yellow drawing and add the required 3mm hole for pcb standoff. it will only work from one side due to space.is it worth it or without standoff is better?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 13, 2023, 10:05:48 pm
content: I would try and use the existing screw holes as much as possible. Use some hollow nylon standoffs and some longer screws with matching threads.Maybe you could do something like this:

author: VEGETA
author_rank: Super Contributor
timestamp: March 14, 2023, 05:40:06 am
content: Quote from: Kim Christensen on March 13, 2023, 10:05:48 pmwell, using the connectors screws is not possible because the 4 connectors has to be on their place and height, any difference in height will result in mismatch and the controllers won't fit in.as for your other suggestion of extending it and put a plastic spacer, this is my suggestion above. however, my suggested one is snap fit in, not screw which is better. one standoff might not be perfect but still nice and certainly will do benefit.I have another suggestion which is getting small plastic standoffs, two of them to be put near the battery terminals and have them screwed so that they don't have much space under the battery. this is the more optimal solution but it will require that I ship the 2 standoffs and the 2 screws which is not really that optimal for me.My shipping plan is this: use nextsmartship company so that pcb manufacturer ships pcbs directly to them, then I ship the screws and standoffs to either pcb manufacturer or shipping company itself. i guess pcb company like pcbway will accept buying the standoffs and screws for me then put 2 of each in every board package... it is just that i don't want unnecessary things if i could getaway without them.EDIT:the screw i found is this:https://www.digikey.com/en/products/detail/keystone-electronics/29300/2746317standoff (female) is this:https://www.digikey.com/en/products/detail/keystone-electronics/24420/1532931screw head is 1.6mm, i guess it can fit under the battery.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 14, 2023, 03:50:45 pm
content: Quote from: VEGETA on March 14, 2023, 05:40:06 amThe connectors would stay exactly where they are. What I meant was something like this viewed from the side:

author: VEGETA
author_rank: Super Contributor
timestamp: March 14, 2023, 04:07:04 pm
content: certainly seems interesting. but this way my board will be mounted in the air even with 4 screws it will not be optimal.also, how to connect to the solder pads this way? the idea is to never have wires at all.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 14, 2023, 06:01:43 pm
content: Quote from: VEGETA on March 14, 2023, 04:07:04 pmWon't it "be mounted in the air" anyway? Wasn't your idea to use inter-board connections as standoffs between the original and your mod board? Just make the screw & standoffs the correct length so you can still use them. No "wires" required.

author: VEGETA
author_rank: Super Contributor
timestamp: March 14, 2023, 06:36:13 pm
content: Quote from: Kim Christensen on March 14, 2023, 06:01:43 pmwell, in my original suggestion it will be soldered directly to the original board. only part of the mod board will be hanging on air which is where half of battery size is, which could make a problem.I made mod board solder pads a lot bigger than original ones so that the user can solder them properly since the original ones are extremely small vias! I mean there is no male pin which could fit nicely there, let alone aligning it to the original very small pad.as for using original components leads after cutting them... well, this is not required since some may ditch them. I said this as an extra comfort, so that instead of desoldering these points then clean the joint then align the new mod board... you could just cut the leads and place the board then just solder. it may give a bit more sturdiness too.I attached a new image showing 2 screw holes of 3mm diameter for M2.5 screw to be used with 5mm threaded spacer mentioned above. I think this solution is very sturdy and at least deserves testing with various spacers of sizes near 5mm to see which one is the best fit. then shipping the board with such screws and standoffs despite being an extra step but gonna put it on PCB assembler since they will assort the individual PCBs into packets... so might as well put the screws and standoffs.On the other hand, still waiting mariush answer to my questions about his LDO circuit suggestion without diode... but overall the layout now should be perfect with no problems... routing should not be a problem too.also, an important question is assume i charge with 100 mA charge current, battery is 3000mAH capacity, and it is now at say 3.7v... with this charging current, how long does it take for it to be 3.8v? could not find calculator for this.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 14, 2023, 07:06:54 pm
content: Quote from: VEGETA on March 14, 2023, 06:36:13 pmAh... Ok I think I see what you're doing now. There'll be no traces on the bottom side of your mod PCB where it overlaps with the original PCB? If so, you could even put a very thin piece of doubled sided tape between them (with gaps for the interconnection pads) and effectively glue them together. That could work quite well.QuoteNo real way to determine an accurate state of charge from the voltage alone, so that's probably why there is no info on that. The SOC curve is pretty flat at 3.7V so your battery could be anywhere from 25% to 80% full at that voltage.But we know that an almost dead 3000mAh battery would takemorethan 30 hours to charge at a 100mA rate because charging efficiency is not 100%.

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 07:07:05 pm
content: I don't know why you wait for my answer.. If you feel it's needed, add it.this : an important question is assume i charge with 100 mA charge current, battery is 3000mAH capacity, and it is now at say 3.7v... with this charging current, how long does it take for it to be 3.8v?It's a very difficult question to answer. The voltage of a lithium battery doesn't go up and down linearly, as the battery charges and discharges.Have a look for example at a LG 3100-3200mAh 18650 cell datasheet :https://files.gwl.eu/inc/_doc/attach/StoItem/5230/Datasheet_LG_MH1.pdf1C means charging at 3100mA for 1 hour to charge battery - so the datasheet says the standard charge is 0.5C or 1.5A, so battery will charge to 4.2v in about 2 hours.See page 7 where it's graph showing charging at 1A or aprox. 0.33C ... you can see the red stuff... voltage going from around 3.2v to 4.2v in 160 minutes... after that it's still some time to trickle charge/top up.You can also see it reaches 3.6v at around 30min point , and 3.7v at around 55-60 min ... so that's around 20-25 minutes at 1A charge current. At 0.1A, it's gonna take that difference x 10 ... or around 2-3 hours.On page 5 and 6 you can also see discharge graphs... red is 0.2A discharge ... you can see such battery still provides energy down to around 3.3v-3.4v ... your power consumption is maybe in the mA range, not 0.2A so it's gonna discharge even slower.The capacity of a battery will depend with charge and discharge rate, if you charge at such low currents total capacity is gonna be higher, but don't account for 3000-3500mAh, aim more towards 2200-2500mAh and scale the times accordingly.for battery locking and preventing it from popping out ... you could resort to some basic stuff like a couple of zip ties going through some through holes on the pcb.But the other guy is right that the weight of the battery alone is an issue, and could cause the whole pcb to flex and shake if someone moves the console and that could cause weak solder joints...Actually very good idea to replace the middle two screws with slightly longer screws and have the pcb sit on the plastic of those two sets of ports, and use longer screws to lock your pcb down. On the other end of the pcb, just use some suitably tall spacers (or some rubber pads/whatever)

author: VEGETA
author_rank: Super Contributor
timestamp: March 14, 2023, 07:35:13 pm
content: Quotewell, you suggested something and I wanted to see if your suggestion is better than mine. I read that providing such voltage at LDO output is not really a good thing.Quotecharging current could be bumped to 200mA easily. the charger IC allows 500 mA but I don't want to go that far since in original design 5v rail does not really take much power so I fear if I added 500mA to it then it could be stressing the PSU. but 200mA is fine, assuming it won't be hot and so on. 500mA is doable as I said but I want to avoid it unless it is a must.discharge current could be < 1 mA. since original ML2032 has nominal discharge rate of 200uA and the dreamcast manual says it can retain the charge for 20 days without charging despite battery capacity is just 65mAh.The idea is I want the user to put a charged or new 18650 cell which could be at 3.7v, if it is done like this then i guess no problem will ever occur.I mean assume he played for 1 hour, it will be 0.2A charging current which is a lot more than < 1 mA needed for discharge. so maybe playing for 1 hour will give capacity equals to weeks and weeks of discharge right?the user should put any 18650 and it should work fine.Quotecan be done on this design via ribbon cable opening slot.Quotewhich is why I added the 2 holes in last post. these 2 holes are for M2.5 screws which has a standoff under the board. with this, the board is not flying in air but rather sitting on 2 standoffs directly under main weight item which is the battery.Quotethis will make the pcb floating above the original board, how to solder all these joints? doing wiring is not what i intended.the intended use is the user to put the new board on top of old one, align it very well, and solder all joints. joints are made very very big to take a lot of solder to firmly tighten the board not just for mere connecting boards signals together. this is easiest mod job. with new standoffs suggested, it will be even better.

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 07:54:04 pm
content: QuoteThat's super basic stuff, just use some suitable headers, like for example this:(20 pins)https://www.digikey.com/en/products/detail/harwin-inc/D01-9922046/3727867or(32 pins)https://www.digikey.com/en/products/detail/omron-electronics-inc-emc-div/XR2P-3241/1829614or this (64 pins) :https://www.digikey.com/en/products/detail/mill-max-manufacturing-corp/350-10-164-00-006000/357045There's cheaper headers with square pins or non gold plated pins ... like for example $0.01 per pin if you buy 100 or more :https://www.digikey.com/en/products/detail/adam-tech/PH1-01-UA/9830231orhttps://www.digikey.com/en/products/detail/adam-tech/PH1-02-UA/9830266You can use a sharp blade or nail clippers to separate one of these with lots of pins into lots of single pin headers.You solder them to the base (original) board, install the base board back in the case, unscrew the two screws in the center, positions your pcb on top of the plastic and the header pins go through the holes of your pcb.Use slightly longer screws to lock your pcb in position, then solder the other end of those header pins to your pcb pads.

author: VEGETA
author_rank: Super Contributor
timestamp: March 14, 2023, 08:09:47 pm
content: well the holes in original board are very small. what is the diameter of standard resistors\capacitors leads? I searched and found they are 0.6mm, about the same as your pins above. my mod board holes are 2.5mm so should be perfect.the user here should have proper desoldering tools to be able to remove the solder from these tiny holes properly. a good thing in this suggestion is that i won't need stand-offs anymore.your idea seems tempting really, and i think me or any user who does not have proper desoldering tools can just heat the holes and insert the new pins... this worked fine for me.do you have any note on the pcb design itself? like final idea\opinion before i start routing tomorrow.i will try to make the board as you mentioned, extend it to reach the 2 screws holes. dimensions won't be very precise but could be tuned later on. will make that area without copper to avoid any issues. connector plastic is about 2.5~3mm height so your 2.54mm could be very good and I can get any screw to be working on such coordination.

author: VEGETA
author_rank: Super Contributor
timestamp: March 15, 2023, 09:02:02 pm
content: I have finished everything, please check images here:https://imgur.com/a/bm5PuzG- added the PCB extension and 2 3mm holes for screws as agreed.- re-positioned holes to best I could. measurements are really hard and could result in some inaccuracy. gotta check when boards come but overall won't prevent the board from working.- layout is complete now.any tips\comments?as a reminder, I will be following your suggestion of using the 2 screws to fix it in place + pin headers to solder the holes.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 15, 2023, 09:22:40 pm
content: QuoteI see a single slot instead of 2 holes which would have been stronger. But I guess you're trying to keep the screw mounting tolerance loose?

author: VEGETA
author_rank: Super Contributor
timestamp: March 15, 2023, 09:51:48 pm
content: Quote from: Kim Christensen on March 15, 2023, 09:22:40 pmit is more of a rail to be able to fit the screws nicely, at least for this first board. i will check it, if it was perfect then i will convert it into holes.

author: VEGETA
author_rank: Super Contributor
timestamp: March 23, 2023, 10:56:39 pm
content: Quote from: VEGETA on March 15, 2023, 09:02:02 pmi think i settled on this being final. do you have any last comment?since if not, i will send it to pcbway for fab + assembly.

author: VEGETA
author_rank: Super Contributor
timestamp: May 24, 2023, 07:59:12 pm
content: hello, I have made the circuit... it works but not always. here is the schematic:https://www.eevblog.com/forum/beginners/nimh-3x-aaa-batteries-charging-circuit/msg4751381/#msg4751381what happens is i connect the battery, without 5v supply for now, so it should just output about 3.2v after LDO+Diode.... and it does.but most of the times I get nothing, when checking the dual mosfet package connected to protection IC... I get nothing or very low (2.3v) signal on the two gate pins which effectively shuts down the mosfets and disconnect the circuit. meaning over charge or over discharge but the circuit is not doing anything really.but when I probe in multimeter voltage mode between battery negative and dual mosfet sources... sometimes it gets the battery full voltage and the circuit gets activated.then when disconnecting the battery, the output starts ramping down slowly from 3.2v to 0v despite not huge resistor and capacitor (C5=10u).EDIT: looks like it starts working when i touch the dual diode package pins... what do you think? even when it gets activated by this move, when i gently disconnect the battery and reconnect it.. it does not start again unless i touch again. Pin 4 is the one i need to touch in order for it to work, it is DOUT.EDIT2: actually i made 2 boards, the 2nd board suffered a small short which busted a small trace which connects power to protection IC. However, when I temporarily connected the trace the board worked without touching anything!but as you guessed, i am not in the lab but rather away. all this just quick and dirty testing. when i return i will patch the traces properly and try to make sure 100%. then i will add more resettable fuses to power entry to traces just in case.

author: VEGETA
author_rank: Super Contributor
timestamp: May 25, 2023, 07:55:30 pm
content: i have fixed the broken traces but unfortunately the same result.the board does not work until i touch M1 pins.COUT from protection IC is 0v while DOUT is 2.65v with respect to Pack- voltage which is battery negative terminal.I tried using multimeter probes (in voltage reading mode) to connect battery + terminal of 3.9v to DOUT just one touch and it worked fine.so is it that i wired the signals in wrong way to the degree that protection ic does not output enough voltage for DOUT and COUT?other measurements:GND to Vpack+= 2.9v.battery voltage (Vpack+ to Vpack-) = 3.95v.so there is a voltage between the 2 mosfets of charge and discharge which is equal to about 2.9v. I don't think this should be normal right? but could not find a solution or explanation for this in datasheet.EDIT: i found the solution for the circuit to work is to connect GND and Vpack- (battery negative) together.... what is going on? and when battery is removed and reinserted quickly i would need to short them again to work.please help

author: VEGETA
author_rank: Super Contributor
timestamp: May 26, 2023, 09:09:38 pm
content: after some readings and discussion, i got to realize that it needs the charger to be connected when first plugged... or shorting vss to V- as indicated in datasheet!i connected the charger and it worked immediately.

author: VEGETA
author_rank: Super Contributor
timestamp: May 29, 2023, 09:10:11 pm
content: I tested the boards alone and on the final application (dreamcast) and they work as intended. i just need to change the board shape to better fit inside.looks like i missed that note in datasheet which is correct based on real tests. no problem for me.