Simplest way to add li ion to your projects without fire risk - Page 1
Forum section: electronics / beginners

author: Beamin
author_rank: Super Contributor
timestamp: November 04, 2018, 02:03:03 pm
content: So is this the simplest way to add li ion batteries to your projects that would normally run on batteries like nicd or nimh in a low cost simple solution?I counted 8 parts plus the cell.So I have all these li ion batteries that I have been collecting over the years but never a safe way to add them to projects. Seems like I could just add this to my projects and I have li ion back up.I have had bad luck in the past trying this and using the same volts cells but different currents and the project would run off the battery but never recharge. Could this be the simplest solution? I haven;t checked to see where you get these chips yet, but imagine they are cheap.

author: GeoffreyF
author_rank: Regular Contributor
timestamp: November 04, 2018, 02:09:22 pm
content: Generally - you need a chip to do it because the amount of current which is safe varies during the charging cycle. This is different from most other types of rechargeable batteries. There is more to it than that, but that's a start. It's easier, safer and even cheaper to simply purchase a board for this purpose.Your schematic is a good way to have a fire.Not all Lithium batteries are rechargeable.

author: Audioguru
author_rank: Super Contributor
timestamp: November 04, 2018, 02:35:04 pm
content: The DW01 IC is called a Lithium batteryprotectionIC in Taiwan but maybe it is actually a crude charger IC that is missing many details of a real charger IC.

author: JackJones
author_rank: Regular Contributor
timestamp: November 04, 2018, 03:04:55 pm
content: It's not a charger, just for protection. It's often paired with a TP4056 charger IC.The most common little battery protection/charging modules you get from aliexpress use those two, along with FS8205 mosfet for the protection IC.

author: ogden
author_rank: Super Contributor
timestamp: November 04, 2018, 03:20:35 pm
content: Quote from: JackJones on November 04, 2018, 03:04:55 pmRight. Those shall be considered as "Simplest way to add li ion to your projects without fire risk".

author: voltsandjolts
author_rank: Unknown
timestamp: November 04, 2018, 04:25:25 pm
content: Also avoid batteries made by a manufacturer with "fire" in their name.

author: Beamin
author_rank: Super Contributor
timestamp: November 04, 2018, 04:29:24 pm
content: Quote from: Audioguru on November 04, 2018, 02:35:04 pmThat's what I thought those mosfets did but wasn't sure.Is there an one cheap IC solution that will charge it in place of what I came up with? I saw the OC and OD pins and thought it would also charge.Whats the simplest way to charge a li Ion with minimal parts. I like to build things and figure out rather then just buy a premade board. This isn't a product and will go on many things, but it would be nice to just plug in the project use it then recharge without worrying like you could do with nicds and a trickle charger.

author: KL27x
author_rank: Super Contributor
timestamp: November 05, 2018, 06:50:37 am
content: When I first started playing with li ion, anyone I asked said I was going to burn my house down. But if you can make a stable voltage regulator, you can charge a li ion battery.1. A li ion cell needs to be limited to 4.2V on the terminals.2. A li ion cell has to be limited to a certain amount of charge current.3. Don't charge a cell that has gone under 2.7V at full current. If you want to recharge it at all, you ought to tickle it with something like 1/20 C until the voltage is up around 3V before stepping on the gas. The best way to prevent this is to use output protection/cutout, so the cell gets disconnected when the voltage drops below the cutoff threshhold you need. (For higher relative draw for the cell's available output rating, you might want to cut out at 2.7V. For a lower relative draw, you might want to cut out at 3V.)The amount of current depends on the cell, but IME 99% of li ion cells can handle 1C charge current. (Some can handle 100C+)So if you do not want to use a dedicated charging IC, a very simple way to charge a li ion cell is to make a 4.2V power supply, using an LM317. And then put a series power resistor on the output in order to limit the max current. Example, if the battery has 1Ah capacity, 1C charge rate is 1A. 4.2V-2.7 (for a dead cell) is 1.5V differential. 1A = 1.5V/R. R= 1.5V/1A. 1.5 ohm resistor in series will ensure that the max charge rate is less than 1A if the cell is completely dead. The internal resistance of the cell will mean that the charge rate is actually lower than 1A. The last third of charging will take longer than it should, but it will be safe in my opinion. As long as you can build a reliable constant voltage supply that you trust.But you can buy charging IC and boards relatively cheap. And if it is too much trouble to add it to any/all of your devices, you can just put a charging port in the device and charge it with your bench PSU. Or a single charging board with a modest or adjustable charge rate. But you still have to ensure that you don't over-drain the cell. You should be able to do that in a variety of more complicated ways, if you want to. But again, there are voltage detector IC's that are made exactly to do this. Just connect to a suitable logic level power FET and you have a simple cutout.

author: Beamin
author_rank: Super Contributor
timestamp: November 05, 2018, 10:09:39 pm
content: Quote from: KL27x on November 05, 2018, 06:50:37 am

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 05, 2018, 10:12:14 pm
content: Does it have to be lithium iron? Other lithium chemistries are much more stable, though pose their own engineering trade-offs.

author: Beamin
author_rank: Super Contributor
timestamp: November 05, 2018, 10:13:35 pm
content: Quote from: KL27x on November 05, 2018, 06:50:37 amI don't know if I trust myself to make that work. From watching my bench power supply with a bunch of USB powered things li ion, it stays constant current within the 0.001mA range then the last 20% of the time the current goes up slightly then down, as it approaches 0 the charger just stops suddenly. That seems very specific to use a LM317 and resistor.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 05, 2018, 10:23:16 pm
content: I don't have any problem with KL27x s answer with two additional caveats. First, this applies to single cells. There are other problems when charging series or parallel cells. Second, there are slight variations in the do not exceed voltage for different Lithium chemistries. His advice is specifically for the type called Lithium polymer, or Lipo. Finally, even if you do all this right there is more chance of burning your house down with these than with other battery chemistries. Watch your batteries for signs of damage and don't leave them unattended without additional precautions. Are you really sure that your charger design can handle a big power line surge or other rare event?

author: Beamin
author_rank: Super Contributor
timestamp: November 05, 2018, 11:47:40 pm
content: Quote from: Mr. Scram on November 05, 2018, 10:12:14 pmOther chems are not rechargeable that I know of and I doubt any of my junk bin batteries are anything different or exotic.

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 05, 2018, 11:51:26 pm
content: Quote from: Beamin on November 05, 2018, 11:47:40 pmThere are plenty of secondary cell lithium chemistries to play with, most of which are safer than lithium ion. That's just the one we got stuck with because it's both fairly cheap and energy dense.https://www.mpoweruk.com/lithiumS.htm

author: kjr18
author_rank: Regular Contributor
timestamp: November 06, 2018, 02:07:04 pm
content: It kind of depends on what cells you have, etc. If your cells have built-in protection, you can skip that. For charging, tp4056 can do it with just two or three other parts. If you need higher voltage than battery voltage, boost circuit is needed, lower than cell voltage, some linear or buck regulator.Some cheap chinesium products depend on built-in protection to terminate charging, you can recognize these by their power supply, typically 4.2V and around 500ma output.The simplest way would be use of simple building blocks: charger/protection board, buck converter/linear reg, boost converter. You don't need anything more. You can even make some small boards yourself (if you are space restricted), or buy some.

author: Rick Law
author_rank: Super Contributor
timestamp: November 06, 2018, 09:40:59 pm
content: Quote from: Beamin on November 04, 2018, 02:03:03 pmQuote from: Audioguru on November 04, 2018, 02:35:04 pmSince you are looking to use your stock of lithium battery to power something, a battery protection circuit is exactly what would be desirable. Instead of rolling your own, why not just buy a protection circuit board. Boat loads of them out there most are based on the DW01 (or copies).But, you didn't say anything aboutwhat you like the battery to power... a radio? an RC race car? a flashlight? a clock? (etc. etc.) And, what is the requirement (voltage, current, etc.) of the thing you want to power? No one can come up with a good solution without first knowing what is the problem to be solved.Most rechargeable lithium cells are 3.7v, but NiMH cells are 1.2v cells. Unless you are powering something that had 3 NiMH cells (3.6v), you have a voltage mismatch. There areboost or buck convertersandboost plus buck convertersout there to boost (increase) or buck (decrease) the voltage to your exact need. You can build one too... Buck circuit, boost circuit, boost-then-buck circuit... Boost+buck is the funnest, don't matter the input voltage (within limits), you can output the entire range from below your supplied voltage to above your supplied voltage (within limits).Since you want to power something that initially has NiMH or NiCD, one can assume the current draw is not too high. You still need to know what it is. I have a boost+buck that can do around 500mA, nice, simple and small. But if I try to use that for something requiring 1A or more, I can make a fire place out of my work bench. So, you need to know more about the load before you decide if you need a car, a van, a truck, or a train.

author: KL27x
author_rank: Super Contributor
timestamp: November 06, 2018, 10:07:06 pm
content: QuoteThe USB charge can be described as both current and voltage limited. If you limit the voltage to 4.2V per cell, then the only way it can exceed its own max charge rate is when it is discharged significantly. For sake of argument, let's say a given cell must be discharged at least halfway before connecting it to 4.2V constant voltage source will allow for a dangerously high current.So for this particular cell, if it were completely discharged, the USB charge circuit/IC (that is custom tailored to charge it as fast as safely possible) would be limiting the charge current to a given amount up until the cell was halfway charged. At this point, there is no longer any need to limit the current. At this point, the charge current will naturally taper off because of ohms law. 4.2V-Vbat is going to decrease. And the internal resistance of this particular battery will cause it to draw only the max safe current at this halfway point; thereafter, the current will taper off as Vbat rises.I am speculating that the current on the device you witnessed "rise at the last 20%" is because it used a simple series resistor or somesuch to initially limit the current rather than an active current control. Once Vbat reaches a safe level, it switched this passive limiting device out of circuit so that is would no longer unnecessarily reduce charge current. Thus the current draw spiked a little at this point.The only reason a USB battery charger has to turn off at all is if the voltage is a bit higher than needed. If you used a charge voltage say 0.1V higher than the max voltage the cell can handle, you can get that last 10% of capacity to charge a bit faster. But you need to turn off the charger when Vbat reaches 4.2V. If you charge with 4.2V or less, there is no reason you can't just leave it on there, indefinitely. Also, the main reason the USB charge circuit has to detect when the cell is charged is so it can flip an output line which can be connected to an indicator light. So the user can watch a red LED turn to green, and know the cell is done charging.The graph you will find in a typical (good active) charging IC datasheet represents the current passed in order to safely and practically charge a cell in the fastest time. There is no need to follow this curve. There is nothing magic about it. Your current graph can look totally different, if you are ok with a longer charge time. You just have to limit max current and keep voltage under and up to 4.2V.Yes, there are different chemstries needing different voltages. And batteries with multiple cells in series will need some extra precautions (for instance, I charge one particular 4S pack I use to only 16.6V, instead of 16.8V for starters). But there is no special precaution (I'm aware of) to charge li ion cells in parallel. For all intents and purposes, charging 2, 3, or 100 (matching) li ion cells connected and used in parallel is no different than charging a single cell that happens to have the same construction but is 2, 3, or 100 times larger in size. The reason NiMh cells are squirrely to charge in parallel is because Vbat is not a function of SoC. As you charge a NiMh cell, Vbat will rise, then fall, then rise, again. At a given Vbat, there are multiple states of charge. In li ion, Vbat is a function of SoC. Thusly, if one cell has more charge than the other, this means Vbat is slightly higher. And current will flow from that cell to the other. Simply put, li ion cells are self-balancing, in parallel.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 06, 2018, 11:01:51 pm
content: Cells in parallel or series are not a problem if they are identical in capacity, initial state of charge and aging characteristics. If not, cells in parallel will not share current equally and if precautions are not taken one may exceed it's charge rate limits. Series cells will not all charge to the same state. Eventually some cells may overcharge before the string reaches the charged voltage for the string.You can often go a long time before encountering these problems. Whether you worry about them depends on your risk tolerance.

author: Beamin
author_rank: Super Contributor
timestamp: December 02, 2018, 12:26:51 am
content: Quote from: blueskull on November 06, 2018, 10:26:33 pmWell when I build my hobby projects I would be the one supplying the power bank. Also leaves me with cost of certification and take all the liability. I wonder if I can sign a contract with myself to limit my liability to me, myself, and maybe even, I!My scenario is vauge because the application is general. Always building things that run off 3 or 5 sometimes 9 volts. Have tons of 3.7V liion cells around from taking things apart. They are all one cell 3.7 but since they came out of all different consumer electronics the capacity is variable depending on which fits or is at the top of the junk batter box. So I wanted to order a bunch or cheap/simple chips so that next time I build something I can connect a barrel jack or preferably a usb charger to it and charge up the project and not worry about the battery blowing up. Back with nicads this was simple: connect your batteries to your project, just put a trickle charger to a barrel jack in the back of your projects, plug in when needed. Much like when you set your cordless phone down in its cradle. I'm not worried with output voltage or building buck/boost converters because that will be done already with the project, just a simple charging IC or circuit where I add to junk box 1 cell liion.Why did this dude get banned? He had 10,000 posts thats a lot of work for trolling.