LOL I AM THE BEGINNER ! using lipo battery to light doll house with LED  - Page 1
Forum section: electronics / beginners

author: withwings
author_rank: Newbie
timestamp: November 28, 2017, 08:38:56 pm
content: I have purchased 25 pito 3 volt lights to light a doll house and need it to be lit for 10 days. I can not use anything stronger then a 3 volt battery with these tiny lights. I understand the wiring with the LED UV lights but I don't understand the the LIPO conectors??Also what size LIPO I need? this is where i bought the led'shttps://www.modeltrainsoftware.com/pin-connectors.html

author: james_s
author_rank: Super Contributor
timestamp: November 28, 2017, 08:44:10 pm
content: Is there any reason you need to use a LiPo battery? They are capable of delivering high current and have fairly high energy density but it doesn't sound like you need those traits here and LiPos are somewhat temperamental. They are easily damaged if excessively discharged and can burst into flames if over-charged or short circuited. I would think some old fashioned alkaline D cells might be a better option for a beginner.You can determine the size of the batter you need by looking up the current that one of the lights draws, either that or measure it. Then multiply it by the number of lights you want to use and you can figure out the mAh they will consume and multiply that by the number of hours you need them to run and you will have the needed battery capacity.

author: withwings
author_rank: Newbie
timestamp: November 28, 2017, 10:21:11 pm
content: I need one that will last 10 days for the length of the display. I was told they would last that long

author: rstofer
author_rank: Super Contributor
timestamp: November 28, 2017, 11:00:16 pm
content: Your link doesn't lead to a datasheet for LEDs, only connectors...You need to know how many millamps the LEDs will require. Then you need to multiply by 10 days times 24 hours/day. A 20 mA LED (common type) would need a battery with 4,800 mAh capacity, At least...A standard 18650 battery has about 2800 mAh capacity so 2 in parallel would be required. But that doesn't answer your question because I have no idea how many mA your string takes and you didn't specify (exactly) which battery you were going to use. And I haven't accounted for the voltage. 10 days is a LONG time.

author: Tom45
author_rank: Frequent Contributor
timestamp: November 28, 2017, 11:11:13 pm
content: I think these are what he has:https://www.modeltrainsoftware.com/nano-string.htmlUnfortunately, no info on current draw.If it were me, I'd go for lower current, perhaps 8-10 ma. Most small LEDs like those would be just about as bright at that lower current. Arranging that would be trivial for most of us here, but he is an admitted beginner. So he needs easy to understand and implement suggestions.

author: rstofer
author_rank: Super Contributor
timestamp: November 28, 2017, 11:24:44 pm
content: Quote from: Tom45 on November 28, 2017, 11:11:13 pmCan't do that without nailing down some numbers. Everything else is a bad guess.Apparently, a string of 12 LEDs runs on 3V but there is no indication of how many mA. One way is to just buy the strings, wire all of them to a pair of AA batteries and measure the current. Using the 18650 battery may require a diode in series with the battery to drop the voltage a bit.It may turn out that a pair of D cells works just fine but it is all based on the unknown mA rating.

author: withwings
author_rank: Newbie
timestamp: November 28, 2017, 11:31:55 pm
content: Here is the right link,https://www.modeltrainsoftware.com/smd-chip-leds.htmlI have 25 of the smallest lights.The pico is the size and the 3 volt. I am a SHE and I do not understand anything the math or the language you are speaking lol. I am a artist/sculpture and I came to this sight to find someone smart to help me. Pretend you have walked into the kitchen and there is your mother and now you must explain this to her (because I am probably as old of your mother)..... I know ten days in along time but I was hoping that since they were so small that if I used a huge or strong battery that I could keep them running the whole time the doll house is on display.

author: kalel
author_rank: Frequent Contributor
timestamp: November 29, 2017, 12:17:27 am
content: Welcome to the forum. LEDs will have a problem when running directly from a LiPo battery. A single LiPo cell has voltages of about 3.6 to 4.2V (when fully charged).The problem with supplying anything more than 3v to the 3v LED version is that the LEDs might start drawing too much current and die/burn out.If you wanted to use a higher voltage battery, you would need to lower the voltage to 3v by adding extra components such as a diode, a resistor, etc. You could also lower the brightness of the LEDs and make them run longer at less brightness. Before adding anything, exactly what to add needs some calculations first, and for this you need more data for the LEDs from the seller or manufacturer or a way to experiment/measure them.Would size be a problem? If not, and if I got things right, they recommend this battery holder as the highest capacity one they have (AA is better than AAA):https://www.modeltrainsoftware.com/aa-holder-separate-switch.htmlI don't know how long it would last, but you could buy more than one, and join them together for extra capacity (red wire with red wire, black wire with black wire, called a "parallel connection"). This should not be dangerous if you are using them (e.g. 2 packs joined together) with 4 fully charged batteries from the same pack. If one battery pack is less charged than the other, the "full" pack will try to "charge" the other "less full" one, until they are at a balance. This could cause problems. If this sounds like something to try out, before connecting them this way and following my advice, please have someone more knowledgeable than me confirm that it is safe. I am not a professional or experienced in electronics.

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 12:22:59 am
content: I won't have a problem hiding the battery so yes I would try ANYTHING !!!

author: kalel
author_rank: Frequent Contributor
timestamp: November 29, 2017, 12:36:29 am
content: I just noticed/realized we are talking about 10 days, that is a long time unless the brightness/current is limited.How bright do they need to be?

author: ez24
author_rank: Super Contributor
timestamp: November 29, 2017, 12:45:50 am
content: It is surprising that the current is not given. FYI on some LED basics.https://learn.sparkfun.com/tutorials/light-emitting-diodes-ledsthey talk about current (you do not need to know everything in the article)here is a calculatorhttp://ledcalc.com/they say use 20ma if you do not know it.If you read this data page on SMD LED, this one is 20ma (about 1/2 down). So you can use 20ma for the calc everyone is asking for.http://uk.farnell.com/avago-technologies/hsms-c191/led-smd-he-red/dp/1058373If you google "d cell mah" you get 20,000 mAh so divide this by 500 you get 40 hours. So it is going to be hard to last 10 days. Is there anyway you can plug into the wall?Using a 18650 is tricky for so many reasons.Using D cells, you would need 6 of thesehttps://www.ebay.com/itm/1pcs-2-x-D-Size-Cell-Battery-Holder-Box-3V-Case-With-Wire-Lead-UM-1x2/192351107886?hash=item2cc904fb2e:g:YbEAAOSwH-dZ-cna

author: John B
author_rank: Frequent Contributor
timestamp: November 29, 2017, 12:53:11 am
content: Where does the battery have to go? Ie, does it have to fit inside the dollhouse somewhere or can it sit underneath, out of the way etc.A simple plug and play solution would be to use a 6v lantern/torch battery, then buy one of these cheap DC/DC modules to set the output to 3v.https://www.ebay.com.au/itm/LM2596-3A-Adjustable-DC-To-DC-Step-Down-Converter-Buck-Module-Voltage-Regulator/232274686302?hash=item3614a6715e:g:j3EAAOSw4A5YzI3HIn fact you will be able to set the brightness to your liking, and it will stay at that for the 10 days. You'll need a multimeter to check the output voltage before hooking the LEDs up otherwise you'll burn them out in seconds if the voltage is too high. Also 20mA per LED may be overly bright.

author: rstofer
author_rank: Super Contributor
timestamp: November 29, 2017, 12:53:58 am
content: Quote from: withwings on November 28, 2017, 11:31:55 pmI, OTOH, have no artistic ability whatsoever - kudos to those who do!I imagine that measurements are out of the question so why not start with a pair of D cells and experiment? Is there enough time to try that before going live?If one pair of D cells doesn't last long enough, try two pairs.Less technical answer than I gave above: the current required by the string of LEDs is like the mileage your car gets. So many milliamp or so many miles per gallon (actually, gallons per mile, but who's counting) - both are the rate at which energy is consumed. So, if you have a very long trip to take and you can't stop for gas, you need to figure out whether your tank is large enough or you need to carry gas cans.Same thing with the batteries. You need so many milliamp-hours to light the LEDs (milliamps is the instantaneous current, milliamp-hour is the instantaneous current times the number of hours) for some long period of time (similar to miles) so all you need to do is figure out how big the batteries need to be. HOWEVER, we know the hours, what we don't know is the milliamps. We need to know the milliamps for one string and we need to know how many strings. Measuring the value is the easiest and most probably correct solution. Get some LEDs and a cheap Digital Multi-Meter (DMM) and we can talk you through it.OR, you can just grab a couple of large batteries (D cells) and try it. Kind of like bringing a tow truck on your long trip. Just see how it works and leave the math for others.

author: xrunner
author_rank: Super Contributor
timestamp: November 29, 2017, 12:55:08 am
content: They sell the "nano" LED on another page, as I suspected they are simply 20 mA SMD LEDS, nothing out of the ordinary.QuoteBut as you all know (but not the OP) there is no reason to run them @ 20 mA if you want to conserve power. Simply add a resistor. I work with these quite often on my model RR and they areverybright @ 20 mA. You can easily cut the current in half and they will still be bright. Up to the OP's requirements of course.

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2017, 01:10:00 am
content: Quote from: withwings on November 28, 2017, 08:38:56 pmOK, I have read this and the following posts.Firstly I second what everyone else said: you do not want to use a LIPO battery.I strongly recommend you use a 6 V lantern battery, like one of these:http://data.energizer.com/pdfs/1209.pdfThey have a large capacity, they are easy to use and they are safe.Since it is a 6 V battery you can put two of your 3 V LEDs in series (connect the wires end-to-end) before connecting to the battery. You should be able to run about 4 LEDs like this for 10 days off one battery. It will require many batteries to run 25 LEDs.Unfortunately this kind of task is better suited to mains power. Is it not possible to buy a string of Xmas tree lights and use that? It is the right season to buy them after all.

author: james_s
author_rank: Super Contributor
timestamp: November 29, 2017, 01:26:19 am
content: If you use ordinary alkaline batteries you can use series pairs of two cells, and as many pairs as necessary can be ganged up in parallel to get the lifetime you need. I don't think 10 days is unreasonable for LEDs, a lot of modern LEDs can be very bright with only a few mA. We have a little string of LED christmas lights that came on a decorative tree and that string of 10 lights with some blinking and some steady run for about a week on 4 AA rechargeable cells.

author: Brumby
author_rank: Unknown
timestamp: November 29, 2017, 01:30:17 am
content: Welcome to the forum. We do have several female members - but most are male, so that is the presumption, unless we are otherwise informed. We have been informedWe can appreciate you don't understand the maths and the language. We do - and we will try to help as much as possible.There are two main points we need to get a firm hold of to be able to offer some answers - and they both are details about the LEDs. The first is the current that each LED draws when it is working and the second is the voltage across the LED at the same time.Don't panic about the following - it's more me talking out loud...The type of LED used is a surface mount package, size 0603 (1608 metric) - but that doesn't help a lot with the current and voltage numbers we need. There are LEDs that run from 5mA to 20mA - but if we use the top of the range for our calculations, then you should be reasonably well covered for getting the right capacity of battery.AHA!I found a reference to the current: 20mA.https://www.modeltrainsoftware.com/smd-chip-leds.html(halfway down the page)The main trick is to get the voltage right. One more detail that will help is the colour. Different colours operate at different voltage ranges - and even for a given colour the actual voltages can vary between one model of LED and another.I found the following statement: "Get these chips already wired, tested, guaranteed, and fully ready to connect to your power supply.No resistors need to be added, we have done that part!". This is good news - to a point. In the images given, there is a resistor in the 9V version (which is to be expected), but I can't see any resistor for the 3V version. They mention 3V supplies using AAA, AA and coin cells which suggests the LEDs could run at around 3.0V or 3.1V ... but that's a guess.Lipo batteries can provide voltages around 3.7V to 4.2V which is far too much for these LEDs. The forward voltage drop of a diode might be a step in the right direction, but there are still some issues to address.Ah, wow.... 9 replies while I was typing this up!!

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2017, 01:34:44 am
content: Quote from: james_s on November 29, 2017, 01:26:19 amSomething doesn't quite add up though. According to the web page (https://www.modeltrainsoftware.com/smd-chip-leds.html) the LEDs draw 20 mA each. Yet they say you can run 10 chips from a 3 V coin holder. That would be 200 mA from a coin cell. I don't think a coin cell could do that for very long, if it all. So I'm not sure. I would want to get one of them and measure it. I might also want to increase the series resistance to reduce the current draw. Possibly put 3 LEDs in series on 6 V rather than just two.All of this is very technical for the person asking. For us it is trivial, but for the OP not so much.

author: Brumby
author_rank: Unknown
timestamp: November 29, 2017, 01:38:15 am
content: I, too was a little curious about the run time....Read here:https://www.modeltrainsoftware.com/3v.html"In our tests, 6 lights lasted over 12 hours on one battery. By 12 hours they were noticeably dimmer. A test of the battery at 12 hours showed the voltage was down from 3.0 to 2.6 volts. The lights continued to stay on at a nice level for several additional hours before another battery was needed."This was on a single CR2032? Hmmm......

author: xrunner
author_rank: Super Contributor
timestamp: November 29, 2017, 01:45:27 am
content: Quote from: Brumby on November 29, 2017, 01:38:15 amEnergizer CR2032 specs -Quote

author: james_s
author_rank: Super Contributor
timestamp: November 29, 2017, 01:52:43 am
content: It sounds like they may be relying on the internal resistance of coin cells to limit the current to the LEDs. Sometimes you can get away with running an LED directly from a battery without a separate current limiting resistor but it's not something I would recommend. If in doubt, use a resistor, you can always reduce the value or eliminate it if needed.

author: cdev
author_rank: Super Contributor
timestamp: November 29, 2017, 02:20:29 am
content: I just want to say welcome to the forum. LEDs are amazingly good at showing some output at extremely low levels of current. You may be able to get incredibly long life with even a moderately sized battery if you reduce the current down to just a few MA you may have enough brightness. I have LEDs that light surprisingly brightly at 2-3 ma.Why does it have to run all night?

author: Brumby
author_rank: Unknown
timestamp: November 29, 2017, 02:41:45 am
content: Quote from: cdev on November 29, 2017, 02:20:29 amMy guess is that it will be part of a larger display - and once set up, everybody will be banned from the area until the end of the event.

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 02:44:44 am
content: IMHO the best option would be to connect them in series strings, add a resistor to limit the current and run them from a higher voltage. Eight strings of three, (yes you'll have one left over) each consisting of three LEDs with the two wires to the middle LED each soldered to ONE wire of the OTHER colour of the end LEDs. That will give a string that takes 20mA max and has a bit under 9V across it when running. If you want a lot of brightness, add a 270 ohm resistor (solder it to the free red wire of the end LED) and you'll have a string that will be quite happy running from a 12V Lead Acid battery, as long as the battery isn't connected to a fast charger or a running vehicle. A float (trickle) charger would be OK. The strings would connect in parallel - free lead wires of all the resistors together, then via a 1A fuse to the battery positive (and also via a switch if you want one), all free black wires togethyer and to the battery negative. You can use as much flex as you need between the joined LED string connections and the battery - cheap thin flat twin cable (aka 'bell wire' - get the stuff with a stripe down one wire so you don't get them mixed up), will do nicely. Put the fuse at the battery end.Over 10 days, running 24/7 they'll need a bit under 35AH. If you want a lead acid leasure battery to survive in cyclic use, you don't discharge it past 40%, and it may be difficult to get it above 90% charge on a cheap charger so only 50% of the nameplate rating is really usable. Therefore the minimum battery capacity would be 70AH. A 60AH battery would be discharged to 35%, which is pushing it a bit but would be OK for a one-off. A >100AH car battery from a scrapyard would probably also do, but you can never be sure how much capacity a scrapyard battery's got left. Charge the battery beforehand taking it off-charge no more than a couple of days in advance, and if you want the battery to survive, get it back on charge within a day of the end of the display. DO NOT leave it running till the battery is flat - I figured for 10 days, if you go over that the odds of killing the battery stone dead go up steeply with each extra day.For the odd one out, if you *MUST* use it, use a 720 ohm resistor then treat it like one of the three LED strings. It will start off a bit dimmer with a fully charged battery and end up a bit brighter. Alternatively you could do two strings of two, with 470 ohm resistors. Again the brightness wont match, but four slightly different may be easier to distribute artistically than one.N.B. you cant switch individual LEDs On/Off - you could however switch any string as a whole.If you want lower brightness, try using higher value resistors - I wouldn't advise going lower for brighter as there is a big risk of blowing the LEDs.If in doubt *ASK*!

author: ez24
author_rank: Super Contributor
timestamp: November 29, 2017, 04:01:50 am
content: So far my favorite answer is use LED Christmas lights. The second one is use a 6 volt lantern battery with two LEDs in series.It would be nice if you let us know how you solve the problem and post some pics of the dollhouse. It is very easy to attach pictures.According to thishttp://www.techlib.com/reference/batteries.htmlThe 6v has 11,000 mAh. So for 24 LEDs (I assume you bought 25 and you have to use 2 in series) you have a current of (24/2) x 20ma = 240ma. So if you divide 11,000 mAh by 240ma you have 46 hours (watch the units divide out). This gives about 2 days, so you need 5 of these connected together. This is doable but painful ($).We are getting into the area of golf cart batteries. I am surprised 25 LEDs would use so much power in 10 days.This is a very simple problem that is not easy to solveGood luck

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 04:21:57 am
content: The '3V' LEDs at the URL the O.P. posted, don't have any series resistor. They are relying on the internal resistance of a 3V coin cell to limit the current enough for them to survive. If you connect them direct to a larger battery, they'll probably blow as there wont be enough internal resistance to limit the current sufficently. If you connect two in series, direct to a 6V lantern battery they'll also probably blow. Using a higher voltage and a properly calculated series resistor or other current limiting circuit is the easiest one of the very few way to run them reliably from a large battery.

author: John B
author_rank: Frequent Contributor
timestamp: November 29, 2017, 04:37:07 am
content: Those cheap chinese LM2596 modules also come in adjustable constant current varieties too....just saying.

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2017, 04:48:41 am
content: Quote from: Ian.M on November 29, 2017, 04:21:57 amIt's true they don't look like they have a series resistor. However the text claims that they do. I have been trying to work it out.If I had them in my hands I would examine them closely, measure them and then calculate a series resistor accordingly if needed.With all of this technicality it doesn't seem like a "plug and play" solution for someone who doesn't have the knowledge.

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 04:58:57 am
content: Quote from: John B on November 29, 2017, 04:37:07 amThat's a lousy idea as directly paralleling LEDs typically results in current hogging. The one that has more current gets hotter, its Vf goes down so it grabs even more current till it blows (thermal runaway). Then it depends on if there is enough current to blow it open circuit. If so the current through the other LEDs goes up by a factor of N/(N-1) and the thermal runaway process starts again with another LED. If not, it shorts them all out and the whole lot go off.Quote from: IanB on November 29, 2017, 04:48:41 amThe illustrated 3V LED doesn't have a resistor, and that would be consistent with white or blue LEDs with 3V Vf, but it seems they do other colours for 3V and one would not expect 3V Vf for some of those colours, so those probably do have resistors.@O.P: Please post a close-up photo of one of your LEDs with the full lead length visible in the photo.

author: rstofer
author_rank: Super Contributor
timestamp: November 29, 2017, 05:46:24 am
content: The vendor also sells a dual AA battery holder for these LED strings so the internal resistance of the coin cell isn't the only method of current limiting.

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 05:46:50 am
content: The event is 100 miles away. No electricity available because of cords. I can't stay for ten days and too far to keep driving there

author: IanB
author_rank: Super Contributor
timestamp: November 29, 2017, 05:52:37 am
content: Does it need to be illuminated 24 hours a day? Can someone switch it on and off at appropriate times?There is unfortunately no way around it. Having something lit up 24 hours for 10 days is 240 hours in total. Even with the most economical lights that will require a very big battery.

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 05:58:47 am
content: Battery powered programmable digital time switch?

author: John B
author_rank: Frequent Contributor
timestamp: November 29, 2017, 07:52:20 am
content: Quote from: Ian.M on November 29, 2017, 04:58:57 amConstant voltage it is! I guess I am wondering whether its worth "complicating" things past a plug and play module. Without some active circuitry the lights are just going to dim as the source voltage decays.

author: soubitos
author_rank: Frequent Contributor
timestamp: November 29, 2017, 08:24:12 am
content: You might find this useful.https://easyeda.com/catech75/TP4056FLEXADV_V3_00-9fe9350f414a4cacb9a8683de565d007It is made so that it charges the LiIon battery/ies from virtually any power source you might have in hand and uses a joule thief circuit to power a common 12V LED string (can be found around 1$/m these days).I just got the pcbs for this two days ago together with most of the parts for the board, others i need to wait to arrive from China via snail mail.If you find low power led string (2,4W/m are the smaller i can find locally) this will power it for many hours on a single 18650 cell easily.You will need more cells in parallel and certainly you cannot expect it to keep the leds on for 10 days straight on a single battery anyway and unless you use A LOT of cells, this will make sure you will recharge the cells safely and also has all the protection you need from overcharging and overdischarging.

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 05:06:35 pm
content: no not really

author: rstofer
author_rank: Super Contributor
timestamp: November 29, 2017, 05:40:12 pm
content: I wonder if a solar garden light (or equivalent) can be hacked. I don't know whether solar cells work from indoor lighting but they might.Does the lighting really need to work ALL night long or just work for a few hours after dark?If the lighting needs to work during daylight hours, this might not be a good approach.Still, why wouldn't a doll house have solar energy?

author: kalel
author_rank: Frequent Contributor
timestamp: November 29, 2017, 05:48:24 pm
content: Solar cells (at least on cheap ones) are very poor indoors. Perhaps if the room has tons of light, but I have tried a unit and it only gets a few seconds of light (with 2 LEDs), after a few days. The current supplied is limited too, usually set by an inductor, I'm not sure it could run 24 LEDs (at least effectively).

author: soubitos
author_rank: Frequent Contributor
timestamp: November 29, 2017, 05:48:39 pm
content: garden solar lights are not a viable option hacked or not... lots of them are designed around an YX8018 joule thief chip which charges a NiCd/NiMh battery during daytime and discharges it to light a single LED.. there are other YX8xxx chips to light 2-3 leds but unfortunately, i cannot see the YX8128 (i think) anywhere which is charging a li-ion battery and can go up to 1W in LED power....

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 06:03:09 pm
content: Lets do the math to see what minimum battery capacity you actually need. If you can get away with less current (and brightness), the battery capacity required will reduce proportionately. Also we are going to work in WH (Watt hours) rather than the more common AH (Ampere hours), as we need to know the total energy. All calculations rounded to three significant figures.Assume the website is accurate and the LEDs each draw 20mA at 3.0V.10 days * 24 H = 240 H (hours)20 mA * 3.0 V = 60 mW60 mW * 240 H * 25 LEDs =360 WHAt 3V, that's:360 WH / 3 V = 120 AHFor comparison:An Energiser E95 Alkaline D cell is good for about 2000mAH. Over its usable life the voltage will drop from 1.5V to 0.8V averaging about 1.2V, so it can deliver 2 AH * 1.2V = 2.4 WH. That's 0.67% of the energy you need and I'm not even going to bother calculating how many D cells that is.Another comparison:A premium 18650 Li-Ion cell , the Panasonic NCR18650B is rated at 3400 mAH. Its average voltage over its entire usable discharge voltage range will be about 3.7V so it actually stores 3.4 AH * 3.7 V = 12.6 WH. That's 3.49% of the energy you need, so the absolute minimum will be 29 18650 cells.Unfortunately a LED driver that runs from a bank of Lithium cells, wont be 100% efficient - 85% isn't unrealistic for a good one, and generic 18650 cells wont have the high capacity of the Panasonic one. Good quality ones are typically in the range 2000mAH to 2600mAH. Fakes may be much lower. Assuming 2200mAH cells and 85% ( 0.85 ) efficiency in the LED driver, each gives you 2.2 AH * 3.7 V =8.14 WH, result * 0.85 = 6.92 WH effective energy. That's 1.92% of the energy requires so you'll need 52 cells.A further fly in the ointment is Lithium cells behaviour at end of discharge - if you discharge them below 3.0V you will damage them and they may be unrecoverable + attempting to recharge deeply discharged Lithium cells can be hazerdous, so if you use to simple a controller that doesn't have over-discharge protection, any delay getting to them at the end of the event and you'll probably have to scrap them.That scrapyard 100AH car battery I suggested earlier probably has about 60AH capacity left (make sure it load tests OK before purchase). If you don't want to kill it stone dead, you cant use more than 40AH of that. The average voltage over the full discharge range of a Lead Acid battery is approximately 12.3V.40AH * 12.3V =492 WH, result * 0.85 = 418 WH effective energy, which is 137% of the energy you need, so there's margin to spare.Even if you decide that a measly 2mA is bright enough, you'll need six 18650 cells to be reasonably certain they'll run the LEDs long enough.For brightness testing, you could do a lot worse than putting a 100 Ohm resistor and a 1Kiloohm potentiometer (aka 'pot', wired as a rheostat), in series with ONE LED and powering the resulting assembly from 5V. You can use a USB charger wall wart for the 5V if you don't have a variable lab grade power supply. If the wall wart output is over 5.2V, add a Silicon diode in series to drop the voltage a bit.Turn the pot to maximum resistance and the LED will get slightly under 2mA. Turn it to minimum and it will get about 20mA. To measure the LED current, measure the voltage across the 100 ohm resistor. 1V is 10mA, so simply multiply the reading in volts by 10. (If its under a volt and the reading is in mV, divide the number by 100).Its also a good idea to measure the voltage across the LED when you are happy with the brightness.Please also measure the voltage across the LED as close as you can get to 2mA (200mV across the 100 Ohm resistor) and 20ma (2V across the 100 ohm resistor), If you cant get all the way up to 20mA, and you added a diode earlier, turn back the pot, remove the diode and try again, taking care not to go over 20mA.Post the final readings here and we can help you find a cost-effective battery system that will do the job. The 2mA and 20mA LED voltage measurements are to help us design or recommend a suitable driver circuit.

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 06:42:26 pm
content: I am really impressed with ALL your willingness to assist me! I have been reading through all the replies and trying to find a solution. I have never made a doll house before,yet I was familiar with the old way to light a doll house and found that they have not yet moved with tecnollagy to LED lighting. So I went looking and found that train moldels had. Now some of you have mentioned a "STRING" of led's instead of my indevidual lights. Well this would work if I was dong track lighting lol in every room. But to make a doll house LOOK realistic it needs to have lighting in many places. Now I was planning on using up to 5 lights possible in each room. Like a lamp on a table and four strung together to make a chandelier. Now they do have like four already strung together on just two wires that would work for a Chandelier.https://www.modeltrainsoftware.com/4-led-smd.htmlthey also have instructions for installation after reading some of your comments now I am ever afraid of their instructions !https://www.modeltrainsoftware.com/installing-leds.htmlmy plan was to use maybe five single lights in each room run all the wires up behind the walls to the ceiling. wire each room together and then conect all rooms together and tract to power source. Now I can run each room seprate and and have many power sources becasue I have a huge hiding space as part of my structure. Timers or dimmers or any thing I can add to make it work is fine I did buy a remote that will dim the lights as pointing it at each rooms sensorhttps://www.modeltr/Users/REDADRONE/Desktop/24201296_1944587892225561_1237606415_o.jpgainsoftware.com/led-remote-control.htmlThe doll house is on display 10 days 9 to 9 and I will not be able to switch anything on it once its set. I really do appreciate all of you and your understanding of my ignorance of electroics ! Like I said I am an artist and sculpturehttps://www.facebook.com/paula.nerhus.9

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 07:12:46 pm
content: wow you have out done yourself

author: Ian.M
author_rank: Super Contributor
timestamp: November 29, 2017, 07:42:30 pm
content: Thanks for the photo, that really does look like its a bare SMD LED brought out to user friendly wire ends.The dimmer link was badly borked:https://www.modeltrainsoftware.com/led-remote-control.htmlOdds are its a simple PWM controller. Its input voltage needs to match the LEDs you are using. It will help with extending the battery life, but a digital timeswitch programmed for 12 1/2 hours each day (so it comes on 15 minutes before opening and goes off 15 minutes after closing) will immediately reduce the daily consumption by 48% without compromising on brightness. If you are going to use the dimmer, you need to know if it remembers its settings if disconnected over-night, and comes back on when reconnected. If not, you cant use it with a timeswitch.The next thing we need to know is how urgent is this project? If its got to be ready in the next few days, you are S.O.L. as we wont be able to resolve the problems quickly enough. If you've got a couple of weeks or more so you've got time to get parts the prospect's very good. In-between its more iffy - it all depends on how much time you can put in, how quickly you can get parts and how easily you learn and understand new concepts. If you're not comfortable with wiring circuits from a schematic, and you've got a teenage kid around with good marks in Physics, rope them in to help!

author: ez24
author_rank: Super Contributor
timestamp: November 29, 2017, 08:02:07 pm
content: Next are LEDs in the eyeshttps://www.etsy.com/shop/paulanerhusNice dolls. Will they be in the doll house?Seriously, since the doll house is to be seen, is there anyway someone could replace batteries every couple of days? Could you use a car battery?Have you heard of the Arduino?

author: withwings
author_rank: Newbie
timestamp: November 29, 2017, 10:20:26 pm
content: THANK YOU! no my dolls will not be in this house. I am making a mouse house lolI could use a car battery if it is possible

author: ez24
author_rank: Super Contributor
timestamp: November 29, 2017, 11:20:52 pm
content: It is rare that a newbie sticks with us - thanks Usually they get too confused by all the answersDo you have or access to a multimeter? Do you order from Aliexpress, Ebay, or Amazon? If yes, then maybe a cheap voltage regulator and a car battery might work.I am thinking of something like thishttps://smile.amazon.com/SMAKN%C2%AE-Converter-Power-Supply-Module/dp/B00ODL140M/ref=sr_1_3?ie=UTF8&qid=1511994327&sr=8-3&keywords=12v+to+3v+converterBut other members probably will have a better solution. Also I would contact the company and tell them you have 25 LEDs and you want the current use of them. Ask them for the datasheet for the LEDs, everyone would like to see this.It is the current that is driving us nuts.Can you solder the connections? If not maybe something like thishttps://smile.amazon.com/HTTX-Alligator-Clips-10-Pack-5-Pair/dp/B06XNVB66F/ref=sr_1_9?s=electronics&ie=UTF8&qid=1511994539&sr=1-9&keywords=alligator+leadsYou would need something like this for the car batteryhttps://smile.amazon.com/Alligator-Booster-Battery-Charging-Charger/dp/B06XSHQLFZ/ref=sr_1_46?s=electronics&ie=UTF8&qid=1511995196&sr=1-46&keywords=automobile+battery+clampIt would be a very good idea to have a fuse, here is one optionhttps://smile.amazon.com/Replacement-Connector-Emergency-Universal-Chargers/dp/B01857INDU/ref=sr_1_6?s=electronics&ie=UTF8&qid=1511995316&sr=1-6&keywords=automobile+battery+clampBut 200a fuse ? Too much I think. Ten days unattended I think should require a fuse (but much less than 200a). I do not think I have even seen a 200a fuse.Here is another fusehttps://smile.amazon.com/2-pack-Gauge-Fuse-Holders-FUSES/dp/B01NBD7PU9/ref=sr_1_4?s=electronics&ie=UTF8&qid=1511996515&sr=1-4&keywords=fuse+holderSomeone mentioned a buck which is another 12 to 3v convertor and this would be good (maybe the best) if you know how to use a multimeter to adjust it (to 3v and x amps)So I think I (I have a multimeter) would use a buck like thishttps://smile.amazon.com/GEREE-Converter-Transformer-Synchronous-Adjustable/dp/B00TANQW96/ref=sr_1_8?s=electronics&ie=UTF8&qid=1511996987&sr=1-8&keywords=buck+converter+dc+to+dcBut you need to adjust it to your needs, 3v and the required current.So in summary here is what I would use:- car battery- jumpers- car battery jumpers- fuse holder- buck convertorAgain thanks for sticking with usand look forward to pictures

author: Brumby
author_rank: Unknown
timestamp: November 30, 2017, 12:25:37 am
content: Here is a suggestion that is crude - but simple - using a 12V car battery.It relies on the fact that LEDs will work at slightly lower voltages than specified - but at the cost of reduced brightness.Take 5 of your LEDs and connect them in series - that is, make your own string of 5. They will need to be connected with the + of one connected to the - of the next, just like batteries. Connect the free ends of this string to the car battery and see how brightly the LEDs shine.If that isn't great, then extend the string to 9 LEDs and usetwo12V (borrowed?) car batteries connected in series, giving 24V.As with all things simple, there are tradeoffs - and in this case, there is one which might be a deal breaker... As the battery/batteries discharge the voltage will drop, affecting the brightness - with the concern that, before the end of the exhibition, the brightness will have dropped below acceptable levels. Unfortunately, without at least a multimeter, testing of this will take ... ... 10 days per test.

author: Gregg
author_rank: Super Contributor
timestamp: November 30, 2017, 12:42:39 am
content: To save power, perhaps you could incorporate some passive IR sensors that would turn on the lights only when someone came near the dollhouse. Search for "PIR sensor" "PIR switch" "Passive infrared" etc. for some pictures and ideas.

author: Ian.M
author_rank: Super Contributor
timestamp: November 30, 2017, 01:19:31 am
content: 5 nominally 3V LEDs in series off a battery which when fully charged and rested will be at about 12.6V, certainly under 13V?That's between 2.6V and 2.5V per LED to start with, dropping to maybe 2.4V to 2.3V as the battery discharges. If you want to get an idea of how dim that will be, take the 3V 2xAA battery holder that came with the dimmer kit, and with fresh batteries (or at least ones new enough to give the full 3V at its output), put a single Silicon diode*in series with the anode lead connected to the red lead of the battery holder, then connect a single LED, black leads from the holder and LED together, red lead to the cathode lead of the diode. The diode will drop enough voltage to put the LED voltage in the 2.4V to 2.5V balllpark and you'll see just how feeble the glow from those LEDs will be without having to wire them all up first.The car battery itself is a great idea - we've just got to be smarter what we put between the battery and the LEDs. e.g. an EBAY (or Amazon which will be quicker) LM2596 buck module adjusted down to 3.5V a 47 ohm resistor in series with each individual LED would be a good start. the black leads of all the LEDs go together, the red lead of each goes toits OWNresistor and the other leads of all the resistors go together. You would need to set the output voltage of the LM2596 module to 3.50V *BEFORE* connecting any LEDs as over-voltage could easily blow them. Check its still 3.50V powering a torch bulb, then you are OK to hook it up.You can carefully trim the brightness with the voltage adjustment - *DON'T* go over 3.95V - you may want to practice with the LEDs disconnected.This would be compatible with using a timeswitch - just put the timeswitch between the LM2596 module and the battery. Remember, car batteries can supply dangerously large amounts of current so always put an inline fuse in the positive lead next to the battery terminal. 1A should be suitable for this application. Reverse connection would kill the LM2596 module so either be very careful or put a silicon diode*in series with the battery positive lead as well, cathode away from the battery.* The diode should be a nominally 1A 1N400x series, or 3A 1N540x series (where x is 1 to 7) , or similar. The end with the stripe round the body is the cathode, the other end is the anode.

author: Brumby
author_rank: Unknown
timestamp: November 30, 2017, 01:51:41 am
content: Quote from: Ian.M on November 30, 2017, 01:19:31 amThat's why I added the 24V (nominal) alternative. Having 2 batteries also doubles the available energy capacity. Want to try 3 batteries and a string of 13 LEDs?All these ideas are well and good - for people like you and me - but for someone who has been quite open and honest about their abilities, I just wanted to offer some alternatives that they could manage.The result may not be any good, but it is an easy experiment - and WE do not know what level of brightness would be acceptable.

author: IanB
author_rank: Super Contributor
timestamp: November 30, 2017, 02:01:01 am
content: Rather than asking to buy resistors, buck modules, time switches and so on, how about a simpler option?On the web site selling these, they have LEDs pre-wired with a series resistor for 5-12 V DC:https://www.modeltrainsoftware.com/smd-chip-leds.htmlThis is nice, because two of these could be put in series off a 12 V battery. Not only that, but at 6 V per LED the current draw would be much reduced from the maximum. (If we say the resistor is sized for 20 mA at 12 V, then the current would be approximately 4 mA at 6 V.)So now, we could consider running 12 pairs of 2 LEDs from a 12 V car battery for a total current draw of only 12 x 4 = 50 mA. Over 240 hours that is 12 Ah. That might even work running the 5-12 V LEDs individually off 6 V lantern batteries (which have a nominal capacity of 10 Ah for the alkaline version).Therefore, proposed solution: Use the 5-12 V chip LEDs with pre-installed series resistor. Group up to 8 LEDs to run off a 6 V lantern battery. Use 3 or more lantern batteries according to the number of LEDs required.

author: Ian.M
author_rank: Super Contributor
timestamp: November 30, 2017, 03:01:55 am
content: Yep. That would be good. Brute force it with off-the-shelf parts all from the original supplier to avoid egg on face from failure to deliver to, or failure at, the exhibition.

author: Brumby
author_rank: Unknown
timestamp: November 30, 2017, 04:09:29 am
content: I must agree, too. Getting the LEDs already set up with a resistor makes life so much easier to help out our OP.If they can borrow a 12V car battery, using strings of 2 in series would save on purchasing lantern batteries.

author: paulca
author_rank: Super Contributor
timestamp: November 30, 2017, 01:20:54 pm
content: 12V DC Programmable timer (like a VCR or kitchen oven timer)https://www.amazon.co.uk/sourcingmap-Digital-Power-Programmable-Switch/dp/B008999RYY3V Regulator to give you the voltage for the LED strips (or wire 4 strips in series).https://www.thebatteryshop.co.uk/yuasa-12v-60ah-620a-silver-car-battery-ybx5075-hsb075-8590-p.asp(60Ah car battery or borrow one)