Simplest 3S or 4S lithium ion protection circuit?

[eccerr0r]

Well, I ended up ordering one from china (ugh) ... probably need to pay tariff on them, but oh well... or really?

Since it will take a month before I get it, I decided to draw up a circuit using easily available parts to build one that assumedly has the same structure as the made in china ones:

- 4S
- Protection from overdischarge
- Protection from overcharge
- Balancing function

The design I came up with is pretty horrible, uses about 5 or so mA which will consume and then proceed to kill a 2Ah pack in 2 weeks with no load. Alas this is about as good as it gets, using generic ICs - used generic LM324 and LM358 op amps, and all through hole components.

Then I decided to see what would happen if I tried to layout the design so I could possibly fabricate it with a bit of ferric oxide and a blank. YOW, too many parts and wires to draw, too lazy. I ended up shelving this for now *sigh* ... BOM is like:

- 2 LM324
- 1 LM358
- 5 2n7000
- 2 IRF630
- ~25 resistors
- ~10 signal diodes
- ~5 zener diodes

and though it's still not perfectly accurate, it should be able to both protect charge and discharge, as well as rudimentary balancing. There's no microcontroller so there's no fuel gauge, but the protection should work I hope.

I probably could omit the balancing and charge protection for my purposes but they would be very helpful to have since I don't have a charger and needless to say no balancing charger...

So anyone come across a simpler 4S design that uses off the shelf parts?

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Here is something you might want to take a look at

https://www.ebay.com/itm/3S-4S-6S-10...53.m2749.l2649

I have bought one but I have not had the time to hook it up and try it

But when I have some time to devote to this device I will post my findings

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Yeah I bought one, not exactly that because I need protection more than balancing at this point, but it's in the mail.

Was just wondering if one can be made easily in the meantime. This unfortunately uses little SOIC8 ICs, so might not be easily sourceable components.

I ended up hacking up yet another design that leaks 10x more energy, but very simple to understand and debug Not going to build it, it uses up way too much power, will kill a 2Ah pack in less than 2 days

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

If you find what you are can you please post it I would be very interested in it

Thanks

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

This is my super simple design, it's very, very crappy but *should* do as it was designed. Main problems are that there's no voltage calibration (voltage offsets may not be correct), drains a lot of current, and even oscillates

However it should do what it was designed to do: protect from overdischarge, overcharge, and even balances (though very poorly):

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Dammit. After thinking about this and playing with some lithium ion batteries I have... even 2S packs need balancing...where did I ever see that people don't balance 2S...unless you get real lucky and find cells that match perfectly...
Just that I'm playing with old used cells, the capacities are all over the place, and my cells are nowhere near matched. I wonder when I'll have a cell immolate...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

I have not found a solution for this problem with cells that are not balanced

But I have found a solution ( for $20.00 the last time I bought them ) if you want to use a battery pack that is you used for a power tool and it is the power tool that runs on 24 volts

This is one that I used for my battery operated soldering station and battery are made by Samsung and the batteries are very balanced and you can find them at Lowes their brand Kobalt

Here https://www.lowes.com/search?searchT...4+volt+battery

The running time on my battery operated soldering iron was about 2 hours at 400*C
I was very pleased with the results ( I was Desoldiering some panel indicator light bulb and installing new ones where 120 volt AC was not near by the machine I had two machines that I had to do this on) this was the first time that I have used this battery operated soldering for this long at one time

If you are wanting a 12 volt version then also look at Harbor Freight ( yes I know what you think but hear me out about this idea ) the NEW line of power tool that they have

https://www.harborfreight.com/12v-20...ery-56566.html ( for about $20.00 )

These battery packs have Samsung batteries in them

I have done some testing on them and results are very good but I have not seen this series before but I did look them up on google and they do have the data sheet for this battery

Now I have not done any real testing on the charging protection board but I will do some testing soon because I have a project that I thinking about doing that I am going try this battery pack on

I hope this helps you

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

I actually don't care too much of the exact voltage, but higher is better. However I was thinking more like several tens of ampere hours after putting everything together. The old tired cells I have already are pretty worn but I figure if I have a *lot* of them it will still be sufficient even with the poor shape of the cells.

I suspect that I still need to figure out which cells are weak and do real balancing...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

I have found that closer the milliamperes match the better the BSM boards work

( but I also look at how long a battery stays above 3.00 volts and { how many milliamperes are showing at this point in time} and use this as a comparison which to me is a better way of matching cells )

I have seen people on YouTube take cells that match in milliamperes in one cell slot and match them to the next slot

Now you might 3 batteries in one slot and 4 batteries in the next slot and so on I have not tried this approach yet but I given this idea some thought a few times before but I have not yet tried it myself

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

still need a source for more cells...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Are you looking for 18650 or something else let me know what you are looking for if it something else if not 18650

Let me know either way I might be able to help you

Do these batteries need to be well known brands or can be other brands

How many cells are you looking for

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Still haven't figured out a way to deal with mismatch and theoretically I won't care if it's 18650 or not... I have a few li-ion pouch cells that I'm planning to put into Frankenstein...

I also have two 26650 cells that have protection on them, question is whether I want to use them and thus need to remove the cell protection circuitry and use the pack protection...

[ChaosLegionnaire]

Re: Simplest 3S or 4S lithium ion protection circuit?

just a humble safety reminder here to members tinkering with lithium batteries. for high density lithium battery packs, once they catch fire, the fire can be impossible to put out and can burn for days. read the following articles on the dangers:

Why the Fire that Incinerated a Tesla Was Such a Nightmare to Put Out

Why Tesla's electric cars can burn hours after a crash

What First Responders Don’t Know About Fiery Electric Vehicles

stay safe, brothers! im not gonna be the one responsible for cleaning your ashes off the floor!! lol!

[petehall347]

Re: Simplest 3S or 4S lithium ion protection circuit?

them damn things get hot pretty quickly . last time i played at trying to rebuild a battery pack it ended up with it being thrown out of the door out of harms way . it didn't set on fire though as i expected it to .

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

IMHO it's either luck or sloppiness. If it's luck, it wasn't my fault and it is what it is. If it's sloppiness, it's my fault anyway.

I've shorted cells by accident and burned myself once, but luckily noticed before immolation.

And ahh...got the protection board. Might need to get a few more for other uses...

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

And ahh...got the protection board. Might need to get a few more for other uses...

Can you please post the link where you are getting them from

I once was real sloppy and some what of a hurry to get a battery case a part on a pouch battery using a metal prying device and the battery went violently into a fire ball hissing and sparking got it out of the house and near a water hose and put it out —> scared the crap out me

I have lot more respect for these batteries and lot more careful about how I take a part battery cases

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

Fleabay... They haven't been so bad, most that have decent rep work well, it's the low overall rep that have problems. Just need to watch out the "too good to be true" vendors.

And no, water on lithium is not a good idea. Best to deal with batteries when they are discharged and don't shove metal into metal if you're not sure it's safe to do so. Then again, shorting for a short period of time (like milliseconds) shouldn't be a big deal. Just avoid it, whenever possible.

I guess another good thing is that these expended old batteries have high internal resistance and thus cannot dump out all their energy fast, so one has more time before they immolate.

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

Pouch battery once you short it there is no going back it goes directly into cell failure right away

If you do this to a 18650 battery it might spark a little bit and hiss a little bit but does not go directly into cell failure

[sam_sam_sam]

Re: Simplest 3S or 4S lithium ion protection circuit?

I guess another good thing is that these expended old batteries have high internal resistance and thus cannot dump out all their energy fast, so one has more time before they immolate.

Let me know what kind of run time results you get with these type of batteries and if they are useful when you put your battery packs together

I am very interested in your results

[eccerr0r]

Re: Simplest 3S or 4S lithium ion protection circuit?

interesting... I shorted a prismatic cell for a second or so, which I guess it is sort of pouch, the wire got red hot real fast and I burned myself as I didn't notice... Bad me.

The first set of worn 18650s I'm using is basically from the same set of cells from a laptop. It's no magic - from a dead laptop to a custom pack, the battery isn't any better than before, but at least I can run fairly heavy loads without having to worry about cells overdischarging. I was able to power a 50W car headlamp, which is a bit high for the headlamp technically, but the cell condition was so crappy the voltage dropped down significantly. But the light did turn on for all of a good few minutes and the battery was consumed.

However not quite dead, after disconnecting, it will run the lamp a few more seconds after reconnecting. Also I was able to run my netbook with the pack and a DC-DC converter even with it partially discharged, but eventually it too could not power the DC-DC converter and shut down.

Eventually I need to recharge it of course. So, I tried charging it earlier today with +20V, it did not like it very much. It shut down fairly quickly once the batteries got up to voltage. I put a resistor in series and it charged much better, staying at voltage up until 16.8V or so as expected.

I will need to add more cells of course. As well as adding monitoring so I can do some pack analysis...