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Trying to make a little powerpack for my boat with old 18650 cells. I am planning on a 1 kWh pack, so charging each cell individually is not an option...

I have planned to set up 10 packs of 4 parallel, and 3 in series giving a nominal voltage around 12 V (this setup makes it easier to check for bad cells for my use). Since the cells are used the need for a protection device is critical.

To charge these packs I need a very very cheap solution.

Solution 1 is to use cheap TP4056 with a battery protection such as this one, 5V Micro USB 1A 18650 Lithium Battery Charging Board Charger Module+Protection for 1 USD a piece and set three of these up for each pack. This module has an builtin battery protection device, a MOSFET ML8205A (I have no idea what this is, but it has high power and current handling capability).

Solution 2: Use cheap 3S basic balance chargers (I have seen these for as low as 3 USD) and get some device to cut the power when under critical charge for each set of parallel.

Any ideas?

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2 Answers 2

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The TP4056 can only charge a single cell at up to 1A. You need a 3 cell charger that can do several amps. 1kWh at 12V equates to 83Ah, which would take over 10 hours to charge at 8A (longer if the batteries are old).

Protection circuits are used to prevent catastrophic over-charge, over-discharge or over-current. A Li-ion charger should automatically limit the peak voltage, a fuse protects against over-current and a voltmeter or low voltage alarm can tell you when the battery is getting low. Protection circuits may not be necessary but they do provide an extra level of protection, particularly against failure of a single cell in a pack.

However protection circuits are not a substitute for balancing. Used cells probably won't be well matched, and weaker cells will reach peak voltage sooner, so balancing is essential (a protection circuit would simply cut off, leaving the pack unbalanced and under-charged). If you want to charge and balance all the packs at once then connect all the balance taps from each pack together to make a single 3S battery.

I suggest using a high current balancing charger such as this, which is cheaper than trying to use a bunch of low power chargers (each of which needs its own isolated power supply).

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  • \$\begingroup\$ Thanks for your reply. Will I not have to have 10 of these balance chargers to make a battery of 1 kwh? The protection device I mentioned was a "cut of" device that cuts the power when under 2,9V. I thought that a TP4056 would charge any number of cells in paralell, even though it will take a lot of time on only 1 amp. So in my configuration I would need 3 TP4056 for each battery of 3S and 4 in paralell. Or am I very wrong on the basics here?? \$\endgroup\$
    – Tor
    Commented Jan 31, 2015 at 21:56
  • \$\begingroup\$ The TPS4056 is a single cell linear charger chip that can barely manage 1A without overheating. It can charge as many cells in parallel as you like - if you don't mind waiting (about 3.5 days to charge an 83Ah battery). To charge a 3S battery you need 3 of them, each with it's own isolated 5V 1A power supply. Cheap - but inefficient, unwieldy, and very slow. On the plus side, that arrangement should keep the cells balanced (so long as none of the chargers fry after running at max power for 3 days continuously!). \$\endgroup\$
    – Bruce Abbott
    Commented Feb 1, 2015 at 2:43
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From what I've seen and read, multiple TP4056s do not need a separate power source. I've seen them used from a single power source with inputs in parallel to said power source. Even if the power source is able to pump out 50 A at 5 V, the TP4056 will only draw a max 1 A (however will have heating issues at 1 A, and a heat sink is recommended). The data sheet also states that the TP4056 will also take up to 8 V on the input.

Where I find a problem with your situation is charging the 3S with 3 TP4056s. If the batteries are already wired in series (whether it be via tabs holders or what ever you are using) I don't see how you can separate the charging leads of the different TP4056s from touching and therefore causing them to also go in series on output? Maybe I am missing something, or just brain farting. Anyways, hope I cleared up some issues regarding the TP4056 input stage.

As for balancing, it would be necessary if using batteries of different age groups and capacities, however these nifty boards might be able to help with that. They can do about 400 W, which is double what the one above could push, however extra time and DIY patience is required: 3S 40A 11.1V 12.6v li-ion BMS PCM battery protection bms pcm with balancing for lithium LicoO2 Limn2O4 18650 li battery.

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