Wanted: Small 3S lipo balance charger module with pcm

[Psi]

Hi,

I'm looking to replace the small 12V SLA battery in my home automation control system with 3 lipo cells in series.
(This is a home built DIY system, not an off the shelf system, so no comments saying i should leave it alone and just replace with another SLA)

To do the switch i need to find something to both charge and protect the lipo cells.
I want to float charge them at 3.9-4.0V per cell so they are always ready but never charged so high as to cause damage over time.

Has anyone seen a small module for sale with the following specs

- Small, either a bare pcb module or a small box (eg, around the size of a SSD)
- Around 12-14V DC input
- Will balance charge 3 lithium cells in series with a programmable cutoff voltage
- Charge current around 0.5 - 2A   (it really doesn't matter to much if it takes ages to charge)
- Will protect the 3 lipos from over discharge and disconnect them from the load.
- Has a built in DC boost controller on board, since input is 12V and 3x lips are 12.6V

I've been browsing aliexpress and other sites but all i can find is PCMs or chargers, nothing that is all in one.

Any ideas?

[Dubbie]

I looked for something like this recently and came up with nothing. Keen to see if anyone here has suggestions.

[hli]

Does it really need to be all-in-one? Ebay and Ali have tons of balancer/protection boards, and a CV/CC module is also not too expensive. For the latter - look for one with 3 LEDs, as they can show you end-of-charge (they detect when the constant current has dropped below 1/10th of the set current). Maybe you get two boards of nearly the same size, then you could sandwich them.

[Psi]

The protection module on lipos is a last resort and shouldnt do anything unless there is a fault.
So i would still need a proper lipo charge controller with disconnect and its own protection

[electronicsdude]

Would something like this work? BMS plus charger
 http://s.aliexpress.com/ArIj2MV7

[Psi]

Maybe, its cheap enough to try

[hli]

I seriously doubt that this is a charger. Most likely it is only a balancer+protection board:

• no mentions of a charge current
• there is no charger IC on the PCB (the 3 SOT23-6 are for the balancing and protection)

I have a similar board in a recent project of mine, which acts as a balancer for a simple charger (a XL4015 CV/CC module, together with a relay to disconnect it from the battery).

[Jeroen3]

I have searched for this recently.
You can only get protection boards or charger board. Not both.

[station240]

Few problems with your understanding, and hence implementation.

1) Cells are nominal 3.7V, min 3.0V, max/charge 4.2V, so 3S is 11.1V, 9V, 12.6V.
So charging a heavily depleted battery from 12-14V input needs buck, charging a battery with higher state of charge need boost.
2) What sort of voltage range is your home automation control system rated to ?
3) no figure is given for the size of the cells or the amount of current you system draws.
4) There is no "float charge" for Lithium Ion, unless you want to damage the cells. They are pretty much Constant Voltage charging with current limit, the stop charging point is when current drops to a low value (75mA is a commonly given value).

An easy way out is to get a LiFePO4 SLA replacement battery,  they range from not cheap to silly prices. However it's a black box, with self contained electronics to manage/protect the cell. Also they are configured as 4S 3.2V nominal per cell.

[Dubbie]

Not sure why you think OP doesn’t understand that stuff, but I also I wanted to point out that you can float charge lipos if you are careful with temps and choose voltage and batteries carefully.

See: https://www.electronicsweekly.com/market-sectors/power/float-charging-lithium-ion-cells-2006-02/

[Psi]

Few problems with your understanding, and hence implementation.

1) Cells are nominal 3.7V, min 3.0V, max/charge 4.2V, so 3S is 11.1V, 9V, 12.6V.
So charging a heavily depleted battery from 12-14V input needs buck, charging a battery with higher state of charge need boost.

The charger does buck internally, this was more of a given since a battery charger by design has to step down voltage.
My comment was that the charger needs to boost the 12V coming in so a higher voltage so it can charge a 3S lipo above 12V input. This sort of lipo charger with boost is common in the RC world where you can charge a 6S lipo from 12V DC wall adapter.

2) What sort of voltage range is your home automation control system rated to ?

Currently the 12V bus is used to run 12V door locks and some step down regs for other things. Those are rated for 15V.
The door locks are probably ok up to 13.8V

3) no figure is given for the size of the cells or the amount of current you system draws.

Doesn't really matter, i gave the charge current needed as 0.5 - 2A.
System draw is complex as it depends what its doing and it will shutdown the SBC's if mains fails. In that state it just needs 500mA for door locks and 100mA for primary control MCU

4) There is no "float charge" for Lithium Ion, unless you want to damage the cells. They are pretty much Constant Voltage charging with current limit, the stop charging point is when current drops to a low value (75mA is a commonly given value).

You can float charge a lipo easily as long as you don't need full capacity. You are simply charging them up to a set voltage which is under their 4.2V max. 3.9V for example which provides long lifespan.
The current goes to zero once they hit 3.9V and charging is stopped by design.

An easy way out is to get a LiFePO4 SLA replacement battery,  they range from not cheap to silly prices. However it's a black box, with self contained electronics to manage/protect the cell. Also they are configured as 4S 3.2V nominal per cell.

That is useful to know, i didnt know they existed. Thanks

[Red Squirrel]

I was searching for this stuff real quick for fun, as I was thinking it would be neat to make some "smart" battery packs that use 18650's and simply take an unregulated DC input directly for charging and has the charger portion built in.  Could use these for various things that require battery power and standardize a couple packs for use in these projects.   But I found a lot of these chips don't actually have a lead for each cell but state they can charge multiple cells, how does this work exactly?  Don't you need to balance charge lithium ion batteries?  You can't just stick multiple cells in series unless you want to celebrate the birth of your country.    Or can you actually get away with that if you limit the current and voltage enough, but just sacrifice a bit of charge?

This is where lead acid batteries are nice since you can just stick a bunch of cells in series and float them indefinitely.  That's basically what the telcos do and all the equipment runs off DC.  Solar would be similar too.