Hello,

So I built a 5s 18650 battery pack with 5 Samsung 30q. I originally thought I had a BMS but i think what I have purchased is actually just a protection board, I don't know how much balancing it will do. Anyway, I was originally planning to charge with a CV step-up converter (and current limited supply) to 20V for a start. However I have since read that charging is more complicated than that and I should be charging CC followed by CV and a limited current. And I need to probably find a better way to balance the cells.

Either way, the battery pack is being used as a portable power supply (where I need about 19V) so I need to find a way to charge it that is portable and could sit within the sealed package. Charging could come from a 5v or 12V source (not worried about how long it takes to charge from a lower voltage source).

Could anyone recommend a suitable board to charge this battery pack from those sorts of voltages of supplies?

Any help would be much appreciated

 

Have you considered one of the inexpensive chargers on the market? iMax B6 and its clones are pretty cheap (https://www.ebay.com/itm/IMax-B6-Di...hash=item2aab612bb5:m:mZhteNE7dD7mQCts2OfxcSA ).

 

You must use a charge balancing controller. A protection board will prevent disastrous failure but can still allow individual cells to get to a voltage sufficiently high to dramatically shorten their lives after a few cycles. A protection board alone will probably make the imbalance worse since it will cut off all charging as soon as the lowest-capacity cell reaches the overcharge limit voltage. That cell suffers from being overcharged while others may stay undercharged.

Constant current is a bit of a misnomer for lithium ion charging. The important thing is not to keep the current constant but to be sure that the current does not exceed the allowable maximum for the cells. It is perfectly OK if the current is far below the maximum. However, if you apply a voltage equal to the allowable maximum (or even less, depending on the start of charge of the cells) and don't have current limiting, the current will exceed the allowable maximum. Constant voltage charging, with proper balancing, assures that the maximum recommended charge voltage isn't exceeded. Most chargers end charging when the current falls below some threshold which ideally is dependent on the cells' rating. Keeping lithium ion cells on "float" charging where the voltage is maintained at the maximum for a long time is somewhat harmful. Some chargers have a timer function as an extra measure. Lithium ion cell total deliverable energy over the useful life of the cell is actually increased if the cells are always undercharged to some extent.

Charging from a source voltage less than the cell voltage will require a boost converter to power the charger circuit. You may be able to find an integrated charger with all the required functions on a single board, but I rather doubt it.

 

@ebp
Check out the iMax B6 and its clones. It has an additional feature as well. Fully charged cells degrade more rapidly than ones charged to about 3.8V each. As a result, the old NiCd/NiMH procedure of charging the night before using is not recommended. May modelers, myself included, routinely discharge cells to a storage voltage and only charge to the full voltage just before we need it. That charger not only charges, but allows you to discharge to a storage voltage.

I am not selling iMax, but I have one, and it replaced 3 other MCU-controlled chargers I had collected over the years. I have not puffed a cell since I got it last Spring. One wasted 5S battery pack will pay for that charger easily.

 

Thank you very much for all that advice.

I have looked at the IMAX b6, it's brilliant but I really want to build an enclosed battery pack, what I need is a PCB not a whole device really if that makes sense?

I bought the BMS thinking it was a balancing one as well, I have since realizdd it's just a protection board. So I will need a balance/charging board. Can anyone recommend me one for 5S please?

The one I bought is this one: https://www.ebay.co.uk/itm/5S-15A-L...BMS-18-5V-Cell-Protection-Board-/292775291492

The current supply will be limited a long way below what the batteries can take so I'm not worried about that. Sounds like I was on track originally with my step up board and all I need now is a balance board for the cells. I will probably just charge the battery to 19V (3.8V per cell) for a start as I don't need the whole capacity not the cells and I'd rather be safe and keep them longer for now. So set the step up board CV to 19V and let the balance board do it's thing. Then I expect I shouldn't have any problems, I just need to find a suitable balance board?

 

The product you've bought is fine , and is all you need .
Just make sure all the cells are approximately charged to the same voltage before you wire them permanently in place ...
If each cell has it's own connection to the circuit board , this indicates that each cell is monitored individually and kept within safe limits ...
Technically it does not 'balance' the cells , but it still protects them completely.
The one disadvantage with these is it charges to 4.2 V... if cells are charged to 3.93V they will last 10 times longer (4000 cycles ) but give only 65% capacity, this may not be important for many applications as 400cycles (4.2V) is quiet a lot.

If your input voltage is 19V this may prevent charging to the full 4.2V ..I'm not sure