Charging 48v battery with unknown charging voltage

[sargi]

Hi there - I've been lurking on here while fiddling and buying lots of bits and bobs, and appreciate the help you guys give by sharing info. This is my first message on here - I couldn't find anything that answered my question so here goes:
I have a 15ah lipo that has a charging voltage (stated on the charger) of 55v and a float of 59v, an eclipse lipo 15ah that has 58.4v on the charger, but I can work out the upper charging voltage by checking the headway cell specs and multiplying (the case is transparent!), but I have hit a snag with my 3rd battery.
It is a 10aH but came with no charger: http://www.ebay.co.uk/itm/Electric-Bike-Battery-48v-10ah-li-ion-battery-/321780348303?
and I have 2 questions.
Firstly, I've checked the voltage and it's at 53.3v, so if I charge it with one of my other chargers that states 55v up to 59v floating charge, will I explode if this battery's limit is lower? It should have a built in BMS so I wondered if the BMS would just shut off the current when it hits the upper limit - is this the case? Is it safe?

The second question is:
I intend to use solar panels and a genasun lithium charge controller, and would like to be able to charge all 3 batteries at the same time - can anyone shed any light on the practicalities or pitfalls, and if this is safe to mix batteries of slightly differing voltages if they all have BMS? I'm trying to save myself a few quid on new batteries and as I haven't started messing around too much yet but your advice or help would be greatly appreciated.

 

[flippy]

48v pack would be a 13S with a charge voltage of 54.6v.

personally i would grab a knife and rip off the blue heat shrink and check what is inside. re-ducktaping the pack is a lot cheaper then blowing it up with the wrong charge, especially if there is no BMS to bleed off the cells or shut it down on overvolt.

lipo mantra: measure twice or blow up your house once....

 

[sargi]

I'm thinking I might cut the sheathing off in the morning and have a proper look, a fire would be catastrophic.
I made a mistake in my previous message, my first two batteries are lifepo4, I guess I'll know the third in when the sun's up!

 

[flippy]

if it is a 15S lifepo4 you can still charge with 54.6, but you need to be sure what it is first.

 

[dogman dan]

Given the situation, I see not much you can sensibly do, except remove the shrink carefully, and see what you actually have. try hard to avoid using anything metal, if possible cut a tiny nick, and then just tear the shrink.

Another possibility, charge to 53v, then measure one cell group. 53v won't overcharge it, unless it's actually 12s which is not very common. That could tell you lifepo4, from NMC or other charges to 4.2v lithium. Either way, you may as well just open it up, and count cells before doing anything.

13s very likely to be charge to 4.2v, and charge it to 54.6v. 14s could be a real weak lifepo4 (charges to 3.65v), or a charges to 4.2v pack. 15 or 16s means a much much better chance it's lifepo4.

Once you have it open, you may still have to charge to 54v or so, and measure one cell to get a clue what it really is. But you might see a label, and while you have it open you can install balance wire plugs. So you can add a bms, or at least keep it balanced manually.

 

[sargi]

I hear you guys, thanks for the guidance. I took it apart and it has an 18/8amp BMS with chinese writing on, and has loads of 18650 cells.
I'll separate the pack out next week to study it more, but it looked like the cells were in groups, with only each group being connected to the BMS - does this mean that the cells are likely to be unbalanced within each group?
And regarding the BMS, if it shuts off when it has reached it's maximum, and this is a safe voltage, why can't I use a higher voltage charger?

 

[flippy]

high voltage cutoff is sadly misnamed, it should be "too high voltage cutoff"

just charge to 54.6 and don't go over. you only gain cell damage.

 

[dogman dan]

NO 54.6v could still be too high. Not likely, but it could be.

Count the groups of cells. Then we can guess if 54.6 is the right voltage. If it's 13 groups of cells, using the 54.6 charger could be ok, but don't use it if it's 12.

If it's 13 cells, (cell groups I mean) then it's very likely to be a charge to 54.6 pack, with cells that charge to 4.2v.

If it's 14 cells, likely to be charge to 4.2v, but full will be 58.8v

If it's 15 cells, likely to be lifepo4, charge to 3.65v x 15

If it's 16 cells, very likely to be lifepo4, but charge 3.65 x 16

The bms may stop overcharge in time. Lifepo4 is very tolerant of overcharge, up to even 4v.

 

[sargi]

Hi guys. So here are a couple of pics of the pack.
They're 3.7v cells, and it looks like there are 52 of them. They're wired in bunches of 4, so does this mean it's a 13s4p? And if so, should they be charged at 13x 3.7v, or 13x4.2v?
I apologise for not quite getting my head around these batteries, I'm a little unsure of the charger voltage, and if that refers to the voltage the charger kicks out, or the voltage the batteries are charged to. And can a 54.6v lifepo4 charger be used to charge a li-ion pack of the same voltage?
I'll be getting a genasun lifepo4 charge controller soon, and am trying to work out which voltage to get it customised to so that it can serve the largest number of batteries safely.

 

[sargi]

Here's a close-up of the cells, 3.7v

 

[sargi]

When checking the voltages, I noticed most groups being charged to 4.1v, but one group being about 3.8v. Now, with the right charger, should I expect the BMS to balance this, or am I looking at replacing a dodgy cell?

 

[Nobuo]

Charging to 54.6V will make the BMS drain all the other serials until this one will reach 4.2V. It will take several time to achieve, you should charge that paralleled group separately.

 

[Ykick]

13S4P - you’re getting the hang of this.

That P group with the lower voltage I’d charge 1S up to the others in series groups. If you don’t have an RC Charger maybe use old cell phone charger but monitor the voltage as cell phone chargers top out over 5V?

Or, get real fancy and rip the 1S BMS from an old cell phone battery (they all have 'em) and rig that to be a 1S charger. I wired USB plug on one to get readily available 5V input. 1S phone battery BMS regulates the output so it won't overcharge. Very handy item for your toolbox.

The BMS might balance it but almost certainly take a long time and depending on how the charger behaves at termination it still may not properly balance your pack.

Easier to just charge the low group 1S and then test everything. Since it’s opened up I’d rig known load and do IR tests on the groups.

Youtube has plenty good videos about IR testing. Many RC Chargers can do it although I don’t trust them as much as a basic manual IR test - voltage/amp measurements and simple calculations.

 

[sargi]

Thanks for that. I've ordered an Imax B6 charger so hopefully it'll all balance nicely.

 

[sargi]

OK guys, I took apart my other li-ion battery (I thought it was lifepo4), and it is also a 13s, so I can use the same charger! So out of the 3 batteries I have, 2 are of the same voltage and type, so I'm pleased - means I should be able to charge them all with the same genasun solar controller when I'm on the road.
So, I now need to confirm, this lifepo4 battery seems to have the same charging voltage and type as the other li-ion batteries, so could I just check with you informed lot if this is definitely the same?
http://www.ebay.co.uk/itm/48v-20Ah-LifepO4-battery-upto-1500w-4Ah-charger-uk-seller-free-postage-/252119877025?hash=item3ab38405a1 I didn't get to 54.6v multiplying the 3.6v of a lifepo4 cell, but the image on the charger says 54.6v (although I've read on here that they're often altered internally), and it doesn't state the charging voltage in the spiel, but the closest figure is the over-charge protection voltage is 54.75v - any pointers please?
Thanks again x