Battery charging in parallel

[Bgt2u]

Just a quick question for everyone. If you have 4-48v 10ah lipo battery packs, wired in parallel, and they are rated 2 amps normal charge (or 5 amps fast charge), what amperage charger should be used for either a fast or normal charge? Or does that rate even change when wired parallel?

 

[itsid]

it does change

simple math actually.. each pack 2Amps.. 4 packs = 8Amps
and similarly for fast charge... each pack 5Amps, four packs = 20 Amps

I'd stay just below tbh..
say 1.7 and 4.5 (making the charger provide 7 or respectively 18 Amps)

ideally though get a multipack charger though and do not charge in parallel,
that way you do not have to think about balancing the individual packs too much

'sid

 

[Bgt2u]

Thank you. One question comes to mind though. If l use a multipack charger, how do l not charge in parallel, without disconnecting them, if packs are wired that way? Also, if each pack has it's own bms, than doesn't that help, due to auto cut off voltage?

 

[itsid]

well.. if you solder the packs together that'd be a problem
if you use a a splitter with proper connectors
you can swap and charge individual packs no problem

the individual BMS can be the problem here btw..
say one BMS shuts down because of a full pack
the charger sees that as an increase in current demand
usually upping the voltage
.. if set to 18A limit for example that current is now split to 3 packs
and each pack could draw 6 amps (too much already)
and if the BMS are not limiting to 5amps, then the remaining batpacks will overheat and maybe die.
if the BMS has a over current or voltage protection for the charging phase they
might switch off before the battery is actually fully charged and you will have the false assumption the batpack is dead.

So yeah, combining batteries is not always a good idea
A smart charger with multiple ports
can charge all batpacks at the same time,
while reading and evaluating all individual BMS responses.
So no such nasty errors can occure as easily.

'sid

 

[Bgt2u]

Great, thanks again for the detailed answer. To avoid all for mentioned problems, I will just connect the packs with unpluggable type connnectors, and charge them separately.

 

[Bgt2u]

My neighbor gave me 4-48v battery packs, instead of my AGM's, so l figured l'd give them a try. Where do l find a multiport charger? I couldn't find anything close on eBay. I would hate to have to use 4 separate chargers...lol.

 

[itsid]

Well there are LiPo chargers for RC enthusiasts that can charge 14S batpacks
(some even several at once)
but I cannot tell you which one to buy or what to look out for I'm afraid..
I don't have any or any use for one (so I haven't cared enough to look for what's what)

'sid

 

[Bgt2u]

I totally understand. I did some looking into the RC stuff, and they use parallel charging boards, but no one specifies what voltage the boards are, or are capable of handling. Everyone seems to be only charging multiple small 3.7v lipo packs....Oh well! In the meantime, until l find a better way, l will just purchase a single 54.6v 5A charger, and charge one pack at a time (an 8 hour process...ugh!).

 

[itsid]

oh they do.. it's the "S"-es they list..
14S capable is what you'll need (that'd be a 58.8V charger)
an S denotes the number of cells in series (hence the letter)
a cell has 3.7V nominal and a 4.2V fully charged (your 54.6V charger thus is a 13S)

since most batteries in the rc world are even serialized a 14S charger is what you need to look out for.
(and yes, they charge 1, 2, 3, 4, 5, 6, 7... S packs just as well.. and 13S too )

13S btw are nominal 48.1V and fully charged 54.6V (sounds familiar?)

But be sure to look out for one that actually can charge multiople 13/14S packs

some can charge multiple packs but just ONE 14S at a time (together with three 6S or so)
that wouldn't help too much.
and keep in mind that that means 1.1kW of power (55V at 20Amps) so you need a beefy powersupply as well

'sid

 

[Bgt2u]

Cool, good information. I do have one more question. The packs that l got from my neighbor are wired 5 parallel/13 series. Wouldn't that make them a 13s, requiring 54.6v charger (versus 14s/58.8v)?

 

[itsid]

Cool, good information. I do have one more question. The packs that l got from my neighbor are wired 5 parallel/13 series. Wouldn't that make them a 13s, requiring 54.6v charger (versus 14s/58.8v)?

yes I know they are 13S

13S btw are nominal 48.1V and fully charged 54.6V (sounds familiar?)

just as your charger is

.....
a cell has 3.7V nominal and a 4.2V fully charged (your 54.6V charger thus is a 13S)

BUT

since most batteries in the rc world are even serialized a 14S charger is what you need to look out for.

since chargers for up to 14S are just more common
than ones that can charge up to 13S
And the important bit I think you are asking for

(and yes, they charge 1, 2, 3, 4, 5, 6, 7... S packs just as well.. and 13S too )

So forgive me,
but I think I already answered that question

'sid

 

[Bgt2u]

Multiple battpack charging with low amp charger

I have not been able to find a multiport charger that will work for my application. All 4 of my batpacks are the same, have a BMS, slow charge at 2A, and fast charge at 5A. Could l simply (slowly) charge all of them at once, with a 5A charger, providing 1.25A to each pack? I figure once each pack reaches it's max voltage, each BMS will cut off, but at no time could any pack overcharge due to the max 5A charge rate. Is this correct, and would a slow charge of 1.25A (vs 2A), cause any damage to the batpacks?

 

[itsid]

Simple anser: NO, you can't

more complicated answer:
the term BMS is not a guarantee for charging safety.
Some just record cell state and shut down on errors
(irrecoverable shut down to prevent a fire)

Some actively monitor and report back states to let the charger know what to do exactly.

Very few are actively limiting (turning off power just before overheating and recovering on their own to reuse that battery later on)

So once a battery actively cuts off (and not just let's you and/or the charger know it's fully charged) it's a fair guess that that battery will no longer be working at all.

Now.. a dumb charger would in theory be still charging all the batpacks
it's just likely that three to four of them are rendered dead afterwards.
A smarter one sees the "jump" in demand and cuts off charging,
so one dead and four half charged batpacks.

You need a charger that takes the monitoring result of each pack and cuts off itself
PER pack

I'd rather get a power strip and put 4 such 5A chargers into service tbh.

'sid

PS I thik Graupner has a battery charger that at least can do two 14S at a time
(200 bucks IIRC) I'll check

 

[Bgt2u]

Thanks again for your input...l'm sure the batpacks thank you too��! Per your suggestion, l am just going to put 4 chargers on a power strip, and charge them that way. It also is a lot cheaper than the multiport charger option. I have wired the batpacks to a (4 slot) blade switch, so l can disconnect them all at once before charging, without unplugging anything. Now l just have to buy 3 more chargers, until then, it's one at a time...ugh! One moe quick question for you, What size fuse do you recommend that l use for each batpack (48v, 10.5ah, 13s3p)?

 

[itsid]

that largely depends on the cells in use in each batpack.
well solely on the cells if it weren't for the BMS...

You need a spec sheet to tell what rating the cells have exactly.
and only that can tell what fuse to install.

if they're clear sleeved maybe you can read the model number of the cell wrap *shrugs*

'sid

 

[Bgt2u]

The cells are: Sanyo 18650GA, rated at 3500mah. Right now, l have each pack fused at 35A. I feel that is a bit much, but at least l have some protection.

 

[itsid]

okay so Sanyo 18650GA..
(hopefully originals.. since they're with the VC6 Sonys amongst the most copied ones I'm afraid)
but let's just say they are original Sanyo 18650GA

Those have a peak discharge current of 10 Amps, a max constant discharge rate of 8Amps.
Since you have a 3P batpack
the maximum discharge current per battery is 30Amps and the recommended constant discharge should be lower than 24Amps.
Any fuse higher than 30 Amps is pointless and no suitable battery protection whatsoever I'm afraid.
(it'll prevent a dead short.. but that's it.. you can still destroy the batteries without the fuse popping)

I understood you correctly that you power the kart with all four of them simultaneously, right?
(two per motor/controller combo, correct? max demand thus is 43Amps IIRC per pack of two batteries)
So personally I'd get a 45Amp fuse and put that on a parallel pack of two
gives you enough safety margin to never exceed the 8amp constant rating they have
you can also pick a 50Amp for each twin-set.. or a 25Amp per battery
that should still suit your needs rather well
and gives you the warm feeling that the battery
will never even have to reach their max discharge rating which will keep them safe and hopefully cool at all times.

'sid

 

[Bgt2u]

Yes, all 4 packs are wired parallel, into the 2 controllers. I figured 35a was too much, however without going to the store, l used what l had. Since each pack comes with it's own fuse holder, l will use 4-25 amp fuses. Thanks again for the advice!

 

[itsid]

you're very welcome!

Just one side note: if you have two seperate controllers, I see no point in wiring all four in parallel then splitting them up into two parallel controllers again.

that way you can maybe spot differences more easily
say the left is draining faster than the right..
so either a wire became loose or a bearing seized or something

pairing all, splitting back up is only really usefull if all you do is drive in circles all day
(so one motor is meant to take more load then the other)

..just saying

'sid