charging multistar li-po...series or parallel 20s 74v

[Ixlr8]

As stated above, I'm running multistar li-po in 20s1p.....these are rated apiece at 14.8 and 10ah )10,000mah, the way I will be running them will be 20s1p so the voltage will be 74v at 20ah
Question , I have two ways of charging these ...I can charge them in series with a 72-84volt charger going through a separate balancing board. Or would it be better to charge them with my rc charger in parallel, the charger has a balance built in and I will be using a parallel board in order to charge all the batteries at the same time. Cost is of some concern but it figures out to be about the same, so the main thing I'm looking for is safety and correct balancing of a full charge ....I would very much appreciate any help, comments or better ideals..thanks in advance.

Sorry my original posting was a total mess up I had just got off a double shift at work and obviously was not with the program

 

[amberwolf]

As stated above, I'm running multistar li-po in 20s1p.....these are rated apiece at 14.7 and 10,000mah, the way I will be running them will be 20s1p so the voltage will be 72v at 2ah

That's very confusing, and either you're not giving us the right details, or you are misunderstanding how to figure totals from packs/cells.

If they are individually 10Ah, then even in series at 1p (which they are at individually as well), you can't get them to 2Ah, because you'd have to cut the actual cells up and take out 4/5ths of their material to reduce them to that capacity.

They will still be 10Ah even in the series of multiple packs.


However, if they are 2Ah as individual packs, they will *still* be only 2Ah when series up but as 1p.

So either you have 10Ah packs that make a 10Ah 20s 1p pack, or 2Ah packs that make a 2Ah 20s 1p pack, but you won't be making one from the other.

 

[wesnewell]

Assuming you're talking about 5 4s packs in series, then the easiest way to charge them would be a a 20s bms and 84V charger.

 

[dogman dan]

Yes, a bms and full pack voltage bulk charger is definitely easiest. If any cells fail to balance adequately with that method, they are bad cells to be weeded out.

So not safer to use the bms and 20s charger than the RC chargers. However..... Step one for safely running cheap ass shoddy manufactured RC lipo is to sort out any bad cells. Maybe you get all good ones, I did my last 48v 15 ah buy. But other times I did not.

Where I'm heading with this comment is, it might be a very good thing for you to have a cheap 50w rc charger as well. Then you use that charger to run the first 10 cycles or so, charging each pack individually each cycle. Balance them a few cycles, then do some cycles not balancing them, and see how well each cell performs. Keep the discharges moderate, stopping by 3.75v or so. If any cell falls way out of balance used this moderately, (more than .1v ) get rid of that pack. Normal would be at least 5 cycles with none of the cells much more than .05 out of balance.

Then when you are satisfied that all your cells have no defects, assemble the pack with the bms and ride happy. And as always, don't store or charge that thing where a fire would be dangerous.

 

[Ixlr8]

hi, and thanks for your input...............yes 5 4 packs in series

Maybe I explained myself wrong................each battery pack puts out 14.8v at 10ah(10,0000mah) when you put 5 in series you have 74 volts at the same amp hour,,,,ok now you add another series pack in parallel with the first and you have 74volts at 20ah (20,0000).....................any more suggestions out there?... the only problem I see is the 72-84volt charger I have will only do 6amp charge, do you think that would do it?

I could see why you would question my original message amberwolf thats for bringing it to my attention,,,no more typing in my sleep..LOL

 

[Ixlr8]

well looks like the 20s charger I was planning on using no longer wants to charge, can anybody recommend a descent one?
the one I was planning to use I had to hook an auxiliary balancer board to it ...........anybody ever run into a 20s charger with balancer?....oh this is for li-po batteries .........thanks

 

[wesnewell]

Any 84V charger will work. A 6A charger sounds like a good option to me, assuming it doesn't exceed the max charge amps of the BMS you use. Some BMS's have a 5A or less limit. If you want to know how long it will take to charge an empty pack divide the pack AH rating by the charger amp rating. So ~1.67 hours for a 10ah pack.

 

[dogman dan]

Once you have 20 ah, then you can parallel them, then add the bms. To get more specific, you can build two 72v packs, then parallel the main wires, and parallel the balance wires too, then attach the bms.

It would also be an option to parallel individual 4s packs in pairs, then do the series connection of the pairs. Either one works about the same really. They just take different connection methods. I've tended to pair up packs myself, then series. I do this only so I can run both 48v and 24v devices.

 

[Ixlr8]

So nobody every run into these?

 

[wesnewell]

I've never seen a 20s balance charger. 14s is the largest I've seen. Over that I'd pair a bms with a bulk charger at the proper voltage, which would be 84V for 20s.

 

[Ixlr8]

sounds good, so do you or anybody know of a good bulk charger that could be used?

 

[wesnewell]

A few of many places you can get them.
https://bmsbattery.com/16-series-emc-chargers
http://www.aliexpress.com/store/group/72V-84V-87-6V-88-2V-etc/313864_259126766.html
http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1311.R1.TR3.TRC2.A0.H0.X72v+charger.TRS0&_nkw=72v+charger&_sacat=0

 

[bionicdan]

couple of us here would like a test dummy for this $140 2000w one https://bmsbattery.com/ebike-charger-ev-charger/799-c2000-2000watts-lifepo4li-ionlead-acid-battery-charger.html#/425-cool-waterproof/426-ac_voltage-180264vac

 

[KINNINVIEKID]

I would use a pair of NES 350-48 power supplies run in series for this.
I have a pair (in parallel) for my 44.4V Multistar setup.
They have a wide range of voltage adjustment.