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Splitting up a 14s pack to balance

Posted: Jul 26 2019 9:23am
by la8rat
Hi. Just got my first ever battery welded together. Went very easy with my diy car battery welder.
Ive added 3 balance leads 5s 4s and 5s to make the 14s.

Is there any technical reason why i cant and 4 charge leads at cell 1 negative, the join between 5 and 6, the join between 9 and 10 and cell 14 positive.

Thinking i can use my duel 6s balance charger to charge the 2x5s cells and then the 4s after.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 10:49am
by fechter
Should work except you have to do one section at a time. You can't do more than one at time unless the balance chargers are isolated.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 11:15am
by la8rat
fechter wrote:
Jul 26 2019 10:49am
Should work except you have to do one section at a time. You can't do more than one at time unless the balance chargers are isolated.
Cheers for the prompt reply.

Would charging the two 5 packs at each end together be ok leaving the 4s in the middle to charge on its own after?

My charger is the ..HTRC C240 rc charger LiPo DUO AC/150W DC/240W Dual Channel 10A Balance Discharger.

Not had it long but it does seem that the 2 banks are separate. Apart from both using the same power supply.

If i have to do the 3 parts one at a time its not a huge deal.

Thanks again :thumb:

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 12:52pm
by flat tire
A better situation for RC charging would have been to make 2 totally separate 7s packs and get a charger(s) that does >=7s. Then you can parallel or series the 2 packs as necessary with separate harness.

But, you shouldn't have to balance very often at all if your cells are good and you don't discharge too far. So if you have a good bulk charger to charge the entire 14s at once without balancing it really may not matter.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 1:09pm
by la8rat
That option has gone as the pack is built. Plus my charger is dual 6s.
My bulk 52v charger is ok i guess. But i wont be using a bms. The cells are brand new Samsung 35E's

Im only charging up to 4.1 and discharging down to 2.8 for cell life extension

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 1:16pm
by fechter
If the two balance chargers are coming off the same supply, you can't use them at the same time unless you break the series connection between the pack sections.

If you had two separate supplies running separate balance chargers, then you could run them at the same time.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 1:31pm
by flat tire
Why do you mention you won't be using a BMS? That's 100% obvious and it won't stop you from bulk charging.

I haven't used that cell or any 18650 in years but make sure the 2.8 discharge cutoff is leaving all your cells perfectly balanced. It may be a little low for that. You may want to stop above 3v.

Like I said with proper discharge cutoff and new matched cells you probably won't need to balance for MONTHS, riding every day. Figure out what that cutoff is.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 1:45pm
by la8rat
fechter wrote:
Jul 26 2019 1:16pm
If the two balance chargers are coming off the same supply, you can't use them at the same time unless you break the series connection between the pack sections.

If you had two separate supplies running separate balance chargers, then you could run them at the same time.
Ok cheers. I would probably have tried if you hadn't had said :shock: as stated above once the pack is balanced it shouldnt need to much keeping on top of with the cells being new.

Err. Not sure why i mentioned no bms. I didnt think it was that obvious. I was going to use a bluetooth bms so i could keep an eye on state of balance. The only 14s bluetooth bms on ebay sounded a bit naff, and ive read that most bms only balance when charging to 4.2. For that reason i didnt really see the point in having one. As i can set low voltage cut off point on my tsdz2 open source firmware.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 3:11pm
by flat tire
Well because if you had a BMS you would just use that to balance the whole thing at once automatically and this thread would be moot.

Even though that sounds like a big sell on a BMS I don't personally use them since I view it as just another point of failure.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 3:18pm
by 999zip999
Bulk charge check with a cellog or clone . If needed balance charge thru sense wire after fully charged to check then balance if needed. Just learn your pack and monitor and monitor. It will teach you. What amp rate is your discharge ? You may only be able to charge at 4amp thru the sense wires.
I have worn out three sets of sense wires over 6years.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 3:52pm
by dustNbone
This is basically what I do with my 16S lifepo4 pack, I have 2 6S balance leads and a 4S one, no BMS. I bulk charge with a 5A charger, balance charge (with an iMax B6) occasionally.

Balancing only one bank at a time is no big deal, it literally only takes a few minutes at the most as after bulk charging there's very little difference in cell voltages, and that's a pack that's done an insane number of cycles (thousands).

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 9:58pm
by la8rat
My amp discharge rate is set at 10 i may up that to 11.

My pack is only 4p so 4 amp charging is as high as id ever want to go.

Id rather have a slower charge and longer pack cycle life.

Re: Splitting up a 14s pack to balance

Posted: Jul 26 2019 10:20pm
by 999zip999
2 or 3amp better. It depemds on quality of cells.

Re: Splitting up a 14s pack to balance

Posted: Jul 27 2019 11:33am
by la8rat
Got all my charge leads soldiered on today. Im going to use an old 48v 2 amp charger to get the pack most of the way to 4.1 and then use balance charger to top off.

Re: Splitting up a 14s pack to balance

Posted: Jul 27 2019 1:38pm
by 999zip999
? 48v charger what type and what voltage ? Sla or ?Check voltage and polarity.
What cells are they where dod you get them.

Re: Splitting up a 14s pack to balance

Posted: Sep 21 2019 5:54am
by la8rat
Been out riding and enjoying the bike so not been posting.

Turns out my other charger the 52v 2a one outputs exactly 57.4v which perfectly takes me up to 4.1 per cell with zero messing about.
The cells are Samsung pink 35e all brand new from nkon in the Netherlands.

I bought 70. I used 56 in my 14s4p build had 1 dud which i binned used 8 in a separate power bank for phone charging and have a few spare for another little project.

Did a 46 mile ride the other day. Mostly flat down canal into Manchester. Had 48% left at the end.
Im very pleased with the cells and the final pack

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Re: Splitting up a 14s pack to balance

Posted: Sep 21 2019 4:26pm
by 999zip999
Do you have sense wires for cell log ? I would bulk charge check at end of charge and balance if needed. I have a una9plus + thru the sense wire charger up to 8amp if you have heavy sense wires. Just check and love you human bms. Don't find the bottom. Lvc.