Splitting up a 14s pack to balance

Batteries, Chargers, and Battery Management Systems.
Post Reply
la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Splitting up a 14s pack to balance

Post by la8rat » Jul 26 2019 9:23am

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.

User avatar
fechter   100 GW

100 GW
Posts: 14189
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: Splitting up a 14s pack to balance

Post by fechter » 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.
"One test is worth a thousand opinions"

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Jul 26 2019 11:15am

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:

flat tire   1 MW

1 MW
Posts: 1673
Joined: Feb 26 2014 12:20am

Re: Splitting up a 14s pack to balance

Post by flat tire » Jul 26 2019 12:52pm

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.

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Jul 26 2019 1:09pm

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

User avatar
fechter   100 GW

100 GW
Posts: 14189
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: Splitting up a 14s pack to balance

Post by fechter » 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.
"One test is worth a thousand opinions"

flat tire   1 MW

1 MW
Posts: 1673
Joined: Feb 26 2014 12:20am

Re: Splitting up a 14s pack to balance

Post by flat tire » Jul 26 2019 1:31pm

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.

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Jul 26 2019 1:45pm

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.

flat tire   1 MW

1 MW
Posts: 1673
Joined: Feb 26 2014 12:20am

Re: Splitting up a 14s pack to balance

Post by flat tire » Jul 26 2019 3:11pm

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.

999zip999   100 GW

100 GW
Posts: 8936
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Splitting up a 14s pack to balance

Post by 999zip999 » Jul 26 2019 3:18pm

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.

dustNbone   10 kW

10 kW
Posts: 903
Joined: Mar 13 2016 9:59pm
Location: Vancouver, BC

Re: Splitting up a 14s pack to balance

Post by dustNbone » Jul 26 2019 3:52pm

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).

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Jul 26 2019 9:58pm

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.

999zip999   100 GW

100 GW
Posts: 8936
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Splitting up a 14s pack to balance

Post by 999zip999 » Jul 26 2019 10:20pm

2 or 3amp better. It depemds on quality of cells.

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Jul 27 2019 11:33am

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.

999zip999   100 GW

100 GW
Posts: 8936
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Splitting up a 14s pack to balance

Post by 999zip999 » Jul 27 2019 1:38pm

? 48v charger what type and what voltage ? Sla or ?Check voltage and polarity.
What cells are they where dod you get them.

la8rat   1 W

1 W
Posts: 59
Joined: Mar 12 2019 10:34am

Re: Splitting up a 14s pack to balance

Post by la8rat » Sep 21 2019 5:54am

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

Image

Image

Image

999zip999   100 GW

100 GW
Posts: 8936
Joined: Jan 10 2010 1:40pm
Location: Dana Point So. Cal

Re: Splitting up a 14s pack to balance

Post by 999zip999 » Sep 21 2019 4:26pm

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.

Post Reply