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Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 15:37
by Dan007a
After many hours bottom balancing all my cells for my traction pack.
I have hit a drama with my tsm2500 charger.
I believe the usb cable is toast. And have set the can bus up for 126 v (older cells).
I could only fit 42 cells into the spot. So need to increase the end voltage via can bus.

Question for the day.
I have a elcon charger that heen programed for 45 cells.
Can i use the elcon tc charger and just get the bms or check with meter to shut down before i hit 3.4v . ( middle of cc charge curve on the 160v 45 cell tc charger).
Until i get access to the can bus .

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 15:47
by jonescg
These the blue cells you had shipped up?

Yes you can have the BMS switch the charger off if a cell hits the set upper voltage, but this means it doesn't go through the constant voltage stage of the charge, missing out on about 10% of the capacity available. It's also kind of risky if it doesn't stop the charge for whatever reason.

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 16:00
by Dan007a
Yes they are the blue cells. Think I just grab a few beers and baby sit the cells for the first few chargers. Very keen to invest the time to get it right. But the primitive part of me cant wait.
Im happy to stay at 90% charge (heat bulid up and no need for the extra range atm).
Cherrs for the advice

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 16:07
by jonescg
Have you determined if they need to be balanced or not? If the cells are all different states of charge you will have one or two hit the gong well before the others.

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 17:06
by Dan007a
Have bottom balance them all and charged them up in strings of 4x 4 times. And then bottom balanced final time at 2.85 v. At each stage let them rest for 4 hours then check resistance on all cells. Just bringing them up to final running voltage. Then test full drive line at 134v

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 18:54
by antiscab
I presently run a 45 cell - tc charger on a 42 cell LiFePO4 battery, and have done so for 6 months

what bms are you using?

I'm using the old EV Power BMS, direct connected to the charger. cycles the charger on and off when the first cell hits full (top balanced pack)

If the BMS can disconnect the charger, you should be okay.

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 21:00
by Dan007a
Got some CBM400's from evparts was going to use.

https://evparts.com.au/ev-power-bms/cm4 ... odule.html

Re: Lifepo4 pack charging

Posted: Thu, 12 Sep 2019, 21:30
by antiscab
ah yes, so the same BMS as I have

In your case I would still use the master module to disconnect the charger, so that it does cycle on and off.
Be aware though, that BMS is built for a top balanced battery. You will quickly end up somewhere in between top and bottom balanced fairly quickly, even if you do turn the charger off as a soon as the first cells reaches full