DIY LiFePo Not Fully Charging

[pacard17]

Good morning!

I m definitely more of a diy newbie. I built my own lifepo battery for camping about 2 yrs ago. (perhaps used a dozen times but never deeply discharged) I was finding that the battery in position #3 on the xioxiang app was regulary getting charged more quickly and the bms would cut charging in order to balance. they would eventually equalize without issue. but the problem persisted.

i then rearranged the cells. however, the 'new' battery in position #3 exhibited the same behavior. im thinking the bms is bad. i just ordered another one.

so now, i have wired them in parallel, removed the bms and have begun top balancing. before removing the bms, the resting voltage of all cells was right at 3.33v. after about 16hrs, they were at 3.37v. im now at about 40hrs and theyre still sitting at 3.37v. the bench charger is saying it's putting in 1.294a.

im starting to think something is wrong with at least one cell and possibly all of them.

any suggestions?

much appreciated!

 

[TomC4306]

What size are the cells?
What is the charging voltage of the bench power supply?
1.294 amps for 40 hours is 50ah.
3.37 volts can be anywhere from 50 to 80 % SOC.

 

[pacard17]

Hey Tom, thanks for the response. The cells are 100ahr. As to the charge voltage, it's set to 3.65v. It's currently at 3.37v and putting out 4.354 watts. (not sure if that answers your question)

 

[wpns]

so now, i have wired them in series, removed the bms and have begun top balancing.

Hopefully you meant PARALLEL

 

[pacard17]

Hopefully you meant PARALLEL

CRAP. Yes, in parallel. sorry! first post corrected.

 

[wpns]

Hey Tom, thanks for the response. The cells are 100ahr. As to the charge voltage, it's set to 3.65v. It's currently at 3.37v and putting out 4.354 watts. (not sure if that answers your question

So 400AH at 1.3A is 308hours, so it could take a week or two.

 

[TomC4306]

Does your bench top supply have an adjustable current knob on it? Turn it up to Max.

 

[pacard17]

So 400AH at 1.3A is 308hours, so it could take a week or two.

so if im understanding...
-in parallel: 3.65v 400ahr
-in series: 14.60v 100ahr

 

[pacard17]

Does your bench top supply have an adjustable current knob on it? Turn it up to Max.

yes! it has a volt and amp knob (both have course and fine adjustments)

i won't harm anything?

 

[pacard17]

Ok, now it's showing 3.56v, 10.27a! "constant current" light is illuminated (this hasn't changed just pointing out what mode it's in). great.

but do i need to turn the amps down when it gets closer or does physics just take care of that?

 

[TomC4306]

Ok, now it's showing 3.56v, 10.27a! "constant current" light is illuminated (this hasn't changed just pointing out what mode it's in). great.

but do i need to turn the amps down when it gets closer or does physics just take care of that?

Remove one power supply lead from the battery.
Adjust both current knobs to Max.
Set volts to 3.65.
Reconnect battery.
Do not touch voltage knob on power supply.
Should charge with a Max 10 amps until very nearly full. last 20 minutes will be above 3.45 volts.
As long as you don't touch the voltage knob after setting it, physics will prevail.
As the cells absorb at that top voltage current will decline rapidly.

 

[wpns]

Remove one power supply lead from the battery.
Adjust both current knobs to Max.
Set volts to 3.65.
Reconnect battery.
Do not touch voltage knob on power supply.
Should charge with a Max 10 amps until very nearly full. last 20 minutes will be above 3.45 volts.
As long as you don't touch the voltage knob after setting it, physics will prevail.
As the cells absorb at that top voltage current will decline rapidly.

This.

 

[pacard17]

Thanks fellas! I'm on it. Volts is set to 3.65v. Soooooo appreciated!

Back to one of my original questions. Do you think the issue is with the BMS given the details in the first post?

 

[wpns]

Thanks fellas! I'm on it. Volts is set to 3.65v. Soooooo appreciated!

Back to one of my original questions. Do you think the issue is with the BMS given the details in the first post?

Either the BMS or the connections in that area. Try posting some pictures, someone may see something that to you is 'obviously' OK...

 

[pacard17]

it's all disassembled right now for balancing. could i have balanced without disassembly? i was thinking the bms might interefere, especially if it's bad.

given this is my 3rd time disassembling and the problem occurred in the same battery position after swapping cells, im leaning towards it not being a connection issue.

 

[SparkyJJO]

How were your balance leads connected? Did you try putting new ring terminals on in case of a bad crimp?

 

[pacard17]

How were your balance leads connected? Did you try putting new ring terminals on in case of a bad crimp?

again, i swapped cell positions and ran the system multiple times, camping. if it was a connection issue, it would have followed the cell to the new position ie #4 or #1. but it didn't. #3 is always the problem even after switching the cell in position #3. I don't think it's a connection issue.

 

[TomC4306]

When reassembling, clean all contact points with isopropyl alcohol. Battery terminals, busbar, balance lead etc.

Then, with all clean connections and a freshly top balanced set of cells, cycle and determine if something is still bad before condemning the BMS

 

[pacard17]

How were your balance leads connected? Did you try putting new ring terminals on in case of a bad crimp?

maybe i misunderstood your post. for balancing, i have a rod running through the ring terminals for each side (+/-). all are cinched up. the positive cable is attached to one end of the cells. the negative charging cable is on the opposite end of the other rod. but now we're talking balancing. since changing the balancing current, it's moving along much more quickly now. but as for actually using the battery, this is where the problem resides.

 

[pacard17]

When reassembling, clean all contact points with isopropyl alcohol. Battery terminals, busbar, balance lead etc.

Then, with all clean connections and a freshly top balanced set of cells, cycle and determine if something is still bad before condemning the BMS

will do.

 

[TomC4306]

The BMS is not doing the charging. Only monitoring and turning charging on or off for the whole pack. It only monitors individual cells

 

[Daddy Tanuki]

again, i swapped cell positions and ran the system multiple times, camping. if it was a connection issue, it would have followed the cell to the new position ie #4 or #1. but it didn't. #3 is always the problem even after switching the cell in position #3. I don't think it's a connection issue.

no if it were a connection issue with the BMS it would sit in the same location, if it were a cell issue it would follow the cell as moved.

 

[pacard17]

no if it were a connection issue with the BMS it would sit in the same location, if it were a cell issue it would follow the cell as moved.

on second thought, i think you're right. THANK YOU for hanging in there with me until i got it through my thick skull.

so position #3 is always the problem. it's always charging too fast. but Tom just stated the BMS is only responsible for monitoring; not charging. knowing that i've re-done these connections multiple times, i'm stumped.

is it possible the BMS is providing incorrect readings due to BMS damage? otherwise, you're basically telling me the monitoring wire to the third position needs to be cleaned/replaced because everything else would have changed when I swapped the cells.

 

[SparkyJJO]

Typically the little wires from the BMS have ring terminals crimped to them, and they're clamped down to the cell terminal between the nut and busbar. Sometimes that crimp connection on the ring terminal isn't quite right and it leads to bad readings causing trouble.

From your response, it sounds like you already put new ring terminals on once before?

It could be the BMS, it does have circuitry components that could be bad. Not all that common, but I've seen it happen on here before.

 

[pacard17]

Typically the little wires from the BMS have ring terminals crimped to them, and they're clamped down to the cell terminal between the nut and busbar. Sometimes that crimp connection on the ring terminal isn't quite right and it leads to bad readings causing trouble.

From your response, it sounds like you already put new ring terminals on once before?

It could be the BMS, it does have circuitry components that could be bad. Not all that common, but I've seen it happen on here before.

i don't think i redid the ring terminals on the little wire. I'll redo it and see if that helps. i've also ordered a new bms (JBD-SPO4S020A). It was only $35.