Having trouble balancing

[Mattfox27]

I'm having trouble getting these batteries to balance. Batt 1 keeps getting overcharged and then it shuts off the balance charge. Batt 1 is where the solar connects, so I'm thinking it's overcharging. The renogy mppt is just using the default lithium profile and the Daly BMS is all at stock settings.

I have 8x 3.2v Lifepo4 batts, and a Daly BMS.

This is all in a dog grooming vehicle with 6x200w solar panels on roof

I'm using a renogy mppt solar charge controller.

 

[BradCagle]

Did you top balance charge your cells in parallel to 3.65v before assembling cells in series?

 

[mikefitz]

Check buss bars and BMS lead to cell 4, you may have a poor connection.
Or cell 4 is faulty, swap with another and see if the problem follows the cell.
Or the cells were never top balanced.
Or the BMS is faulty

 

[Mattfox27]

Check buss bars and BMS lead to cell 4, you may have a poor connection.
Or cell 4 is faulty, swap with another and see if the problem follows the cell.
Or the cells were never top balanced.
Or the BMS is faulty

Ya I did that already, I checked all the connections and bus bars, I will recheck. This is after heavy use BTW, I also did try and swap that cell out, I have another one I can try. But what happens ia when they try to balance cell one hits 3.65v before the others then the BMS stops balancing.

I did not top balance however all the cells where at 3.2v when I put it together. Can I just put a bench top power supply at 3.6v on this one battery to maybe bring it back up?

 

[Mattfox27]

Did you top balance charge your cells in parallel to 3.65v before assembling cells in series?

No I did not however all the voltages were exactly 3.2v when I put the pack together. It's been working fine for a couple months then this started happening.

 

[BradCagle]

I did not top balance however all the cells where at 3.2v when I put it together. Can I just put a bench top power supply at 3.6v on this one battery to maybe bring it back up?

This is 100% your problem. You absolutely must top balance them to 3.65.

All being 3.2 tells you nothing about SOC (state of charge). At 3.2v the cells could be 50% difference in charge from one another. Can't go by voltage with LiFePO4.

You can cheat and use your bench top power supply to top each cell off to 3.65 individually. You must do them all.

 

[BradCagle]

It's been working fine for a couple months then this started happening.

Looking at your cycle count of 16, you probably didn't notice there was a problem until now.

 

[Mattfox27]

This is 100% your problem. You absolutely must top balance them to 3.65.

All being 3.2 tells you nothing about SOC (state of charge). At 3.2v the cells could be 50% difference in charge from one another. Can't go by voltage with LiFePO4.

You can cheat and use your bench top power supply to top each cell off to 3.65 individually. You must do them all.

So just set the power supply to 3.65 and let it sit for a couple hours? Or is there a special charger I should buy?

 

[400bird]

A couple questions or points
The screen shot shows the balancing is turned off.
It also shows 8 battery "strings" does it think you have 8 cells in series or 8 packs("strings")

Batt 1 is where the solar connects, so I'm thinking it's overcharging...

Can you explain this? Did you connect you solar to one single cell? Or one single pack with the others in parallel?

So just set the power supply to 3.65 and let it sit for a couple hours? Or is there a special charger I should buy?

There's a walkthrough in the resources section.
Short version is fully charge it as far as the BMS will let you. Disassemble and reconfigure pack to put all cells in parallel. Charge to 3.5-3.65 volts with bench power supply. Depending on pack size and charger current this could take days.

Do not adjust the power supply voltage once connected to the pack. Set it to 3.5 volts then connect to the pack. Don't touch the voltage knob again.

Don't take my word for it, go to the walkthrough.

 

[Mattfox27]

A couple questions or points
The screen shot shows the balancing is turned off.
It also shows 8 battery "strings" does it think you have 8 cells in series or 8 packs("strings")


Can you explain this? Did you connect you solar to one single cell? Or one single pack with the others in parallel?


There's a walkthrough in the resources section.
Short version is fully charge it as far as the BMS will let you. Disassemble and reconfigure pack to put all cells in parallel. Charge to 3.5-3.65 volts with bench power supply. Depending on pack size and charger current this could take days.

Do not adjust the power supply voltage once connected to the pack. Set it to 3.5 volts then connect to the pack. Don't touch the voltage knob again.

Don't take my word for it, go to the walkthrough.

Yes so basically it's 8 batts in series to get 24v and batt 1 is where the main positive lead come off to power the equipment and that's also where the current from the solar charger comes in, so when solar is on batt 1 quickly climbs to 3.65v and at that point BMS stops balancing because batt 1 has reached it's limit set in the parameters meanwhile the other batteries where not able to quickly climbs that high. Soy theory is batt1 goes so fast because it's getting so much current from the solar charger...just a theory though

 

[houseofancients]

No I did not however all the voltages were exactly 3.2v when I put the pack together. It's been working fine for a couple months then this started happening.

ALWAYS TOP BALANCE

voltage says nothing about the state of charge

 

[400bird]

Yes so basically it's 8 batts in series to get 24v and batt 1 is where the main positive lead come off to power the equipment and that's also where the current from the solar charger comes in, so when solar is on batt 1 quickly climbs to 3.65v and at that point BMS stops balancing because batt 1 has reached it's limit set in the parameters meanwhile the other batteries where not able to quickly climbs that high. Soy theory is batt1 goes so fast because it's getting so much current from the solar charger...just a theory though

That isn't how current works, the current is the same everywhere in a series circuit. Also, in my limited experience the cell number starts at the negative end. So the most positive would be cell 8.

I'd go back to square one and top balance and monitor from there.

 

[Dynoman]

I agree the next step is to top balance the cells since all connections have been checked. I clean all connections with 99.9% isopropyl alcohol and then torque the connections with an in-lb. torque wrench to specs.

Typically, the Renogy Rover Solar Charge Controller default LI profile is too aggressive for Lifepo4 cells. Which Renogy SCC do you have? Did you get the blue tooth module (BT-1) with it?

Attached is a document on how to top balance cells. It is well written and I used it to top balance cells. It is in the Resources tab at the top of the Forum page.

 

[Mattfox27]

No I dont have the BT for the renogy, yes I feel like the voltage is too high from the renogy charger.

 

[Dynoman]

No I dont have the BT for the renogy, yes I feel like the voltage is too high from the renogy charger.

Which Renogy SCC do you have? I have some experience with the Renogy Rover 40 amp & 100 amp SCC. Both have the battery set to User.