Help with understanding my BMS settings, I'm building 2 12v 271ah batteries....

[smbranch62]

I finally received my 8 cells from China (LifePo4 271ah), I'm attempting to top balance my cells. I have the XiaoXiang BMS and I'm getting the following readout while charging. I turned off the power supply when I got this read out. Should I continue to let it charge until my BMS shut it down (3.65) or was that the right move?


Following are the parameters set on the BMS. I would really like some help so I can know that I have done this correct.





Thanks for the support.

 

[Just John]

Let it charge until one cell hits 3.65v, then parallel and finish the top balance to 3.65v. I spot nothing wrong with your settings. I would however set the low temperature charging protection above zero rather than -1.

 

[smbranch62]

Let it charge until one cell hits 3.65v, then parallel and finish the top balance to 3.65v. I spot nothing wrong with your settings. I would however set the low temperature charging protection above zero rather than -1.

Thanks

 

[smbranch62]

WOW....Thanks to this forum and Youtube I was able to build a 271ah x2 battery. Testing with various loads that will be in the van build. This is really exciting to know that I have saved so much money on drop in batteries.

 

[DThames]

When you are all finished you should have your charger set to not charge to 3.65v per cell, something less. Also, you can adjust those BMS protection settings to be slightly higher than your charger to protect any cell that might want to run too far ahead.

 

[Gadgetnerd]

I finally received my 8 cells from China (LifePo4 271ah), I'm attempting to top balance my cells. I have the XiaoXiang BMS and I'm getting the following readout while charging. I turned off the power supply when I got this read out. Should I continue to let it charge until my BMS shut it down (3.65) or was that the right move?
View attachment 48607

Following are the parameters set on the BMS. I would really like some help so I can know that I have done this correct.
View attachment 48608

View attachment 48609


Thanks for the support.

 

[Gadgetnerd]

Not as familiar with this app, but why charge to 3.65 volts, the cells are happier at 3.55 anyway.(10-90% or 15-85% rule) I can see it's out by about 7mv but that's only an issue because you're charging so high it will make your charge circuit cycle on an off. If you want to balance "perfectly" disconnect everything but the bms and it should have a balance/equalize function no? This is why these bms' have such small balancing currents like 100 or 200 milliamps.

 

[Just John]

Not as familiar with this app, but why charge to 3.65 volts, the cells are happier at 3.55 anyway.(10-90% or 15-85% rule) I can see it's out by about 7mv but that's only an issue because you're charging so high it will make your charge circuit cycle on an off. If you want to balance "perfectly" disconnect everything but the bms and it should have a balance/equalize function no? This is why these bms' have such small balancing currents like 100 or 200 milliamps.

Probably because he is attempting to top balance. Not a lot of need for balance current when done properly, I've turned my "balance" off since it isn't needed.

During normal charging, best to charge to 3.4 volts per cell, and let sit at that voltage (in this case 13.6v) until current drops below one amp. That gets you less than 2 amp hours from 3.65v. No need to charge above 3.4v per cell on a regular basis. If you are in a real hurry, you can use 13.8v (3.45v).

3.0v to 3.4v gets better than 95% of capacity. Or at least that's what my testing shows.

 

[Gadgetnerd]

Probably because he is attempting top top balance. Not a lot of need for balance current when done properly, I've turned my "balance" off since it isn't needed.

During normal charging, best to charge to 3.4 volts per cell, and let sit at that voltage (in this case 13.6v) until current drops below one amp. That gets you less than 2 amp hours from 3.65v. No need to charge above 3.4v per cell on a regular basis. If you are in a real hurry, you can use 13.8v (3.45v).

3.0v to 3.4v gets better than 95% of capacity. Or at least that's what my testing shows.

Exactly John. These cells are not happy at high or low SOC. Also you are unnecessarily asking your charger to put out higher charge voltages which can be hard on your MOSFETs and TVS diodes. Depending on your charger specs you can run 14s or 15s rather than 16s in larger banks to lower the overall pack voltage (you need constant 17/18% overvoltage/amperage to charge) I guarantee your charger will last longer...

 

[smbranch62]

Exactly John. These cells are not happy at high or low SOC. Also you are unnecessarily asking your charger to put out higher charge voltages which can be hard on your MOSFETs and TVS diodes. Depending on your charger specs you can run 14s or 15s rather than 16s in larger banks to lower the overall pack voltage (you need constant 17/18% overvoltage/amperage to charge) I guarantee your charger will last longer...

Thanks for the input. I have been running loads on them for the last couple of weeks and I found out that i don’t have major draws on them. I have the inverter on 24/7, some led lights,110 refrigerator, 2 USB sockets and i occasionally use my indoor smokeless Grill to make some breakfast and it performs like a champ. I have only gotten down to less then 60% of battery life.

my current set up is 2x 270ah batteries (with BMS on both). I am going to now connect them in a way that creates one big battery (8 cell/2each parallel/then series). my question now is, can my 120a BMS handle this or should i get a higher amp BMS?
thanks…

 

[ereams65]

The BMS is all about amp draw, not storage capabilities, so if you're not going to draw over 120 amps, what you have works fine. If you are, then you need to up the ante, so-to-speak.

 

[smbranch62]

The BMS is all about amp draw, not storage capabilities, so if you're not going to draw over 120 amps, what you have works fine. If you are, then you need to up the ante, so-to-speak.

Thx