diy solar

diy solar

New cells and balancing

Bluewatersailor

New Member
Joined
Nov 18, 2020
Messages
38
My cells are about to turn up any day now 8x200 Calb and although I read most of the topics on balance , I like to just get things clear in my head , please bare with me first time with lithium and bench power supply .

My first question is it better to series and parallel charge as one bank 400ah or would it be better to spilt into two banks of 200ah or doesn't it make any difference?

2 charging in series
after clean the bars and batteries top , my plain is to wire them in series and fit the BMS , then connected them to my shore power charge which as a Gel setting of 14.4 v Bulk
Will it be ok to set the BMS to cut off at 3.6v leave them on charge till the BMS cuts off , or what do people suggest ?

3 charging in parallel
Most people seen to charge with a power supply in stages 3.4v,3.5v,3.6v
As I never used these power supply before , am I correct in say before connection the power supply I first set the CV to 3.4v connection the PS to the batteries while switch off then turn it on and adjust the current ?

4 am I correct that I adjust the current set it as high as it can Go depending on the PS make ?.
the voltage should stay at the 3.4v that it's set at and the current will in time drop to zero at which time you move on to the next step.?

Last question
Will P did suggest in his Video that if the voltage of each cell is close when the cells arrive, connecting them in series with the BMS and letting them charge without a load would do the same job
I appreciate some like to experiment with power supply and top balance mostly because they want a capacity test ,
I don't feel the need to do a capacity test ,
So Will P suggestion would the BMS top balance the batteries on there own in time without a load on?
 
Complete how-to on balancing:


Click the download button at the top right.
 
Complete how-to on balancing:


Click the download button at the top right.
Hi thanks and yes read that , just wanted to clear the points up in my posting , especially the last point we letting the BMS do the balancing on it own ,
 
Hi thanks and yes read that , just wanted to clear the points up in my posting , especially the last point we letting the BMS do the balancing on it own ,
The voltage may be the same but due to the voltage profile of LiFePO4 cells the state of charge may be significantly different. The possible consequence of not doing a top balance is that the BMS is never able to fully balance the cells and you end up with less capacity.

The BMS will stop charging when any single cell reaches the set cutoff voltage and stop discharging when any single cell reaches the set cutoff. Thus without first balancing the *state of charge* of all cells the cells are out of sync and your banks capacity is limited on both top and bottom by the cells that started with the highest and lowest SOC, respectively. Long term your cells will lose capacity at different rates but it won’t directly hurt anything.
 
The voltage may be the same but due to the voltage profile of LiFePO4 cells the state of charge may be significantly different. The possible consequence of not doing a top balance is that the BMS is never able to fully balance the cells and you end up with less capacity.

The BMS will stop charging when any single cell reaches the set cutoff voltage and stop discharging when any single cell reaches the set cutoff. Thus without first balancing the *state of charge* of all cells the cells are out of sync and your banks capacity is limited on both top and bottom by the cells that started with the highest and lowest SOC, respectively. Long term your cells will lose capacity at different rates but it won’t directly hurt anything.
Thanks that explain it thanks it's what I guess my be the answer .
Could anyone comment on the other parts please .
2.3.4
Just want to make sure I get it right first time .
 
2 charging in series
after clean the bars and batteries top , my plain is to wire them in series and fit the BMS , then connected them to my shore power charge which as a Gel setting of 14.4 v Bulk
Will it be ok to set the BMS to cut off at 3.6v leave them on charge till the BMS cuts off , or what do people suggest ?

you’ve got 8 x 200Ah lifepo4 cells yeah? If you connect them all in series you will have a single 24v battery, 14.4v isn’t enough to charge them. You could make two 4S batteries and charge each with 14.4v, but it’s not enough to get them to 100% SOC. You need 3.65v * 4 cells = 14.6v to get to 100% charged.
3 charging in parallel
Most people seen to charge with a power supply in stages 3.4v,3.5v,3.6v
As I never used these power supply before , am I correct in say before connection the power supply I first set the CV to 3.4v connection the PS to the batteries while switch off then turn it on and adjust the current ?
You turn on the power supply, set the desired voltage, then connect to the battery. Do not adjust the voltage after attaching the batteries until the charging is complete and current has dropped off.

4 am I correct that I adjust the current set it as high as it can Go depending on the PS make ?.
the voltage should stay at the 3.4v that it's set at and the current will in time drop to zero at which time you move on to the next step.?
Yes you can set the current as high as it can go, within the limits of your battery cells’ and BMS’s specifications.
 
Sorry didn't explain 2 very well
2 if I connected each 4 cells in series which will make a 12v 200Ah bank then connection both bank in parallel so I end up with a 12v 400ah bank ( that sound better )
, then connected them to my shore power charge which as a Gel setting of 14.4 v Bulk **
Will it be ok to set the BMS to cut off at 3.6v leave them on charge till the BMS cuts off , or what do people suggest ?

** Just check the charger Manual and LA setting are 14.5v Float 13.5v so in reality I can just put them on charge and let the charger do it job without worrying about it .
 
Last edited:
Sorry didn't explain 2 very well
2 if I connected each 4 cells in series which will make a 12v 200Ah bank then connection both bank in parallel so I end up with a 12v 400ah bank ( that sound better )
, then connected them to my shore power charge which as a Gel setting of 14.4 v Bulk **
Will it be ok to set the BMS to cut off at 3.6v leave them on charge till the BMS cuts off , or what do people suggest ?

** Just check the charger Manual and LA setting are 14.5v Float 13.5v so in reality I can just put them on charge and let the charger do it job without worrying about it .
Oh gotcha. Yeah that's very close to the recommended charge profile for LiFePO4. I think it's fine, can't imagine it would hurt anything and you'd just end up with slightly less capacity with the lower voltages - but I'd also hope for somebody with more experience and knowledge to confirm.
 
Back
Top