New 16c LifePo4 cells how to be balanced

[rgroothuis]

I'm planning to build a battery system to store PV energy. I want to buy either EVE LF280 or EVE MB31 cells, 16 piece. I've read you need to balance them, bring them to the same voltage level, prior to start using them. Now I'm trying to find out how to balance them. The JK BMS has a 2A balancer onboard, would the BMS do the balance automatically for you? Or do I still need to put all 16 cells parallel and start charging them for many days? If so, which power supply is recommended to be used? Looking forward to your suggestions.

 

[rogerheflin]

If the batteries are new and come from the factory they typically will be charged with the same consistent process and be at the same level. On my 2 sets I checked voltages and voltages were within .01v on all 16 cells (each order was a bit different one was 3.31 and the other was 3.29 with all cells being the same).

I have been able to wire both packs up (no extra charging) and each pack only has one cell that seems to be an odd-ball (when all other 15 cells are fully charge one cell is behind according to voltage). The one cell that is behind is not really a problem since it does not reduce the capacity of the battery.

If the batteries aren't new or aren't the same age (typically new orders will all comes from the same production run/larger shipment from manufacturer) then the charging becomes more important.

 

[rgroothuis]

If the batteries are new and come from the factory they typically will be charged with the same consistent process and be at the same level. On my 2 sets I checked voltages and voltages were within .01v on all 16 cells (each order was a bit different one was 3.31 and the other was 3.29 with all cells being the same).

I have been able to wire both packs up (no extra charging) and each pack only has one cell that seems to be an odd-ball (when all other 15 cells are fully charge one cell is behind according to voltage). The one cell that is behind is not really a problem since it does not reduce the capacity of the battery.

If the batteries aren't new or aren't the same age (typically new orders will all comes from the same production run/larger shipment from manufacturer) then the charging becomes more important.

Thanks for the quick reply, appreciated. Good useful information. Do you have a BMS with balancing capabilities? In your situation is the balancer not taking care to make that cell equal on a voltage level?

 

[rogerheflin]

Thanks for the quick reply, appreciated. Good useful information. Do you have a BMS with balancing capabilities? In your situation is the balancer not taking care to make that cell equal on a voltage level?

I have an active balancer and that one cell on each pack is always inline until the battery becomes fully charged, and then it stays at a lower voltage than all of the rest of the cells. I did confirm with a voltmeter that it really is 3.35 when the other cells are 3.60. I also confirmed that the slow cell does get to a lower voltage before all of the other cells. The balancer might eventually get it. I don't typically have more than an hour of balance time after the voltages get high enough with the sun still out and actively still charging. That time will increase as we come out of winter and maybe the balancer might get it. The one cell does not appear to be reducing capacity of the pack so there should not be a reason to replace it.

 

[rgroothuis]

Thanks for your feedback @rogerheflin . What I would still like to know and understand is how to balance the cells when the first arrive? When you unpack them from the delivery box. All cells are parallel connected and you need to put a power supply of about 3.6V on it. But how many Amps? And for how long? What would be a good power supply?

 

[bolhuijo]

Before you get carried away with wiring them all in parallel and finding a 3.6V power supply, simply measure all 16 of your new cells with your DMM. They will probably be very close to the same voltage, within 0.01V. If that's the case, install them in the battery box and wire them up in the normal way. The JK BMS will begin balancing them as necessary when the pack is near full charge.

 

[rogerheflin]

Thanks for your feedback @rogerheflin . What I would still like to know and understand is how to balance the cells when the first arrive? When you unpack them from the delivery box. All cells are parallel connected and you need to put a power supply of about 3.6V on it. But how many Amps? And for how long? What would be a good power supply?

If the cells are all new from the manufacturer then the cells should have been identically built and identically charged. You simply don't need to balance them because the manufacturers process identically charged them. it does not matter if the are 0% 100% or 30% the cells simply all need to be at the same level whatever that is, and the manufacturer knows how to consistently charge them.

 

[houseofancients]

If the cells are all new from the manufacturer then the cells should have been identically built and identically charged. You simply don't need to balance them because the manufacturers process identically charged them. it does not matter if the are 0% 100% or 30% the cells simply all need to be at the same level whatever that is, and the manufacturer knows how to consistently charge them.

Wrong, one should ALWAYS top balance cells in a pack

 

[MisterSandals]

Wrong, one should ALWAYS top balance cells in a pack

+1

I always top balance first.

But, you have not revealed whether you are making a 12V, 24V or 48V battery. Depending this, there are more important things to do/consider (IMHO) before building a battery(s).

 

[rogerheflin]

Wrong, one should ALWAYS top balance cells in a pack

The manufacturer will have balanced the cells to start with. The entire point of top/bottom balancing is to make sure the charge level of all of the cells is the same. With new cells the manufacturer already did that. And it is pretty unlikely that anyone building commercial batteries is doing extra steps to balance except use the cells with the level the manufacturer charged them to. With new cells it is going to be unnecessary, if the cells are not new and/or are of questionable origin and/or different ages then it becomes necessary.

Now if you want to do extra work that has no point go ahead and do it if it makes you feel better.

 

[hwy17]

Guys there's no wrong way to eat a Reese's.

You can top balance in parallel or you can top balance in series with a BMS. Both can achieve the same exact result with the same precision.

Top balancing in parallel is simple and straightforward. Top balancing in series is constrained by several boundaries that are not that complicated once you've got a grip on them, but are quite a lot to try and fully explain all at once.

Whether one is more arduous than the other depends on how out of balance they are to start with. If I got cells that were all manufactured within 7 days of each other I would build it and top balance in series. I have a batch of cells for my next pack that arrived from like 3 months apart, and those I think I will try out parallel balancing first.

You can even top balance a pack in series without ever hitting over voltage protection, you just have dial up the charge voltage gradually as allowable. You also need your balancer to behave correctly along the way, as far as I understand it not all Chinese BMS always behave correctly.

 

[S Davis]

The manufacturer will have balanced the cells to start with. The entire point of top/bottom balancing is to make sure the charge level of all of the cells is the same. With new cells the manufacturer already did that. And it is pretty unlikely that anyone building commercial batteries is doing extra steps to balance except use the cells with the level the manufacturer charged them to. With new cells it is going to be unnecessary, if the cells are not new and/or are of questionable origin and/or different ages then it becomes necessary.

Now if you want to do extra work that has no point go ahead and do it if it makes you feel better.

It makes me feel better as the packs I did a proper top balance on are better than the ones I put together without and let the BMS take care of things. They stay closer bottom to top .008, ones without .025 Same batch of cells 8 different Batteries.

 

[rgroothuis]

+1

I always top balance first.

But, you have not revealed whether you are making a 12V, 24V or 48V battery. Depending this, there are more important things to do/consider (IMHO) before building a battery(s).

It will be a 48volt pack with 16 cells.

 

[rgroothuis]

For parallel balancing, what kind of power supply are you using? Brand? How many amps?

And what voltage are you using? Will this be one fixed voltage? Or does it need to be according to a LifoPO4 schema? Until what level do you need to balance/charge? Until they are full or they all are the same voltage?

 

[houseofancients]

The manufacturer will have balanced the cells to start with. The entire point of top/bottom balancing is to make sure the charge level of all of the cells is the same. With new cells the manufacturer already did that. And it is pretty unlikely that anyone building commercial batteries is doing extra steps to balance except use the cells with the level the manufacturer charged them to. With new cells it is going to be unnecessary, if the cells are not new and/or are of questionable origin and/or different ages then it becomes necessary.

Now if you want to do extra work that has no point go ahead and do it if it makes you feel better.

That assumes one has the same batch and match of cells, which almost NEVER is the case.
Top balancing can be done in a couple of ways.
1. Manually
2 using a BMS with an active balancer
3 using a passive balancer

2 and 3 may take a good amount of cycles, and depending on the quality of the cells may not ever complete

Also voltage in LifePO4 says 0 , so stop your assumptions

 

[houseofancients]

For parallel balancing, what kind of power supply are you using? Brand? How many amps?

And what voltage are you using? Will this be one fixed voltage? Or does it need to be according to a LifoPO4 schema? Until what level do you need to balance/charge? Until they are full or they all are the same voltage?

Je kunt een lab voeding gebruiken, of zoals gezegt een active balancer.
Als je de laatste methode gebruikt , dan kun je het beste je cellen een aantal uur tussen 3.48 en 3.55 houden

 

[wpns]

Also voltage in LifePO4 says 0 , so stop your assumptions

Indeed. Measuring SOC near the middle of the range is second only to weighing the cells in accuracy.

 

[hwy17]

1. Manually
2 using a BMS with an active balancer
3 using a passive balancer

2 and 3 may take a good amount of cycles, and depending on the quality of the cells may not ever complete

It only takes 1 cycle every time as long as the balancing logic in the BMS isn't broken.

As far as never complete, if the pack is so bad can't stay balanced then neither can parallel balancing.

 

[hwy17]

For parallel balancing, what kind of power supply are you using? Brand? How many amps?

Most people us test bench power supplies.

I'm doing my first one soon and I will use a Meanwell MSP-100-3.3 adjusted to 3.425V or as close as I can get it.

 

[goldserve]

If the cells are all around the same charge, I like to play wack a mole and use a BMS like the jk with 2a balancer to help you. You can go fast and charge the pack until one cell hits 3.45v and that is when you should slow down the current from the power supply. Let it charge slowly and if you have runners, take like a 5 ohm power resistor and bleed the high runner and play whack a mole game. It’s fun!