DIY 28kw/h Storage : EVE LF280k x 32 LiFePO4 Batteries

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17 minutes ago, Crossy said:

Are your cables approximately equal length??

 

You can expect some variation as the packs charge / discharge even if everything is "identical".

 

Thanks for that input Crossy. I just switched to charge the one battery with both inverters to close the gap (30Ah), and was able to see in app that the current made sense at least on lower current. Yes cables are quite equal in length.

 

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[Pink7]

So I have do some more checking and 2 times switch to charge the one battery only to balance the current between the 2 batteries. What happen next is the bms will reverse my operation by less charge current to the battery I just charged up to same level. I also noticed that voltage on the battery who BMS now give less charge have a slight higher voltage so i gues thats maybe why this happens. My first thought is to get both batteries back to fully charged and then I guess or hope there is a voltage calibrate option on the BMS.

 

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[Pink7]

Update: Just come to my main that the 2 JK BMS do not communicate with each other so then that part of my idea will not help, but the inverters do communicate but does they do anything related to manage how much current to charge/de charge each battery/inverter pair? ( INV1/Bat1 vs INV2/Bat2)

 

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[Crossy]

4 minutes ago, Pink7 said:

Update: Just come to my main that the 2 JK BMS do not communicate with each other so then that part of my idea will not help, but the inverters do communicate but does they do anything related to manage how much current to charge/de charge each battery/inverter pair? ( INV1/Bat1 vs INV2/Bat2)

 

Your BMS can't regulate current, it's a purely on-off device, "charge" or "not charge" only.

 

I admit that I'd never thought about the inverter actually controlling the BMS, I've always assumed it was a purely one-way (BMS to inverter) message.

 

Are your batteries completely separate on the DC side? I'd assumed your packs were in parallel which I understand is the normal connection even with multiple inverters.

[Pink7]

8 minutes ago, Crossy said:

 

Your BMS can't regulate current, it's a purely on-off device, "charge" or "not charge" only.

 

I admit that I'd never thought about the inverter actually controlling the BMS, I've always assumed it was a purely one-way (BMS to inverter) message.

 

Are your batteries completely separate on the DC side? I'd assumed your packs were in parallel which I understand is the normal connection even with multiple inverters.

Yes they are in parallel with wires between the 2 breakers.

 

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[Pink7]

9 minutes ago, Pink7 said:

Yes they are in parallel with wires between the 2 breakers.

 

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Is it voltage or the Current (Ah) level who make the parallel connection to transfer current between the packs?

 

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[Crossy]

It's the voltage difference between the packs (effectively state of charge) that drives any current between them.

 

But slight differences in pack/BMS internal resistance will affect just how much of the total charge current ends up in each pack. 

 

At the end of the day both packs will have the same voltage and state of charge, how they get there is outside our control, "You cannae change the laws of physics Jim".

 

[Pink7]

3 minutes ago, Crossy said:

It's the voltage difference between the packs (effectively state of charge) that drives any current between them.

 

But slight differences in pack/BMS internal resistance will affect just how much of the total charge current ends up in each pack. 

 

At the end of the day both packs will have the same voltage and state of charge, how they get there is outside our control, "You cannae change the laws of physics Jim".

 

Thanks for the info. I will just get both batteries charged back up to full status if the weather hold up.

 

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[Pink7]

Got both batteries charged up today and noticed:

 

Both batteries complete charge in same time ( one with 99% and the other with 97% state of charge)

Batteries have exact same voltage when checking with multi-meter. Some differences on the values with BMS. Then inverters show 0.4v more than multi-meter. So all in all not to bad at all but i will do some calibrating of voltage and try reset/recalculate state of charge on the 97% battery.

 

[Crossy]

To be honest I don't think I'd worry about such small errors. The inverters will stop charging when they are happy and the BMS's will look after your packs.

 

Unless things get badly out of balance just fit, forget and enjoy the "free" energy🙂 

[Pink7]

Some days ago I fully charged both batteries then I calibrated my both JK BMS voltages and I Temporary edited the over voltage protection to a lower value so it be triged and to "help" the BMS to understand this wast the 100% left capasity level. After that the 2 BMS been as in sync and all good.

 

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