A123 Battery Pack Surgery

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TheHappyNomads

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After a lot of helpful information provided by members of this forum I'm looking to finally crack into these battery packs to create a 48v 16s unit.

Does anyone have experience doing so with these?

I'm looking for the simplest and safest way to isolate 2 of the 18 cells in series for a 16s system.

Thanks in advance!
 
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Probably the simplest thing to do if you don't already have the inverter would be to get an inverter that can handle the upper voltage or since the cells will settle to 3.4V or less would be only charge to 3.4V/cell (61.2V) or less a cell. 80-90% of capacity is between 3.4V to 3.0V.
Later floyd
 
Unfortunately, that's one of the hangups with my situation is that I already have (2) LV6548 inverters.

Are you saying I could set the charge the cells to lower capacity with these inverters and just eat the loss instead of maximizing the storage capacity?
 
The cells will degrade faster if charged to 3.65V a cell. and the natural resting voltage is 3.4- 3.45V/cell if they are anything like the A123 20Ah cells I have. make no sense unless you absoultely need the 5-10 % extra storage. 90 % is 12.6kWh 100% is 14kWh overcharge protection is 63VDC You would use user defined setup 3.45V/cell 62.1V- 54V 3V/cell which is under the 63 V that is when overcharge protection sets in.its late here and my brain is turning to mush.
Later floyd
 
Agree with floyd. You don't want to go to the "max voltage" of the cells, regardless of manufacturer/chemistry. You want those cells to last as long as possible, life span wise, more than capacity wise.
<10% capacity at the expense of killing the cells possibly years sooner is not worth it, imho.
If you can use the packs as they are, then 18s would yield a range of 55.2V (18 * 3.45)
1705501092356.png

That inverter has a decent voltage range. So it will go all the way up to 60V easily, and looks like it can go up to 62V.
So if we use that as the upper limit, then 18s would be 62 / 18 = 3.44V, as floyd mentions. Even if the inverter can go all the way to 63V, that'd 3.5V per cell. A little high, but better than cooking them at 3.6V.

Now on the lower end, that's going to be 41V, or 2.27V/cell. Which, if I am seeing the right specs for the A123, is a wee low. 2.5V is low end for those. So you'd definitely want to bring the inverter's bottom end cutoff voltage up to 2.55V at least ,if not 2.6V, or 45.9V/46.8V.
 
Great news and info -- thanks guys! I'm definitely in agreement with you on lifespan > capacity.

If I'm understanding you both correctly, I could utilize these batteries in their 18s configuration and just adjust my inverter settings to accommodate the voltages required by an 18s instead of a 16s?

My panels are 48v, does that matter in this equation since they'll just be feeding the inverters who will then in turn control pv energy \ voltage to the battery packs?
 
TheHappyNomads said:
If I'm understanding you both correctly, I could utilize these batteries in their 18s configuration and just adjust my inverter settings to accommodate the voltages required by an 18s instead of a 16s?
Click to expand...
Yes, that's what @Korishan is saying. I was thinking the same thing, to put three packs in series to make an 18S.

TheHappyNomads said:
My panels are 48v, does that matter in this equation since they'll just be feeding the inverters who will then in turn control pv energy \ voltage to the battery packs?
Click to expand...
This is a good question. Somebody more knowledable than me will probably give you the exact answer. In many systems, generaly speaking, the power source (the panels in this case) should have a higher voltage than the output (the batteries in this case). If that was the case couldn't you also think about connecting your panels in series? You don't give your panels specs. In this case, again, the inverter must support the panel configuration, the manual will tell you how you may connect them.
 
TheHappyNomads said:
My panels are 48v, does that matter in this equation since they'll just be feeding the inverters who will then in turn control pv energy \ voltage to the battery packs?
Click to expand...
PV Array MPPT Voltage Range 90Vdc~230Vdc hopefully you have at least 3 48vdc panels in series probably more in each array.
later floyd
 
Looks like those panels are rated for 48V open circuit (will be lower when a load is applied). So putting 3 of these in series should be fine overall with your inverter, as floyd mentioned.

You just want to make absolutely sure that your solar input voltage does not go over your inverter max limit, 230VDC. In 100% direct sunlight condition with cool temps, it's possible for a panel to output higher than its rated voltage.
So, with that said, 3 of these will be 144V, or thereabouts. This is definitely in the safe zone. You just wouldn't want to put 5 in series. Four in series would be the max.
Now, you can add more in parallel. So you could go with 3s2p for example. That would allow for 146V with a potential of 21A, which is still within the specs of the inverter. I didn't look at the Solar input requirements, but usually Amps input is usually 50A, 100A, 150A, 200A, depending on size of the inverter. Check your specs to verify.
 
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