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When to connect a parallel bank?

NMNeil

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I already have one battery bank; 48 volt with 200ah cells. Overkill BMS, and working perfectly.
My second, identical bank is almost ready and I'll be connecting it in parallel with the first.
My question is, do I have take any precautions, such as only connecting if the banks are at the same voltage, or will one bank automatically match the other and the 2 Overkills will take care of the rest?
 
I already have one battery bank; 48 volt with 200ah cells. Overkill BMS, and working perfectly.
My second, identical bank is almost ready and I'll be connecting it in parallel with the first.
My question is, do I have take any precautions, such as only connecting if the banks are at the same voltage, or will one bank automatically match the other and the 2 Overkills will take care of the rest?

It is enough if they are not in the opposite position like full + empty. There will be no extreme Amps flowing.


BUT it is the best if you fully charge both of them ... like top balance for packs.
 
That video isn't a good test. Take 3 or 4 fully charged cells and add one empty cell. He's just testing one full and one empty.

I added two 16s strings to my existing 2 strings.

My procedure for adding new strings was:
1) top balanced the new cells
2) charge old strings to float via normal charge controller
3) take offline the old strings
4) put online the new strings
5) discharge new strings 10%
6) charge new strings to float via normal charge controller
7) shutoff loads and charging
8) wait for new strings to settle so voltage was close across strings (it was .05 off)
9) put online old strings
10) turn on loads and charging
11) At this point the old strings cell voltages were not as flat as the new cells. So I ran an extra long absorb which means an extra long balance. The cells delta came to .01v
 
I disconnected the old string from the system, connected the new string and let it charge. When both were really close in voltage I connected both strings together. The next day I ran a heavy load test on the entire setup to check for hot spots and odd behavior, then just left it alone.
 
I disconnected the old string from the system, connected the new string and let it charge. When both were really close in voltage I connected both strings together. The next day I ran a heavy load test on the entire setup to check for hot spots and odd behavior, then just left it alone.
I never thought of that, too obvious.
My float charge on my first bank is set for 54 volts, and the new bank is sitting at 52.64 volts. I did top balance to 3.4 volts a few weeks ago and this is the voltage the bank settled at after putting the cells in series.
I know Will says to balance at 3.6 volts, but just getting the cells to 3.4 volts took over a week on my 5 amp power supply :oops:
 
That video isn't a good test. Take 3 or 4 fully charged cells and add one empty cell. He's just testing one full and one empty.

I added two 16s strings to my existing 2 strings.

My procedure for adding new strings was:
1) top balanced the new cells
2) charge old strings to float via normal charge controller
3) take offline the old strings
4) put online the new strings
5) discharge new strings 10%
6) charge new strings to float via normal charge controller
7) shutoff loads and charging
8) wait for new strings to settle so voltage was close across strings (it was .05 off)
9) put online old strings
10) turn on loads and charging
11) At this point the old strings cell voltages were not as flat as the new cells. So I ran an extra long absorb which means an extra long balance. The cells delta came to .01v
So how far apart in voltage is safe to connect 4 -16s packs in parallel? I’ve top balanced and placed all 4 strings together in my rack. Of course due to charging time of each 16s pack, my first 3 packs have settled accordingly.
Finally got all Blockmons on and Batrium hooked up, setup and tested. My 4 - 16s packs aren’t paralleled yet. I don’t have voltage of each pack in front me, but lowest cell in pack one was 3.32 and highest cell in pack 3 was 3.46 this afternoon when I completed the Batrium bypass test.
I will test voltage tomorrow but it would seem with all batteries being between 3.32 & 3.46 it would be safe to now parallel all 4 pack to the parabars? I’m using the blue sea 1000 amp bus bars to parallel my packs. Fuse blocks on each pack mounted on front of the rack close to positive terminal.
 

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I don't know the answer of how much delta is too much. You need the voltage of each string. Did the string with the higher voltage settle more overnight? How does each string compare? They should all plateau at some point to close voltages.
 
I don't know the answer of how much delta is too much. You need the voltage of each string. Did the string with the higher voltage settle more overnight? How does each string compare? They should all plateau at some point to close voltages.
I’ll check the voltage this evening. I charged each 16 string at once, so over time each pack naturally settled while waiting to charge each successive 16 pack. (16s4p) So maybe waiting for the packs to all settle to around 3.3-ish may be best before attempting to parallel. I just wasn’t sure either how “close” they need to be.
 
I would wait for the strings to settle to within 1 volt. Mine were 0.5v off. The higher strings came right down. My clamp on meter didn't read any noticeable amperage.

I suspect, but have no proof, that you are probably fine even a few volts delta per string since all strings were charged to "full" and the higher voltage strings represent cell voltages up into the knee. Those voltages will drop out of the knee real quick with even a small load.
 
I would wait for the strings to settle to within 1 volt. Mine were 0.5v off. The higher strings came right down. My clamp on meter didn't read any noticeable amperage.

I suspect, but have no proof, that you are probably fine even a few volts delta per string since all strings were charged to "full" and the higher voltage strings represent cell voltages up into the knee. Those voltages will drop out of the knee real quick with even a small load.
Thanks very much! I agree, I’ll monitor voltages over the next days to see, I’m sure the more recently charged packs will drop like the earlier packs have.
 
I would wait for the strings to settle to within 1 volt. Mine were 0.5v off. The higher strings came right down. My clamp on meter didn't read any noticeable amperage.

I suspect, but have no proof, that you are probably fine even a few volts delta per string since all strings were charged to "full" and the higher voltage strings represent cell voltages up into the knee. Those voltages will drop out of the knee real quick with even a small load.
FYI: Just checked voltage on each of the four packs. These were charged in order 1-4.
#1: 53.6
#2. 54.5
#3. 55.0
#4. 55.3
I’m sure the last two packs will drop voltage as they rest the next fees. I’ll wait before paralleling the packs.
 
So how far apart in voltage is safe to connect 4 -16s packs in parallel? I’ve top balanced and placed all 4 strings together in my rack. Of course due to charging time of each 16s pack, my first 3 packs have settled accordingly.
Finally got all Blockmons on and Batrium hooked up, setup and tested. My 4 - 16s packs aren’t paralleled yet. I don’t have voltage of each pack in front me, but lowest cell in pack one was 3.32 and highest cell in pack 3 was 3.46 this afternoon when I completed the Batrium bypass test.
I will test voltage tomorrow but it would seem with all batteries being between 3.32 & 3.46 it would be safe to now parallel all 4 pack to the parabars? I’m using the blue sea 1000 amp bus bars to parallel my packs. Fuse blocks on each pack mounted on front of the rack close to positive terminal.
@Shawn Hayes very clean setup! impressed.
 
@Shawn Hayes very clean setup! impressed.
Thank. It’s been a chore, learning process. I’ll post more pictures soon. I’ve got more things together since those photos. I’ve just tried to keeps things neat & organized son it’s safe as possible and easy to work on if needed.
I’d like learn more from those folks like you, how other Batrium owners have set their internal Batrium settings once I get it finished. Especially those you have Sol-Ark and Batrium.
 
to hurry things along, you could make parallel connections with a 1 or 2 ohm power resistor. That would limit the current to less than an amp with 1 volt difference, but it would be much faster than just waiting for them to settle out.
 
Thank. It’s been a chore, learning process. I’ll post more pictures soon. I’ve got more things together since those photos. I’ve just tried to keeps things neat & organized son it’s safe as possible and easy to work on if needed.
I’d like learn more from those folks like you, how other Batrium owners have set their internal Batrium settings once I get it finished. Especially those you have Sol-Ark and Batrium.
fyi on this thread with regard to batrium

 
Sounds like the balance resistor heats up the board and causes failure of monitoring IC?

In theory it makes good sense that lowering the maximum temperature allowed for the balancing resistor would improve life of blockmon.

But if it already failed after having a high temperature set point, then lowering it might not fix any issue.

Just some thoughts, I really like the decentralized BMS concept and am concerned about the aspect of balance resistor acting as cell heater.

Both for cell life and IC life.
 
Sounds like the balance resistor heats up the board and causes failure of monitoring IC?

In theory it makes good sense that lowering the maximum temperature allowed for the balancing resistor would improve life of blockmon.

But if it already failed after having a high temperature set point, then lowering it might not fix any issue.

Just some thoughts, I really like the decentralized BMS concept and am concerned about the aspect of balance resistor acting as cell heater.

Both for cell life and IC life.
That's my theory and sounds like others have encountered the same. I had the same concerns about heat and the cells. During balance the post gets warm but not hot. I sent some email to batrium so maybe they have some ideas. Otherwise I think I'll drop the bypass temp limit some.
 
So the devil is in the details. Maximum conditions from this doc state:

- Shunt power with air temperature at 25ºC 3.5 W
Bypass heating above 75ºC will reduce bypass current and will allow cell over-voltage. Keep well below these limits.

- Shunt power with fan-forced cooling at 25ºC 7 W
Prolonged high temperature use may reduce the life expectancy of the PCB and adjacent devices (batteries, wires, etc).

So the software default is 75 degrees, but looks like the value should be set much lower.


 
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