8s2p connections question

Famtraveler24

Solar Enthusiast
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Jul 22, 2020
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Hello all,

I'm planning on building 2 8s 280ah battery packs, each with its own 8s Overkill Solar BMS, and connecting them in parallel so I can have a 24v 560ah system.

Does anyone have a diagram showing such a pack? I'm assuming the total 8s2p has a main negative and a main positive that connects to the positive and negative bus bars?

I've been using diagrams from Explorist Life as a guide, but they use BBs.

Any help would be appreciated.

Thx!!
 

chrisski

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Aug 14, 2020
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I just was working on the drawing today, so I'm open to comments. The fusing is kind of confusing, so I think the green arrows clears this up:

1632364146780.png
 

FilterGuy

What, me worry?
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I just was working on the drawing today, so I'm open to comments. The fusing is kind of confusing, so I think the green arrows clears this up:

View attachment 65910
It looks like a good drawing. What is the max continuous current you expect from the battery. What will it be powering?

BTW: I assume that is not a 2AWG wire from the 225A fuse and the Master Off Switch.
 

chrisski

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It looks like a good drawing. What is the max continuous current you expect from the battery. What will it be powering?
I don’t expect more than 100 amps continuous. So 50 amps from each bank. Mostly a microwave for now.

The inverter is 3000 watts, 24 volts, has a 20 amp plug and can be hardwired for 25 amps.

Depends how this goes, I may turn on the AC with it in April if things are running good.
 

Famtraveler24

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Messages
130
It looks like a good drawing. What is the max continuous current you expect from the battery. What will it be powering?

BTW: I assume that is not a 2AWG wire from the 225A fuse and the Master Off Switch.
This will be powering both the 12v DC and 120v AC systems in our fifth wheel, including 2 13k btu AC units. We will have 3000w of solar to charge the batt. Will also have a 24 to 12 converter.
 

Famtraveler24

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I don’t expect more than 100 amps continuous. So 50 amps from each bank. Mostly a microwave for now.

The inverter is 3000 watts, 24 volts, has a 20 amp plug and can be hardwired for 25 amps.

Depends how this goes, I may turn on the AC with it in April if things are running good.
What bus bars did you use directly off the batteries?
 

jjhdtv

New Member
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Jul 22, 2021
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I noticed the above diagram is exactly what I will be attempting with my fob 16 180ah cells (8S 2P double bms’s). I did notice a few discrepancies from what I hade planned. The parallel positive connections to the buss bar (from each of the 2Ps), I was going to use the 4 gauge with a 100 amp inline fuse. The combined max amps leaving the buss bar to the load will be 200 amps thus will use a 200 amp fuse and 2 gauge. Opposite what is shown above and wanted to confirm. Perhaps the legend is in error in the above diagram, or I’m in error with my thinking.

I would also like to know why a shunt is used. I did not plan to use on. My connection will be direct to an inverter that handles the 24v from a battery. Great forum. Thank you.

Edit. Just noticed 4/0 was called out not 4 gauge. My bad. Drawing is correct but seams to have extra wire capacity.
 
Last edited:

chrisski

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I would also like to know why a shunt is used. I did not plan to use on. My connection will be direct to an inverter that handles the 24v from a battery. Great forum. Thank you
I already had the shunt on the lead acid build its replacing. I also like being able to see amps in and amps out of the batterypack without jumping between two Apps.
Edit. Just noticed 4/0 was called out not 4 gauge. My bad. Drawing is correct but seams to have extra wire capacity.
I tend to make wiring thicker. In part not to deal with a voltage sag from a 3000 watt inverter.
 

jjhdtv

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Jul 22, 2021
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Revisiting this thread as I completed my build, top balanced and now testing capacity. This is a 8s2p build with dual BMSs.
During testing, I realized I must have had a bad bms connection on one of the batteries (low voltage indicated on the bms application). I had issues initially with bad connections, but thought I had fixed everything. Apparently not.

Anyway, the BMS did its job and shut down the bank with the low voltage cell. Testing continued so the remaining bank in parallel took the load.

I now have different voltages on the two banks connected in parallel. I would like to know if I should do anything prior to applying a charger to the complete 8s2p battery (aside from fixing the bad bms connection). Little unclear if the BMSs will bring both banks up even. I would think so as there is a bms for each 24v bank. Just want to make sure and avoid doing something costly. thank you.
 
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