Busbar for 150a continuous 300a peak

Rw3000

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Hi All,

Busbar sizing 5x 6mm2 twisted

image_klhyoy.jpg

Going by googling different specs I think this should handle 150a continuous with spikes of 300a

Anyone else with any tips for high currents?

Andrew
 

daromer

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We cant tell because we dont know what size it is. 20cells with 300a is huuuge.. thats 15a per cell. Beware that higher current just slightest resistance in the busbar Will cause the cells closest to the connection to have higher load. Up to 30a Id wrongly done.


What is the size of that bar? Do you going to run The oposite om the other Side? And what Wire do you Connect the cells with? (You cannot have cell level fuses on that high current. It wont work)
 

Rw3000

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Cells are 12.5ah 1c continuous 3c peak LiFePo4 new cells.

Bar is 5 strands of 6mm2 building wire twisted together about 34cm long. Can just squeeze it into 35mm2 lug

Was going to run cell level fuses but was afraid of resistance overall.

Opposite +ve and -ve to get was even as possible draw on pack
 

daromer

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Should be fine then. But you are in the top end of current on the cells.
 

Redpacket

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As daromer pointed out above, due to bar resistance, you should have the lugs at opposite ends of the pack to get more even resistance & cell load distribution.
Take it this is for a short term use, eg < 1 hour run time & shorter cell life is accepted?
Also, the cells are likely to get warm (at least) when loaded hard like this.
 

daromer

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Yes you need thick wire between busbar and the cells. I wouldnt consider them fuses since those will be so thick that that are way above what the cell can handle for it to be a proper fuse.

Just make sure you have decent pack-fuse instead.
 

Crimp Daddy

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How do you intend to attached the connection to the cells? I would not solder for a high drain application like this.

Would it be possible to consider spot welding 0.2mm or 0.3mm nickel strip to the cell and soldering to the buss bar?
 

daromer

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Spot welding if for sure possible but i would say soldering should be ok. It is in the high end current for sure and spot welded nickel strip doing 30A is alot :D
 

Rw3000

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Don't have a spot welder at the moment, so I will be soldering the connections to the cells.
I will derating the inverter a bit to protect the battery until we are able to build another battery to share the load.

Also thought about making them into 4x 75ah batteries and string them together. Balancing would be hard though unless I could inter connect them or separate BMS for each.

Tried a 4p16s1p similar to the pcb layouts people have been making. Draw 58amps for 15mins cells handled no problem but when charging @ 8amps got to 3.5v and cells went all out of balance by 250mv 3.43v to 3.68v pack closest to +ve side was lowest voltage. Would it be due to resistance in the connections?
 

daromer

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Can be yes
 
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