Overkill BMS

[mikefitz]

it looks like two terminals, not three.

The PCB is only designed to take 2 each side of the metal connection points

 

[Gazoo]

Thanks! Which leads to the ampacity of 5 AWG (or whichever you are using) - which led me to this chart on a car stereo installation forum - should apply here, too?

View attachment 36089

I am far from being an expert on this. I use AWG calculators found on the internet and read what others are using. I have Overkill's 24 volt 100 Amp BMS and Steve assured me using the 10 AWG default wire would be fine and there are only 2 wires instead of 3. He did suggest attaching the BMS wires to a terminal and using a larger AWG from there but I already knew that. I was only concerned about 10 AWG being too light because combined with two wires is 7 AWG.

I am planning on using 4 AWG wire from the BMS's terminal to a 2000kw inverter I have on order. The length will be no more than 3 feet. I want to keep the voltage drop as low as I can and not use a wire that is the size of a pipe. I think the norm is to keep the voltage drop less than 2 or 3%.

Personally I like this calculator which will also calculate voltage drop using more than one wire.

 

[HRTKD]

Combined is 5 AWG.

Wire Combination Calculator

Very handy. Thank you!

 

[Browneye]

Sorry…old thread, but I got my 120A 4s bms with screw posts and wrote Steve about leads.
“Can I put a copper bus on the two terminals and use one 4awg lead?”
They said ‘we use 2 @8 to get 160A, which is the same as one 4awg. And then ONE lug.
Whatcha y’all think???

They said just make sure its rated for ~130A.

I got some 4awg cable, the red is $$. $60 for some wire, shrink and terminals.

Cells are a couple of weeks out.

 

[HRTKD]

I definitely agree on going into a single lug. It's easier and cleaner. But with the copper bus bar there, I would go with a single cable.

 

[Browneye]

Haha.. the copper-pipe bus bars you don’t like. ?

I made one for my inverter and house curcuit and it turned out great. Then I realized the feed from the battery leads for the whole circuit was 6awg, so I’m making a separate 4awg lead for the inverter snd moving the new converter up mext to the new lifepo pack.

I was just thinking a single lead would be a cleaner setup and more reliable, as long as it was heavy enough to carry the current.

I have decided to drill and tap the pack bus bars for the smaller ring balance leads as well. Got those terminals today.

 

[HRTKD]

There are a couple reports on the forum of flattened copper pipe making poor connections at terminals. Apparently flattened copper pipe can be challenging to get completely "flat".

 

[Browneye]

Not in a large vice. Mine turned out really well. Too many lugs on one post is much worse. Worse yet with the wrong size lugs.

Frankly Im cofused as to why they use multiple leads into one lug when the bms board has one large contact patch. Confusing as hell. Must have to do with spreading out the amperage load.

I’ll never have more than 60A in or out anyway. A 100A bms would have been fine.

230A cells.

 

[time2roll]

I cut and drilled a battery terminal bus bar to join the two BMS terminal and use a single #4 wire connection. Works great to at least 80 amps.

 

[notarichman]

I used 1" copper pipe with the next size smaller pipe inside it. flattened it out and drilled holes to make battery bus bars. a lot of work
flattening the nested pipes, but looks good. I really tightened the terminals all along the bus bar and will go back to check the tightness
after a few days. Hope it works!

 

[Browneye]

They need to be tinned if they mate to aluminum posts.