Parallel connecting four 48v 100AH batteries - cables or busbar

Hedges

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I like Ben but I disagree with that video and would never use an AC breaker for 48VDC which in this case is really 54Vdc.
AC breakers depend on Zero crossing and that does not exist with DC. You get an Arc going in that breaker and it won't matter if it fly's open. It may work and it may not but I would not take the chance.

QO breakers (at least some of them) are DC rated. Two pole breaker interrupting circuit and that voltage isn't a problem.
Short-circuit current interrupt rating may not be high enough for lithium, need to figure out battery bank capability and wire resistance.

Some other breakers (e.g. from Midnight) have higher ratings, as do some fuses.
 

robby

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QO breakers (at least some of them) are DC rated. Two pole breaker interrupting circuit and that voltage isn't a problem.
Short-circuit current interrupt rating may not be high enough for lithium, need to figure out battery bank capability and wire resistance.

Some other breakers (e.g. from Midnight) have higher ratings, as do some fuses.
I can’t remember what brand of breaker I have installed but it is the same as the Schneider 250A.
breaker. It has a super long throw between the contact.
 

Tony Scott

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Thanks for the link. When I originally said "busbar" I was thinking of a solid copper bar going from one terminal to the next. It there a harm in daisy chaining the connecting cables - a cable from 1+ to 2+, then a second cable from 2+ to 3+, then another from 3+ to 4+? Same for negative and then conencting cables go back to inverter from 1+ and 4-

manual states: section 2.2 you need bus Bar to ensure study even current flow between multiple batteries.
 

Cajunwolf

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Use copper. I found copper stock in all kinds of sizes and lengths. I have four Chins in a 2s2p 24-volt bank using all copper bars. I can look it up, but I think I paid $74 for two 1/4"x1.5"x24" copper bars. these are the positive and negative parallel buses. The series bars are 3/16"x1"x6," and I cut to length then drill to go 0ver the terminals. I forget what that cost, not much. In my situation, cables took up too much space and cost more besides being a lot more work. Once I get it together, I will post pictures.
 

JustPractical

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I did mine this way.
It’s going to be up to your physical constraints and budget.
I used different gauge cable from Ben but used same panel and breakers.

That looks like it will work, but I hesitate to to put things in that are that far from standard. My other grief is I will be selling the home in 3-4 years, and anything overly unusual will get flaggged by whoever inspects the hosue for the buyers.
 

Tony Scott

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That looks like it will work, but I hesitate to to put things in that are that far from standard. My other grief is I will be selling the home in 3-4 years, and anything overly unusual will get flaggged by whoever inspects the hosue for the buyers.
I WOULD NOT BELEIVE ANYTHING THIS GUY SAYES AFTER WATCHING HIM TOUCH A LIVE CIRCUIT. Amp’s kill, .5 amp’s will put you in the ground, There is no reason to touch a live circuit, if you have any questions how about talking to a master electrician when it comes to the panel. This fool in this video will get someone killed.
 

Tony Scott

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That looks like it will work, but I hesitate to to put things in that are that far from standard. My other grief is I will be selling the home in 3-4 years, and anything overly unusual will get flaggged by whoever inspects the hosue for the buyers.
Then build it to code
 

Hedges

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I WOULD NOT BELEIVE ANYTHING THIS GUY SAYES AFTER WATCHING HIM TOUCH A LIVE CIRCUIT. Amp’s kill, .5 amp’s will put you in the ground, There is no reason to touch a live circuit, if you have any questions how about talking to a master electrician when it comes to the panel. This fool in this video will get someone killed.

At 48VDC to 58VDC, with rubber shoes and dry floor, pretty low risk.
But as you say, "no reason to touch a live circuit"

At 12VDC or 24VDC we would normally put a wrench on automotive starting batteries. Best to disconnect negative first, so wrench contacting chassis doesn't cause harm.

My 48V battery bank has just fuses and wires connecting it to inverter (which has breaker), so I had to put a wrench on a live terminal at some point. If I was doing that with higher voltage I'd definitely use insulated tools. In my case, floating DC and a ground jumper to the node I'm wrenching on would be one approach, with ground bond last.
 

alvirtuoso

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Use a Busbar!
I did not use anything to shield the exposed copper, but it is already inside a case so for my setup it was not needed.
I used these. They come with covers so in your case that may be perfect. I did not need the covers so I dumped them.
Victron
Should busbar in between cells be the same amp rating as Tfuse between battery bank and inverter? In my case, i have 400amp T-fuse with 4/0 cable from bank to inverter. I have 16s 48v 302AH LifePo cells
 

robby

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Should busbar in between cells be the same amp rating as Tfuse between battery bank and inverter? In my case, i have 400amp T-fuse with 4/0 cable from bank to inverter. I have 16s 48v 302AH LifePo cells
Are you asking if the Busbar itself should be the same amperage capacity as the main T-Fuse to the Inverter.
No I would use a Busbar that has a higher rating than the T-Fuse and the wire. You cant go to big with the Busbar rating, just make sure the terminals can fit.
 

alvirtuoso

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Are you asking if the Busbar itself should be the same amperage capacity as the main T-Fuse to the Inverter.
No I would use a Busbar that has a higher rating than the T-Fuse and the wire. You cant go to big with the Busbar rating, just make sure the terminals can fit.
Does busbar on each cell draw same amp as the entire bank's main positive?
 

Hedges

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Does busbar on each cell draw same amp as the entire bank's main positive?

You would have to sketch cell and busbar configuration to be sure we answer this correctly.

If you have a series string of cells, e.g. 16s LiFePO4 for 48V, each busbar carries the same.

If two strings in parallel, e.g. 16s2p (would have two BMS), same is true. But after two positives connect together, conductors beyond that carry 2x what the busbars do. (same for negative.)

If each cell pair wired in parallel e.g. 2p16s, we hope all carry the same current, and cross tie carries zero. But if a fault develops (open circuits between busbar and cell), then one cell and maybe one busbar would carry 2x current.
 

rmaddy

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Out of curiosity, why does everyone plan to use such long bus bars for connecting batteries in parallel? What's wrong with using a small bus bar such as the following (just an example of the type):


Assuming you chose one with sufficient amp rating, wouldn't this be easier and cheaper than some multi-foot long copper bus bars?
 

railcon56

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I'm putting together 4 batteries and I'm going with the Victron Power In. I figured by the time I buy thick copper bars. For $140, I can get 2 1000 amp busbars in a nice package for less than 2 650 Amp busbars. Or closer to that amount.
 

timselectric

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Hedges

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Out of curiosity, why does everyone plan to use such long bus bars for connecting batteries in parallel? What's wrong with using a small bus bar such as the following (just an example of the type):


Assuming you chose one with sufficient amp rating, wouldn't this be easier and cheaper than some multi-foot long copper bus bars?

Long cables could join on such a busbar.
I think some people are using the long busbar to span between batteries. Cost isn't bad if you buy metal stock.
Either way, want to balance length & resistance of parallel paths.

I don't find either "copper" or "brass" in description of that Amazon link. The 250A rating may be peak. They seem rather small.

I have that "type" in my system but it is rated max 48V.

Not sure why the low voltage given what its job is but that is its rating.

Probably safety rules for human access. Higher voltages require it be out of reach of prying fingers, unless they know how to use a tool to reach the conductor.
 

rmaddy

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I don't find either "copper" or "brass" in description of that Amazon link. The 250A rating may be peak. They seem rather small.
I wasn't recommending that specific bus bar, just pointing out that type of bus bar.

Using the shorter bus bar I mention would only require the battery cables to be at most a few inches longer than when using a long bus bar. Certainly a negligible change in resistance.
 
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