Wire gauge between batteries and busbar vs busbar to inverter

[jpvb]

Hi everyone,

Please see attached hand drawn schema. I would like to parallel my 24V batteries via a busbar. This busbar will be connected to a 3000W inverter, so I need a wire able to hold 125AMP continous. I will go with a 1/0 AWG.

My question is about the ones in pink... batteries to busbar (all the same length of course). Am I right to think that max current pulled on each cable will be 125/4 = 31 AMP ? Can I connect each battery to busbar with a 6 AWG wire? If yes, I suppose that I should place a 50A fuse on each?

Thanks for your help !

 

[HRTKD]

The DC amp draw at 3000 watts draw (on the AC side) would be 147 amps. 3000 / .85 / 24 = 147 The numbers would change depending on how efficient your inverter is. Mine is .93 instead of .85, but .85 is a conservative value to use.

1/0 wire is fine as long as the distance isn't too long between the inverter and bus bar. Could you get away with smaller wire on each battery? Yes. But do you want to be ordering different size wires and lugs? I put 2/0 in both places in my 12 volt system. Otherwise, 6 gauge cable between the battery and bus bar is acceptable.

Use a wire gauge calculator to answer questions like this.

Interactive Wire Size Calculator

Battery Chargers, Inverters, Solar Components, and Wiring Supplies for Boats, RVs, and Off-Grid Applications.

baymarinesupply.com

 

[rmaddy]

My question is about the ones in pink... batteries to busbar (all the same length of course). Am I right to think that max current pulled on each cable will be 125/4 = 31 AMP ? Can I connect each battery to busbar with a 6 AWG wire?

I suggest you use the 1/0AWG for all battery connections. Think about what happens if one battery shuts down for some reason. Now the load is across 3 batteries, not 4. What if two shut down? Now the load is across 2 batteries. 6AWG wire will become a safety issue.

Also, using 1/0AWG for all connections lets you start with one battery and test the whole system. Then you can add each battery as needed.

 

[12VoltInstalls]

Could you get away with smaller wire on each battery? Yes.

Plus it never hurts to overcable batteries- the cost difference is minimal, and they’ll NEVER get hot.

 

[timselectric]

Plus it never hurts to overcable batteries- the cost difference is minimal, and they’ll NEVER get hot.

Definitely agree.
My inverter calls for #2. But, I ran 2/0. I prefer to use the largest wire/ lug, that will fit. It stays at room temperature, no matter what the load.

 

[jpvb]

Thanks for all your advices guys! I will go with the same size for all wires.

 

[rmaddy]

You should also put a fuse on each battery. The type and size depends on the type of battery and its rated max continuous discharge current.

 

[WYtreasure]

Hi everyone,

Please see attached hand drawn schema. I would like to parallel my 24V batteries via a busbar. This busbar will be connected to a 3000W inverter, so I need a wire able to hold 125AMP continous. I will go with a 1/0 AWG.

My question is about the ones in pink... batteries to busbar (all the same length of course). Am I right to think that max current pulled on each cable will be 125/4 = 31 AMP ? Can I connect each battery to busbar with a 6 AWG wire? If yes, I suppose that I should place a 50A fuse on each?

Thanks for your help !

Welcome to the party jpvb.

Sounds like you are getting great info. What are the specifics of your batteries?

There is a link in my signature to some great battery safety information.
Enjoy the show.

 

[onmountainuphigh]

You should also put a fuse on each battery. The type and size depends on the type of battery and its rated max continuous discharge current.

Can you explain that a little more? If there is T-fuse between the bus bar and the inverter load, wouldn't that handle any short?

 

[rmaddy]

Can you explain that a little more? If there is T-fuse between the bus bar and the inverter load, wouldn't that handle any short?

Batteries in parallel should be individually fused, in addition to the big main battery fuse, if the max current from the battery bank is higher than the max continuous discharge current of each individual battery. The smaller individual fuses protect each battery from too high of a discharge current.

 

[onmountainuphigh]

Batteries in parallel should be individually fused, in addition to the big main battery fuse, if the max current from the battery bank is higher than the max continuous discharge current of each individual battery. The smaller individual fuses protect each battery from too high of a discharge current.

That makes sense, because when I read battery manuals, they specify a max discharge current. A lot of server rack batteries have a breaker on them—do these function as overcurrent protection for the individual batteries?

 

[timselectric]

That makes sense, because when I read battery manuals, they specify a max discharge current. A lot of server rack batteries have a breaker on them—does these function as overcurrent protection for the individual batteries?

Yes

 

[JRH]

Can you explain that a little more? If there is T-fuse between the bus bar and the inverter load, wouldn't that handle any short?

 

[SkippyJonJones]

Batteries in parallel should be individually fused, in addition to the big main battery fuse, if the max current from the battery bank is higher than the max continuous discharge current of each individual battery. The smaller individual fuses protect each battery from too high of a discharge current.

Isn't this also the job of the battery BMS? Or, is that just not reliable?

 

[timselectric]

The BMS is the last line of defense. It's job is to protect the battery, not the rest of the system.

 

[wme]

Look at some of the battery tests that folks post on Utube. Some show a 100 amp bms delivering 150 amps for minutes before "tripping"