Dc breaker for battery disconnect question

[BartHenry]

If using a breaker as a battery disconnect, and I have let's say a 400ah battery, then wouldn't i need a breaker rated for 400A?
Let's look at the EG4 as an example... you have 4 batteries ea with a 100a breaker, BUT if you use a Nader 250a breaker as a disconnect, then wouldn't it trip before the batteries. What if your using lead acid batteries ?

 

[cs1234]

If using a breaker as a battery disconnect, and I have let's say a 400ah battery, then wouldn't i need a breaker rated for 400A?
Let's look at the EG4 as an example... you have 4 batteries ea with a 100a breaker, BUT if you use a Nader 250a breaker as a disconnect, then wouldn't it trip before the batteries. What if your using lead acid batteries ?

A 400amp battery is normally only going to send out 400amps if something is requesting 400+ amps, unless there is a failure causing it to dump everything.

You need a breaker rated for what you are trying to protect beyond the battery, be that the wiring or the inverters / chargers and such. If you have wiring rated for 200 amps, you wouldn't want a 400amp breaker.

Lead acid or lifepo4 doesn't make much difference at the rated breaker level of 250amps, of your 250amp breaker example. It makes a difference on the AIC rating of the breaker, as a lifepo4 battery will have a different maximum amount of amperage it could unload when it shorts out.. up into the thousands of amps. You need to make sure your breaker can stop that on it's AIC rating if you are using it in place of any other type of short circuit protection like a T class fuse. Many T class fuses have AIC ratings up around 20,000 amps.

 

[fmeili1]

You usually connect the battery rack to two battery bus bars with one 4/0 AWG positive and one 4/0 AWG negative (<=600A, depending of how many batteries you've installed in the battery rack). From the bus bars you connect each inverter with 2/0 AWG and in these positive wires you need to install one breaker for each inverter. So the current is max. 100 amps between the bus bar and the inverters.

 

[timselectric]

What load do you have that will need 400a?

 

[BartHenry]

What load do you have that will need 400a?

I don't, I was just wondering "if" your system could pull that much, wouldn't a 250a breaker (used as a disconnect for maintenance) be nuisance trip all the time.
Like when you have to power down the inverter.... this is not a real life scenario, I was just asking if a breaker should be sized to match your battery bank.

 

[timselectric]

I don't, I was just wondering "if" your system could pull that much, wouldn't a 250a breaker (used as a disconnect for maintenance) be nuisance trip all the time.
Like when you have to power down the inverter.... this is not a real life scenario, I was just asking if a breaker should be sized to match your battery bank.

Wiring should be sized for the load. And breaker should be sized to protect the Wiring.
My 280ah batteries have 125a breakers.
But will never see anything close to 50a loads.

 

[BartHenry]

Wiring should be sized for the load. And breaker should be sized to protect the Wiring.
My 280ah batteries have 125a breakers.
But will never see anything close to 50a loads.

I guess I'm just over thinking it.

 

[Gavin Stone]

I guess I'm just over thinking it.

You aren’t overthinking it. I had the same confusion when I first started out. Amp hours of batteries are just the capacity. Like the amount of water in a bucket. How fast that water pours out depends on the size inverter and voltage you’re using. Divide the inverters total wattage potential by the nominal voltage. Which Eg4 inverter were you referring to?

 

[BartHenry]

You aren’t overthinking it. I had the same confusion when I first started out. Amp hours of batteries are just the capacity. Like the amount of water in a bucket. How fast that water pours out depends on the size inverter and voltage you’re using. Divide the inverters total wattage potential by the nominal voltage. Which Eg4 inverter were you referring to?

I was referring to eg4 batteries with the 100 amp breaker built in...just as an example

 

[Gavin Stone]

I was referring to eg4 batteries with the 100 amp breaker built in...just as an example

Ah I see. Well the same logic applies. It’s whatever inverter you are using that sets the size of the breaker and wire size.

 

[Scat]

Thank You All
For you comments for Sizing wire, breakers, and fuses.
This clears up alot for me.
Thanks Again
Scat