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diy solar

Do Server Rack batteries have properly specced circuit breakers?

rhino

Solar Wizard
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Jun 6, 2020
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Minnesota
Since I had been looking at circuit breakers for DIY parallel battery setup I wanted clarification on properly specced circuit breaker for DIY battery compared to what all the server rack batteries are using.

What are the actual breakers(to lookup specs) used in these server rack batteries and has anyone actually tested that those breakers would protect the battery when it is short circuited?

My biggest question is what is the interrupt rating of those breakers? A Midnite 175A DC breaker for example has a AIC of 50kA at 125VDC and are considerably larger than the ones I see in server rack ones.
 
Basically, anything in the server rack battery is there to protect the single battery.

If you put many server rack batteries in parallel you may not have proper protection for your inverter DC input maximum current without its own breaker.
 
Basically, anything in the server rack battery is there to protect the single battery.

If you put many server rack batteries in parallel you may not have proper protection for your inverter DC input maximum current without its own breaker.
That's partly what I am wondering.. I don't see this caveat mentioned when there are a lot of people using multiple server rack batteries in parallel.
 
As long as the breaker can protect the battery that is enough in my opinion.

Hypothetical scenario:
You have a 6x eg4 48 volt batteries in a rack servicing 1x 6500 watt inverter.
That is 6x feeders with over-current protection at source and and 1x branch circuit fused at the start of the branch
Lets further say that you used a mega fuse for the branch circuit with relatively low breaking capacity.
Lets even further say that you have a dead short on the branch circuit.
Likely the first thing to open would be the BMS FETs on each battery.
Then the mega fuse gets a chance, if it fails to quench the arc then the battery breakers should trip like dominoes thus clearing the fault.
Not ideal but better than a catastrophic failure.
The current on each feeder circuit is only as high as its own dead short ampacity.

It is possible that the resistance on the branch circuit could be high enough that none of the batteries see enough current to trip but that would be a disproportionate system.
Eaton/Bussman calls this concept "selective coordination".
From memory Littelfuse calls this fault isolation.

If I'm wrong I want to know.
 
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