Voltage ratings on DC circuit breakers. "Max voltage"?

Corlington

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I'm looking at this DC circuit breaker from Blue Sea Systems: https://www.amazon.com/dp/B000KOTALG

It says "48V DC MAX" and it's a 100A circuit breaker. I've read that these are thermal breakers. 100A @ 48V is 4800W. So it'll trip if you use ~4800W. If I were to use this in a 12V system, 100A @ 12V is only 1200W. If it's a thermal breaker, that won't be enough heat to cause it to trip, right? It would take 400A to reach the same 4800W of heat.

If it's meant for a 48V system, why would they list a "max voltage"?

I already bought it, and now I'm thinking I made a mistake. Can anyone offer any insight?
 

upnorthandpersonal

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It works based on current, not power. It just has a max voltage rating of 48V (which actually excludes a lot of systems since e.g. a '48V' LiFePO4 battery has a higher nominal voltage than 48V). It's fine to use these with 12V systems (note the "about this item" section: Max voltage: 48V DC, Interrupt capacity: 5000A @12V, 3000A @ 24V, 1500A @ 42V) - the reason it's less at higher voltages is due to arcing.
 

Pappion

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Your assuming a dead short. CB should trip for an overload. Should take more time for minor overload. There are specs for that.

DC arcs, it's used for arc welders. Higher voltages could weld CB closed. Interrupt capacity is an arc spec.

AC passes thru 0v, and may extinguish an arc.
 

kuranaga

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I'm looking at this DC circuit breaker from Blue Sea Systems: https://www.amazon.com/dp/B000KOTALG

It says "48V DC MAX" and it's a 100A circuit breaker. I've read that these are thermal breakers. 100A @ 48V is 4800W. So it'll trip if you use ~4800W. If I were to use this in a 12V system, 100A @ 12V is only 1200W. If it's a thermal breaker, that won't be enough heat to cause it to trip, right? It would take 400A to reach the same 4800W of heat.

If it's meant for a 48V system, why would they list a "max voltage"?

I already bought it, and now I'm thinking I made a mistake. Can anyone offer any insight?
nope!

the voltage drop of 48V is not over the breaker, but (mostly) over the load. a 100A breaker always trips @100A! (well according to its spec curve!)
 

OzSolar

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This can be quite the can of worms that few of the popular YouTubers adequately address if they even touch on so its good that you are asking the question.

Where is this fuse on your system? If this is right off your battery many will suggest a Class T fuse but it will still be nice to have this breaker for ease of troubleshooting and maintenance. What kind of battery do yo have?

Generally speaking the lower the the voltage the higher the AIC rating of a breaker. "Max voltage: 48V DC, Interrupt capacity: 5000A @12V, 3000A @ 24V, 1500A @ 42V"
 

Pappion

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Class T is the best, but costly.
I'm using second best ANL. Being careful how I do it. 150A ANL at each Lifpo4 battery, rated at 100A output. Using 4awg wires which should limit peak "interrupt" current.
The CB seems like a convenient switch, but it has resistance and will cost you efficiency. A battery switch is better.

BTW: You did not say what type of battery you using.
I used a 60A CB with 2 lead acid batteries on my old camper and it did just fine. The wiring was only 6awg.
 

timselectric

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I'm in the circuit breaker camp.
I'll take a breaker over a fuse, in almost all instances.
It gives you the same protection, with being reset able. (Instead of replacement) and, it gives you a handy disconnect.
 

Corlington

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Where is this fuse on your system? If this is right off your battery many will suggest a Class T fuse but it will still be nice to have this breaker for ease of troubleshooting and maintenance. What kind of battery do yo have?

I have a 170 Ah Renogy LiFePO4 battery (12V nominal). I think it will internally shut off if you exceed 150A draw.

Yes, this breaker is intended to be connected between the battery and the positive bus bar. I have an ANL fuse there now, but the cheap fuses I could get on Amazon keep breaking. Literally cracking without any indication that there was an overcurrent condition. No discoloration, no melting, and also no reason for more than 100A to ever be drawn (no shorts happening.) The cheap fuses use a single rivet on each side and there's a lot of play in them. The fuse holder is solid, but my van bounces and vibrates a lot, and I don't have any other explanation for going through three fuses. The only reason I know they are broken is because I'll hit a bump and my inverter will chirp at me because it lost power for a split second. They crack and then still provide a connection until I hit a bump where they momentarily disconnect.

I figured I would invest in a good brand circuit breaker instead.

I only have a 600W inverter, and a few other low power devices (DC fan, fridge, etc.), so I figure 100A is all I need. My converter charges at 60A, and I do occasionally use that when the sun's out, but not when it's at it's peak (otherwise I wouldn't bother plugging in), so it's about 75A charging at most. I have more ANL fuses between the positive buss bar and every other device: fuse block, converter, inverter, charge controller. They've never broken or blown, and their devices are mounted on the same panel, so they receive less stress than the one going to the battery.

It works based on current, not power.

Thank you!
 
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Pappion

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Your batteries LiFePo4 BMS may limit to 150A, after a (software) delay. Hardware current limit is faster and about 10x higher. Instantaneous current is tremendous. Possibly dead short the BMS FETS and make the current limits useless.
 
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