12v Circuit Breaker?

[jroeiii]

Looking for feedback on this ... I am in the process of putting together an overhead console to control all the lighting / radio on the cart, with a significant amount of experience in CAR audio on 12v systems.

Ideally I want to install a circuit breaker between B+ / my fuse panels using 8ga wiring in between. This would isolate the power when / if I need to work on components down the road, (I could pull the fuses also).

I see a number of 12v 300AMP or lower units but very few labeled as "48v".

Is it safe to assume I can use a 12v 300AMP as a 48v 60AMP breaker? (4-5x increase in voltage since it will have up to 58volts on a full charged pack, with a 5 x reduction to AMPs)

[Sergio]

That is incorrect.

You can always use a higher rated voltage fuse on lower voltage system, but the current has to be the correct one.

If You need a 30 amp fuse @12v, You can use a 30 amp fuse @600v

The only purpose of the voltage rating on the fuse is to stop a possible arc once the fuse blows.

[joesam]

only purpose of the voltage rating on the fuse is to stop a possible arc once the fuse blows

What I like about Sergio's answers on this forum is that he not only tells you the WHAT something is....but the WHY (hi-volts DC=arcing). Being fairly thick headed - the "why" has always helped me retain when I learn.

Sergio - why does it seem different in A/C? Years ago I was assisting in converting a 460VAC motor system to 208VAC and had to put higher amp fuses in the control circuit. Why?

[jroeiii]

What I am finding is a bit inconsistent which is why I am looking for input - specifically the 48v to 12v voltage reducer - It has a 7.5A fuse on the input (48v) and 30A on the output (12v).

The draw amperage is lower due to the higher voltage

The output amperage is higher due to the lower voltage

[Volt_Ampere]

Listen to what Sergio said!!!! The voltage rating on a fuse is only a maximum. The current rating is what really matters. On a reducer, the input current is much less than the output current so the input fuse would have a much lower current rating than the output fuse. They could have the same voltage rating. Most fuses are rated for higher voltages than we use them for on a golf cart.

[greg-g]

Sergio can you reread his question and maybe post a different answer I think he wants to go the other way

[klanel]

Originally Posted by joesam

Sergio - why does it seem different in A/C? Years ago I was assisting in converting a 460VAC motor system to 208VAC and had to put higher amp fuses in the control circuit. Why?

If the motor draws a fixed wattage, then using the formula p= E x I explains why.

P equals power in watts
E is the voltage
I is the current

If the voltage say halves, the current draw will double if the wattage remains constant.

[Volt_Ampere]

Fuses are designed to respond to Current not power. You size the fuse for the max safe current in the circuit it is protecting and make sure that it's voltage rating is higher than the max voltage the fuse will see across it when it blows.

[Gregorio]

Try Crimp Supply. They have 48vdc breakers.

[Sergio]

Blue Sea Systems, the company that makes the fuse boxes that lots of folks here use also makes DC breakers.

Here is a link to a 30amp version

Here is a link to a 30amp version