I need some help- circuit breaker question 6V vs 12V

[Drbrown]

Circuit breakers are an extremely important part of a car. If you buy a replacement circuit breaker, I recommend you be sure to get a Made in USA unit, either NOS or used from a trusted source, via forum classified ads (Fordbarn, V8 Club, HAMB) or eBay etc.

I'm a non-conformist when it comes to stock electrical systems in older cars. The majority of forum members here don't experience or haven't experienced the problems I have ..... (1) Unprotected by a circuit breaker or fuse, my '47 ignition circuit shorted and melted the wiring insulation, and (2) my stock dual-circuit breaker serving both headlight/parking light systems overheated internally a few times and shut down the lighting unexpectedly - in the dark .... no evidence of shorts in the system.

I rewired using over-sized wire for a 12 volt system, converted the system to blade-type fuse boards serving every device, and incorporated relays for the ignition circuit, headlights and fog lights. At the cost of sacrificing some of the car's hidden vintage character , the benefit is safety, lower overall electrical system resistance, easier starting, brighter lighting and easy roadside repairs.

[JSeery]

This is a later model CB panel, but it is the same basic arrangement. All of the earlier wiring diagrams I have seen (41 and up) show the two CBs, but are not clear on the amperage ratings or which one connects to what.

[rotorwrench]

Originally Posted by mshmodela

V=IR, or I=V/R. 30A = 12V/R , divided both side by 2.

30A / 2 = 12V /(R x 2) = 15A = 6V / R where R is the resistance of the breaker. So a 30A, 12V breaker would pop with only 15A at 6V.

Amps are current draw or flow and volts are the carrier in a circuit. The theory applies to a circuit but the circuit protective device is largely only affected by current that flows through it. Voltage only affects it when it is a lot higher. If you look at most circuit protective devices, they have the current and maximum voltage printed on them. Cheap automatic reset breakers made in third world counties may not though.

In aviation, we use the same manual reset type breakers for both 12 and 24-volt systems since they are both below 32-volts DC. There is no difference.

This is an old thread.