Quote:

Measure the resistance with an ohm meter. Then divide voltage (12 volts) by the resistance and it will tell you what the amperage draw is

I = E / R

Amps = Voltage divided by resistance.



Not trying to bust on you or anything but you can't use these figures for any kind of coil.
A coil which is what is in the solenoid or any relay takes a different amount of current to maintain it than to energize. Your formula works for maintaining but that is not the max current which is what you need to fuse for. Personally I fuse at 30 amps. I am not trying to protect the circuit so much as just prevent a complete meltdown.

If you really want to know hook a Simpson or equivalant anolog current meter capable of 30 amps DC in series with you solenoid. Move the stop on the meter to just below what you are seeing the meter go to when you apply the t-brake. Keep reapplying the t-brake and moving the stop until you see no movement in the meter hand. This is peak current. Then multiply this figure by 1.20 and use wire and fuse rated for that current. If your digital meter has a 30 amp capability and a hold maximum feature. You can hook the meter up set it for hold maximum apply the t-brake and get the peak current a little easier. This is how we read relay current when we do not have a testset available on signal systems. You could also do this and take note then check your solenoid every so often as we check relays at work to make sure they are in good condition.

GUESS WHAT I have never applied this to the race car. Why, because I run 10 gauge wire and a 30amp self reseting circuit breaker and know it will always work. Been bitten by a failed fuse once not again.

Leon

Career best 8.02 @ 169 at 3050# and 10" tires small block power.