Join Date: Aug 2001
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Re: Relay Questions (Jump in here Leve!)
Nothing NEEDS a relay. If the switch and wiring can handle the current then it's fine. Take the power (wattage) divide by twelve and that's the current in amps the circuit will have to carry.
Example: 2x150 watt KCs = 300, divide by 12 = 25 amps. A switch designed to carry that kind of load will be larger and much more expensive than one to control a relay. Obviously a relay is a good choice there.
As far as relays go, you just need to find one capable of handling the load. For the 25 amp KCs, you probably want at least a 30 amp. 40 would be optimal (at least 50% overload is a good target) but you have to decide if the extra cost is worth the added margin of safety.
A relay should not affect your fuse selection at all. In the KC example, you would still use a 30A fuse. Keep in mind when your jeep is running it's actually around 13.5 volts so the current will run less than you're calculating at 12V. Try to use the lowest fuse value that will operate the circuit without blowing.
As for placement, it's a matter of preference. As long as you use the correct wire you can put it anywhere. I bought a fuse/relay center originally for a Saturn brand new for for about $10. It's real nice to have everything together in one place. Other people don't mind hanging them all over.