Originally Posted by 406 bug
I thought relays are use because many regular switches are not capable of hanlding the higher amp loads. I use 30 amp swithces at a cost of 3.95ea. rather than high dollar relays.
The best uses of relays are to keep high currents out of the cabin, as Cape Cod Bob said, and to reduce power loss to the device being switched. If you are using 30 amp switches instead of relays, you have to mount the switch where you can reach it. This brings high current carrying wires into the cabin and it usually results in long runs of wire from source to device.
A couple of points to remember:
- You're dealing with a low voltage system. If you have a 2V drop, that represents almost 14%, given 14.5V from the alternator.
- High currents yield high heat when circuits get shorted.
A relay is more than a switch; it's a remote crowbar. You use low current to switch high current. Benefits:
- lighter wires to controls, where space is usually at a premium,
- reduced wear on switches,
- ability to use a lower current fuse on each relayed control circuit,
- much lower risk of fire in case of shorts in the cabin,
- usually shorter runs of heavy wire from source to device,
- less voltage drop to device, so it works better.
Just getting higher rated switches doesn't gain any of those benefits.