whiteknight
10-19-2008, 11:00 AM
I see way to often people adding new high current circuits to there rigs with no relays to operate the device. This will lead to problems up the road and a unreliable electrical system.
Most aftermarket switches (rocker, toggle micro,etc) can usually only handle a max of a 10 amp load, after that you are causing damage to the switch. The idea behind having a relay installed is to take the heavy current away from the switch. This will allow much smaller gauge wiring to be done under the dash and keeps the heavy gauge high current wires out from under the dash where they do not belong.
An example.
A pair of small fog lights usually draw from 8 to 10 amps. If the lights were only run through a switch, the switch would burn out in a short period of time. By using a relay, you end up moving the heavy current through the relay and not through the switch. A normal 5 terminal relay will only draw about 0.2 to 0.3 of an amp to turn on. so that's only a max of .3 amps that is going through the switch. The switch will last a life time.
You can get relays that can handle a 30 - 80 amp load, very cheaply.
Most general purpose relays have a set of normally open contacts and a set of normally closed contacts and are wired internally as shown in the picture posted below. The two terminals that turn the relay on and off are (85 and 86), The terminal for your main power in is (30), and the terminal for main power out for a normally closed circuit is (87) . If you want a normally open circuit you would use (87A) instead of 87. Some relays reverse the 87 and 87A markings.
When wiring your electrical system. The correct way to wire things like fuel pumps, cooling fans, fog lights, nitrous controls, etc. Is to use a relay to control the circuit. This will save you a lot of grief up the road !
Attached image(s) http://whiteknight.ca/FORUMS/uploads/post-2-1107041803.jpg
Most aftermarket switches (rocker, toggle micro,etc) can usually only handle a max of a 10 amp load, after that you are causing damage to the switch. The idea behind having a relay installed is to take the heavy current away from the switch. This will allow much smaller gauge wiring to be done under the dash and keeps the heavy gauge high current wires out from under the dash where they do not belong.
An example.
A pair of small fog lights usually draw from 8 to 10 amps. If the lights were only run through a switch, the switch would burn out in a short period of time. By using a relay, you end up moving the heavy current through the relay and not through the switch. A normal 5 terminal relay will only draw about 0.2 to 0.3 of an amp to turn on. so that's only a max of .3 amps that is going through the switch. The switch will last a life time.
You can get relays that can handle a 30 - 80 amp load, very cheaply.
Most general purpose relays have a set of normally open contacts and a set of normally closed contacts and are wired internally as shown in the picture posted below. The two terminals that turn the relay on and off are (85 and 86), The terminal for your main power in is (30), and the terminal for main power out for a normally closed circuit is (87) . If you want a normally open circuit you would use (87A) instead of 87. Some relays reverse the 87 and 87A markings.
When wiring your electrical system. The correct way to wire things like fuel pumps, cooling fans, fog lights, nitrous controls, etc. Is to use a relay to control the circuit. This will save you a lot of grief up the road !
Attached image(s) http://whiteknight.ca/FORUMS/uploads/post-2-1107041803.jpg