Why relays

[gtx69]

What is the purpose of putting relays on the headlights,fan,and fuel pump.Does it take less amps or do you still need to upgrade the alternator?

 

[PDFROGMAN]

What is the purpose of putting relays on the headlights,fan,and fuel pump.Does it take less amps or do you still need to upgrade the alternator?

relays are usually used to complete the ground circuit, rather than putting 12 volts through switches, less heat, longer contact life for the switch

 

[rdrunner1974]

relays

relays are usually used to complete the ground circuit, rather than putting 12 volts through switches, less heat, longer contact life for the switch

Relays are used to get the power closer to the point of use. They are seldom if ever used on the" GROUND CIRCUIT" as the 12 volt still needs to be switched or you would have a HOT 12 volt wire to your accesory if you attempt to switch the ground.:no:
Check the link and you will see the benifits of using relays for your headlights as the switch only uses enough current to energise the relay.
http://www.madelectrical.com/electrical-tech.shtml

 

[Domino]

Air systems in trucks use a very similar concept. A small air line from the brake pedal valve signals a relay near the axles to open, thus connecting the air tank(s) to the brake chambers via a larger line.

 

[PDFROGMAN]

Relays are used to get the power closer to the point of use. They are seldom if ever used on the" GROUND CIRCUIT" as the 12 volt still needs to be switched or you would have a HOT 12 volt wire to your accesory if you attempt to switch the ground.:no:
Check the link and you will see the benifits of using relays for your headlights as the switch only uses enough current to energise the relay.
http://www.madelectrical.com/electrical-tech.shtml

I did a poor job of explaining let me see if I can explain better
what I meant by "completeing the ground circiut"
power is routed to the relay when u flip the switch it grounds the relay.
the relay is energized to complete the hot lead to power the device
sorry I should have been more descriptive

 

[ChgrSteve67]

Another way of explaining it is that a relay allows a low voltage\amp switch\circuit to turn on\off a high voltage\amp device.

Thus allowing you two use two seperate power sources. One for the switch and another for the device you are controlling.

Generally the power used for the headlights and other devices are drawing power from various points in the stock harness and because of other devices, connectors and bulk head connectors there is a certain amount of power thats loss. So by installing relays you can wire the relay in the stock location that the device is drawing power from for control and then run seperate power lines to the device that needs a direct draw of power from the battery or other power source through the relay.

Clear as mud.

 

[Revhendo]

Another way of explaining it is that a relay allows a low voltage\amp switch\circuit to turn on\off a high voltage\amp device.

Thus allowing you two use two seperate power sources. One for the switch and another for the device you are controlling.

Generally the power used for the headlights and other devices are drawing power from various points in the stock harness and because of other devices, connectors and bulk head connectors there is a certain amount of power thats loss. So by installing relays you can wire the relay in the stock location that the device is drawing power from for control and then run seperate power lines to the device that needs a direct draw of power from the battery or other power source through the relay.

Clear as mud.

Dude, you were good with low amp switch controlling high amp circuit.

 

[gtx69]

Thanks everyone

 

[scotts74birds]

Very well said Steve. GTX69, the whole point of this is to not run a high current component thru a regular switch. Example, my 95 Ram heats-up and burned the headlight switch because I live in the country, and use Hi-beams all the time. I installed a relay under the hood so that instead of all the current needed to power the high-beams being sent thru the headlight swithch, the large current goes thru a relay, that is activated by a small current from the switch now. In a nutshell, a relay is an electrically operated switch, capable of controlling a larger load than the switch itself is capable of. Clear as mud?