trdslinger

I'm no electrician, but I do see how a relay works thanks to the yotatech write up i just read. My question now is why is it wrong or bad to have higher voltage going through a switch? Are switches just not able to handle the voltage or something? In the past I always wired up my stuff with only switches.

Babypig

I think that it's just that you really don't want to have a lot of amperage at the switch. The relay energizes the switch with a minimum of amps. Just cuts down on something going wrong with the switch. I think.

4Crawler

iTrader: (3)

It is the current, not the voltage that a relay helps with. A relay can switch 20-30 amps typically and only takes perhaps 0.10 amps to turn it's coil on, which in turn closes the load contacts. A typical switch is rated for 5-20 amps, so theoretically could handle that much load. A relay has the advantage of closing and opening the contacts very quickly, which reduces arcing and contact wear. A switch can be open or closed fast or slow, depending on how you flip it on or off.

Other advantages of a relay is that you can locate it near the load it will control. This minimizes the voltage drop of a long wiring run. Also, you only need to run a small gauge wire from it's coil to the switch inside the vehicle. A lot easier to run small wires than heavy wires. Also safer, too, since you keep the high power stuff outside the cabin. Below is a shot of my headlight relays. They are located about 12" from the headlight. I was able to eliminate 2.0 volts of drop from the stock headlight wiring (which uses a switch):



And finally, you can make a relay turn on or off automatically. For example, I wired my fog lights with a relay and switch. The relay gets power from the parking light circuit and the switch grounds it to complete the circuit and turn on the relay (which in turn illuminates the fog lights). The advantage is that if I forget to turn off the fog light switch, they will go off automatically when the parking lights are turned off.

trdslinger

Sounds good to me. I want to wire up some offroad lights. I haven't purchased the lights yet, but I do know that some I've seen are sold as kits with the relays, switches, and everything. I've been checking out stuff like the painless wiring fuse blocks, relays, inline fuses, etc., but I think until I buy my lights I won't know exactly what I need. It's also hard to know who manufactures the best lights, their durability, longevity, etc. Big bunch of confusion for me. I am pretty sure that what I want is a rectangular 5x7 100W to 130W halogen type lamp, with black finish. Got any suggestions as to whos lights are better and why???

4Crawler

iTrader: (3)

Get the lights you want. If they come w/ relays, use them, if not get a relay and add it. You can get them at most auto parts stores, Radio Shack, or Painless if you want a nive complete kit. I've always liked the Hella light kits, they come complete; fused relays, switches, wiring, connectors, etc. A 30A Bosch-type headlight relay will handle most lights, 30*12 is 360 watts, so would handle a pair of 100s or 130s.

trdslinger

I'm thinking about buying the KC 6X9 . I think 2 of them ought to give me as much light as I need. Their warranty looks good too. I was also looking at some Hella Rallye lights. I don't remember what model #. I just want rectangular lenses and black light bodies. I'm wondering why KC says they include a 40A relay in their kit. I know Amps times Volts equals watts, so I could only figure that they think people will keep adding lights to the circuit. The relays are the same price, so they probably just figure they are saving themselves a bunch of phone calls and frustrated customer complaints.

4Crawler

iTrader: (3)

A higher rated relay may hold up a little better than a lower rated one when pushed to the limits, and if indeed it is built heavier inside, it may have a few millivolts less voltage drop. But I imagine that marketing has something to do with it to. If you see two similar kits and one includes a 20A relay and one a 40A relay, you figure the 40A relay has got to give you more light, after all 40*12 is twice as much as 20*12. But the relay will only flow as much current as the load can accept from the power source.