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Old 01-03-2009, 04:01 AM
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Relay place

Hi guys, just some questions, I wonder... what is the best place to install a relay? Should be close to the Acc (fuel pump, lights), close to the power source (switch, fuse, dash) or right in the middle?

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Old 01-03-2009, 04:36 AM
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From an electrical standpoint, it doesn't matter where the relay is physically located in the circuit. The relay is just an electrically operated switch to make and break the circuit. If you are installing a new circuit, make sure you are using wire that will handle the load (can't hurt to go a bit bigger, if it's a long distance). If it were me, I'd try to find a convenient place for the relay that would be easy to access, it case it ever needed replacement, and where it wouldn't be likely to get wet.
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Old 01-03-2009, 12:00 PM
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Thanks, I'll consider the load and the access
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Old 01-03-2009, 04:39 PM
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Typically relays are used to keep high current carrying wires out of the passenger compartment. At least thats the theory. Seems to me there is a lot that goes though the steering switch and comes into the fuse box. Which is in the pass. comp.
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Old 01-03-2009, 05:02 PM
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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.
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Old 01-05-2009, 11:20 PM
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Quote:
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:
  1. You're dealing with a low voltage system. If you have a 2V drop, that represents almost 14%, given 14.5V from the alternator.
  2. 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.
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Old 01-06-2009, 05:58 AM
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Grouch nails it.

Vince
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Old 03-29-2009, 01:42 PM
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Quote:
Originally Posted by V305
Hi guys, just some questions, I wonder... what is the best place to install a relay? Should be close to the Acc (fuel pump, lights), close to the power source (switch, fuse, dash) or right in the middle?
I place relays at the most conveniently accessible safe location that keeps the load circuit as short as possible. Since the switching circuit is a very low load circuit, I don't worry about how the relay location affects it.
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