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Do I really need a relay with an electric fan??

Discussion in 'The Hokey Ass Message Board' started by 57wagon, Sep 28, 2004.

  1. 57wagon
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    Kenosha Wi.

    57wagon Member

    Just got the new radiator installed in my model t, and was hooking up the temp switch that was on there before I got the car...

    Looks like the switch was hooked up to the negative side of the fan motor, positive was hooked to a direct hot wire with an inline fuse...

    I saw in the speedway catalog that there was a relay that would lower the voltage to the switch when starting the fan..

    Anybody have any experience with these?? I have it hooked up with no relay and it seems to be working... Just don't want to fry anything if possible.

    thanks,
    steve
  2. Hellbilly_Buzzard
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    Hellbilly_Buzzard Member

    The only reason you need a realy is for high current applications. Most standard switches are not able to "hot switch" higher current loads (i.e. headlights).

    I am running an electric fan off of a 1A toggle switch with an inline fuse. Works fine.
  3. Hot Rod To Hell
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    Hot Rod To Hell Member

    A relay is a REALLY GOOD idea on ANY high amp draw electrical device...
  4. CRAP
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    Colorado Springs CO.

    CRAP Member

    when I test wired my fan it worked great, then when I wired it for real I kept blowing fuses and the fan would surge.
    Craig
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  5. Slide
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    Slide Member

    Really depends on your switch. Most electric fans pull at least 15 amps, some 20 amps or more, so you'll need your switch to be able to handle that load. Most parts stores carry toggle switches and/or push-pull switches that will handle anywhere from 30-60 amps, so that would work. If you're using one of those thermostatically-controlled deals (or a low amp rated manual switch) you should use a relay.

    I have a 30-amp rated push-pull switch on my car. This let me put a decent-looking knob on it too keep it from looking out-of-place on my car.
  6. Hellbilly_Buzzard
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    Hellbilly_Buzzard Member

    What amp fuse are you running?
  7. Petejoe
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    Petejoe Member

    I have hooked up three of them with no problems. I aways just use a good high amperage switch and hook it up with a heavier gauge wire to the highest amperage circuit i got.
  8. 57wagon
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    57wagon Member

    The switch ( adjustable temp switch ) is rated for 20 amp 250volt it currently has a 20 amp inline fuse in it now..

    It did work and didn't blow yesterday, which was the first day that I hooked it up, cycled it a few times and seemed to work fine.. I guess I am just being paranoid?? Maybe??
  9. Model A Vette
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    Model A Vette Member

    Be careful about what kind of fuse you are using if you don't run a relay. I used an old style glass "Buss" fuse for a few years without a relay. The fuse was supposedly the correct amperage but it would "de-solder" the ends of the fuse due to the high current load. I converted to a bosch relay and the fusable link from an Audi and have no problem now. I also switched to a sensor from a Chrysler minivan electric fan setup. That turns on the fan at about 185-190. I used the sensor in the ground side of the relay wiring.
  10. 57wagon
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    57wagon Member

    I don't know where the sensor came from or who made it,, but it has a knob on it that you can turn to adjust when the fan comes on and turns off....

    I have it set to come on when the temp gets to 190. Good thing to think about with the fuse though, it is a glass buss type inline fuse.
  11. DrDano
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    Fort Collins, CO

    DrDano Alliance Vendor

    [ QUOTE ]
    A relay is a REALLY GOOD idea on ANY high amp draw electrical device...

    [/ QUOTE ]

    I completly agree here. Use a relay. I had a electric fan in a '63 ford pickup and I found out he hard way how important a relay is. Left me stranded in the middle of the intersection in town when the fan overloaded everything and I lost power to my ignition. Wire in the relay or have an auto-electric shop do it. It wont cost much and is worth the time and money to do it right.
  12. burndup
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    burndup Member

    A relay is great for all the reasons mentioned, but get a high quality one, a cheapie will burn out over time. (contacts are like points contacts, burn up and no longer conduct)

    A relay also chews up a little current, too, on top of it all.

    A big meaty switch (high amp rating, higher than the fan draws) is a good idea for a failsafe solution, but what I dont like is that you are bringing (thick, hopefully) wires thru the firewall that are carrying a high current load... and assumably these are near the rest of your wiring... In the admittidly odd instance these wires fry, it may take a lot of your electrical system with it....

    I say, keep all the high current shit in the engine area, and have the low current stuff running thru the firewall and under the dash... so yeah, thats another vote for a relay.

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