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electric fan wired to tach terminal on dist?

Discussion in 'The Garage' started by blazerpro79, May 17, 2005.

  1. blazerpro79

    blazerpro79 1/2 ton status

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    hey guys while i was fixing my numerous eletrical problems i figured id replace my bearing-shot clutch fan with an electric fan.

    i want to wire the fans power to my distributer on the tach plug, being that it is a good ignition source, i dont wanna deal with wiring to my fuse box being that i have a few things in there already... and if anything fails, the fan will fail. also i want it on ignition, not thermo-controlled...

    so ... is the distributer tach terminal a good ignition source for my electric fan?
     
  2. 4trolls

    4trolls 1/2 ton status

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    thats where Its hooked up on my jeep sort of ,its HEI but no problems with it yet
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    is a '79 blade or glass fuse panel?

    Lots of reasons to go with the fuse panel wiring over anything else IMO, at least with the blade type panels.
     
  4. Boondocks

    Boondocks 1/2 ton status

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    If you really must hook it up to an existing circuit that is hot only when the ignition is, how about the electric choke circuit?

    Also, I am assuming you are powering the fan relay and not the fan itself from this connection.

    Otherwise, I'm with dyeager535.
     
  5. blazerpro79

    blazerpro79 1/2 ton status

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    its got blade fuses, not sure if they are stock though :dunno:

    the PO did a lot of work to it (most of it was unneccessary and mickey moused). so far new motor and almost all electrical has been replaced bc of him
     
  6. blazerpro79

    blazerpro79 1/2 ton status

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    it actually wouldnt turn over... my guess is a tach requires very little power, while an electric fan takes much more than a tach... but i was freaking out bc i changed my cap, rotor and coil, at the same time as hooking up the fan so i was a getting frustrated trying to find the problem... then i unhooked the fan and BAM it started up...

    its got a lot of stupid old wiring jobs and the PO messed it up pretty bad. its a DD and i need to make sure the fan is never off when the motors running... i have my ignition slots used on the fuse board (i think their is only two).

    any where else you guys would suggest bring ignition power to the fan? ill check the ignition choke... but my carb choke is there i think...
     
  7. 4trolls

    4trolls 1/2 ton status

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    I guess I'll have to take another look at the jeep in the daytime :confused:
     
  8. Jonny-K5

    Jonny-K5 1/2 ton status

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    isnt the tach terminal on HEI just a signal, not a 12v power source? you still have to hook up a 12v wire on a tac, then a signal wire goes to the tach terminal on the dist. no way would that run a fan.
    fans take alot of power. run a relay or hook it up right using the fuse panel.
     
  9. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I wouldn't do that. They need to be thermo controlled otherwise they will be trying to cool the engine when it doesn't need to be cooled. I also think that would be harder on your t stat, a t stat failure COULD ruin a motor. One thing I've learned with my K5 is that do it right the first time or forget it. I wired in my flexalite fans with the controller that came with them. It's thermo controlled and works flawlessly. I also have a manual switch too to turn them on early if I want.

    Another thing is your altenator. Depending on the fan(s) you run but my dual 13.5" fans pull 29 amps! Thats a lot. when the fans are off when the engine is cool it gives the altenator a chance to charge the battery for a few minutes before being worked hard by the fans, especially with dinky 78 amper alts. most of our trucks have.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    The oldest blade fuse panel I've seen is 1983, so excuse me if yours is different. (I can probably post a picture of an '82 though, so if it might help my description, let me know) Screw it, here it is:

    [​IMG] Blue wire is plugged into one of the accessory terminals. Using a GM connecter is a better idea.

    The '83 fuse panels (and up, although design changed around '85) have blade fuses in most locations, thats a given. However, there are also one terminal ports that are typically empty. You can't fit a fuse in them if you wanted to. THOSE are where you should get your power. Some are 12V ignition, some are 12V battery. Check your fuse panel out, let us (me? lol) know if that sounds right. You can check which are hot at which time with a voltmeter. The connectors are universal for GM, although each terminal is "keyed" so you can't put the wrong connector in the wrong terminal. PO's typically use blade connectors or bare wire ends stuffed into these. :(

    A fan setup is exceedingly simple if done right. You use one relay (per fan typically) and four wires to each relay.

    12V from the battery to the relay, 12V from the relay to the fan motor, 12V ignition to the relay, and another wire to whatever you use to control the fan, either a temp switch or controller.

    The only reason to run a manual switch inline with a temp switch is if you intend to bury the fan (or need to keep it from blowing mud underhood) or race. A manual switch is placed inline with the temp switch or controller, and just stops the temp switch or controller from grounding that wire.

    It may sound like a lot, but it's not. As was mentioned, do it right, and be done with it. Splicing into existing wires is asking for hard to troubleshoot (and VERY annoying) problems in the future. Your fan 12V ideally will come off the battery, switching that wire is a bad idea, switches people typically use don't handle that kind of draw well. Besides, the relay setups allow you to make your long runs (ignition switched 12V, fan switch-es) with much smaller and easier to work with wire.

    As was mentioned, fans do not need to be on all the time. It increases wear on them, increases load on charging system, increases noise, and is pointless when the vehicle is moving at a decent speed.

    I'm running dual fans, (wired up like GM does) a 78amp alternator, and have no problems with my charging system.
     
    Last edited: May 18, 2005
  11. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    As long as the rest of the truck is stock. Add an aftermarket stereo and other electrical items and it isn't enough, don't ask how I know.
     
  12. blazerpro79

    blazerpro79 1/2 ton status

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    i dont know how accurate that is... im running a 78 amper it has no problem powering 2 sets of 6" pro comp offroad lights, 130watts a set, my headlights, and my stereo with a 500watt sony amp... if anything, the volt guage will drop 1 or 2 volts... usually down around 13 or possibly 12... and thats at idle, when im moving it never drops below 14
    my battery is never low either... i dont recall it ever giving me trouble (i probably shouldnt be saying that!!! ;) )
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Stock electric fans are reputed to draw as much as 30 amps (each?) at startup but I'm sure thats not accurate. Maybe 15 amps.

    Derale's bigger fans use between 8 and 18 amps. Two fans going at 10 amps each, headlights and heater on, a 78 amp alt is going to start hurting when you draw even more such as stereo equipment. Idle is where the issue really is, but then again, fans shouldn't be needed off-idle in 90% of the time.

    Some of their dual fans that pull 4000CFM draw 50 amps!

    Derale
     
  14. blazerpro79

    blazerpro79 1/2 ton status

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    i have a 16" derale tornado... never falls under 12 volts
     
  15. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Lights don't pull much compared to fans.

    My electric fans pull 30 amps, ignition pulls 3, A/C pulls probably 10, 2 to trickle charge battery, lights, probably 15-20. That only leaves about 15 amps left. thats hard on the alt. That also doesn't include a stereo. I went to a 100 amper and it's barely enough. But.....my stereo has the power to eat 100 amps and plenty of "and then some."
     
  16. BobK

    BobK 1/2 ton status

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    You can use the HEI power source to trigger a fan relay but the power that goes through the relay should be from the Battery or,preferably the alt.

    Make sure the power wire is fused or run a fusable link inline.

    E-fans suck alot of amps and will tax a factory circuit that's in good shape let alone a circuit that's been "mickey moused".

    I STRONGLY urge the use of at least ONE 30 amp relay for EACH e-fan you run.
    Make sure that each relay used has a fuse equal to,but not exceding the amp rating of the relay.
     
  17. dyeager535

    dyeager535 1 ton status Premium Member

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    Should it be from the alt?

    My rudimentary understanding of the electrical system is that the battery acts as a "cushion" for loads on the electrical system. The electric fans "spike" when they turn on, is that any harder on the alternator than if through the battery?

    Could be multiple other reasons, (wiring ease, cost, variations) but I know GM didn't do that either, they came off the battery.
     
  18. BobK

    BobK 1/2 ton status

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    I can understand concerns about "spikes".But the fans would put a momentary high load on the alt(amp draw).If that's what you mean about "spikes" you may have a point.
    Those momentary loads should not be a problem for a an alt. that is rated high enough.I mean a stock alt rated at 60amps is prob. going to struggle with the load of e-fans.
    I had to upgrade my alt to a 140 amp alt. when I did my e-fans.

    Look at todays cars with all thier electronics.The factory started putting in 100-120 amp alt's.

    I have power for my fans coming from a power dist. block which is connected directly to the alt.(via about 4ft of 8g wire).No issues for me.I run 2 30 amp relays and those are protected will inline fusable links.
    The main power wire coming from the alt. is protected with a fusable link as well.

    I mean the factory ran all the electronics off the alt.It was a large splice in the wire harness,I'm sure you've seen it.
    Yes things did run off the battery but only when the alt. wasn't supplying enough juice or the eng was off.

    The Battery connects to that splice in the harness as well.That's also why the terminal on the back of the alt. is live even when the ign. is off.

    Dorian,I'm sure you are aware of all of this.Just noted this for the others.

    In the end,either way is safe.
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    Yeah, instead of using the junction block like we have (way back on the firewall) GM started using a lead taken off the positive battery (from what I've seen) to a junction block near the battery, which is where fan power, among other things , is taken. Mines off a newer FWD Cadillac.

    I'm sure GM "over-engineered" the wiring for safety/durability, but I'm not going to try and find out just how much. :)

    I'm pretty surprised that my 78 amp alternator isn't affected by the fans more (can't even tell when one comes on) but that's partially due to the fact that not both come on all the time, although I've tested it with both on.
     
  20. blazerpro79

    blazerpro79 1/2 ton status

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    Update On E Fan

    ok this fan sucks a lot of power... haha. im gonna buy a bigger alternator soon, maybe 110 amp.... im not gonna running my lights and stuff until i do. ive been driving it around today, and it hesitated to start once.
     

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