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Electrical questions

Discussion in 'The Garage' started by Bubba Ray Boudreaux, Jun 7, 2003.

  1. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    Okie dokie pokies, here's what I got going on.

    All the info I've read on these Ford fan swaps has these fans drawing around 40 amps while on.

    Will everything thing stay safe using 50 amp relays?

    Inline fuse. Stay same amperage or use a bigger, say 60 amp fuse?

    Diodes, diodes, diodes............This is sucking me dry...............The tech articles that I'm referencing has part numbers listed, or they are called "freewheeling" diodes. Went to Radio Shack, don't have them. Went to Radio Shack's website, not listed. Here is what I did find though on the website. The diodes are rated something like 30 amp so on and so forth, and have surge ratings like 200 amp. Am I looking at what I need and don't know it? And last, but not least, how the **** do diodes wire into something? The wire coming off of them look so thin and what would your suggestion for protection be?
     
  2. 4x4k20

    4x4k20 1/2 ton status

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    from what i understand diodes just let the power flow one way. never heard of a freewheeling diode
     
  3. HarryH3

    HarryH3 1 ton status Author

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    50 amp relays should hold up pretty well in that application. /forums/images/graemlins/cool.gif Just make sure to use relays that are rated for continuous use. Some big relays, such as Ford starter relays, are not rated for a 100% duty cycle and will burn themselves up pretty quickly.

    I've been in the electronics biz for 25 years and have never heard of freewheeling diodes. /forums/images/graemlins/wink.gif But I think I know what whoever gave you that name meant... /forums/images/graemlins/thumb.gif An electric motor becomes a generator when it spins with no power appplied. To prevent this from pushing current back into your electrical system when the fans are "freewheeling", a diode could be inserted into the power supply line to only allow current to flow TO the fan motor. However, since the fan motors get totally disconnected from the electrical system anyway when the relay is switched off, I don't see how it would be much of a problem anyway. /forums/images/graemlins/thinking.gif I don't recall seeing any diodes installed inline with factory fan setups. Do the Ford wiring diagrams show one?

    One place that you often will find a diode is across the coil side of a relay. When power is removed from a coil, the collapsing magnetic field causes the coil to generate a pulse of electricity. A diode across the coil will short out the pulse and prevent if from feeding back into the main power. /forums/images/graemlins/cool.gif
     
  4. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    [ QUOTE ]
    However, since the fan motors get totally disconnected from the electrical system anyway when the relay is switched off, I don't see how it would be much of a problem anyway. I don't recall seeing any diodes installed inline with factory fan setups. Do the Ford wiring diagrams show one?

    [/ QUOTE ]

    I've been going off the wiring diagrams that I found on these sites that have these swaps done. The reasoning behind using the diodes according to the people that have done the swaps is this; once the engine is turned off the fan is still spinning (of course this depends if the fan is set to run with the thermo switch and what not) and the fan motor is still generating electricity while spinning, so the diode gives a path for this electricity to escape and can't come back, equaling a longer lasting fan motor.

    Even though I got a B in my college Auto Electricity class, it was none of this real world stuff that we go through and I suck at it.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    There isn't anywhere for the electricity to come back from so I wouldn't worry about it. /forums/images/graemlins/cool.gif The fan will be generating electricity, but with the path to ground open at the relay, there is infinite resistance in the circuit so no current can flow.
     
  6. Bubba Ray Boudreaux

    Bubba Ray Boudreaux 1 ton status

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    So I should have no worries about excess wear on the motor, this is a Ford fan so I've already got one strike against the swap /forums/images/graemlins/rotfl.gif
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    GM never used anything except the relays on their electric fan setups, which shouldn't be a "manufacturer specific" feature.
     
  8. Panther

    Panther 1/2 ton status

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    Can you post a link with these diode-containing schematics/descriptions? I've have never heard of a free wheeling diode and can't even think of a place to even put a diode to correct the (fan spinning) effect you're describing.
     
  9. HarryH3

    HarryH3 1 ton status Author

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    The diode would go in the power line to the fan. It would allow voltage to go TO the fan, but would block any voltage from feeding back FROM the fan. It would also decrease the voltage to the fan by .7 volts when the fan is running. /forums/images/graemlins/frown.gif It would take a pretty beefy diode to pass the current that's required by those fans, along with a monster heat sink to keep the diode cool. It's basically a waste of time and money though.
     
  10. mattman

    mattman 1/2 ton status

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    This may not help much. I found a site a while back about using the mustang fan (much larger). The guy used a diode and I believe it was for spike since when energized, the fan made a quick large power spike. Use google and you might find the article. The guy was an electronics engineer and had part numbers schematics and everything. Very detailed. Just didn't bookmark.
     
  11. Panther

    Panther 1/2 ton status

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    But you should already have a relay in between the fan and battery. If you don't, then that is a problem. When the switch turns off the relay (when this "problem" occurs), the battery/fan line is open.

    Plus you've got the .3 or .7 volt drop.
     
  12. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    But you should already have a relay in between the fan and battery.

    [/ QUOTE ]
    We've already beat that dead horse... /forums/images/graemlins/wink.gif
     
  13. MarcS

    MarcS 1/2 ton status

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    Listen to Harry, you don't need the diode if the relay disconnects the fan. The "freewheeling" is just how the diode is used to protect against a power surge when power is removed from coils(relay,motors etc..). This is actully how an ignition coil works. Points or pick-up in distributor disconnects power from ignition coil, this creates a high voltage surge to dist cap to your plugs.
     

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