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Cooling Fan Wiring  Rating:  Rating
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 Posted: 06-13-2005 06:03 pm
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StabnSteer
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Just looking for suggestions here - I've found lots of good information on using relays to get power to my fans (a dual-fan setup behind the radiator) but haven't really found any good info about what gauge wiring is needed to handle the amps of fans.

Just for info, based on suggestions I've read online, I'm thinking of using a pair of 30 amp relays PER FAN, or if I can find 'em, something like a 70 amp relay per fan to simplifiy things. I have no idea what my fans actually pull amp-wise as they were received with the original car in a box, but I'd think 20-30 amps is a decent ballpark guess.

But what gauge wiring can handle a constant 30 amp pull? Are there calculations one does to figure this out (amps/distance), or is there a standard for gauge/amps?

Thanks all!!

--Erik Karlsson
75 JH

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 Posted: 06-13-2005 06:45 pm
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Brett Gibson JH5 20497
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Erik, cant help you with the wiring size but I do have a tip, Frank Shwartz from 2004 East coast Nationals fame tipped me to this site were relays / and plug harnesses etc; can be picked up for very cheap in all differant sizes and styles.

No affilation etc: just trying to help.

http://mcm.newark.com/

Brett. 

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 Posted: 06-13-2005 08:08 pm
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Mark Rosenbaum
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There are ways to calculate all that stuff, but usually one just looks up the data in a suitable reference source.  If you examine pages 2 and 3 of the British Wiring catalog at
http://www.britishwiring.com/CAT02_07.PDF
you'll see good reliable guidelines for the wiring size(s) you'll need.  Note that this is a .pdf file and you'll need Acrobat Reader to open it.

For your fans, each relay's contacts must be rated for the full current they will carry, never less.  Only a few solid-state 'relays' allow doubling up to increase the current rating, and this is permissible only if the manufacturer explicitly says you can do it.  Note that relay contacts are rated for a much lower DC (automotive) current than AC (house) current -- and when dealing with DC current, relay contacts quickly either weld themselves shut, or burn away, when you exceed their rating.

Finally, using two relays in parallel, each able to carry the current required by a fan, results in only a slight increase in reliability.  This is because both relays will wear at about the same rate, and when the first one fails, the second can be expected to fail shortly thereafter.  It's generally best to have the second relay sitting in the car's glove box as a spare.

 

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 Posted: 06-14-2005 03:42 pm
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Ron Earp
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You know, at the current levels we're talking about (8-10 amps) you could use 10 or 12 gauge US wire and wire them straight with a fuse, as long as the run length isn't extraordinary. You can check some other charts for voltage drop over length, but 10 ft isn't a problem.  Eliminates the relay and is one less part to fail.  The fuse will protect the circuit from overload/fire hazard.  Mine are straight with fuses, but I want somplicity and reliability as well as easy troubleshooting at the track if something goes bad.

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 Posted: 06-15-2005 02:33 pm
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StabnSteer
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I dunno - I had a single fan in a Ford Escort that was wired with a 40 amp fuse. I was not particularly cognizant of things like amps back in those times and figured electricity was electricity...I almost found out how to barbecue an Escort when I put something like a 15 amp toggle to turn the fan on (the wires I soldered to the switch mercifully desoldered themselves before catching things on fire). These things can pull some serious current...especially with two of em, so I'd rather go overkill!!! :)

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 Posted: 06-15-2005 03:54 pm
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Ron Earp
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Sounds like your switch or wire were underrated. My 8 amp draw is just what I measured on one of my fans, so, if I were wiring it (which I did) I doubled it to 16 amps and put a fuse in line at 15 amps - no troubles thus far. 

Watch switches too - I've had some that were rated in big letters on the box at 20 amps, and in little letters on the box at 7 amps continious, could be you had one such as that.  Obviously the continious rating is most important unless you are wiring something that is a momentary use switch.

Your fuse was definitely too high - you want the fuse to blow at a amperage a little above what the fan might draw under normal circumstances so that it will blow if a problem develops.  A 40 amp fuse wouldn't blow if the circuit drew 25 amps, far above what a normal fan will draw. Again, depends on the fan but just match everything up logically and you'll have no problems.

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 Posted: 06-04-2006 01:22 am
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jensenjoe
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Ron, you are right on the ball! In the electronic industry, we double the ratings for devices placed on an electrical circuit. I had an instructor that once put it this way, "Do you drive close to the edge of a cliff just because you can?"

Double the ratings of all devices, and rate your fuses just above peak current loads.

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