elec fan amp ratings

951mat · #1 (**permalink**) 08-09-2009, 07:25 PM

I bought a fan/shroud combo from vintage air. I believe Tripac makes the fan and Cooling Components sells them to Vintage. Its only 2.625" thick, which is great. Supposed to move 2500 or 2700 cfm, which I think will work for me. The question i have pertains to the recommendation of using a 70 amp relay when I install it. I need to figure out what size relay I had on my old fan, but I doubt it was that big. Can this thing really draw more than +/- 25 amps??? I assume it can draw more at start up, but surely not 70??? I only have a 100 amp alternator, which I thought was big.

Thanks for any help.

undy · #2 (**permalink**) 08-10-2009, 04:54 AM

I would imagine your fan will draw around 20 to 25 amps. Automotive relay manufacturers tend to rate their relays on the ragged edge of failure. The extra amp capacity of the 70 amp relay will give you some appreciated increased relay longevity. I'm running the Bosch 70 amp on my 2800 cfm flexalite. The x-tra capacity gives me a zero volt drop across the relay's contacts.

Dave

Ron61 · #3 (**permalink**) 08-10-2009, 05:58 AM

Same here. My fans drew 30 Amps and I used a 70 Amp relay which they recommended.

Ron

951mat · #4 (**permalink**) 08-10-2009, 06:39 AM

Thanks for the info, I feel better about it now. Now I can start trimming this thing to fit with no worries.

vettestr · #5 (**permalink**) 08-10-2009, 10:12 AM

The big numbers are a result of spikes or surges and arcing. Running demand may only be 25 or 28 amps but spikes of 50+ amps are real. A diode across the feed wire eliminates the arc back across the relay contacts.

kitcarbp · #6 (**permalink**) 08-10-2009, 10:27 AM

Ditto the above info.

FYI- Rule of thumb SPAL gave me, is that the running current of a fan like these are typically 10 amps/1,000 cfm of rating. This is one way to debunk many aftermarket fan claims. A manufacturer's high cfm claim without the high current draw to match is suspect and not to be believed. Always try to get the fan performance curve which shows evidence of fan's performance in cfm's versus inlet restriction (look at SPALs website, they share it all).

vettestr · #7 (**permalink**) 09-20-2009, 10:03 AM

I posted a source for 50 amp relays with built in diode protection. They also have other electrical goodies at a decent price. Here is a CC post link Source for electrical goodies