Electric fans

[Dwight]

I buy 40 amp relays and bases from Del City.

A couple of months ago Coach bought a new fan for his Cobra. I don't remember the brand but it was a high dollar name brand. The tech guy told him he needed a 70 or 80 amp relay and fuse for the new fan.
I have never seen a car fan that pulled that kind of amperage so I called B.S.

When the fan arrived I tested it. 11 amps was the max I could get it to pull.
Coach send the fan back and bought a different brand.

Dwight

[BOBOCobra]

I think you are overthinking this. It is pretty simple, more air and/or more water. If the issue is at idle you need to move more air for sure (bigger/more fans) and see what the temp difference is between the rad and the motor. If the rad is 190 and the motor is 220 (as an example) the issue is more water. Rather than change the crank pulley, make a smaller WP pulley and overdrive it. If the rad is not cool enough you need more air through it. your only choice is bigger and badder fans. get the air fixed first, then the water. If you get the air fixed and have a temp sensor and proper water flow the fans will shut off whenever they need to. Let the system do its job. as a general rule, I use 100 degrees over ambient as the max target temp in traffic driving for a BB motor in a confined space. it may go 105 over, but that is the range. ambient has an impact as well as bay circulation but get the proper air flow thru the rad, then look at the water and then let the system work.

[Gaz64]

Originally Posted by Dwight

I buy 40 amp relays and bases from Del City.

A couple of months ago Coach bought a new fan for his Cobra. I don't remember the brand but it was a high dollar name brand. The tech guy told him he needed a 70 or 80 amp relay and fuse for the new fan.
I have never seen a car fan that pulled that kind of amperage so I called B.S.

When the fan arrived I tested it. 11 amps was the max I could get it to pull.
Coach send the fan back and bought a different brand.

Dwight

Why do some car manufacturers use 70 amp relays, because 30 or 40 amp relays don't have the metal cross sectional area for the high current terminals.

I would always rather over-engineer, than a have a fire.

https://www.ebay.com/itm/12V-4-Pin-7...-/153075476588

Gary

[cycleguy55]

Originally Posted by Gaz64

Why do some car manufacturers use 70 amp relays, because 30 or 40 amp relays don't have the metal cross sectional area for the high current terminals.

I would always rather over-engineer, than a have a fire.

https://www.ebay.com/itm/12V-4-Pin-7...-/153075476588

Gary

I took a different approach when my cooling fan relay quit. I installed a pair of 40 amp relays in parallel, protected by a circuit breaker. My thinking was the pair of relays will share the load and either of them can handle it, should the other fail.

How will I know if I have a failure of one or the other? As of right now I have no idea, though I could test them periodically by unplugging one at a time. Given their location that seems like a particularly masochistic approach. Regardless, my theory is a relay failure is highly unlikely if each is running at well under 50% load capacity, so hopefully I'll never have to deal with it. I know I won't if I end up installing the PROFORM controller mentioned in my comments a week ago.

[Tom Wells]

Oh, no!

You've just created Schrödinger's relays!

(see Schrödinger's cat...)

Sorry, just couldn't resist.