I have installed a dual electric fan that was laying around my buddies garage to cool my Chevy 502. It pulls real hard and when functioning properly keeps me running at a nice 195 max temp. The problem is that when the car gets hot the fans run intermittently. It'll kick on for a few seconds and then shut down and then kick on again. I am running an aftermarket universal thermostat with a 30 amp relay. It was blowing the 25 watt fuse and I switched it over to a 30 amp circuit breaker and was running fine until it all heats up, and thats when it starts shutting down. The relay gets real hot and I find what seems to be an oily substance around the relay and its mounting block. I don't understand fully how a relay works and I am wondering if the current draw on these fans is higher than 30 amps (that's what the relay is rated at) would it explain this behavior? Should I bum it up to a 40 or 50 amp relay with accompanying rated fuse? Do all single pole double throws work the same way and is any SPDT relay interchangeable within my mounting block? Thanks in advance!
electric fan relay problem
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It is quite possible that the total amperage draw of the two fans is close to 30amps. If it were mine I would do one of two things. I would either separate the two fans and run each off their own relay or go with a single 40 amp relay. Of course you must make sure that your wiring is sized properly for that higher amperage relay.
Vince
Vince
I currently have 2 vehicles with twin fans---both 454
The fans in the pick-up came with 2 separate relays, and they are relatively small fans--I think 10"--for that big radiator--one fan is a high speed and the other is slower.
The 59 Elky has twin Spal fans----relay recommended for each fan by Spal.
Bryan
Oh forgot----40 amp relays
The fans in the pick-up came with 2 separate relays, and they are relatively small fans--I think 10"--for that big radiator--one fan is a high speed and the other is slower.
The 59 Elky has twin Spal fans----relay recommended for each fan by Spal.
Bryan
Oh forgot----40 amp relays
The best way to describe the way it behaves when it gets hot (210-215 degrees) is when the fans are really spinning hard, you disconnect one of the leads. Before they stop spinning completely, if you reconnected the wire and they start to spin again. It will do this for awhile until it cools down. When I first installed the fan, the wiring block that was attached to the fan had several pins that when I tested it ran both fans at a low speed and other pins ran both fans at a high speed. I wired it to the high speed pins to get maximum pull. I'm guessing that I can separate the two fans and run another relay and temp sensor....though I prefer not to as to keep the wires to a minimum. The wires that came from whatever car manufacturer that produced these fans used relatively small wire to power the fans. The gauge of wire I used to get power to them is larger.....would bumping up the relay to 40 or higher (with a corresponding fuse or breaker) be too much for the electronics in the temp sensor kit if it was designed for 30 amps? Thanks to all for your input.
Doc here, 
imp:
First, you must determine the DRAW of your fan motor, It should be printed on the motor, or in the spec sheet for your system..Then you must match your relay accordingly, for continuous contact ratings..If the fan draws 22 amps , your relay will be 30..if it draws 33 amps, it will be 40 amps contact rated.
Most likely the reason for the heat, is the wire is UNDERSIZED at present, and your pushing a fire..The wire from the FUSE link and battery to the NORMALLY OPEN CONTACT on the relay (#87) SHOULD be at least 10 gauge, and the wire from the CENTER WIPER (#30) to the FAN MOTOR, should be at least 10 GAUGE.
The RELAY COIL power wire (#85) should come from a switched, FUSED (1 amp) source The Other side of the RELAY COIL (#86) Should go to the temp probe, BOTH these wires may be 14 gauge.
Under sized wiring will heat the whole system including the relay, because much of the current is being turned into HEAT , doing no useful work because of the resistance in the wire runs..
The "Goop" you see coming out of the relay could be caused by heated TAPE adhesive running back down the wire , OR the insulating paint from the relay coil windings itself (which would account for fan motor dropout as the coil would be shorting across itself) ,OR it could be the plastic INSIDE the relay base melting from the heat itself...IN EITHER CASE, your about 1 step away from a meltdown and fire!
The Wire and Relay, or Switch gear Should NEVER be hot if it is the proper gauge..If it is , It is Too small to do the job. (In ANY circuit!!!!)
YOU DO NOT over fuse (or oversize a relay) to make up for this..This is just promoting a Fire (like sticking a penny in place of a fuse in an old style home fusebox...more home fires were caused by this than any other cause..then the wire becomes the "Weak Link" in the system instead of the fuse link..) The correct procedure is proper wire size, and matching fuse link.
The motor switching on and off MAY also be a normal consequence of engine heat from the probe , you won't be able to determine that until you correct the wiring ...
Docimp:
imp: First, you must determine the DRAW of your fan motor, It should be printed on the motor, or in the spec sheet for your system..Then you must match your relay accordingly, for continuous contact ratings..If the fan draws 22 amps , your relay will be 30..if it draws 33 amps, it will be 40 amps contact rated.
Most likely the reason for the heat, is the wire is UNDERSIZED at present, and your pushing a fire..The wire from the FUSE link and battery to the NORMALLY OPEN CONTACT on the relay (#87) SHOULD be at least 10 gauge, and the wire from the CENTER WIPER (#30) to the FAN MOTOR, should be at least 10 GAUGE.
The RELAY COIL power wire (#85) should come from a switched, FUSED (1 amp) source The Other side of the RELAY COIL (#86) Should go to the temp probe, BOTH these wires may be 14 gauge.
Under sized wiring will heat the whole system including the relay, because much of the current is being turned into HEAT , doing no useful work because of the resistance in the wire runs..
The "Goop" you see coming out of the relay could be caused by heated TAPE adhesive running back down the wire , OR the insulating paint from the relay coil windings itself (which would account for fan motor dropout as the coil would be shorting across itself) ,OR it could be the plastic INSIDE the relay base melting from the heat itself...IN EITHER CASE, your about 1 step away from a meltdown and fire!
The Wire and Relay, or Switch gear Should NEVER be hot if it is the proper gauge..If it is , It is Too small to do the job. (In ANY circuit!!!!)
YOU DO NOT over fuse (or oversize a relay) to make up for this..This is just promoting a Fire (like sticking a penny in place of a fuse in an old style home fusebox...more home fires were caused by this than any other cause..then the wire becomes the "Weak Link" in the system instead of the fuse link..) The correct procedure is proper wire size, and matching fuse link.
The motor switching on and off MAY also be a normal consequence of engine heat from the probe , you won't be able to determine that until you correct the wiring ...
Doc
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