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Discussion Starter · #1 ·
I want to wire in a flexalite #121280 fan controller to my radiator fan that draws 40amp startup approx. This controller only is rated at 30amp, 20 continuous. Will this work or should I wire in 40 amp relaybetween fan and this controller? Also what would the diaghram for that look like. Thanks
 

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the 'Duracell Project'
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2,643 Posts
why not buy a 40 or 50 amp controller?
i think you already know the answer
no it probably won't work, yes you need the relay

a lot depends on the fan, if it runs below 20A, the controller may last for years
relays can vary so much and may handle the load if it's only momentary
i'd rather not risk it, just add the relay or update your towing policy

as for the diagram: the output wire from the controller to 86 on the relay (pic)
30 is a fused wire from the battery
87a not used
87 to fan hot wire
85 to ground
your safe with #10 wire on 30, 87 and fan ground, use a 50A fuse unless they recommend a fuse
85 and 85 use little power and could be wired with #22 wire


 

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Discussion Starter · #3 ·
why not buy a 40 or 50 amp controller?
i think you already know the answer
no it probably won't work, yes you need the relay

a lot depends on the fan, if it runs below 20A, the controller may last for years
relays can vary so much and may handle the load if it's only momentary
i'd rather not risk it, just add the relay or update your towing policy

as for the diagram: the output wire from the controller to 86 on the relay (pic)
30 is a fused wire from the battery
87a not used
87 to fan hot wire
85 to ground
your safe with #10 wire on 30, 87 and fan ground, use a 50A fuse unless they recommend a fuse
85 and 85 use little power and could be wired with #22 wire


why not buy a 40 or 50 amp controller?
i think you already know the answer
no it probably won't work, yes you need the relay

a lot depends on the fan, if it runs below 20A, the controller may last for years
relays can vary so much and may handle the load if it's only momentary
i'd rather not risk it, just add the relay or update your towing policy

as for the diagram: the output wire from the controller to 86 on the relay (pic)
30 is a fused wire from the battery
87a not used
87 to fan hot wire
85 to ground
your safe with #10 wire on 30, 87 and fan ground, use a 50A fuse unless they recommend a fuse
85 and 85 use little power and could be wired with #22 wire


Trying to use the parts I have instead of buying new high dollar controller. Thanks anyway.
why not buy a 40 or 50 amp controller?
i think you already know the answer
no it probably won't work, yes you need the relay

a lot depends on the fan, if it runs below 20A, the controller may last for years
relays can vary so much and may handle the load if it's only momentary
i'd rather not risk it, just add the relay or update your towing policy

as for the diagram: the output wire from the controller to 86 on the relay (pic)
30 is a fused wire from the battery
87a not used
87 to fan hot wire
85 to ground
your safe with #10 wire on 30, 87 and fan ground, use a 50A fuse unless they recommend a fuse
85 and 85 use little power and could be wired with #22 wire


OK you got your cheap dig in. Go some where else and be a smart @#$.
 

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It would be helpful to know who’s fan of fans and the architecture of the system if running multiple fans.

40 amps is a pile of power the whole damn lunar lander used 20 that was navigation computing, house keeping, life support and engine control.

A 30 amp controller will work for a while, but I’d carry a spare.

Bogie
 

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Old(s) Fart
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6,015 Posts
I want to wire in a flexalite #121280 fan controller to my radiator fan that draws 40amp startup approx. This controller only is rated at 30amp, 20 continuous. Will this work or should I wire in 40 amp relaybetween fan and this controller?
You can run a T5 trans behind a big block. It will work... until it doesn't.
Look, not only is it a bad idea to use an undersize controller from a reliability standpoint, but it's a good way to start a fire. The undersize relay and wiring can overheat, and at some point it will catch fire. Either use a higher current relay, or get the proper controller.
 

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Old(s) Fart
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If all the controller is switching is a relay ,what's " overloading " it ?
The OP is asking about using that 20A rated controller to directly switch the fan. Several people (myself included) suggested he could use the controller to switch a new, higher current relay, which in turn controls the fan. The "undersize relay" I was referring to is the 20A one that's built into the controller now. Obviously if he uses that only to control another relay, it's a non-issue, which is what I said in Post #6.
 

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the 'Duracell Project'
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2,643 Posts
Trying to use the parts I have instead of buying new high dollar controller. Thanks anyway.

OK you got your cheap dig in. Go some where else and be a smart @#$.
not sure what the cheap dig is or any smart ass comment
i explained why it wouldn't work, suggest a relay and fuse size and then posted a wiring diagram any car guy could follow
 

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Discussion Starter · #12 ·
Fan is flexalite #104367 15" fan, should have posted originally, original controller has expired. Instead of buying new controller at $160-175, I have in hand a 121280 controller 30amp controller, a 40 amp relay. My thought was if I wired as follows would it would work safely. Idea was fan, then 40 amp relay, then wired to 121280 controller with 30 amp relay. Idea being to have controller go thru 40 amp relay to switch on fan and how one would wire that. Just trying to learn as I go. Thanks
 
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