Power for pwm fans

Fifty

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My truck (18 Chevy) uses a pwm radiator fan.

after all of the trial and error, I have figured out how to control a spal brushless via Hptuner with oem wiring.
However I need to run two 12 inch spal brushless fans go get enough cfm. The single 16 inch wasn’t doing it.
Cbr is making the new fan shroud with new fans. Just waiting as fast as I can.

my plan for wiring is to wire the first fan as normal using the oem wire harness...

but...

tap the signal wire, and run that to the second fan as well.

then run a power (12v/red wire) direct to battery (fused of course) and the ground wire to a chassis ground right on the radiator bulkhead.

It is my understanding that the fans have a continuous power going to them and they don’t do anything unless the signal wire says turn on and how fast.

or should I tap into the oem fan harness and run a wire from the 12v to a relay, and run a power line from the battery, through a fuse, to a relay, to the 2nd fan?

that way the power only goes to the 2nd fan of the first fan on oem harness is getting power too?
 

Fifty

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I need to get my power probe out and wire up the truck...
 

joshmx88

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I think you should power the second fan off its own power circuit with a relay and individual ground connection. Use the signal wire from oe fan for both new fans, splice out to both fans, this should be a pwm voltage signal. That should let you run both fans with the same signal but two power circuits.
 

Fifty

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Gotcha. I’ll use a wire off the oem fan positive to trigger a relay. And then use a fused line from the battery via the relay to the second fan. And then the ground from the second fan to the chassis.
Off to find a relay comfortable enough with spal fan juice.
 

jon coleman

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is one relay for two fans enough?, i ran two on a three way 6 switch, 1- 0ff- 2, but each fan had its own hella 12 volt relay with heavier gage wire, the fans love the juice, also, i was told way back to use switch to Ground relay closed, that way any chaffing , between relay and switch bare wire touching frame/ grnd.,will just turn on whatever is 'relayed', lights , fans ,whatever
 
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Fifty

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yellow is the pwm signal.
Red is 12v
Black is negative/ground

Oem harness would go to fan #1.
I would splice off the oem harness to fan 1 for the pwm signal and have it go to fan #2.
I would splice off the oem harness to fan 1 for the 12v and have it go to the relay to trigger it. That would allow a fused 12v to go from the battery to the fan#2.
The fan #2 would run its negative to the chassis ground on the radiator support.

Otherwise I’d just skip the relay and run a fused 12v straight from the battery to the fan assuming the fan won’t draw power until a signal is sent via the pwm wire. Bypass the relay?
2E0B562C-FEED-40AF-A34B-142FA2DD406A.jpeg
 

Fifty

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(Please ignore the red pencil)
So green is 12v
Black is negative/ground
Yellow is pwm signal.

so this way would skip the relay
38D88EDF-2BA6-4ABA-A1ED-0ECA102434E8.jpeg
 

jon coleman

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(Please ignore the red pencil)
So green is 12v
Black is negative/ground
Yellow is pwm signal.

so this way would skip the relay
View attachment 223691
(Please ignore the red pencil)
So green is 12v
Black is negative/ground
Yellow is pwm signal.

so this way would skip the relay
View attachment 223691
first is how i wired mine, All you need is 12 v to close relay, from gm oem harness, i am Asuming the ground is not critical to hook into harness, ie the computor Only sends 12 v to fan period, if Thats the case, ground can go any where, i would trust two relays more than one stock oem wire on two spal fans.the second pic is what you can do, no swith, just ground,relays i like are the junkyard ones from Japanese cars, pull right out and work👌😉
 

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Fifty

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I have to keep mine bcm controlled. I’m still using the stock genv computer.
it’s a bit of a nightmare system. Can’t bypass the fan.
If I can NOT run a relay to get fan#2 working tandem with fan#1 all the better. Less wiring, less failure points, less splicing into fan#1 harness.

I sent off an email to spal seeing if their fan will draw power from the 12v if it’s able. Or if it only draws power if there is a pwm signal.
If it draws power always if able then I’ll have to run the relay or the battery will always be dead.
 

jon coleman

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hmmm, yes, if the fan is simple + - , hook up 12 v & ground & we have Air!, but, if there is a Third pole, for a ' signal' than That IS the relay basically, the signal wire can usually be a smaller gage, but the main should be heavier, my spal fans drew some VOLTS!!😵, w0w, just did a quick search on this, man o man, this is outta my paygrade, looks like its no problem IF you know what to do, sorta like chinese math, easy, but there looks to be answers if your lucky surfing the internet👌👍
 
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Fifty

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The pwm signal part took about 5 months to figure out. But I eventually got it.

but just wanted to see if anyone else had take a pwm system, let’s say for a silverado or something and added a second fan because of a larger radiator and shroud set up.

but yea, if I can get away with no relay... that would be ideal. I hate adding possible failure points.
 

jon coleman

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The pwm signal part took about 5 months to figure out. But I eventually got it.

but just wanted to see if anyone else had take a pwm system, let’s say for a silverado or something and added a second fan because of a larger radiator and shroud set up.

but yea, if I can get away with no relay... that would be ideal. I hate adding possible failure points.
heck, run one fan on the stock oem, then run the other on a stand alone relay& after market adjustable thermostat, of course, more stuff to fail...
 

Fifty

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Lolz... you sound like the gent who got me into this predicament!!!
 

Fifty

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From Brent at Spal (who is a wealth of info and is so helpful to us “aftermarket custom trying to do what’s not meant to do” folks):


The brushless fans do not require relays. Actually relays cause more wear on the brushless fans (electrolytic capacitor wear.) So don’t use a relay with a brushless fan. It’s also very hard on the relay with the capacitance inside the motor. The fan has MOSFETs inside that connect the motor to the battery when needed, and disconnect the motor when it isn’t needed.



When the fan receives a valid PWM signal, it will wake up the motor and run the fan. When the valid PWM signal quits, the motor enters quiescent current mode ‘sleep mode’ and waits for the signal to run. So it does draw power all the time, but it will be microamps of current until the fan wakes up. So nothing to worry about.



Red/Black of both fans go directly to the battery with a fuse on the red wire. The White/PWM wire will go to your PWM signal outputs. That’s it. With brushless fans you don’t trigger them separately, you would just have both fans come on at the same time and run as fast as required. So only one PWM signal would be required. Typically we don’t separate fans until they serve different functions, or work on different systems. So if they are both radiator fans they should run at the same RPM for ‘best’ results.
 

michael.gonzalez

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so if you want to just run brushless on an old car, you simply run toggle switch ,12 v to the signal input on fan?, nice, saves grief of relays
I don't believe so.

You need a PWM signal (Pulse Width Modulation), not a constant 12V.
 

Fifty

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Michael is correct. You would run a pwm signal. I believe they sell thermostats that are geared for pwm and then there are also pwm controllers.
I believe lingfelter bought the rights to spals pwm controller
 

dzrt performance

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Michael is correct. You would run a pwm signal. I believe they sell thermostats that are geared for pwm and then there are also pwm controllers.
I believe lingfelter bought the rights to spals pwm controller
sorry, but NO you dont need a PWM signal OR a relay to run these Spal brushless fans.

there are four wires, two STUPID oversize power and ground and two small control wires.

with a simple toggle switch, you can control it either by switching 12v OR ground, you also connect one control wire to 12v from the switch and the other to ground. the fan will soft start once power or ground is applied. i have no idea why Spal used such large wire....the last set i installed they were big 14 or 16 inch fans that had 8 guage wire feeding them. they pulled about 10 amps. 16 or even 18 would have worked depending on how your run is.

in your installation, i would have wired up both fans to constant power and ground and you should have been able to take the PWM signal to both fans and it should work fine. ust make sure to ground the second control wire.
 
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