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**hellosailor** · 09-09-2016, 15:02

"A dimmer IS a rheostat" That's like saying "a car is a chevy". Not quite. A rheostat is a potentiometer and either one CAN be used as a dimmer. By putting a variable (or selected) resistor in the fan circuit, you can lower the voltage to the motor and lower the speed. But a modern dimmer will be a solid-state device that supplies pulses of electricity. Supply pulses 50% of the time, you get about 50% speed from the fan, and use 50% power. A plain rheostat uses 100% of the power all of the time, so there is reason to use the electronics. Except, some motors get insulted and they overheat when you use pulses instead of regular DC. And there's that RFI problem. So yes, a simple rheostat is a great way to go, low-tech lot cost. You can still pick the wrong one and wind up burning it out. And if a dimmer makes things buzz...it can be really annoying as well. There are many ways to skin a cat. Might almost be simpler to just add or replace with a quieter less powerful fan.

CharlesV · 09-09-2016, 20:33

Well then I did have it right the first time.

Why not go to a junk yard and pull the fan switches out of junk cars? Buy 10 and make sure you get the circuit boards with them. This would give a 3 or 4 position switch.

Ok go ahead you guys, NOW whats wrong with this idea?

Sternwake · 10-09-2016, 01:21

Quote:

Originally Posted by CharlesV

Ok go ahead you guys, NOW whats wrong with this idea?

These 3 and 4 position switches require a series of resistors elsewhere and a bunch of wiring and connections.

I'd rather not turn battery power into that much heat, or light, just to slow a fan.

My vehicle's blower motor pulls 18 amps on highest speed. I imagine most are similar and the resistors for low medium high are calibrated for an 18 amp motor at 13.6v. a 2 amp fan would likely respond poorly to this method of attempted speed control.

especially when a PWM motor speed controller can be had for less than 10 dollars and require only 4 wires be smushed under set screws to operate.

Heck if the whining of a 13khz LED dimmer was not present or did not bother the user, one could control the fan from super slow to max, fully variable, for under 3$.

https://www.amazon.com/LEDwholesaler...BK5FKAR96S26F6

21khz, 10 to 40 volts, 15 amp rating, 12$

https://www.amazon.com/Controller-Ad...eed+controller

Some 12v computer fans come with a potentiometer for speed control:

https://www.amazon.com/Silverstone-P...verstone+ap182

1.3 amps on High, 0.05 amps and silent on low.
This fan did not like fastest speed and battery charging voltages. RIP.

In the future I will be feeding a PWM signal for speed control via the 4th wire to an Industrial Noctua 3000 rpm fan. This 2000 rpm one is IP67 rated:

NF-F12 industrialPPC-2000 IP67 PWM

I have a 1500rpm Noctua pushing air through my fridge condenser. Noise decreased, duty cycle decreased. Amp draw of fan less than half of 120mm fan provided with fridge. running 24/7/345 going on 4 years next month.

**hellosailor** · 10-09-2016, 12:12

" pull the fan switches out of junk cars?"
Like the junkyard, if you can find a pick-a-part yard because they are becoming uncommon, is not going to let you destroy the resale value of an entire climate control system just to pull out a switch, and a resistor board that's buried in the dash and trim.
And then again, assuming you can get them, that's like saying "I'll go buy some shoes, send me a dozen at random, two ought to fit."
You need to do some load calculations. Otherwise electricity can range from boring to extremely exciting. Or, as the man said, you buy one online that already has the correct speed control built with it.