Thread: How can I tell if my electric fan is drawing too much current.

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Something is fishy if the thing draws 60 amps and squeals the belt when the fan kicks on......dont have a fiero manual to see what the fan is fused for. You say that it has two speeds and you have high speed wired now.

What year fiero is it from? the 84 fan motor uses a ceramic resistor and the 85/86 does not.....not sure how the resistor is wired in but that suggests that the 84 fan uses the resistor for the low speed whereas the later motor must have two input wires.

Suggest that you measure the current draw on low speed. Most electric fans pull 15-22 amps. Could the fiero start the fan on low speed and then, after it is running, change the speed to high using a relay? It doesnt make sense to have a low/high speed without beginning in low speed.

mike

Denny---Please tell me more. I really don't have it "handled". I don't want to have to add a whole whack of electronics to this thing, but I don't want to replace the fan either. What do I have to add to what I have to make things work correctly?

here is a way to do it with two temp sensors and two relays. The low temp sensor is attached to the coil of the first relay which provides power to the second relay. The second relay uses the normally closed contact to power the low speed fan circuit. When the temp reaches the set point of the high temp sensor, it completes the power to the coil of the second relay and moves the contacts so that the normally open now has power for the high speed fan. Also, at the same time, the low speed contact is opened so the low speed fan circuit loses power.

Here is a neat site that explains relays if you are not familiar with all the terms.

http://www.bcae1.com/relays.htm

You could control the dual speed fan using one temp sensor and one relay (your current setup) plus a toggle switch (Single Pole, double throw). You would connect the output of the realy to the input to the toggle switch. Then, you would hook the normally closed toggle switch output to the low speed fan motor. The normally open circuit would connect to the high speed fan circuit. You would have to remember to turn the switch back to the low position.

The more I drive this car, the more impressed I am with how cool it runs, without the fan coming on. I think maybe I will try to cheat a bit, and just run the set-up I have, with power going to the low speed input to the fan instead of the high speed. This may provide all the fan cooling I need, and if you guys are correct, it shouldn't spike so high on amperage draw when it starts up, so consequently shouldn't blow the 30 Amp fuse. I will do my amazing ammeter stunt, and let you know the results. Thank you robot and Denny for your input.
Brian

If it gets hot, speed up!!!! good luck

mike in tucson (where fans are required)

Today I wired the fan so that it comes on at the slower of the 2 speeds. (it has 2 different input wires, one for hi-speed, one for lo-speed, and a ground. I repeated the amazing ammeter stunt, and this is what I found---it momentarily spikes to 60 Amps, then settles in and runs at 15 to 17 Amps. I am going to give this a try and see what happens.

Brian,

I'm sure you know this, so for those who are curious . . . An electric motor's maximum torque occurs at zero RPM, hence the amperage spike. That's why my Porter Cable 3.25 HP router, and man other electric motors have a "soft start." That feature brings it up to RPM without the heavy spike.

And another "DAMN! I wish I'd thought of that!"

Originally posted by brianrupnow
Today I wired the fan so that it comes on at the slower of the 2 speeds. (it has 2 different input wires, one for hi-speed, one for lo-speed, and a ground. I repeated the amazing ammeter stunt, and this is what I found---it momentarily spikes to 60 Amps, then settles in and runs at 15 to 17 Amps. I am going to give this a try and see what happens.

something to compare those #'s with, a starter draw should be 60 to 90 amps. when you start your car and the heater fan motor should draw around 16 to 18 amps. on hgh. sounds about right.

Whoa! Whoa! WHOA!! No starter sucks a measily 90 amps not even a motorcycle!! More like several hundred amps.

My 6.2L diesel starter draws 1,600Amps about twice the normal V8.

Originally posted by kcress
Whoa! Whoa! WHOA!! No starter sucks a measily 90 amps not even a motorcycle!! More like several hundred amps.

My 6.2L diesel starter draws 1,600Amps about twice the normal V8.

when you buy a starter this is how its rated. a lot of dif. things can change this, but if everything works right, motor turns free then thats about all it needs to turn the motor.

cant see that very good but its 9v- 60 to 90 amps. 10000 rpm

Today I went for a 50 mile cruise with the roadster pickup. This thing is amazing, in that the temp stayed at a constant 150 degrees, and the fan never tried to kick on at all. I had to set in my driveway for 5 minutes with the engine idling before the temp went high enough for my fan to come on. It came on, ran till the engine temp fell back to about 175, then shut off. I waited till the temp came back up and the fan came on again. I let it cycle on and off about 5 times, and there is no fuse blowing, so maybe hooking up the low speed wire on the fan has fixed my problem. The v-belt drive to the alternator squeals a tiny bit when the fan starts, but my fan belt is fairly loose, and I'm out of adjustment, so will have to buy a shorter v-belt. Touch wood---maybe the problem is solved.

Originally posted by DennyW
kcress
You must be driving a tank

Bench testing car starters, and light trucks= 60-150 amps some gm's as high as = 250 amps

A good starter will normally draw 60 to 150 amps with no load on it, and up to 200 amps or more while cranking the engine. The no load amp draw depends on the rating of the starter while the cranking amp draw depends on the displacement and compression of the engine. Always refer to the OEM specs for the exact amp values. Some "high torque" GM starters, for example, may have a no load draw of up to 250 amps.

Have you read any good books lately ?

id hate to have to kick start that motorcycle.

Originally posted by DennyW
The only thing I can remember that took amps like that was a M88 Tank. They called the starter energy Little Joe. It was a 4 cylinder car engine that turned a generator to create enough amps to start the Tank.

kcress. the # dont add up. you got a 12v bat, with 600 to 800 CCA with a 100 amp alt. and you got 1000 amp + draw on the bat. every time you crank it up. i really dont think it would crank it one time but i know it wouldnt the second time. alt. wouldnt never keep that bat. up.