Voltage drops when turn on electric fan

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challenger57

cuda57
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My voltage drops from 14-15 to 12 when I turn on my newly installed elec. fan. I did not use the thermocoupler with relays due to confined space. I ran my power source straight off the battery to starter post using 12 gauge wire with 30 amp fuses and 30 amp switches on both speeds. Both speeds pull 11 amps at the fuse. I am using a 140 amp powermaster alt with upgraded to 8 gauge wire back to the solenoid and a 10 gauge ground from alt to frame. With both speeds on I get 12 volts at the alt. I did the total rpm speed at the alt using powermasters calculations and get 16,700 not to exceed max of 18,000. Is it a must that I use the thermocoupler with relays? It does use 30 amp fuses also but much bigger in size. Thoughts appricated!
 
What ever you put in the circuit, will have no effect on your voltage drop. Is this a internal voltage regulator?
 
Adding the relay will add a little bit more drop actually.

If this is 12v at idle I wouldn't worry about it.
If it's 12v max with the fans on something is wired to lightly and it can't get the amps through it that it needs to keep up..
 
Adding the relay will add a little bit more drop actually.

If this is 12v at idle I wouldn't worry about it.
If it's 12v max with the fans on something is wired to lightly and it can't get the amps through it that it needs to keep up..
^^^ Yes, rev it up to 1500 or 200 RPM and see what the voltage does.
 
A 10 gauge ground is small for such a massive alternator, do you have any other engine/alt to frame grounds?

You would be better off using a relay and avoiding the long run of wire to get to your switch and back.
 
Regardless of what the rest of the system is doing, if you only have 12 right at the alternator, then either the alternator is turning too slow, or there's something wrong with the alternator.
 
="TrailBeast, post: 1971262837, member: 19664"]Adding the relay will add a little bit more drop actually.

If this is 12v at idle I wouldn't worry about it.
If it's 12v max with the fans on something is wired to lightly and it can't get the amps through it that it needs to keep up..
I dont see how! Either a Alt problem or a Regulator problem.
 
I dont see how! Either a Alt problem or a Regulator problem.

Or a wire capability problem that adding another small load from a relay to the system will make slightly worse. :D
He said he's running the supply right off the battery post, so you can't get much more direct than that so adding a relay won't make it any better.
It will just add the small load of the relay on top of the current problem.
 
Or a wire capability problem that adding another small load from a relay to the system will make slightly worse. :D
He said he's running the supply right off the battery post, so you can't get much more direct than that so adding a relay won't make it any better.
It will just add the small load of the relay on top of the current problem.
Ok it will add a small load, but if the system was working correct, would not make any difference.
 
Ok it will add a small load, but if the system was working correct, would not make any difference.
That was the point :D
That and it still hasn't been clarified if that 12v is only at idle or with some RPM's
12 at idle with high fan loads on it wouldn't be bad at all.
 
Change location for pulling fan power to the charge stud on alternator. See if you get a change in voltage
 
Let me answer some questions. Yes it is an internal volt regulator, I also have a ground strap from chassis to the block and the voltage stays low even at higher RPM. One thing I forgot to mention and I am sure it is important. the last time I drove it I had the fan on low speed and when I got back the fan motor was smoking. After it cooled I had to literally manually turn the fan blades to get the motor to turn. It still turns on ok now but does not spin freely with a flick of a finger. The motor gets hot in low speed and cools down in high. Do you think the motor drag could be causing the volt drop. Sorry for the lack of info. Not much wire involved, just from starter up to switches and out to fan.
 
Electric motor drag always causes voltage drop, more specifically an amperage draw increase.
Still your alternator should be able to overcome that, not that the motor getting that hot is ok.
It does sound like something isn't putting out like it should.

On the fan you really should have relays for the two speeds right by the fan with as short and as large a wire as you can stand (like 10ga) and use your switch wiring to activate the relays.
I'd bet those wires and or switches get hot, right?
 
Let me answer some questions. Yes it is an internal volt regulator, I also have a ground strap from chassis to the block and the voltage stays low even at higher RPM. One thing I forgot to mention and I am sure it is important. the last time I drove it I had the fan on low speed and when I got back the fan motor was smoking. After it cooled I had to literally manually turn the fan blades to get the motor to turn. It still turns on ok now but does not spin freely with a flick of a finger. The motor gets hot in low speed and cools down in high. Do you think the motor drag could be causing the volt drop. Sorry for the lack of info. Not much wire involved, just from starter up to switches and out to fan.
I'd be more inclined to think that there is too low a voltage to the fan motor in prevent excess current draw. Sounds like the wiring to it has some bad connections, or the low speed dropping resistor is wrong or addled.

If the alternator is not putting out more than 12v at 1500 or 2000 RPM, then something is wrong with the alternator (like blown diodes) or the field wiring is messed up.

BTW, OP, when you say alternator voltage, are you measuring it right at the output stud on the alternator with a test voltmeter, or with a test voltmeter at the battery, or are you reading this on a dash gauge? The answer to this is important to be able to figure out what is going on.
 
If the alternator is not putting out more than 12v at 1500 or 2000 RPM, then something is wrong with the alternator (like blown diodes) or the field wiring is messed up..

Exactly what I said earlier OR IT IS TURNING TOO SLOW, meaning the pulley ratios, engine speed OR BELT SLIP is not turning the alternator fast enough

He has not field wiring "it's a one wire" I believe
 
Do you think the motor drag could be causing the volt drop. Sorry for the lack of info. Not much wire involved, just from starter up to switches and out to fan.

While your description sounds like a motor is AFU, you said they only draw 11 amps and you have them fused with 30A A 140A alternator properly working should pull that
 
Have you tried an optical tach to verify the belt(s) is not slipping? 11 amps for both speeds sounds odd. Sounds like the alternator is power limited by belt slippage.
It would help to know more about fan motor, like model number. Speed control methods vary.
 
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Yes it is a one wire alt. I have 2 local car shows this week end, after that I will pull the alt and take it to a local guy here who specializes in alts, starters and elect motors and let him do a load test and then get back here with results.
 
Conclusion, I had the alt checked today and it is fine even with load. So the winning guess is number 16 - 67Dart273 with belt slippage. All weekend I kept getting belt chips all over the engine bay. I put a new belt on today and went to tighten the lower bolt through the slot bracket and it kept spinning, so I had to put a nut on back side and now I have 14.5 at idle and 14 with fan and lights on, rev up and it goes back up to 14.5. So I guess with the bolt not holding the alt tight I was getting slippage. Oh and as I mentioned in my #19 reply I had 2 shows to go to this past weekend, at the show sat. I got a trophy for pro street tubbed. So thanks for all the responses.
 
Well just OUTSTANDING!! Don't feel too bad you didn't find it, slipping belt has happened to some of the rest of us, too!!
 
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