electric cooling fans

[kglowacky]

Thinking of replacing my current junkyard Dodge dual cooling fans with a new set. I would like to get some that draw less amps than my current ones. Not sure what mine draw but when they turn on it drops the amp gauge below 11. Anyone using a set that bolts right in and are happy with them? would like a one piece 2-unit bolt in. Again got these out of a junkyard 5 years ago and the alt. works fine while running everything else until they come on. During the day all good at night when it drops. Had alt checked it is 110 amps. all good.
Thanks

Can someone move this to electrical. Thanks

[RustyPile]

Originally Posted by kglowacky

Thinking of replacing my current junkyard Dodge dual cooling fans with a new set. I would like to get some that draw less amps than my current ones. Not sure what mine draw but when they turn on it drops the amp gauge below 11. Anyone using a set that bolts right in and are happy with them? would like a one piece 2-unit bolt in. Again got these out of a junkyard 5 years ago and the alt. works fine while running everything else until they come on. During the day all good at night when it drops. Had alt checked it is 110 amps. all good.
Thanks

Can someone move this to electrical. Thanks

Changing to a different fan probably won't cure your voltage drop problem.. Fans that have good cfm ratings draw about 20 amps each. That's 40 amps just for the fans. They should be relay activated and the wiring should be no less than 10 gauge.. If the fans are wired on separate circuits, 12 gauge will work.. If your alternator is less than 85 - 90 amps output, that's part of the problem..

My truck had a 78 amp alternator when a previous owner converted to internal regulator. I installed dual fans and the 78 amp alternator would just barely keep up.. At night with lights and AC running, it simply wasn't enough alternator.. I switched to a 100 amp alternator, 8 gauge charging wire to the battery and problem solved..

[kglowacky]

I have a 110 alt. I have a LS 1 swap. The new gauge wire is 10 on the fans to a separate relay for each fan. I am thinking the old Dodge fans are drawing more then 40 based on the fact the original wire looks like 8 or 10. ( I spiced in before the original plug of the fan unit.) Looking at some new replacement fans the wire size appears to be 12 or 14. or I will need to upgrade my alt to 120/130. trying to avoid this.

[Joyridin]

Changing from relays to a PMW set-up will do wonders. The fans come on slowly as needed and only hit full speed if needed. I have twin fans in my C10 and you can't see the volt gauge move at all driving in any temperature.

[kglowacky]

What is PMW?

[Joyridin]

Pulse Width Modulation. GM uses it on their electric fans and fuel pumps.

Instead of the fans coming on full blast and a specified temperature, then shutting off causing a huge load to be dumped on your alternator, you set the temperature down a bit lower and as the vehicle gets warmer, the fans slowly come on. If/when it hits your maximum temperature, the fans will be running at full speed. Most of the time though, that doesn't really happen because the fans have been running at half speed keeping the temperature in check.

GM has used this on their fuel pumps since around 2015, maybe a bit earlier. Since the fuel pumps are being modulated constantly, there is not need for a return line. When the car needs more fuel, they speed up the pumps. When you are idling, the pumps run slow. It saves the pumps and again, reduces the need for huge alternators that are capable to handle the huge load dumped on them.

Here is the fan unit I used. I have the HF-125 for my twin Derale fans. Supposedly the Derale PMW unit is not too good.
https://www.autocoolguy.com/home

I heard a few people use this one also. I have never used it. It is available at several places.
https://www.northernradiator.com/HIG...S?pageSize=200

[LS short box]

Over on LS1tech.com in the "conversions" forum there is a thread dedicated to PWM fans.

[kglowacky]

Good info. But not sure it will help my problem. which is I am wired that when I turn on my A/C the fans through 2relays turn on, this draws my volts at idle negative, It has nothing to do with engine temp. I know what you are going to say is then this is a problem when the pcm turns on both fans for engine temp. Yes and no. Most of the time the pcm only turns on the first fan and that is enough to cool the engine down and not draw enough amps to make me negative, The second fan when turns on is usually a short duration and I am running down the road at enough rpms to keep me positive. So I think I need smaller amp drawing fans so at idle I am positive,. Down here in Houston I got to run A/c almost always. . Beware I am very poorly educated in electric amps and volts so if this makes no sense I understand.

[Joyridin]

Originally Posted by kglowacky

Good info. But not sure it will help my problem. which is I am wired that when I turn on my A/C the fans through 2relays turn on, this draws my volts at idle negative, It has nothing to do with engine temp. I know what you are going to say is then this is a problem when the pcm turns on both fans for engine temp. Yes and no. Most of the time the pcm only turns on the first fan and that is enough to cool the engine down and not draw enough amps to make me negative, The second fan when turns on is usually a short duration and I am running down the road at enough rpms to keep me positive. So I think I need smaller amp drawing fans so at idle I am positive,. Down here in Houston I got to run A/c almost always. . Beware I am very poorly educated in electric amps and volts so if this makes no sense I understand.

The PMW set-up will not draw the amps unless both fans are running full blast.

Either way though, you have some other issue. Here are the fans I am running. These work cherry on my truck. I have A/C, electric fans, Dakota gauges, decent stereo, and a bunch of other electric items and the alternator doesn't drop a bit when the fans kick on.

https://www.summitracing.com/parts/der-16927

[kglowacky]

thank you I will look ino this fan set up

[Richard]

Good to the see the full amp draw does not change with the PWM setup was mentioned. With PWM control you get less heat at motor with variable speed or lower speed set points. There is some heat generated at controller. It is much less than a variable voltage setup though because voltage remains constant @ 12v.
A few remarks- note that typically a lower watt fan (lower amp draw) will move less air. With a good fan setup you do not necessarily needs fan/fans at full speed with A/C on. Am using a single oem 850 watt 19" PWM fan on my truck. The PWM signal is coming from the stock e67 ECU. A pressure sensor in the A/C lines sends information to ECU which will command fan @ 50% duty cycle when it is required. This method only turns fan on when needed, when pressure rises. ie- low speed or around town driving. Fan really not needed at highway speed. The duty cycle (fan speed) will change with engine cooling needs as well. The higher speed always takes priority.

[A1971Blazer]

I'm running a 2 fan set up. The fans came with the Entropy swap radiator.
I first had 20 amp fuses and they would pop every time the fan kicked on.
I called Entropy to see what the amperage was and they recommended 40 amp.
I settled for 30 amp and they are sufficient with 12 gage wires, as the wires only run about 12-14 " long from the relay.
I wired the AC through the trinary switch to turn on fan 1 when the head pressure triggers the relay, and fan 1 through a separate relay for the engine temp trigger from the PCM.
Fan 2 is PCM triggered only when the engine temp calls for it.
At highway speed the fans hardly ever come on without the AC, and with the AC on, the fan will cycle as needed.
Fan 2 rarely comes on, unless I'm sitting still with the AC on.