Electric Fans Impacting Idle Speed

[70rag383]

Hi All,

I'm having an issue where my idle speed lowers and is very erratic when the electric fans kick in. I have 2 SPAL fans connected via relay that kick on when the engine temp reaches 190F. This occurs when I'm at a stoplight or stuck in traffic. I usually have to give it more accelerator as the car feels like it's going to stall. I have a voltmeter installed and it goes below 12V when the fans are running which tells me that perhaps the alternator does not have enough amps to keep the engine going. This is the first time I've experienced this issue. The car has 17K miles since the car was restored in 2018. The alternator and optima battery were new at that time. Any thoughts on how I can pinpoint the problem and fix this?   

[Brads70]

I tried a couple stock type alternators when I went to electric fans. I found they could not keep up and killed the battery eventually. Mopar alternators do a poor job at idle rpm's. Ever notice headlight diming at idle...?
The solution I found was one of these alternators and the bypass wire to battery.
https://www.qualitypowerauto.com/item_557/Chrysler-Mount-Mega-Amp-Alternator.htm

It's been on my car for about 10 years now with no issues.

[70rag383]

I tried a couple stock type alternators when I went to electric fans. I found they could not keep up and killed the battery eventually. Mopar alternators do a poor job at idle rpm's. Ever notice headlight diming at idle...?
The solution I found was one of these alternators and the bypass wire to battery.
https://www.qualitypowerauto.com/item_557/Chrysler-Mount-Mega-Amp-Alternator.htm

It's been on my car for about 10 years now with no issues.

Thanks Brad. Sounds very consistent to what I'm seeing.

[dodj]

You issue can also be caused by poor/loose/corroded connections causing high resistance. The higher the current draw, the more poor connections impart your electrical system by increased voltage drops...ie..like electric fans turning on.  So while it may be your alt, it may just be a bad connector. Prior to buying new parts, verify all your wiring is good. Take the connections apart, don't just look at them and decide they are good enough.

[70rag383]

You issue can also be caused by poor/loose/corroded connections causing high resistance. The higher the current draw, the more poor connections impart your electrical system by increased voltage drops...ie..like electric fans turning on.  So while it may be your alt, it may just be a bad connector. Prior to buying new parts, verify all your wiring is good. Take the connections apart, don't just look at them and decide they are good enough.

I'm fanatical about the wiring and have made improvements to the bulkhead wiring and also completed the ammeter bypass and installed the relay setup for the headlights, all thanks to members on this forum. Good advice from you to check it all again before I buy any new parts. Thank you!