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Old 08-09-2010, 09:11 PM
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Idle RPM goes down when dual electric fans are switched on

Hey fellas,

When I switch on my dual fans the RPM drops noticeably. I just put in a 100 amp 1-wire alternator. It was not doing this before the new alt. but the old one was not charging at all. Thanks.

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Old 08-10-2010, 06:52 AM
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The alternator is causing the rpm drop because of the additional electrical load imposed on it by the fans, especially when they first come on. As the electrical demand increases, the alternator will become harder to 'turn', thus the drop in idle rpm. This is not so noticeable when the engine is above idle such as when driving. My T-Bucket does the same thing when the fan comes on (I'm running a CS130 alternator).
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Old 08-10-2010, 06:55 AM
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one wire alt's

those things don't like to charge at idle. but do fine running down the road.. just like rocks said.. big draw will reduce rpm's. i have one also and does exactly the same. but runs 14v down the road..
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Old 08-10-2010, 01:00 PM
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Ditto what the others have said about the drag of the alternator. If it really bugs you, you could install an idle kick up solenoid like they use for A/C.

Vince
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Old 08-18-2010, 03:31 PM
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Thanks fellas,

I just raised the idle 200rpm. It sounds even nastier.

66 Caprice

538 HP 383
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