Isuzu SUV Forum banner

Headlight Drain?

1815 Views 4 Replies 3 Participants Last post by  wrenchmonster
When I turn my headlights on, I can hear the engine drop in tone, like they're draining the battery. The RPMs don't appear to change, just the engine sound. Any ideas? Do I need a new battery?
1 - 5 of 5 Posts
Howdy. The sound is probably nothing to worry about. Do your headlights dim at all while driving? Do they brighten up when you give the engine some gas? If so, you may have a weak or corroded ground connection on that circuit. You may also want to check out your charging circuit to see your alternator performance. How is the state of charge in your battery?

By the way folks, it's best to check the alternators performance on car. If you take it out and have it bench tested, you could be missing out on a bad connector or bad wiring in the charging circuit. The test I like the most is to look at the output signal of the alternator on a lab scope. Should give a nice, even, wavy pattern.

The test for the battery is called a "battery load test" or "stress test" and is best done on a VAT40. You can't simply hook up your voltmeter, read 12.6V and determine that your battery is in good shape. My 2 cents.

I don't know what the state of charge is, I'll have to check. The lights are fine, though -- no dimming or brightening while driving or anything. If you don't think it's cause for concern then I won't either :D
Correct me if I'm wrong but doesn't your alternator use quite a bit of power for the belts when it needs to provide more power? I could be thinking of when old cars had generators instead of alternators. If I'm not mixed up this should be the reason that you hear the engine drop tone. Is the tone drop similar to an electric fan turning on?
Howdy folks. Kickingtrees, perhaps I'm reading your message wrong, or perhaps it's the way you worded it, but NO, your alternator doesn't use power for belts. Belts are crank driven. More belts take can take away horses, that's why there are items like fan and AC clutches so as not to draw HP away when not needed. Perhaps this is what you are referring to?

State of charge has to do with a battery effectiveness. Study Ohms law if you are really interested in the matter. A nine volt battery has nine volts, but can't provide enough amperage (electrial pressure) to power much of anything.

1 - 5 of 5 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.