Alternator shutting off?

Busted Knuckles · 02-13-2014, 03:22 PM

I've noticed this winter, with my headlights and wipers on, that my alternator seems to shut down while at idle. This appears to be leading to damage to the battery, and I had to replace one this past summer, but got a pro-rated refund. Now the new one is showing signs of weakness.

As I'm warming up the engine, the voltmeter shows 13.5-14V, idle speed around 1,200 RPM. This is normal and healthy. But, as soon as the engine warms up, the RPMs at idle drop to 750-800 RPM and the voltmeter drops to 11.5 to 12V. Revving up to 1,200 RPM sometimes gets the volts to 12.5V, but I don't see 13V again until I'm driving with RPMs above 2,000.

I noticed this with my old alternator before it bit the dust a couple of years ago. The new one did the same, so I thought it was normal. But, because I spend a lot of time in commuter traffic, I've seen the voltmeter drop to as much as 11v while stuck in line at a stop light.

I'm wondering if anyone else has experienced this, is it normal, or do I have a problem?

02-13-2014, 03:22 PM	#1
Busted Knuckles 12psi boost Join Date: Dec 2007 Location: Atlanta Posts: 300	Alternator shutting off? I've noticed this winter, with my headlights and wipers on, that my alternator seems to shut down while at idle. This appears to be leading to damage to the battery, and I had to replace one this past summer, but got a pro-rated refund. Now the new one is showing signs of weakness. As I'm warming up the engine, the voltmeter shows 13.5-14V, idle speed around 1,200 RPM. This is normal and healthy. But, as soon as the engine warms up, the RPMs at idle drop to 750-800 RPM and the voltmeter drops to 11.5 to 12V. Revving up to 1,200 RPM sometimes gets the volts to 12.5V, but I don't see 13V again until I'm driving with RPMs above 2,000. I noticed this with my old alternator before it bit the dust a couple of years ago. The new one did the same, so I thought it was normal. But, because I spend a lot of time in commuter traffic, I've seen the voltmeter drop to as much as 11v while stuck in line at a stop light. I'm wondering if anyone else has experienced this, is it normal, or do I have a problem?