replaced the alterator on the Suburban last fall when it seized. really have not used it since till the day when tranny went out in the pick up. I fired it up and let it run for 3/4 0f an hour to warm up and melt the snow off the windows. When I came out the lights were dime, fan running slow and wipers barely moving. Alternator not charging. when I reved the engine, up went the gauge and it started charging. Now every time i start it i have to give it a quick rev to get it to charge. Once the needle on the gauge goes up it keeps charging even at idle
I have seen that on rebuilt alternators. Usually the problem is the incorrect voltage regulator has been installed in the alternator. It could have too large a pulley causing too low alternator rpm at idle, but you would have noticed that when you installed it. It wont hurt anything if give it a little rpm when you start it. I had one years ago that had the wrong regulator and it wouldnt charge at idle at all. It was fine over 2000 engine rpm but would stop charging when returning to idle.
Don't the new alternators need to see a certain RPM before they work ?
Yes. The problems arise when some rebuilders use the same voltage regulators in all of the same style of alternator. Depending on the alternator rpm at engine idle the cut in speed varies depending on the pulley arrangements on the original installation. The oem alternators have voltage regulators tailored to the idle rpm to ensure that the alternator will cut in properly. Usually there isnt a problem with a rebuilt alternator. Even on the suburban mentioned here he didnt notice the problem until he let it idle to warm up. If he had driven away as soon as he touched the gas it would have started charging. The alternator that I mentioned that wouldnt charge at idle was rebuilt by a local shop. I took it back and he tested it on the test bench and found it wouldnt charge at low rpm. Changed the voltage regulator and it was good afterwards. A few days later he found out that his supplier sent him voltage regulators that had been boxed wrong. Apparently they were for an alternator for a gen-set.
