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Massive voltage drop under high RPMs

Old Jul 26, 2020 | 01:25 PM
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rbracy10406's Avatar
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From: New Jersey
Default Massive voltage drop under high RPMs

*** Found the issue. Brushes are shot. Must have been bouncing making intermintent contact. Ordered a whole new alternator because i dont like the whine of the bearing ***





Hi all. Long time no see. As some of you know, i have altered a lot of the electrical items in my car and made some upgrades. I recently let my car sit for about 3 weeks while I was away on buisness. I left my LCD instrument cluster in what I call "test mode" which leaves the computer running at full speed and prevents it from going into its low power mode it usually does when the car is t running. This dropped my battery down to about 5V over the 3 week period. Being a little impatient (and stupid now that I think about it), i jump started the car without giving the battery a good charge. Long story short, the battery did eventually make it back up to about 12.6 (car off) and started well on its own. When the car runs at idle and lower RPMs i am getting around 13.6 to 14.2 volts even with the AC on high. For some odd reason, when i accelerate hard and get the RPMs above 3/4K, my voltage suddenly spikes down to 2.4 volts and my battery light comes on until I lower the RPMs. I am assuming that the massive load from the dead battery may damage the alternator causing it to short at high rpms but I just wanted to get some input and see if people have seen this before. Below is a graph of one of my test runs. I was running everything electrical I could with the AC on max teying to see if I can get it to fail which is why i only got to a max of 13.6V.

When I ran this test, i put a brand new battery in as well as a new belt just incase it was slipping. The tensioner is very tight so I dont think that is bad either. Alternator was replaced about 6 years (50ishK) ago so it could definitelybe bad. The bearing always had a slight whine right out of the box that always bugs me too. Also, before I replace the alternator again. Does anyone know of a decent upgraded alternator?

 

Last edited by rbracy10406; Jul 26, 2020 at 02:59 PM. Reason: Resolved
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