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Voltage stability / alternator question

EFI Wiring Fundamentals

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I have a LSA/Turbo Porsche Cayman manged by an M150. (for ref: instagram.com/jordon.musser/ ) Mostly irrelevant for this post, but none the less for background. I am using this alternator:


That I had Shop A rebuilt for more output, supposedly 160A. I am running an electric power steering pump, dual electric scavenge pumps (low mount turbos), IC water pump, IC fans (2x) engine bay fans (2x) rad fans (2x) etc. Car wouldn't charge well, in my eyes intermediately although it did seem to charge better at elevated RPM. Voltage would fluctuate from 12v to 13.5. So I took the alternator to shop B, who converted it to a single wire and rebuilt it (again) supposedly they tested it at 800rpm and it was putting out 80amps. so pretty solid considering the overdrive on it when the engine is 800rpm, it has got to be over double that. This seemed to be a LOT better, but still got more fluctuation than I expected (every now and then it would dip below 12v at idle but then pop back up to 13v+). my ASSUMPTION is that I am exceeding the capability of the alternator.

1) Recommended higher end shop to go through this alternator? (other than my local alt shops, because clearly that isnt working)

2) What should I expect for voltage regulation from the alternator? Ive never had this problem before (either the alt works or it doesnt) so I have never really paid attention closely to the voltage stability before

3) I am limited big time in space, are there any other small alternators I could look at that can do big amps? I have to remove the engine to swap the alternator so I am willing to spend more than I should to get it right this time.


I would pick up a cheap current clamp so you can actually measure how much current is being pulled from the system, then you will know if you have a capacity problem or a regulation problem.

Something like this will do (make sure you get one that can do DC amps - many cheap ones only do AC): https://www.ebay.com/itm//153507698586

Copy, got one on order.

Update. Good call on the amp meter. I didnt own one so I didn't even think about it. I measured the car idling with out the alt hooked up, about 80amps with headlights off and stereo off. I turned the steering to lock and got about 100amps. So I figure when all 3 pumps are on, stereo is on and head lights I probably could pull 160+ easily. Obviously that would be a rare combo because third pump would only be on in a straight line more than likely.

I hooked the alternator up and measured amp draw there.. it was really inconsistent. I busted out my thermal imager, and sure enough the stud I use to make the amp wire connection was very hot. I replace that stud with a larger one and ensured the lugs were clean and tight. boom, 120A at idle stable and the car is charging.

So the real question is.. do I need to spend $500 on a 270A alt (i did find one) or is my 160-180 amp alt enough (i dont have the real number, only an estimate from the shop that built it). Considering on a track day (worst case) I would not have head lights on, no stereo, and likely only using 2 fuel pumps most of the time (would have boost turned down) is that enough headroom?

The car only sees a few thousand miles a year, so even if the alternator dies at 10k miles I am fine with that, but I dont want to lose it at an event because I was cheap over $500

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