Running a Power Master GM 25SI alternator. 16 volt with the XS adjustable regulator. Works fine 2-3 outings then quits. This weekend was the 3rd one. The block is grounded to the cage. The alternator case is grounded to the cage not only bolted but with a cable. The battery is grounded to the cage. Voltage drop between the negative battery terminal and the alternator is less than 1 volt under load. The posistive cable is sized 02. It has one connection at a fire wall bulkhead shared by the starter, alternator, and main feed to all the other components. The only other junction is the main cut off switch. The car cranks very easily at 15-1 comppresion, ignition on, with 34 total. It seems like the failure occurs when starting 1st thing in the morning. Battery is alway charged with the cars circuits disconnected at the main switch. Pulley size is exactly what they suggest. Never had an issue with the previous alternator. It just didn't have enough capacity. They suggest a ground from the battery. I don't buy that. There isn't a production car in the world that has a negative cable from th ealternator to the battery. Could there be a spike during crank? don't know. And if there is why does it take a month unttil it fails. I'm at a loos.
Doug

We have had ZERO luck using anyones adjustable 16V regulated alternators. Finally got HOP to admit they shoudl not even sell them but some guys with lithiums need/want them.

Hi Doug,
I'm the first to admit I am not great at wiring stuff. BUT, I was having issues with my alternator a few years ago and tried a bunch of stuff, and ultimately this is what worked for me.... adding this, my issues went away.

https://www.summitracing.com/parts/..._loSQQI_of_3jUTSy5FIEHr94KxoCwzcQAvD_BwE

Maybe this will help?
Brent

Doug, the only thing I can think to suggest, whether I am right, wrong, and someone agrees or disagrees, I would connect the charge back wire directly to the positive, NOT A SHARED power post that runs back to the battery. My understanding is that hooking up the alternator to a shared power post, the alternator is backfeeding the battery, after it is giving power to all your accessories first. I believe this can cause a potential spike. (Again, just my understanding) When hooking up directly to the battery post, the alternator is purely feeding the battery, and the battery is feeding your accessories. Why did your other alternators have no issue? I wish I could explain that. But I would say with the new alternator having issues, if it were my car, that is where I would PERSONALLY start. It may not make any difference, but just my opinion. I even did this with my dads car with a 75amp XS Volt alternator and it made a big difference when I simply hooked it directly to the battery.

I run an XS Volt adjustable regulator alternator from powermaster, part number 8148. Turned up to 18.5 volts, 65 amp charge at idle, 150 amp at full throttle. I originally had it hooked up to my common power post, and it would not function 100% the way I felt it should work. Never failed, but there was a time or two where it stopped charging. I simply ran a wire directly from the alternator to the battery, and never had an issue since. It’s been on my car since 2019. It does such a good job I never have to charge my battery on race day.

Again, right, wrong, or indifferent, agree, disagree, I think that is where I would start.

RJ

forget grounds to the cage. Run a ground direct from the battery to the block. Prodcution cars dont have 15-1 compression LOL

I run a duel pole disconnect main switch and run the alternator wire all they back to the main disconnect switch isolated from the main battery feed - as far as grounds I have found running an isolated ground from the battery to the front of the car solves a lot of electrical gremlins - I still ground the entire chassis but all the electronics and other things run to the isolated ground bar up front. What do you have the regulator charging at - I set mine to charge at 16.9 volts under load - if your charging at 18+ it will burn up the regulator One thing to consider with a single pole main disconnect - your alternator will always have a parasitic drain on the battery as the regulator is hot with the main disconnect switch off

My question would be WHY even use an adjustable regulator. The only reason we tried was for lithium batteries. I no longer use an adjustable regulator and not an issue. Both card work fine unregulated with a 16 volt alternator. As stated earlier we had ZERO luck with Powermaster or House of Payne alternators with adjustable regulators.

A few answers to coments. It did have a HD solenoid disconnect in the alternator line during the 1st failure as pictured in post #2. It was removed because we thought the alternator may have spiked during coastdown when the engine was shut off as there was no path for the current to disapate. Granted it would've only been a second or two. I agree with post #3 that maybe the shared power could be an issue. If I have to, I'll rip the carpet up and run a new cable. Could do a second ground at that time as well. The car always cranks very easily. That to me says at least the starter has a good ground. All the accersory grounds are on a common stud except the fuel pump (grounded at battery) and fans (grounded at chassis). It runs at 18.8-18.9 volts. Powermaster suggested 19.3 volts. But MSD states that is too high. XM battery say's they have racers running 19.3 volts with no ill effects. I asked the Power Master tech guy about swapping to a standard style 16 volt regulator. He told me that both types are robust.
Doug

Had an Eagle Talon TSi years ago that fried 5 alternators in a row, some only lasted a week. It was heat that was killing them, ironically the popular upgrade was to a GM alternator

I recently had a non-diode protected Bosch style relay take out my delay box. I realize you removed the master disconnect relay. Thinking out loud.

What is failing on the alternators? Stator? Rotor? Diodes? Brushes? A little postmortem autopsy may be in order here.

To be honest they went back to Summit. The windings, rotor, and diodes all looked good. Nothing burned up. Though I did not test them. I suspect the regulator.
Doug

So you really were having regulator failures, not alternator failures? Not trying to be a d$ck here but like anything, if you don't know what the problem is, it's hard to find a solution. Just a thought, I've never worked around a 16 volt system. What is the desired charging voltage? There are regulators available for Motorola alternators with about a 15.5 volt setpoint. I would think you could also use a simple voltage divider to "fool" a conventional voltage regulator into controlling at a higher voltage.

II don't know if you can easily switch styles but I have been running a GM CS130 from Orielly's for years. I have replaced it once in 12 years and it turns out it wasn't really the alternator it was my continuous duty relay starting to fail.

Took a number of retured failed alternators and phone calls before HOP admitted the regulators were and issue. I have been running 16V alternators for years. On MSD 7AL boxes, Digital 7's and Grids and never had an issue there. The only reason we tried the adjustable was when running a lithium battery as they will not tolerate even 18 volts

I know how to test all the components except te regulator. And if it is the regulator, then what caused the failure? Lead acid batteries normal charge point is around 14.6 volts. 14.6 / 6 cells = 2.43 volts per cell. Multiply that by 8 cellsin a 16 volt battery and the normal charge rate would be 19.47 volts. So the regulator set point would ideally be set close to that number. I suppose there is a way to add a external regulator as well. That still doesn't gaurantee success. I saw a lot of wierd failures at FCA when working in the electrical lab. Already talked to one charging system engineer. Waiting for a call back from another. Maybe the regulator is just poor quality. Stay tuned
Doug