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Just a quick question as I am done fighting with my parts supplier. I bought a reman alternator and put it in. Now the gauge and my VOM and my DVOM all show between 17VDC and 18VDC at around 2000 RPM.
I can see that the alternator has it's own voltage regulator on the back of it.
Question: Nothing special with our cars I need to know right? Just go get my replacement? I hate throwing a fit and finding out I was the dumb a$$.
Nothing at all special about the 928 alternator. As you note, the voltage regulator is integral to the alternator. It's rather easy to change out, just a couple screws. The regulator assembly includes the brush holder and brushes. Sometimes "rebuilders" will leave the old parts in there if the brushes aren't too worn, and the unit makes current and voltage when tested.
Recommendation: With the alternator on the sellers table, ask them to remove the regulator. Look at the brsuhes, wheich should be close to 1/2" long. The slip rings now visible on the armature should still be smooth with no grooves. If either one of these things is not true, the alternator was likely just cleaned and resold. Regardless, have them install a new regulator.
Be aware that 18 Volts has the potential to do some serious damage, especially in later cars with more electronics. I notice that caps used in later fan controllers are rated at 16V, for instance. So after you get the new regulator fitted and charging voltage is again under control, make sure all the electronic modules work OK.
Only the alternator itself can be responsible for an overvoltage condition like this. It is important that you have a workable battery installed in the vehicle but even an issue with that that wouldn't result in this level of consistent overvoltage.
Just get a replacement or have them rebuild it properly. Don't let them give you any bull - the alternator is clearly the problem here - and at these levels could have damaged your car. As Dr Bob says check the operation of everything after you get this fixed.
Important to remember that your "parts supplier" isn't likely to be the one that rebuilt the alternator.....so Dr. Bob's suggestion isn't likely going to happen.
Your "parts supplier" isn't going to have to "eat" your defective alternator....they just need to send it back and get another one....or send it back to their rebuilder and have it checked.
Therefore, there should be little or no argument. Tell them what is wrong as you hand it to them.
If the rebuilder checks it out and finds out that the failure was caused by something you did when you hooked it up (possible), then you may have an issue.
Well that fiasco is behind me now. The replacement alternator is in with a fresh, off the shelf battery. Both were finally replaced under warranty. I now have a healthy charge of 14vdc at idle and no more that 15vdc at 3000 RPM.
I even had time to polish the old fan and pulley. Now to get the rest of this neglected old shark looking and working as good as the charging system!
kind of random, but one day I wanted to see if it was possible to increase the amount of energy an alternator would output. It turns out I found a company that did nothing but rebuild alternators. They actually did 928 alternators as well. I plan on using them in the future.
kind of random, but one day I wanted to see if it was possible to increase the amount of energy an alternator would output. It turns out I found a company that did nothing but rebuild alternators. They actually did 928 alternators as well. I plan on using them in the future.
Did they say how much they could add during the rewind? It would be nice to have a little more buffer than the 90 amp stock output. I don't plan on adding any high draw accessories but knowing I could, as well as run everything all at once without having to pull from the battery would be comforting.
There is a limited amount that can be done in the same case style. People talk about wanting more current from their alternator but most don't really understand either what they want or what they might get...
If you rewind an alternator with heavier duty windings (heavier gauge) you typically just get less but thicker windings. This makes for a potentially higher output current but with lower sensitivity. The net result is usually less voltage & current generation at low RPM, but more current at high RPM.
Most people don't really have issues with how much current their alternator can generate at high RPM - only how much can be generated under hot idle conditions and how much voltage droop you see under those conditions.
You can get marginally better results with higher quality ($$) components and you can trade reliability (e.g. run hotter) for more output. The best way is to get a bigger alternator - but this is a difficult fit in a 928.
Be sure you know exactly what results you will get at hot idle before you pay big bucks that may not pay off for the real issue you are trying to solve.
Incidentally increasing the voltage set point of the regulator almost certainly won't help much. The alternator is power limited at hot idle and a higher setpoint will cause voltage droop to simply start sooner (e.g. at higher RPMs) It will increase cold charging current but will also increase the range of voltage drop you will experience (not an obviously good trade off).
01-06-2015, 11:58 AM
18VDC from 15 min old alternator
