The Patman

But...but...but what about us fellas with the more "vintage" year models...with even more aging equipment even weaker alternators? (yes, I said aging equipment)

Dictys

No nothing special that I am aware of to be honest, it made a big difference together with the other little fixes. My front harness was bad shape due to heat issues, so I made a new one and this improved matters but not perfect. Then I had the Bosch rebuild and no problem since whatever the outside temps and heat soak.

WallyP

My auto electric rebuilder (personal, not 928 Specialists) said that he could get several different regulators, with different temp curves...

Alan

But assuming you are from where you say you are on your avatar - then that means at the most up to a very occasional peak of ~90F ambient.

Alan

Alan

Yes and that may be worthwhile - however on a 928 (unlike most cars) the temperature of the alternator tells you very little about the temperature of the battery. So this might also allow a much higher degree of overcharging while hot in very hot locales.

Alan

marine928

I run a 130 Bosch reman coupled with LED conversion, deoxit on every electrical connector, fuse, & relay. Have also changed out most major grounds as well. Electrical issues due to age are a big problem on our cars and need to be properly maintained as Speed noted.
I think that more amps going into the system causes less stress on the alternator and the electrical system especially during the summer. Heat decreases the efficiency and is one reason we have cooling shrouds.
Every time a new load is added to the mix the alternator and regulator must compensate. Increased alternator output lessons the stress and speeds up the charging rate/time to the battery.
200amp is overkill but 130-150 amps keep our cars electrical system and computers running more consistently, with less stress.
Just think of an under powered a/c system. The compressor continually engages which will soon wear it out much the same way an alternator that is continually trying to keep up with demand does especially under harsh conditions.
Just my opinion based on experience.

Alan

You can think this - but you'd be wrong! dittoNo - mostly not - It may seem like stress, but it is actually designed in compensation that lowers the output voltage & current at high temps - to protect itself and the battery - so it is reducing stress (voltage & current and battery charge rate) - the stress you sense is mainly in your head as you worry about the low voltage. Now if the battery is draining too fast at hot idle (which it can do in very high ambients [>100F]) there is some stress, battery self heating and potential for low state of charge damage - but this is rare.
Faster charging is only good if you stay under the max charge rate for the battery which varies with temperature. Overcharging a battery is much worse for the battery (life & death) than undercharging it (takes longer to reach full charge). You have to understand the limits before you change things. Having a higher current capable alternator actually changes exactly nothing about how the battery will charge. The only things that affect charging are the alternator nominal voltage set-point and the temperature & load deration factors in the regulator (and the effects of other system loads).
It makes exactly no difference what the maximum current capability is until you hit that limit, you won't get any more current unless the voltage is higher (either set higher or droops less that the comparison case). A higher rated alternator 'may'* see less stress at a given load but the stress on the rest of the cars systems won't be changed (if it's at a higher voltage it will be stressed more not less - but within reasonable limits it doesn't matter either way - it's not stress you need to worry about - unless you are boiling the battery).
I'm sorry but you have some major misconceptions about how the alternator system works. You also don't understand the AC system operation. When AC is selected the compressor always runs continuously, it only stops if the evaporator freezes up. The alternator is purpose designed to always run continuously also - regardless of anything else.

*many high current alternators are just regular alternators with different regulators - these end up more highly stressed. I don't believe that of Carls' versions but it is the case with some.

It is really not helpful to state things that clearly cannot be true. However you are not alone here - almost nobody understands alternators. They only seem to be simple - they are not easy to understand in context.. especially wrt battery charging which is also by no means as simple as it seems to be.

I'm not trying to be a jerk here - just trying to keep the facts straight. All kinds of drivel is posted about alternators every year here by many people - it's no wonder folks aren't developing any better understanding. I just try to point out the major errors and keep the story straight.

Now we shouldn't really have to understand all this - Porsche should have just done a better job in the first place.

Alan

Speedtoys

Wow.

Speedtoys

Would a thread selling 150A gasoline be too much?

marine928

So if I understand you correctly it really does not matter how many amps the alternator puts out...so a 30 amp alternator will be as efficient as a 60amp due to the fact that it runs continuously and the charging rate is constant.
That funny because the manufacturer of my boat motor as well as all the others decided that the 50 amp alternator was not sufficient to fully charge the battery during extended periods of low rpm use when under extra load from accessories.
According to your theory since the battery can only take x amount of charge then we don't even need 60 amps. Is that your conclusion?
As far as a/c goes, park your car/suv in the sun with the ac running and see how well it performs after an hour.

I am curious as to what causes the lights to dim at idle when the ac kicks on and why does the idle drop in some cases as well. I had this symptom until I converted to the 130 amp. Cleaning contacts helped but the 130 alt made all the difference.

Speedtoys

That's not his conclusion. Just what you gathered from it...and others.

A higher rating alt MAY deliver more current at lower RPMs. Depends on design. That's what your boat dude was really saying, and some here desire, whether for real or imagined reasons.

A battery is a chemical reaction, and its slow, and you dont 'dump' Amperage into them to 'fill' them quicker.

It will answer for the draw you have, and work to slowly charge the battery based on temperature..which Alan has covered quite well...because batteries are chemical reactions, and temperatures are important.

If you have 50a of total draw, and your use-case isn't trolling the waters or hours at idle speeds in traffic, a 'larger' alternator is just making you wallet light.


A 150A alternator in a 60a environment, is a 60A alternator.

marine928

I agree that a 150amp is a 60amp in a 60amp environment. That being said I and others feel that a 60amp in not a 60amp in our environment due to the extra pull required to overcome the resistance encountered by old wiring, old light bulbs, corrosion and other sundry electrical issues that go hand and hand with a 25 plus year old car that relies on good constant electrical current to operate properly.
Resistance is futile!

Your statements work in a perfect environment where everything is pristine. Laboratory conditions. Not real world as described above for most of us.

Speedtoys

Then fix it.

A 150a alternator is not the solution to those problem. It is the solution to a bumper to bumper wiring fire.

Alan

No - I never said anything of the sort (as you well know). Unless you have significant enhancements to the current consumers on the car - you don't need an alternator that can deliver more max amps than stock, and as I have explained earlier in this thread the 'capability' to deliver more max amps often comes at the expense of less idle amps - so that would be pointless for most folks. Oh and the charging rate is never constant. Now you have introduced 30A and 60A cases for some reason...? I have no idea why.. So what you needed was more idle RPM amps not more max amps. Higher max amps and higher idle amps are not at all synonymous, they are in fact in direct conflict I never said anything close to that (read what I wrote). Batteries can accept huge charging rates - however charging at a too high a rate will damage a battery, at temperature it will damage it much faster and at lower current levels. Charging a battery at too high of a voltage (=> current) will cause the electrolyte to boil, at some excessive point the battery can explode. It is good to understand this before you increase the system voltage setpoint of a regulator - or reduce its temperature derating too much.

I fail to see the relevance of this to the fact that you misunderstand how the compressor is controlled. The compressor performance is worse at low RPM - as you would expect. The difference is that the alternator tries to compensate for low RPM use while the compressor doesn't.

Why be curious. the voltage drops. It drops because the alternator has insufficient performance at idle - and you need more idle current performance to fix this. You just added an additional electrical load (clutch) and the idle RPM dropped because of the increased load on the engine from the compressor and also from the alternator at lower RPM. The alternator loads the engine much more at low RPM than at high RPM. And at idle RPM's it's voltage output is very sensitive to RPM changes.

That you may have got increased idle current performance in your high max amp alternator was DESPITE the higher current windings - not because of them.

In this case regulator changes and perhaps design changes (pulley ratio, case design, rotor design etc) gave you better idle performance. The higher current stator windings certainly made the idle current capability worse than they could be in the same design with a lower (say stock) max current rating.

So be careful what you look for - you may get the opposite of what you think you are getting (and pay $$$)

Alan

marine928

Speed, as I said earlier, I have addressed 70 percent of the resistance due to outdated wiring and other things that draw extra current due to their age and design.
My dim and idle drop became nonexistent after the 130 amp install, which has led me to my conclusions. Nobody is arguing that the stock alternators are not sufficient under normal operation above 1500 rpms. The issue rest solely with low rpm ( idle in traffic, hot days for extended periods) charging.
Alan conceded that a higher output amp will perform better under these conditions given the totality of circumstances.
In a perfect world we could completely redo our wiring and the low idle charging issue would be moot. That's not the case, so we look for cheaper alternatives that appear to compensate albeit right or wrong.
Electrical issues rank right at the top in this forum especially for the later model 87 and up cars, chiefly because of the enhanced systems that rely on constant electric current.
A 60 amp system will not correct this issue with all things considered absent a complete rewire as you stated.