Hey guys, my alternator finally gave up the ghost, and my car is dead until I fix it.

I was considering a high output alternator rebuild from Prospeed Marketing Group (in the electrical section). These guys rebuild the stock 110 amp alternator to 140 amp, and put in a higher voltage regulator, upping it from 13.5v to 14.4v, for about the price of a remanufactured alternator from Vertex.

I am concerned that there may be some hidden risks from running this upgrade on the DME, or something related....?

Anyone have any knowledge on this? I would love to reap the benefits claimed on the website, but not at the expense of my Motronics, etc...

Somebody let me know something quick, I need to make a decision and get back on the road (wife is getting stingy with her truck).

Thanks.

 

It will be just fine with no risk to your electrical components.

Your bulb life might go down slightly from higher delivered voltage but the light output will go up at the 3.5 power of the increase. Their marketing hype might be a little over stated as they are not raising voltage from 13.5 to 14.4. It is really only going from about 14.0 to their 14.4. And that 14.4 is only maximum at low amperage draws. Turn on all your electrical stuff and you will never be near that high. But it is still a fine idea since you have to change anyway.

Of course there is the quality issue, which I have no clue about.

 

Not to mention that the alternator only puts out as much power as the demand. If you've only got 50-amps of current being used by all the car's components, only 50-amps will be generated by the alternator (V=IR).

And by having the battery hooked up, the output voltage will be drawn down close to the voltage of the battery. That's due to the voltage drop across the battery. So even though the stock voltage is around 14.0v, I only ever see 12.5-13.0volts.

So really, what you're getting with the 140-amp rebuild is POTENTIAL in case you need it. If you never draw more than the 110-amp rating of the old alternator, you won't notice a difference with the bigger one.

Some people actually go the other way around. They put in the 65-amp alternator from a 924. Smaller, lighter-weight.

 

You raise a point though, Danno, and that is the operating voltage of the car with the stock Bosch reglator and its effects on the battery. The stock regulator only allows 14.0 volts maximum as far as I can tell. The difference between 14.4 and 14.0 in batery recharging rate is pretty dramatic with just that extra 0.4 volt differential. Brings up the battery in everyday normal running *MUCH* faster and you get a higher operating system voltage.

I used to see around 12.5 with normal light electrical loads. Put in an adjustable one like these guys are selling and set it to 14.3v. Now my system voltage is a hair under 14.0v. Pretty dramatic improvement, no?

The extra amp capacity probably isn't of much practical use to most of us 944s. But if you need a rebuilt alternator may as well put in a beefier diode bridge and maybe stator.

A situation where these bigger alternators work well is in offroad use with a truck running light bars, winches, etc. and crawling around at 1500 rpm. The bigger alternators will put out more amps and keep a higher system voltage level. Some of these guys have such a high electrical load they will be sucking battery power if they have a smaller alternator spinning at low rpms.

 

The only downside I can imagine is possibly cooking the battery on a long distance daylight run, a lead acid battery's optimium charging voltage is 13.8v, a good regulator with quality ground leads and feed cable will do this quite happily, higher voltage will charge your battery faster when it is down but when it is fully charged the battery will always be drawing current from the difference between 14.4 and 13.8v, although this is only 0.6v the current flowing constantly into a fully charged battery will not prolong it's life.

 

Shark... good point on the off-roaders. I had an '80 model Toyota with a winch (Warn M-6000), wired direct to the side-post connections on the battery. Winching logs up a steep slope would pull the voltage in the system so low that the engine would die, even with a tool box propped on the accelerator pedal to bring the revs up to ~2500. These logs were in the 12"-18" by 15'-25' range, coming up a 45 degree or steeper incline. It would happen even when rigged double-line with a ****** block.


I'm guessing that the voltage was dropping below some critical threshold value for some component in the system.

It would always re-start easily enough, and this was an infrequent activity, so I never tried to find a magic cure.

Aside from Martin's comment on "cooking" the battery (boiling the water out of the electrolyte?), the only downside I can see to a voltage boost is if you're actually using all the power that it makes available (lots of accessories). Then the extra heat in the alternator might shorten its life a bit.

Jim, AKA "Mr. Firewood"....

 

Martin, the battery issue is why Bosch insists on putting in the low (14.0) voltage regulators.

We can go on forever talking about what we should set our regulators at. Most battery manufacturers recommend their wet, maintenance free batteries (what most of us are using) be charged at 14.8v with a float charge of 13.4v. So how are we supposed to vary the voltage?

What I concluded when selecting my 14.3v regulator setting is: you never get 14.3v over to the battery, you are lucky to get 14.0v unless you have done some high class heavy duty rewiring - that is only a 2% drop. The alternator (stock) won't put out 14.3v once you get the amp draw up. Plus voltage is going to drop when the alternator gets warmed up. Fords and Chevies are running alternators that are almost 15v and you don't see people complaining about batteries burning out quickly.

My battery and system voltage would never pull up unless I was driving the car cross country for 10 hours. Now how many times do you do that? If one is concerned about overcharging the battery on a long trip, turn on your radio and parking/fog lights - that will knock voltage down.

Prior to rewiring and changing out the regulator I my system was always around 12.5 volts at the best of times and under 12 with big loads, now I'm at 13.9, or so, and I am happy and could give a rat's *** if my $70 battery dies even a few *years* early.

There is a reason these are called 12/14 volt electrical systems. I don't think readers should be concerned about upping the regulator a bit as the benefits far outweigh possible detrimental effects on the battery, if any. Remember, having a battery stay at low voltage also shortens its life.

 

I doubt the gain per loss would be significant, but wouldn't the stronger Amp alternator require alittle bit more work to turn, Unless of course it's just more efficient. I'm sure the hp loss is probably not significant but the Alternator does eat up alittle power that could be applied to the road doesn't it. Lets see W=(VI), and W=(Horse Power something something...) Just my sleepy two cents.

Back to bed

 

Alternators are fairly efficient. The load they place on the engine is only in direct proportion to the current-draw reqirements. So if you've got a 110-amp and a 140-amp alternator both suppplying the car with a 50-amp output, both will be placing about the same resistance on the belt.

It's just when you get to their limits, that there's a difference. The 110-amp alternator being required to put out 120-amps will have a higher internal-voltage drop and will heat (and overheat) its windings and regulator more than the other one.

But until you hit that limit of the smaller alternator, but both will be functionally identical.

 

Ok, so I found a shop locally that said they could do the upped voltage regulator (although they claim it won't make a difference) and 140 amp internals.

I sort of feel like I'm going to end up getting shafted, though, because they didn't write anything down (including my name) and said it would be $80.00, which it was.

- And they had it ready in a day.

I am picking it tomorrow, and am wondering if I can stick the ohms meter on it when installed and verify that I got what I asked for? Any tips on that procedure?

Thanks.

 

No, you can't just stick your meter on it. You need to load the alt with a current draw.

That was a pretty good price those guys gave you.

If you are really afraid just go back to them and ask to watch the alt tested. They will put it in a machine that spins the pulley and loads the electrical output. Load to 50 amps - if you get 14.0 volts at 1500 rpm you are sitting pretty fine.

 

Hmm, so no way to test it on the car?

 

Sure, you can test it on the car. You just have to put in an amp-meter inline with the alternator output (so ALL current is measured). Then run the car, turn on lights and accessories until you get a 50-amp draw. Then use a volt-meter to measure output voltage across the output terminals.

But this is really a test more of the voltage-regulator than of ultimate alternator output. To really test that, you'd have to increase the load to 100-amps, then 110-amps, then 120-amps, so on and measure the voltage drop and temperature increases in the windings and regulator.

 

UPDATE: Got screwed.

The $80.00 alternator looks like they just spraypainted the greasy alternator and handed it back. As soon as I fired up the car, I hearded the familiar bearing-roar...
(This was actually a working core that I had, that we removed when the bearing started making noise). In addition, nothing seems remotely different on the car's voltmeter. Think it's possible to rebuild an alternator and forget the bearing replacement? In addition, one of the plastic components on the back got the housing cracked in their possession, and was then painted over...

I went to another shop, which did some "research" to see if 140 amp upgrade was possible... They just called back and said they could do it, but it would be expensive, and I would get the increased amps at upper RPMs, but would actually suffer a substantial DECREASE during around-town driving...

Their price to rebuild is $145.00 (1 year warranty) - does that sound like a fair price?

Now, in addition to being without the Porsche for a month, I've got to figure out how to get my money back from shop #1 (which incidentally was a 45-min. drive each way from where I live)...

-Could've bought that Prospeed unit for the $$ I'll have tied up in this - but then again, if it only makes the amperage at high RPMs....?

Comments?

 

Keith, sorry to hear you got a bad shop. What were they doing spray painting it anyway? That is just a bare alloy case that only needs to be cleaned up.

Who knows what they did, but they likely didn't put in a higher level voltage regulator, like 14.3 or 14.5. And to get more amps out I don't know how they could do it for $80 and make any money.

Get your money back if you can, having a *HUGE* mean looking guy that is real hyper accompany you helps. I had this black college frat brother that was a starting lineman. Went about 280lbs. Man was it fun when we pulled this game one time.