checkmate1996

So, I'm trying out the mod for the gm delco alternator swap. (write-up to follow) In short, with the lights on, defrost on, two electric fans spinning...I'm getting about 12.1-12.2 (read through digitial volt meter at battery) volts @ 750-800 RPMS idle. At roughly 1700-2000 RPMS I was reading 13.4-13.5Vs.

These measurements seem low. Am I wrong?

I'm also hearing what I think is a relay clicking off every 5-10 seconds....which I'm not quite sure what that is or why...maybe aux fan relay?

Thoughts?

Alan

At that voltage the alternator is not supplying enough current to power everything and is relying on the battery for a significant current - so not good...

I have no idea what the clicking is - do you see any voltage fluctuation related to it? It would appear your alternator rpms (ratioed from engine crank) are too low for it to generate well at the engine idle rpm. This is what Dave Anderson discovered some time ago with a similar Delco alternator.

Your options are to decrease the size of the alternator pully or increase the size of the crank pulley... there is probably limited room to move smaller on the alternator pulley (and this increases the risk of belt slip) while the crank pulley change is a lot of work...

Of course one possibility you should check first is that you don't actually have belt slip happening at low rpms (this is where it is most likely to slip)... It needs to be tight.

Or you could use an alternator that works better at low rpm...

Or live with depleting the battery at idle - not good for extended crawling in traffic... or bettery life in general

Alan

checkmate1996

Alan,

Thanks much for the feedback.!! I went back tightened the belt again just to make sure. I tightened it as much as I possibly could. Now with all accessories (minus radio), cooling fans, lights, dash lights, clocks, defrost - I was maintaining 12.4-12.5 at 850-900 RPMs.

Do you think is more acceptable?

Also, what I don't understand is the v belt pulleys on my old bosch alternator and the new one are both 2.5" in diameter.
So what the heck were the other guys doing to make it 14.4V at idle? I'm confused...

Alan

The alternator still isn't keeping up... but its better... the battery drain will be lower but still there - you need to be targetting 12.7v or above to be not draining the battery.

Since you achieved better results from this - belt slip is a real possibility - maybe it isn't cured yet... you might want to get a new belt and ensure the pulleys are clean and totally de-greased (clean with alcohol & dry)

Alan

checkmate1996

Alan,

I will give that a try as well. THANKS!

I still would like to hear from toofast or others on who it seemed to work without much effort.

jon928se

Just a thought and I may be completely off beam here, - it's early am here in OZ so I'm not firing on all cylinders yet.

Isn't the excitation voltage for the stock alternator fed through a resistor thus providing a lower reference voltage at the alternator ?

If the Delco alternator is set up to need +12v to the excitation circuit - ie more than the stock alt, it wouldn't produce enough volts at idle but would do at higher rpms as it self excited ?

Landseer

Brad,
I'm getting 13.5 or a hair more at idle, but not 14.
Am seeing steady 12.5 or so with accessories, but am not running as many as you.
Turn signals cause needle to blip.

I think you've made the switch successfully. If the relay clicking has stopped, then why don't you drive it a while.

Mine is sustaining the car very well, though I'm not running much in the way of electrical loads.

Remember, too, Alan has cautioned to observe closely during hot weather for any changes in performance. On the other hand, the V8 camaro used these as well, up fairly high, and that engine was absolutely packed into that hood compartment.

Curious to hear from others.

Landseer

Delco excites with the tickler voltage that the 928 delivers, even the early ones.

toofast928

Chris where did you pick up that alternator? Sounds like something is wrong with the unit.

Landseer

How exactly should it work?

toofast928

Are you using the Painless wire connector?

The Delco connections are:
Large battery wire to Batt terminal.
Red wire of Painless wire adapter to batt terminal.
White wire of Painless adapter to be spliced into Porsche harness, Green wire

At idle speed should get 12.5v. Off idle 14.3V (new batt installed). Thats it, you may need to adjust the pot in back of the dash pod for more accurate voltage gauge reading but its that simple.
Tony

checkmate1996

First, I appreciate all the replies. OK. Here's the latest update:

I took Alan's advice and cleaned the pulley with some brake kleen. Then I tightened the alternator belt as much as I probably could. I probably have 1/32nd inch clearance between the PS pump and alternator.

Now, with all accessories on, dash lights (speedhut gauges), clocks, dual electric cooling fans, defrost on, I was maintaining 12.8-12.85v at 800RPM Idle. This gets me above Alan's recommended 12.7v, which is good.

I then took her out for about a 45minuted spin and held 13.5V constant.

I also noticed that my POD gauge is approximatly .5V off from my digital measurement from the battery vs what is being displayed on that dash. So it helps to know that as well.

So, all-in-all, I think I'm OK and definatly better than where I was with the BOSCH alternator. My results sound consistent too with Landseer.

So...the alternator was 49.95 plus the GM universal pigtail was $8. The vendor threw int he 5mm worth of spacers for free. Shipping was $14 from the ebay vendor, so for $72 out the door, I am pleased....atleast so far!!

Any other thoughts?

Alan

Brad - It sounds good...

For those of you with 12.5v at idle... not so good - your battery is (at least partly) running the car. You are not charging at idle but you are presumably generating some power - just not enough to keep up...

Given Brad's results you may need to tighten your belts...

It seems a bit counter intuitive but the most likely time for a belt to slip is at idle... the electrical loads on the car don't go down much at low rpm and thus the alternator has to extract more power from every engine cycle. Its loading to the belt will also tend to vary more due to its 3 phase (120 degree) generation and less inertial damping by the rotor at low rpm's - this makes partial slip initiation more likely (think of it like belt hopping or jittering).

Ergo - tighten the belt & if it increases idle voltage with a given load - that was your issue.

Alan

checkmate1996

Thanks again Alan.

I will be writing a my own 'documentary' with pics here shortly.

Imo000

Alan, it’s not belt slippage, at least I don’t; think. His voltage went up slightly but so did the idling speed.