j.kenzie@sbcglobal.net

Well I don't have it yet, but I want to prepare for its hookup. I took my old Bosch alternator out. It has two terminals: D+, the exciter wire and B+, the output wire, which on my model connects to two cables, one to the jump post, and one to the starter and battery. It is grounded through the case.
The new alternator has a pigtail with two modest-sized wires, D+ and B+, which the instructions say one goes to the exciter wire and the other goes to the existing B+ cable. Then I should connect a heavy cable from the new alternator's output post to the battery (starter/battery).
My question is can I simply connect my existing B+ cable to the new output post and connect the B+ pigtail to the output post as well? It seems like equivalent circuits and the B+ cable seems heavy enough.
Essentially, my old alternator had two connections and the new one has three, but I think two will go to the same place. I am sorry if this seems complicated but I was hoping one of our experts or someone who has BTDT could point me in the right direction.
Thanks in advance.

Jack Riffle

Hi Dave. I have BTDT but I will have to check my connections for you, since it's been awhile. In addition to running another wire to the jump start terminal, you will also want to make sure you ground that new alternator. I used a 1 ought wire direct from alt. to frame. Any questions you have, call Propower who made the alt. Their tech support is amazing and they really like educating people electrically.

j.kenzie@sbcglobal.net

Thanks, Jack. I appreciate you insight.

Mitch Johnson

I just completed this and ran a wire (16 ga.) to the jump start terminal for the voltage sensor (yellow wire), I have found that the grounding through the alternator body is sufficient without any additional wiring. Only thing I can find to complain about is the performance at idle speed...but there is a noticeable increase in headlight brightness...FWIW.

Alan

Yes - connect the starter and jump post connections direct to the alternator big terminal. You can then attach the B+ pigtail to the same place. But its possible the B+ pigtail is intended to go to the battery direct as a reference voltage source - in which case normally a small guage wire can be run to the battery terminal - however on a 928 that is not anything like so easy to do... I'd contact their tech support and see how important it is to the regulation. It really should work well enough with it just connected to the big terminal anyway.

Alan

j.kenzie@sbcglobal.net

Thanks, Alan. I could not think of a reason that wouldn't work.

Mitch Johnson

I was unable to get ahold of the the source for Carl's alternator to discuss the voltage sensing connection, so I then decided that having the alternator output be dependent on the alternator output, that I would run a remote voltage sense....only a week or so but I am happy with the route I went.

Chuck Schreiber

Mitch,

Is the performance at idle "worse" than stock, or are you saying it's not that "great" until you reach higher rpms?

Jack Riffle

Hey Chuck, on my 81 I have the idle at 800RPM, so it's increased about 50 RPM from stock and I read a solid 14 V at an idle regardless of what's turned on. I have also verified that my gauge is correct and reads accurately.

j.kenzie@sbcglobal.net

Hi Mitch,
I thought of this too. I concluded that the jump post is connected directly to the B+ cable at the alternator (the B+ cable is two red cables, a large one to the starter/battery and a smaller one to the jump post). Attaching the sensor wire to a new cable to the jump post would be a round-about way of connecting it
to the alternator's output post.
I guess I'm saying your hookup is the equivalent of mine, I think.
Thanks for your advice.

Mitch Johnson

Mine reads about 13V at idle but I won't make any assertions about the accuracy of the gauge.

There is a detectable dimming of the headlights at idle though, and I run idle at about 800.

Does not concern me as I dont idle any more than I have to and the output rating really overcomes any misgiving I may have.

Chuck Schreiber

Jack,

That is impressive! When I turn on the H4s at night and hit the brakes, the 79 dips way down like to 10-12 volts and everything gets dim. The GTS seems to keep up AOK. I can have the AC and the lights at on at night and the gauge reads solid at about 13. How are your newer cars (86.5 and the 87)?

Mitch Johnson

My thinking was that the voltage drop in the wire (however insignificant it moght be) could help to exploit the higher output...really if the demand is always equal to the output then there is a cap.

Alan

It won't make a jot of difference to the performence at idle - only to the actual regulated voltage at higher rpms. It may make a difference to the regulated voltage when the battery is depleted and the alternator is charging it at elevated current. I'm sure it would only make mV of difference - much less than the typical drop you will get at idle...

I have mentioned before my concern on these high power alternators. In evaluating thier specs I found several that can output over 50% more current than the stock alt output at > 3000rpm using the same basic bosch chassis.. (or std delco) however all the ones I could find specs on actually output less than the stock bosch alternator at low (idle) rpm. To me that is a pointless & entirely useless trade-off.

I'd love to have someone prove they have an alternator that can produce 50% more current at engine idle rpms - I'd buy one. Build an alternator and test it at engine idle rpm (ratioed to the alternator rpm based on the stock crank pulley and actual alternator pulley).

I'm happy to pay top dollar for this - but I want to see proof its much better at idle... I have yet to find anyone who is willing to build it and measure it & document it to prove it out...

Alan

j.kenzie@sbcglobal.net

Hi Alan,
I'm going by the Mechman website. For the 20-2XX-43G 175 Amp model, they quote 70 amp output at 2000 alternator RPM. Measuring my crank and alt pulleys at 5.25" and 2.25" respectively, I can set my engine idle to 870 RPM and expect 70 amps output.
I have been increasing my idle in the summer anyway so this is no problem, idle is adjustable on L-jet, and I'm pretty sure my old 70 amp Bosch is putting out way less at comparable RPM. Time will tell, but I think it will be a considerable improvement.