Delcotron 12SI problem

[Oldsmoletick]

Olsdmoletick, is your alt factory or an upgrade you swapped in and do you have gauges or idiot lights?

Factory type with idiot lights, when I first start it, the GEN light is illuminated, noticed blower speed was down, dim lights, but as soon as I rev the engine to a certain rpm, (no tach) the light goes out, the blower takes off full speed, lights get bright, lol, just like yours, the light doesn't come back on until a restart. I have yet to investigate it, call it laziness or ignorance, the car hasn't failed, so I haven't payed it any mind. 😳

 

[Bonnewagon]

Papastoy83 I will have to peek up under the dash, it's pretty much stock. Oldsmoletick I am lazy too since after it revs, all is well.

 

[Longroof79]

Somewhere I've read that a slight delay or lag in charging is not uncommon. Even when I put a meter on my CS alt. at first it's only around 12 volts or so until after a few seconds it will kick up to 14.5 volts.

 

[Bonnewagon]

OK, but if I never hit 2500 rpm, it never turns on. That's not right. I think I'll wait for a day above freezing and swap alts, that way I will know for sure what's up. Yes Jack, it's Winter here! :evil:

 

[olds307 and 403]

Make sure the terminal where the power wire goes on isn't loose in the case. I bought an aftermarket 100+ amp alternator, acted like yours. Just never charged like it should. I could see arching on the rectifier when I pulled it apart to tighten it. Tightened that battery terminal and has charged really well since.

 

[papastoy83]

Did some more checking on this mysterious choke heater relay. Found the p/n in my factory parts manual:
GM - 14089568
AC Delco - D1780
NAPA AR740

Just in case the relay is missing/bad/etc. For future reference.

 

[Bonnewagon]

OK, I had to update this topic. I had the time to swap in a known good alternator, same type, and I even changed in new brushes and polished the commutator rings. SAME THING!!! It is dead until I hit 2500 rpm. Now, thinking back I believe this all began when I swapped out the regular GP gauges and put in the '78 silver faced ones. The regular voltage gauge also had a red alt telltale light, the '78 does not. The book says there is an amount of resistance built in to the gauge, or idiot light, or choke heater. Could this be the problem? I'm at a loss.

 

[Longroof79]

Mark,
I think you're on to something there. You might have to add a resistor on the brown wire to enable the alt. to energize. You could perform a test by running a 16 ga temporary wire from a switched +12 volt terminal on your fuse box. Add a resistor inline, and connect it to the L terminal on your alternator in place of the existing brown wire.
I actually had to do that to mine after I added the CS130 alternator. The brown wire developed an open for some strange reason. It had a generator warning light on the gauge that stopped working.
I'll have to go out into the garage to see what ohm resistor I used. However, Painless uses an 85 ohm 5 watt resistor.

 

[Bonnewagon]

Jack, I know there needs to be some resistance in that wire. In fact the factory manual says the slight resistance in the field circuit, or brown wire, is to protect the rectifier diodes. That is why there is at a minimum an idiot light bulb. So I don't know if there should be a lot, or a little resistance. Maybe I have too much, and that is causing the no-charge-until-2500rpm-problem? Maybe my gauge has too much resistance? I am no electrical genius, I know a little, but I don't get this at all. What I do know, is I am loath to open the dash and swap the voltage gauge just to test if the gauge is at fault.

 

[Bonnewagon]

I found this, but it doesn't explain why it happens now and not before. Very interesting. Taken from Joe Guilbeau's Alternator Theory Page.
"It is the regulator’s job to control all of this diode rectifying and modulation of the field strength, in modern day alternators. Some regulators are designed so that the field strength is such that it will not produce an output in the stator windings until a minimal threshold level is overcome.

That is why some vehicles need to have the engines revved, so the alternator “kicks in”. At idle, little or no alternator output is evident. Often, complaints are voiced that do not take the engineering design parameters of alternator design into consideration…”…my brand new 10-Zillion Watt Stereo sounds like crap at idle…” Then I found this- which is relevant since I am using a '78 voltmeter without an indicator lamp. "The lamp circuit cannot supply enough current to the field windings to sustain or generate the magnetic field in order to induce a voltage output on the Stator windings. So, in many applications the vehicles engine must be revved to a higher RPM in order to generate enough initial field strength so that the induced EMF is sufficient to self maintain it. " I think I need to consult my '78 Pontiac manual to see where the wiring differs from '83.