Alternator Light

I am finishing the wiring and I followed the instructions found here, I believe. The wire from the alternator that goes through the pilot light is supposed to be able to conduct to let the light on while not charging but to turn off once electricity is being produced and no longer a potential difference is sensed. Right? Well, it only turns on while the ignition is on and I apply the leg coming out of the pilot light to ground, if I connect it to the alternator is off. What am I doing wrong? I placed the wire on leg 1 of the alternator. Thanks!

 

you didn't say if it was 1 wire or not
typical delco

 

I "think" I did it that way. I am done for the day, but during the week I will check to see where I screwed up. Thanks!

 

Why are we assuming this is a Delco?

Realize that only the Delco "integrated" alternators will work without a regulator. This includes the 10SI and 12SI types ("systems integrated"). Other older Delco styles require an external regulator.

Also, tripilio's description is not very clear. Terminal 1 is the "exciter" terminal that connects to the ignition switch. When the key is on and the engine is not running, the alternator is a sink of current at ground potential. The ignition is a source, current flows source to sink and the light is on. When the engine starts, the alternator self-generates and terminal 1 becomes a source of current at full alternator voltage. Two sources connected together and no current flows. The bulb turns off.

When the ignition is turned off, the bulb is enough resistance that the alternator cannot power the ignition. This is why you need the bulb or a resistance wire or a diode in this circuit, to prevent back-feeding of the ignition coil from the alternator when the ignition switch is turned off.

 

Timgr, that is what I thought. Should terminal 1 while unplugged have continuity to ground or does it have to be plugged and with the key on? On a second look at the pictures I took, I connected terminal 2 to the ignition post of the switch. Is that a problem? Should I have connected it to batt instead? I assumed that with the key on the first step it was the same.

 

I don't know what you'd measure at terminal 1 with the engine off. It will be a sink with the engine not running and the ignition switch on. That might be ground or something above ground. The alternator is not supposed to drain battery power with the engine off, so it might be floating (open) with the ignition off.

Terminal 2 needs to connect to the battery. That's the "sense" connection from the regulator to the battery. It senses any voltage drop at the battery and adjusts the alternator output to compensate. It's a feedback signal. It'll probably work connected to the ignitin switch, but it's not ideal. Jeep loops it back with a 3" piece of wire to the battery (BATT) terminal of the alternator. That will work.

 

Thanks, timgr! I will work on it.

 

I needed that diode on terminal one for mine to work correctly.

 

Great diagram! I can see you ran an extra ground to the alt from the battery post. I thought it was sufficient to be grounded through the bracket. I checked and I had continuity. I guess it would not hurt...

 

...and I will try the diode also.

 

dnb5853, which alternator do you have installed?

 

I used a 94 amp Delco 12SI. A 60 amp 10SI is perfectly adequate for most old Jeeps.
The heavy ground between the alternator and battery ensures that the alternator can produce at peak capacity.
I have a winch so I wanted to have the extra capacity when I needed it.
I pulled that diagram from a GM hotrod site. The ideal arrangement has all FOUR electrical connections.
You can probably get away with no heavy ground, but try tracing a solid ground path from your alternator to your battery; remember the engine mounts are usually not conductive.

 

I have them instaled properly as per above diagrams. Today I removed the wire that goes to the battery and my bulb lighted up veeeery dim while moving my ignition switch to on. As soon as I connected the 2 wire back no more light on the bulb. Why?

 

Is your diode at least 3 watt? I think that’s the requirement.
Is your alternator and it’s internal components good? FLAPS will check for free.
Wire gauge is critical also.

 

Good Info, Thanks for Posting.

 

Mine is 3W. I have a 1N4005 diode. My next step is to take it out and take it to the FLAPS. I will try a better battery first, the one I am using is on its way out. That might also be a factor in my alternator not functioning properly.

 

The 1N400x series of diodes have different voltage ratings but all have the same forward current rating. For example, a 1N4001 has a maximum voltage of 50, while a 1N4007 has a maximum voltage of 1000. The whole series is rated at 1 amp. https://www.diodes.com/assets/Datasheets/ds28002.pdf

This is a part with axial leads, a wire at each end. New design is all SMD (surface mount device) which is probably why the above sheet does not recommend for new designs.

Unless you are working at high voltage, the only advantage to a 1N4001 over a 1N4007 is the price, which could be lower by a few cents. This matters when you are designing a product where a lot will be built.

This is a generic silicon diode, and silicon has a barrier potential of 0.6V. Thus the power dissipation at max current is 0.6 * 1.0 = 0.6 watts.

1 amp could be under-specified for this purpose. I'd pick something like 5 amps, which is not very much at these voltages. Plenty of places to get these -
https://www.amazon.com/BOJACK-Schot...ywords=rectifier+diode&qid=1633439180&sr=8-19
Rectifier Diodes | All Electronics Corp.

Search for rectifier diode and pick one at say 5A or better and 30V or better. Schottky or not, no matter. This is a low-spec application.

You don't really need the diode in the diagram above if you have points ignition. The bulb is enough to starve the coil when you turn off the ignition switch. Should not make any difference, with or without the diode.

I'd also caution that these in-line packages are meant for circuit board mounting, not in the middle of a wiring harness. The leads should be solid copper, and they will fatigue and break with continued minute bending. I'd be sure to mount them where they do not move at all - no tiny movements allowed. I'd use a clamp to the firewall or whatever that holds the harness rigidly where the diode is. A Jeep moves a lot, and abruptly. No movement!

If this circuit did not work like you expect, I would test it by measuring function. I would replace the wire from the ignition switch with a single wire and a switch, either a connection I could take apart (clip leads or whatever) or something like a toggle switch. You need the switch so you can shut off the engine when you turn the ignition switch off.

Your battery should measure around 12.6 volts with the engine off. This is the battery electrochemical potential. First start the Jeep with the wire connected. Measure that the battery voltage immediately rises to something like 13.5 or 14 volts. This is the normal charging voltage. First functional state verified.

Next turn off the ignition and verify that the engine stops when you open the excite wire with your toggle switch. Second functional state verified.

Now leave the switch off, and start the engine. The alternator should not self-excite if you do not rev the engine, and the battery should stay at the same voltage. Final functional state verified.

Now if you bulb/diode setup does not work like you expect, it's something wrong with your setup.

 

Like I said, I believe the battery is causing me trouble. I will try a good one as soon as I can and I will report back. Howard, I cannot assume anything about a component that I have not replaced/repaired since the PO was not keeping the jeep up to any standard whatsoever. If a good battery does not fix the issue, I will get the alternator out to be tested at the auto parts store. Then I will do the timgr tests. Something is gotta give!

 

Veredict: bad alternator. Found one similar at O'Reilly's for under 50 bucks and it is all good. It needs to be reved up a bit to get to start changing, but after that charges with no problem. Thank you all for the help!