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Posted by: ChrisReale Nov 16 2006, 04:42 PM

Is there an easy multi-meter test you can do to see if the alternator has crapped out? I guess the fact that my battery doesn't charge is proof enough, but I just wanna make sure.

Posted by: So.Cal.914 Nov 16 2006, 04:52 PM

When your car is running put the probes on the pos(+) and neg(-) side of

the battery it should read about 13.5 volts.

Posted by: Rand Nov 16 2006, 04:58 PM

Also check your voltage regulator before replacing the alternator.

Posted by: vsg914 Nov 16 2006, 05:15 PM

I assume you checked the belt first?

Posted by: Scott-thundercat Nov 16 2006, 05:44 PM

check the battery voltage before it's started and after- usually goes up by at least 1 volt (otherwise the battery wont charge).... or take it to kragen or autozone and they will test it on the car really easy.

Posted by: McMark Nov 16 2006, 05:59 PM

As mentioned, the voltage regulator can be bad as well. Also, make sure the warning light bulb in your dash is operational (should light when the key is turned on). Without the bulb, the alternator won't energize.

Glad to see you're making progress on this. PM me if you need anything.

Posted by: smooth_eddy Nov 16 2006, 07:41 PM

This was my problem. I think it should flex about a half inch in the middle of the belt. Eddy

Posted by: Brew Nov 16 2006, 07:47 PM

Mark, I'm not doubting you in any way, but...Huh? Really? If the bulb burns out, the alternator wont work?? Is this a common occurence? Should I be carrying a spare bulb? Sorry, this design just seems waaaay stupid, and I woulda never thought to check the bulb if my battery wasn't charging.

Posted by: type47 Nov 16 2006, 08:46 PM

i think he means:
alternator will work, just the "juice" (which goes to the battery thru the circuit in which the alt light is located) won't get to the battery if the circuit is open due to a burned out filament in the bulb.

Posted by: McMark Nov 16 2006, 10:08 PM

Nope, if the bulb is burned out the alternator will not excite and will not charge.

Jim, that's wrong. If the bulb is burned out the alternator will do NOTHING. The electricity created by the alternator does not run through the bulb. Once the alternator is excited, you can take the bulb out and it will keep on charging. But the alternator needs that little kick start to start making power. There's a ton of articles about alternators on the web if you want a clearer understanding.

Posted by: SGB Nov 16 2006, 10:25 PM

Absolutely true. As McMark says, But it RARElY burns out (I've never heard of it happening). I think it is more valuable knowledge if you messing with the instruments.

Posted by: Spoke Nov 17 2006, 09:31 AM

To check the alternator assuming that the belt is ok and everything is mechanically sound, do a test which simulates the voltage regulator applying voltage to the armature to increase alternator voltage.

Sorry, I don't have access to my schematic. (It's at home and I'm in South Korea) So my instruction will lack the actual wire designation. I did this test to separate voltage regulator issues from alternator issues. My low voltage issue was the voltage regulator.

Look at the schematic for the voltage regulator (VR). The top most connection from the alternator provides power to the VR and senses alternator voltage. The center lead in the schematic is the armature positive lead and inside the VR, this lead is connected to what looks like the contacts of a relay. The VR connects this lead to the alternator voltage to increase the voltage and opens the lead if the voltage is sufficient.

If you connect the armature positive lead to the top most connection from the alternator, you will simulate the VR trying to increase alternator voltage. Connect the leads together first then start the engine. If the alternator is ok, the battery voltage should rise to about 15-16 volts. If it doesn't, you either have done this test incorrectly or your alternator is bad.

If you are unsure about the VR connections, do not do this test.

Spoke

Posted by: cary Jan 8 2015, 11:45 PM

Revive an old thread ..............
Just trailered the car home. Electrics went dead.

Saw the volt meter dropping. Decided to pull over and have enough charge to drive it on the trailer. I was concerned earlier when I only had 12.25 volts at the battery with the car running. Wrote it off to the battery being charged with the tender. Guess not ............

I didn't notice the alternator light didn't come on when the key was on. Not Good. Went out and swapped the green to red bulbs. Bulb fired up in the green spot. So bulb is good. Pulled the #9 fuse, it was good.

I did do a fuse box update to a blade type fuse panel. When its light tomorrow I'll drop the fuse panel and look at the red/white wire going to #9.

Any other thoughts?

Posted by: Michael N Jan 9 2015, 12:11 AM

checked my voltage regulator and found that it just wasn't seated all the way. Sure saved me a bunch of time and effort. Hope you have similar luck.

Posted by: cary Jan 9 2015, 12:15 AM

Did that cause the alternator light not to fire up?

Posted by: Dave_Darling Jan 9 2015, 11:18 AM

Yes, when the VR is not plugged in, the alternator light won't light.

--DD

Posted by: type47 Jan 9 2015, 11:44 AM

I'd like to listen to a discussion on how the VR works. Here is a link to the PP elec diagram containing VR and Battery:

http://www.pelicanparts.com/914/parts/Electrical/914_electric_74E.jpg

Posted by: cary Jan 9 2015, 12:30 PM

That's were I'll start tonight when I
get home. I took it off to put on the relay cover.


On a positive note the car ran like a
dream until battery went below
10 volts.
Took it to the PDX Pelican group monthly
Burgers & Beer last night.

Posted by: Dave_Darling Jan 9 2015, 02:35 PM

It compares the battery voltage to the alternator voltage. When the alt voltage is higher than the battery voltage, it disconnects the field windings of the alternator, making it no longer charge. When the alt voltage is lower than the battery voltage, it connects the field windings of the alt, making it charge. It effectively turns the alternator on and off, over and over again, pretty quickly.

That is a simplified version, at least. There are more details, and I think those start taking into account how quickly the electric fields in the windings build up and decay, and how the compared voltages are actually biased so you charge at ~14V rather than ~12V, but the description is a half-decent overview.

I believe the alt light runs off of the alternator voltage wire that goes to the VR. I'm not sure exactly when the power for the light has to go through the VR, but it probably has something to do with the way the light is used to "bootstrap" the alternator to get it to start charging.

--DD

Posted by: cary Jan 9 2015, 09:13 PM

Back in business.

The new Beru VR positions further forward on the relay board. So it wasn't even plugged in the right sockets. Maybe only one leg was plugged in.

One must remember that the alternator light has to come on when the key is switched on. This shows the VR is in the circuit.

Fired her up and we had a 13.7 volt reading on the battery. That's more like it.

Posted by: rhodyguy Jan 10 2015, 10:35 AM

Happy motoring!

Posted by: mikesmith Jan 10 2015, 12:54 PM

There are two rectifiers inside the alternator. One supplies what we think of as the "output" current, the other one is used to supply current for the field coil.

The alternator "works" by moving the field coil and its magnetic field around relative to the stator coils. You have to have current flowing in the field coil for it to create a field, and that current has to come from somewhere.

When the alternator is running, the second rectifier supplies the current. But to begin with, there is no current, and that's where the charge lamp comes in. One end of the lamp is connected to ignition power, the other end is connected to the output of the field coil supply rectifier.

To the earlier points about the charge lamp burning out; in some designs there is a resistor in parallel with the lamp so that current can flow even if the lamp fails.

This connection is also why some vehicles need a diode in series with the charge lamp; if your ignition current draw is low you can actually back-power the ignition circuit from the field coil rectifier.

Much more detail here:

http://brianesser.com/technical-information/alternator-wiring-diagrams-and-information/

Posted by: jdlmodelt Jan 3 2020, 04:14 PM

Okay, alternator wasn't charging. I put 12.5Vdc on D+ and DF. I had already verified good grounding of the engine, alternator, and chassis. With both D+ and DF excited, no charge from the alternator, it just matched the battery voltage. With everything connected correctly and no jumpers, the gen light on the dash is on all the time. from D+ to ground I get 5.5 volts, and from DF to ground I get 5.5 volts. from D+ to DF I get zero volts. All said and done. I bench tested a spare alternator with the same methods and it charged great. I replaced the alternator and all is well. So, just some more trouble shooting data for others to use. Voltage Regulator is fine.