Alternator not showing charge

mlh1936 · August 23, 2008, 07:50:39 AM

My 102A-3 has a 12V belt driven alternator on it. It does not appear to be charging. When the engine is running the volt meter shows less than 12V. I'm pretty ignorant about this electrical magic. What is a simple way to determine what the problem is?
Thanks.

Nick Badame Refrig/ACC · August 23, 2008, 07:55:18 AM

Hi mlh,

First, determine weather or not it has an external regulator. This will help you figure out where to start.

If you have a dc volt meter, you can test it yourself.

if external, this might be the problem. If internal, then the alt. needs to come out and

possibly repaired at a shop. The regulators usually go bad before the brushes do.

Good Luck
Nick-

Busted Knuckle · August 23, 2008, 07:55:46 AM

Quote from: mlh1936 on August 23, 2008, 07:50:39 AM
My 102A-3 has a 12V belt driven alternator on it. It does not appear to be charging. When the engine is running the volt meter shows less than 12V. I'm pretty ignorant about this electrical magic. What is a simple way to determine what the problem is?
Thanks.

Take it to someone who knows electronics!

Busted Knuckle · August 23, 2008, 09:54:43 AM

Seriously, sorry Mal I jest couldn't stop myself! You asked "What is a simple way to determine what the problem is?"

And I answered! Now the truth is Nick beat me to it with the follow up I was gonna add, and he posted it while I was ~~being~~ 'er trying too be funny!

Now we need more info on the alt. in question. Since it's not original (OEM) then none of us really knows exactly what ya got!
My bet is that is a GM style "one wire set up". Now hold on that description is misleading! They all have more than one wire! But with this set up it is internaly regulated and you basicaly have jest one big wire coming from it and going to the baterry. It also will have a small plug with one or two wires in it. These wires are what "excites the field" when it is supposed to be on. Other wise it'd be on all the time and drawing the battery down when the engine is off! I am not an electronics professor so I may not be the most accurate in my descriptions. But what I have descibed is how we do our derby car alts, and they seem to work! To the best of my knowledge if it's not internally regulated it'll have multiple wires coming out of it and going back itno it! and a regulator mounted somewhere with wire going in and out of it! FWIW

BK

Now that I got ya both steamed and confused maybe some of our electro gurus will step in and unmuddy the waters! LOL!!

BK

NJT 5573 · August 23, 2008, 10:07:52 PM

Put a charger on your batteries and keep them up until you solve the charging problem.

JohnEd · August 23, 2008, 11:10:20 PM

OK cowboy....reach in there and give that belt a serious tug. Ah Ha! Just as I thought....tighten the belt. Still doesn't charge....pull the alt and have a shop test it for free.

I saw this exact same problem and the alt pulley had cracked/split in half and fallen away. The belt was laying down in the front of the engine. They had the voltmeter out and was setting the scale when a bystander said "ah, Guys?". Don't ask which position I played on that team.

Do you have the 12 volt condition "at" the alternator +terminal? Even if you have an external regulator I would have the alt checked as they can't check a regulator. You can though by shorting the field to B+ for ever so short a time by striking a spark on the field terminal. If the alt is good you should see the voltage shoot up to 20 volts or so and that means the regulator is bad. Solid state regs are usually cheap.

nufsaid,

John

mlh1936 · August 25, 2008, 09:30:07 AM

Thanks to all who responded. I tightened the belts, but still no charge. The alternator had a placard on it saying "Replacement for Leese Neville 47,000 14V" It had an internal VR. So this morning I dropped it off at the alternator repair shop. Took BK's advice and took it to someone who knew what to do with it.