alternator problem

[garos]

Just had alternator rebuilt. It`s a Parris-Rhone on a 1990 Sunrunner. Now can`t shut engine off with ign. switch. Never had this problem before. I know the alternator is getting feedback but how? I placed the connected wires back on the same way they came off. Two wires to the alternator output. One red & a small brown wire that splits off to a purple wire with resistors in it which seems to come from the ignition or volt meter with 10 volts on it with key on.The red goes to a battery isolator. A purple goes to the exciter terminal. Black to the ground terminal. Have taken alternator back to the shop twice. Nothing is wrong with it. Help.

 

[wire2]

Re: alternator problem

Is the isolator ok? Check with an Ohmeter, it should conduct from alt to batt, but not the other way.

 

[garos]

Re: alternator problem

Thanks wire2. I`m getting about 11 v. on the alternator terminal from battery isolator with engine off. Should not be any reading there?

 

[wire2]

Re: alternator problem

12 v on the red wire is normal. It's only voltage present, current can't flow backwards through the 6 diodes in the alternator.
Can you undo all the wires from the isolator and test with an Ohmmeter? You should get infinity (open) one way and almost short (2-20 Ohms) with the leads reversed. Make sure the battery is disconnected from it.

 

[garos]

Re: alternator problem

Thanks wire2. Tried that and found isolator seems to be o.k. Any other solutions? If I remove the brown wire from the output terminal it will shut off but if it is not connected while running volt meter on panel won`t show a charge and warning light flickers.

 

[CharlieB]

Re: alternator problem

Any possibility of getting a picture of that?

 

[bruceb58]

Re: alternator problem

12 v on the red wire is normal. It's only voltage present, current can't flow backwards through the 6 diodes in the alternator.
Can you undo all the wires from the isolator and test with an Ohmmeter? You should get infinity (open) one way and almost short (2-20 Ohms) with the leads reversed. Make sure the battery is disconnected from it.

You usually can't test a diode with the ohms scale on a meter since the voltage used for measuring ohms isn't high enough to turn on the diode. Your meter should have a diode tester that will measure the forward voltage through the diodes.

My guess is that one of the diodes is blown. You alternator would still possibly test out ok depending on how knowledgeable the guy who is testing it is.

Try measuring your alternator output with you meter measuring AC. By measuring AC, you will be measuring the voltage ripple. A bad diode will add a large amount of ripple. if you measure more than 500mV, you probably have a bad diode.

 

[bruceb58]

Re: alternator problem

Is the isolator ok? Check with an Ohmeter, it should conduct from alt to batt, but not the other way.

You do mean rectifier right?

edit: i see you are talking about the isolator. The isolator can not cause this problem. if the isolator was dead open, you would probably blow the alternator. If it was dead short, then worst case are all the batteries are connected together.

 

[bruceb58]

Re: alternator problem

garos,

I re-read your first post. Are you absolutely sure the brown wire was originally on the alternator output?

 

[garos]

Re: alternator problem

Yes. I left the connectors on the alternator when I had it rebuilt & the spade connector fits over the large terminal. Is there a possibility there is a diode in the circuit after it leaves the volt meter? As I said the brown wire seems to be going to the volt meter.

 

[wire2]

Re: alternator problem

Garos, I think I know where BruceB is going with this, the output of an alternator is usually a larger red wire, not brown. And typically there's a smaller pair of wires to supply the field, purple and orange on my OMC. Can you lay your hands on a wiring diagram?

BruceB, you're correct, a high impedance input meter won't show a diode forward, I was going by the fact that most do-it-yourselfers have an older style VOM, which uses a C or D cell in the Ohms settings.

 

[bruceb58]

Re: alternator problem

I have a feeling that brown wire is your problem and I bet it goes places other than the voltmeter. Normally, you wouldn't have a diode in the wire feeding the voltmeter because it will be dropping your voltage by 0.7V so you will not be reading the actual voltage. Also, the dash voltmeter typically just connects to the wiring near the dash that gets it's feed from the battery(fusible link) or circuit breaker fed from the battery.

With your ignition in the off position and the brown wire removed from the alternator, measure the voltage on the brown wire and the coil. Then check it with the ignition in the on position.

 

[Don S]

Re: alternator problem

Is this a Volvo engine? If so, what model??

 

[Don S]

Re: alternator problem

Thanks wire2. I`m getting about 11 v. on the alternator terminal from battery isolator with engine off. Should not be any reading there?

If you have the main power wiring coming from the alternator and going directly to the isolator, when the engine is off, you shouldn't have any voltage showing at the alternator.

 

[wire2]

Re: alternator problem

If you have the main power wiring coming from the alternator and going directly to the isolator, when the engine is off, you shouldn't have any voltage showing at the alternator.

You're right, Don, I essentially alluded to that in my first post on this thread, but then promptly forgot about the isolator in my subsequent posts. D'oh!
12 v present on the alternator output going to an isolator means the isolator diode is shorted, or there's another (wrong) 12v connection to it from somewhere.
Garos; can you undo the wire from alt to isolator and see if you still have 12v on the isolator stud? There should be no other wires on it.

 

[bruceb58]

Re: alternator problem

Not sure why everyone is so stuck on the isolator being bad. On boats without the isolator, the alternator output goes straight to the battery so you will always have 12V on the output of the alternator.

 

[garos]

Re: alternator problem

This is a chev. engine with volvo outdrive. There is only voltage present on brown wire with ign. on. Voltage at alternator output, which goes to bat. isolator, with brown wire removed is 10 volts with ign. off. Connecting brown wire voltage drops to zero with ign. off. Don`t understand that by just reinstalling alternator would cause the problem of not able to shut down. Haven`t had chance to see if voltage is present on bat. terminal of isolator with alt. wire disconnected.

 

[Don S]

Re: alternator problem

Let me pry a little harder for some information.
1. What YEAR is your engine
2. What MODEL NUMBER is your engine
3. Chevy 4 cyl, 6 cyl, and 8 cyl, have been used for years so your statement " This is a chev. engine with volvo outdrive" doesn't mean much

 

[garos]

Re: alternator problem

DonS, This is a 1990 454 v8 chev. engine. Think it is a 740 volvo outdrive.