| Re: Alternator/Isolator/Battery Problems/Questions [message #247658 is a reply to message #247648] |
Wed, 16 April 2014 20:15   |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma:
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Senior Member |
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| Matt Colie wrote on Wed, 16 April 2014 19:09 |
| gbarrow wrote on Wed, 16 April 2014 18:21 |
Ken,
I took the readings per your instructions. At step 1 the alt was putting out over 16 volts.
I removed the alt took it to Auto Zone it failed the test on their machine. They replaced the alternator under the warranty.
New alternator also puts out 16 volts. The GOOD bulb in the alternator indicator does not light when key is turned on before starting.
Voltage at the alt wire connecting to the gauge cluster in the dash is 0 with key off 12+ with key on 14+ with engine running. So I assume the bulb not lighting is a problem with gauge cluster circuit board or contact points on light slot on the board.
Isolator readings are as anticipated from your flow chart except that the alt wire when disconnected from isolator with engine not running still reads 12+ volts.
Isolator is new- alternator is rebuilt-
How does one verify that the sense wire is functioning? How does the light failure affect the sense wire system?
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Do you mean that the heavy lead from the alternator shows ~12V when disconnected from the center terminal of the isolator with the engine off???
That just cannot happen with a good alternator.
Matt
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OK, Matt is entirely correct.
I would consider these indications two different problems. The light bulb is in the exciter circuit or start circuit for the alternator. You would like it to work correctly but it should not be part of the current over voltage problem since the alternator is starting OK.
You said you read the sense line going to the alternator and it reads about 14 volts. This a correct reading. So the question is why are you seeing over 16 volts at the center terminal of the isolator and only 14 at the sense line. These readings mean you have over a 2 volt drop (difference) between those two points. There is a .7 drop going through the isolator. That leaves an additional 1.3 or more drop unaccounted for.
First why is there +12 on the alternator lead when the lead is disconnected from the isolator? As Matt said, that needs to be found and fixed.
Second I would look at the fusible link. They are notorious for developing a resistance. The fusible link is a 6" piece of 16 gage wire between the horn relay and the big terminal labeled "Vehicle positive" (or something like that) mounted on the aluminum plate that the isolator and boost solenoid / relay are mounted on. Physically inspect this wire. Tug on it and see if it falls apart.
Third - I would get out a volt meter and meter the voltage on the engine side isolator output. I would expect it to be .7 lower that the input or about 15.3. While you are there check the House side of the isolator also. It should read about the same as the engine side. Then work forward in the circuit towards the sense line. First checking the voltage at the other side of the fusible link. If it is OK, continue checking the various wiring components working toward the sense line. You need to find that additional 1.3 voltage drop.
I am assuming that you have the engine side wiring diagram for the coach. If you do not, send me your email address and year of the coach and I'll email you one. Keep in mind that these are old coaches and many times these problems and oxidized terminal connections, oxidized fuses, and worn or oxidized switch contacts. Suspect everything in the circuit as you trace it down.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Thu, 17 April 2014 06:24] Report message to a moderator |
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