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Message |
Mike Lester (Tin_woodman)
Registered Member
Username: Tin_woodman
Post Number: 9
Registered: 1-2009
Posted From: 72.213.22.46
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 16, 2009 - 12:29 pm: | |
Hi all,
I just replaced my failed 4dx batteries and while my MC7 now starts strongly I am getting a flashing light on the instrument panel that says "not gen." If I kick down the high idle it will go away, but comes back at higher rpm. What does this mean and what do I need to do?
Thanks!
Mike Lester |
larry currier (Larryc)
Registered Member
Username: Larryc
Post Number: 214
Registered: 2-2007
Posted From: 205.188.116.203
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 16, 2009 - 12:53 pm: | |
Well Mike I think the alternator is not making any power to charge the batterys. You need to get the volt meter out and check at the batterys for something around 12.5 volts engine off and 13.5 volts engine running.
I am not familiar with your charging system so if everything is tight around both the alternator and the regulator, someone who knows for sure can tell you if shorting the field on the regulator is an OK test for eleminating the alternator as the culprit or not. If that does not increase the alternator output, the alternator is suspect. If it does then the regulator is suspect.
Since you last worked on the batterys, make sure that everything is properly back togather in that area first. Could you have left off a small wire that routes to the regulator?
Again, I'm not familiar with your coach, but it should be OK to run a test wire from the + battery terminal to the Battery terminal on the regulator. If either of those tests brings the reading up then its likely not a real expensive fix. |
George M. Todd (George_mc6)
Registered Member
Username: George_mc6
Post Number: 825
Registered: 8-2006
Posted From: 64.55.111.6
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 16, 2009 - 1:09 pm: | |
Quickly,
MCIs are 24V from the factory.
The regulator side of the field is energized by the reg, the other end is grounded. I'm really against "Shorting the field on the regulator."
Proper alt output should be about 28V, high idle with charged house and chassis batts. 28V should also be present at the BATT term of the reg with the system running and charging. If NO 24V at the batt term of the reg with master on, loose/broken wire from front master switch.
NO wires from batt to reg...
If the trouble is a loose output cable on the alternator, or a loose battery terminal, energizing the field will make a good alt put out about 40 Volts, which WILL burn out a whole bunch of stuff, and/or flash over inside the alternator!
HTH,
George |
larry currier (Larryc)
Registered Member
Username: Larryc
Post Number: 217
Registered: 2-2007
Posted From: 205.188.116.203
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 16, 2009 - 5:46 pm: | |
George,
I know your an electrician and want to learn from you. I have never had an automotive alternator run away with voltage like you describe they will do if grounding the field. I thought they would need more windings or something to produce more voltage.
Can I just use a 12 volt alternator and put a 24 volt regulator on for more volts?
If you have a loose cable, what stops the regulator from energizing and asking for max voltage available if the batterys are low, thereby burning out a whole bunch of stuff anyway?
I have not heard of the flash over inside the alternator, hows that work?
How many volts does the MCI key switch send to the regulator and what component am I going to kill if I just jumper wire 24 to the bat terminal of the regulator for a quick test? If stuck, could I run home with a jumper or will that kill something?
How should we properly isolate the alternator from the regulator and decide where the problem lies? If you have time, thanks for answering. |
George M. Todd (George_mc6)
Registered Member
Username: George_mc6
Post Number: 826
Registered: 8-2006
Posted From: 64.55.111.6
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, May 16, 2009 - 11:50 pm: | |
Larry,
Several questions here, and I will try to answer all of them as best I can.
1st paragraph, regarding voltage: Any alternator is capable of producing a lot more than its rated voltage, and with an OPEN OUTPUT CIRCUIT, a 12V alternator can probably produce 25-30 Volts. We never see this, because when a regulator shorts closed and produces full field current, the high voltage (and current) produced is "absorbed" by the batteries. They won't take that kind of abuse for long, and bulbs fail, etc.
2nd question. Definite maybe, but a 100 Amp 12V alt won't produce any where near 100 Amps at 24V.
3rd Q. YOU'RE RIGHT!!! (Depends on where the open circuit is.) If the open is in the output cable between the alt and the battery cable connection, (the nut on the stud is loose) and the alt is getting full field, which it will as the reg only sees battery voltage, and is asking for charging voltage, the output has to go somewhere, which is the weakest point. This will either be the diodes, or the lacquer insulation on the windings, which is pretty thin.
Q 4. The key switch sends battery voltage to the regulator. The regulator uses its battery and ground terminals to determine what the system voltage actually is, and sends CAREFULLY CONTROLLED CURRENT from the battery terminal to the alt. field terminal to regulate the alternator at the charging voltage, about 28V on a 24V bus.
2nd sentence of Q4, test? You could energize the field for a half second, with the engine idling, without damage, but why? What is it going to tell you? There are other better ways to find the problem besides a sledgehammer.
2nd sentence of Q4, second part: "Run home with a jumper..."
NO, NOT ONLY NO, BUT HECK NO!
Jumping out the reg by connecting the field & batt terms will put the alt into full output, period!
200-300 Amps, at at least 18 Volts per 12 Volt battery WILL fry lots of things, bulbs, batteries, etc.
Q5.
The answer is a test light with a bulb to match the bus voltage, or better yet, some type of multi-meter.
Turn the master on, there must be battery voltage between the batt and ground terms of the reg. (Or the test light must light.) There must also be voltage between the field terminal and ground, both at the reg and the alt, (Test light lit again.) Voltage must also be present to ground at the output cable and stud. (Light lit.)
Start the engine. Voltage should rise to 14/28, and field voltage should go WAY down.
No voltage on reg batt term=broken/loose wire, blown fuse etc, between master and rear.
Voltage on reg batt term, none on field term=bad reg.
Voltage on reg field term, none on alt field term=broken wire.
Voltage on alt field term, same voltage on alt output stud=bad alt.
No voltage on output stud with dead eng=broken output cable, or bad batt switch.
This applies to alternators with one field terminal. (The other end of the field winding is grounded internally.) Alternators with two field terminals have battery power applied to one terminal, and their regulators control them by varying the ground resistance on the other terminal. Grounding the term connected to the reg will indeed make the alt produce full output, if it has batt on the other. Grounding the other wire will blow a fuse!
Grounding the field wire on a one wire alt will damage the reg.
HTH,
George |
Mike Lester (Tin_woodman)
Registered Member
Username: Tin_woodman
Post Number: 11
Registered: 1-2009
Posted From: 72.213.22.46
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 17, 2009 - 9:12 am: | |
Thanks all...I will try to get back over to the bus today with my meter and see what I can find out.
Mike |
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