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Old 11-21-2012, 08:40 AM   #15
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Originally Posted by clyon51 View Post
You could have a frequency problem, so I would first check that:

The output frequency of a generator is measured in Hertz, which refers to the number of alternating current (AC) cycles per second. The standard frequency for electrical service in the United States is 60 Hertz. The RPM of the engine that powers the generator is the factor that determines the frequency, and the generator owner's manual contains instructions on how to adjust the engine speed. Before you can adjust the frequency, you need a way to test it. High-end multimeters include this function, but a cheaper and easier way to measure frequency is to use a Kill-A-Watt-type household load meter.


So check to make sure the hertz is 62 with NO load. If it is higher, then you need to lower engine RPM.

Once hertz is at a proper level, check the volts....124v would be perfect. If necessary to adjust, keep the VOM attached with engine running and warm. Now adjust the POT slowly to 124v. If counter-clockwise lowered before, then start that way first.
My understanding is that the Hertz is controlled by the engine rpm and the voltage is controlled by the Regulator.


I can run an extension cord out the window to where I would sit to adjust that POT. I assume that I can use the Kill-A-Watt meter for that.


But first I have tio find a long screwdriver with a very small phillips tip to fit that tiny screw on the POT. Do you think that radio shack will have such a thing, the one I have that fits the screw is only three inch long after the handle, I will need something at least 6 inch long or longer.


Then I have the issue of securing the front cover of the control panel out and away becuase it has the 30 amp breakers, the start/stop switch and a fuse in it. Gonna be a lot of power running around with that thing open and running and me sticking a screwdriver in there

Are we talking about tiny movements of the POT or are we taling about turns of the POT like 1/2 a turn or more?
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Old 11-21-2012, 09:15 AM   #16
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I prefer to check power right at the circuit breaker. You must not have any load on it when testing. If you must run power to the coach, make sure there is no 120v or 12v items being powered, except that extension cord. Also use as heavy gauge as you can with the shortest run.

You can grab all the wires you want with the genny running, as long as the insulation is in place. You of course do not want to touch any of the metal connections. If you are concerned, get a pair of heavy rubber gloves to make adjustments.

Just make slow adjustments until you see the voltage rise or fall. Then adjust slowly until 124v is reached.
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Old 11-21-2012, 09:48 AM   #17
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I prefer to check power right at the circuit breaker. You must not have any load on it when testing. If you must run power to the coach, make sure there is no 120v or 12v items being powered, except that extension cord. Also use as heavy gauge as you can with the shortest run.

You can grab all the wires you want with the genny running, as long as the insulation is in place. You of course do not want to touch any of the metal connections. If you are concerned, get a pair of heavy rubber gloves to make adjustments.

Just make slow adjustments until you see the voltage rise or fall. Then adjust slowly until 124v is reached.
Here is my setup, did as you suggested, but first I added a gallon of gas to the tank, the genny runs great.

started the gen and watched the Kill-A-Watt, after about 2 min the gen stabilized and kicked in, I62 volts and 61 hertz, carefully stuck my screwdriver in there and started to adjust, turned it left and got it down to 156 volts and then the gen kicked off line and the meter read nothing at all, turned it back to the right and the meter came back on and showed, 165 volts tried turning it further right and it went up to 169 volts, I stopped and moved it back the other way, it was just tiny movements. and when I tried to go below 156 the gen once again went off line. When it did the motor sped up a tad. At this point I shut it down to seek further advice

Rube Goldberg has nothing on me I can jerry rig with the best of them
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Old 11-21-2012, 09:56 AM   #18
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At one point you removed a wire from that large resistor, is that back in place? If not, put it back on and test again.
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Old 11-21-2012, 10:29 AM   #19
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I'm interested in what happens, but I give you less than a 10% chance of getting the voltage adjusted by changing the voltage adjust pot. There's no way it would reach 165 volts on its own. At best, you are seeing some minor changes in the maximum voltage that the gen can reach by slightly changing the load on it. The voltage adjust pot should be changing the duty cycle of the switching transistor feeding the excitation windings. At 165 volts, I'll bet it's nearly maxed out. Keep your eye open for overheated electronic components - such as the heat sink/housing of your voltage regulator and stop running it if it gets excessively hot.

I'd just crank the pot all the way clockwise and test, then all the way in the other direction and test. You won't hurt it for brief periods at either limit, and if it never goes down to near 120 volts, you know it's time to stop playing with it and look for one of two things - a bad connection to the VR, so it doesn't know that the output voltage is too high, or a broken VR, which can't PWM modulate the excitation current. If you are very lucky and the pot drives the voltage down below 120 volts AC at one limit, then you just tweak from there and you are done.

Best of luck!
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Old 11-21-2012, 10:49 AM   #20
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I'm interested in what happens, but I give you less than a 10% chance of getting the voltage adjusted by changing the voltage adjust pot. There's no way it would reach 165 volts on its own. At best, you are seeing some minor changes in the maximum voltage that the gen can reach by slightly changing the load on it. The voltage adjust pot should be changing the duty cycle of the switching transistor feeding the excitation windings. At 165 volts, I'll bet it's nearly maxed out. Keep your eye open for overheated electronic components - such as the heat sink/housing of your voltage regulator and stop running it if it gets excessively hot.

I'd just crank the pot all the way clockwise and test, then all the way in the other direction and test. You won't hurt it for brief periods at either limit, and if it never goes down to near 120 volts, you know it's time to stop playing with it and look for one of two things - a bad connection to the VR, so it doesn't know that the output voltage is too high, or a broken VR, which can't PWM modulate the excitation current. If you are very lucky and the pot drives the voltage down below 120 volts AC at one limit, then you just tweak from there and you are done.

Best of luck!
Cylon you have a great memorie, I don't think I re-connected that wire to the big resiter.
MY neighbor came over with an 8 inch long screwdriver and we just fired it up and we sat and watched the meter, we did not adjust anything.
When it stabilized and the gen kicked in the volts were at 156/157, then it slowely went up to 167/168 the motor gave a grunt or two and the volts dropped back to 156/157 and started back up again, we watched as it did the same thing over and over again for a few minutes.
The only thing thing plugged in and working inside the coach is the clock on the microwave. The two ac units were turned off and nothing else is plugged in to any outlet.
Can the VR be taken apart and repaired or is that a remove and replace deal?
Does the POT have a stop in either direction?
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Old 11-21-2012, 10:59 AM   #21
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Cylon you have a great memorie, I don't think I re-connected that wire to the big resiter.
MY neighbor came over with an 8 inch long screwdriver and we just fired it up and we sat and watched the meter, we did not adjust anything.
When it stabilized and the gen kicked in the volts were at 156/157, then it slowely went up to 167/168 the motor gave a grunt or two and the volts dropped back to 156/157 and started back up again, we watched as it did the same thing over and over again for a few minutes.
The only thing thing plugged in and working inside the coach is the clock on the microwave. The two ac units were turned off and nothing else is plugged in to any outlet.
Can the VR be taken apart and repaired or is that a remove and replace deal?
Does the POT have a stop in either direction?
I re-connected that wire to the big resitor and there was no change, it kept doing the same thing. When the gen was off I plugged in the shore power and the meter read 122 volts and 60 hertz.
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Old 11-21-2012, 11:30 AM   #22
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Can the VR be taken apart and repaired or is that a remove and replace deal?
Remove and replace. The VR is potted and it's very difficult to remove the potting material without ruining the circuitry.

You might check to see if it has an external transistor switch that's shorted. The manufacturers exploded view should show that, if that's the way they did it. It would be attached to a heat sink of some kind.

Quote:
Does the POT have a stop in either direction?
Most pots have a stop. It's rare to find a 360 pot.

But there are two types used in this sort of circuit. A single turn pot, which has around a 220 turn, and a multi-turn pot. Those can be 5, 10, 20 turns. But in all cases, there will be a stop at the end of rotation. Multi-turn pots will click when you reach the end of travel, and there's a slip gear, so it's difficult to ruin them. Single turn pots can be damaged if you try to over turn them.

BTW, you shouldn't have your MW plugged in during your tests. Not good for it to have 150 odd volts on it. Just use a meter. There's another device that may be plugged in and operating when the genset is running...the converter. Also not good to be overvolted.
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Old 11-21-2012, 11:46 AM   #23
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You may be close to needing pro help. That resistor is there for a good reason and I would not keep it disconnected. I suspect the vr is shot. I replaced mine on my Q55-G for $100. Before throwing $$ at it, I would ckeck and clean all connections on the VR and the ECM first. I have a trouble shooting if you need it, just too big to attach here.
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Old 11-21-2012, 11:54 AM   #24
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Remove and replace. The VR is potted and it's very difficult to remove the potting material without ruining the circuitry.

You might check to see if it has an external transistor switch that's shorted. The manufacturers exploded view should show that, if that's the way they did it. It would be attached to a heat sink of some kind.

Most pots have a stop. It's rare to find a 360 pot.

But there are two types used in this sort of circuit. A single turn pot, which has around a 220 turn, and a multi-turn pot. Those can be 5, 10, 20 turns. But in all cases, there will be a stop at the end of rotation. Multi-turn pots will click when you reach the end of travel, and there's a slip gear, so it's difficult to ruin them. Single turn pots can be damaged if you try to over turn them.

BTW, you shouldn't have your MW plugged in during your tests. Not good for it to have 150 odd volts on it. Just use a meter. There's another device that may be plugged in and operating when the genset is running...the converter. Also not good to be overvolted.
I will unplug the microwave, the converter is hard wired how do I disable that? If I pull the main breaker I will not get power to any of the outlets.

Just in case the VR is shot where can I get one that does not cost between 110-150 bucks, I need part number 74074 according to my parts manual
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Old 11-21-2012, 01:08 PM   #25
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Most pots have a stop. It's rare to find a 360 pot.

But there are two types used in this sort of circuit. A single turn pot, which has around a 220 turn, and a multi-turn pot. Those can be 5, 10, 20 turns
BTW, you shouldn't have your MW plugged in during your tests. Not good for it to have 150 odd volts on it. Just use a meter. There's another device that may be plugged in and operating when the genset is running...the converter. Also not good to be overvolted.
I agree with Jim on all his comments. Don't burn out things while trying to fix the gen. Your pot is probably single turn.

I fixed a potted VR with a $6 part, but it took me a long time and there was a significant risk I'd damage it worse while unpotting. In my case the replacement cost was closer to $250-$300 so it was worth it - I'd only spent $100 on my gen. You are lucky that you know the generator isn't damaged - it's working but the VR isn't regulating. Unless you are very determined and have electronic repair skills, there's not much more you can do other than replace the VR after carefully checking all connections to the one there now.
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Old 11-21-2012, 01:46 PM   #26
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Old 11-21-2012, 02:59 PM   #27
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It may be worthwhile checking around for third party companies that sell regulators to fit your gen. I know nothing about Generac, but for Onan gens there are a couple of suppliers that make better VRs. I particularly like the unpotted designs. They can be fixed, and they have fewer problems with heat.
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Old 11-21-2012, 07:16 PM   #28
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Here is the troubleshooting manual for the "NP" series Generac generator:
http://gen-parts.com/Manuals/Y78800.pdf

Circuit diagram is on pdf page 41. Physical connection diagram is on pdf page 42. From what I see and what has been said, if all connections/wires are ok then like others have said, the voltage regulator is bad.

BTW - the high voltage is most likely overdriving the ATS sense circuit which is the source of the buzzing. You really need to disconnect the generator at the ATS switch until you get this voltage issue resolved. Wire in a light bulb to act as a load on the gen until fixed. The high voltage can damage other things like the MW, converter, ATS, etc.

Dave
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