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I have a Caterpillar 25 KW generator runs fine but only

Customer Question
I have a Caterpillar...

I have a Caterpillar 25 KW generator runs fine but only putting out 60 volts

Mechanic's Assistant: What is the complete model and serial number of your machine?

G25UHIS 25 kw I will have to go outside and see if I can find the serial number

Mechanic's Assistant: Are you fixing this yourself? What have you tried so far?

The only thing I have tried was plugging in a small fan to put some load on it without burning something up.

Mechanic's Assistant: Anything else you want the industrial mechanic to know before I connect you?

Fan did not turn. I crank it up once a month but have not been placing a load on it. I do not think it is a fuel etc problem. Thinking maybe voltage regulator?

Submitted: 6 months ago.Category: Industrial Equipment
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Customer reply replied 6 months ago
looks like model should be G25UH1S, serial number is *****
Answered in 3 hours by:
8/3/2017
Mechanic: J Smith,
 replied 6 months ago
J Smith
Category: Industrial Equipment
Satisfied Customers: 1
Experience: Project Manager IV, Assistant Product Manager, Sales & Estimating at WesTech Engineering
Verified

Hi, my name is ***** ***** I can help you with your problem.

The first thing to try is simple. On military generators you are required to hold the master switch in the start position until the engine is at full rpm. This is to excite the field windings and energize the electrical field within the generator head. This could potentially be the problem with your Cat unit. Try holding it in start for a few seconds longer, on the military units it is probably only 3-5 seconds after it starts.

If that doesn't work then you may have lost some of the residual magnetism, a condition caused by lack of use or from shutting down with an active load (try not to do this). There are two ways to fix this:

1. 12 Volt Generator Battery Method

  • Locate the voltage regulator for your generator.
  • Unplug the two wires that connect to the generator brushes. Normally one is red and the other is black or white.
  • Connect the black or white to the generator ground battery terminal.
  • Plug in a light, turn on the generator breaker or switch and start the motor.
  • Connect the battery +12 volts (red cable) to the red wire on the terminals you removed for three seconds.
  • Remove your wires and replace the plug. The generator should now be producing power again.

Note: Make sure you unplug the brush wires from the automatic voltage regulator or you will damage the regulator. Do not contact the voltage regulator or other wires as dangerous voltages may be present that can cause electric shock.

2. Electric Drill Method

  • Plug in an electric drill into the generator receptacle.
  • If the drill is reversible, move the direction switch to the forward position.
  • Start the generator.
  • While depressing the trigger on the drill, spin the drill chuck in reverse direction. This will excite the field and the generator will now produce electricity. If spinning the chuck one direction does not work, try spinning the chuck in the other direction as you may have the reverse switch positioned backwards.

Note: Use caution not to get your hand or other materials caught in the chuck. As soon as the field is exited, the generator will produce power and the drill will turn on.

The reason this works is because the electric motor in the drill will act as a small generator when spun backwards. The magnets in the drill's motor induce a voltage into the motor winding, which is fed back through the trigger cord and into the generator receptacle. From there it goes into the power winding of the stator. The voltage going through the power winding creates a magnetic field which is intensified due to the iron core of the stator lamination's. The rotor intersects this magnetic field as it is spun past the power winding, thus inducing a voltage in the rotor winding. Once current flow is present in the rotor winding the rotor has been flashed.

If these instructions do not help you to restore generator output power, the next step I would take is to replace the Automatic Voltage Regulator as it may be damaged.

Please let me know if you are able to get it working.

Best Regards,

John

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Customer reply replied 6 months ago
I tried holding the start switch longer no change I tried the drill, with the low voltage provided by the generator I can literally stop the drill from turning, tried both forward and reverse. FYI the HZ gauge is pegged out while the Voltage shows about 40-60 volts and the amperage gauge is very low as well. Not sure where the voltage regulator is, I am looking through the manuals now
Customer reply replied 6 months ago
Looking at the manual this may be a SHUNT field activation system R 230 A if that makes sense to you, I don't know if this replaces AVR are supplements it?
Mechanic: J Smith,
 replied 6 months ago

Sorry for the delay and thank you for the information and the photos. I am looking into this right now and will be getting back to you as soon as I can.

Best Regards,

John

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Mechanic: J Smith,
 replied 6 months ago

Okay, I was just reading up on the Shunt R230. The AVR is integrated into this unit. The first step to try is to replace that fuse. I also thought it was odd that you are getting voltage with the fuse blown, but I'm not that familiar with these units to be honest. This is the fuse you need. It is an 8 amp, 250 volt, slow-blow fuse. If it blows the new fuse then the next step I would take would be to replace the Shunt unit. They are about $50 on ebay.

One question I forgot to ask you is if the engine seems to be running at normal RPM's. You did say you didn't think it was a fuel problem or anything so I assumed it was, but just to verify if it is running slow that will reduce voltage output. The most common problem I've seen when I run into RPM problems is not fuel but air due to dirty filters or sticky chokes.

If you have a Radio Shack or other electronics store in your area you might be able to find that fuse locally.

Please let me know how it goes.

Best Regards,
John

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Customer reply replied 6 months ago
we don't have a local radio shack, most seemed to have closed so I ordered fuses from e-bay, I also went ahead and ordered the AVR as well, apparently it comes from China. This is a propane generator and yes the RPMs are actually a little higher than normal. It only has less than 150 hours, even as old as it is (I bought it new for Y2K).
FYI- A caterpillar dealer quoted me $656.00 for the AVR, glad I went to ebay. Hopefully the AVR is of decent quality I have purchased 2 smaller (5kw and 1kw) that were made in China and neither of them lasted very long.
I will let you know when I get the fuse in.
Thanks,
Earl
Mechanic: J Smith,
 replied 6 months ago

Earl,

Hopefully that fixes it. If not we can start digging deeper, but that's what I would do if I were performing the repair. Another place that might have that fuse would be a place that repairs pumps, or hot tubs and pools, the pumps for those units use the same type of slow-blow fuses.

Fingers crossed,

John

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Customer reply replied 6 months ago
Thanks, ***** ***** a place in town that works on hot tubs, I will check with them
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