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Old 10-16-2013, 08:23 PM   #1
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Generator 8 volt output

Started my genny to warm up for oil change. Switched panel to generator power, nothing. Checked system, found I'm getting only 8v output. Started going down the trouble tree: all 3 fuses good, no loose connections found. Checked output at gen mounted breaker, still 8v. It's a northern lights 4.5 kW, about 24 years old. Has worked flawlessly last 3 years. Last used 1 week ago, perfectly normal at that time. What to look for before calling tech?
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Old 10-16-2013, 11:11 PM   #2
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Assuming its running and not making ac volts, it's probably the field coil circuit. There may be fuses or diode blocks in the circuit to provide field coil voltage (usually like 50 volts or less). However, it could be a broken field coil lead wire, Many units of that vintage have aluminum alloy wire that makes up the 4 coils. Copper wire is crimped on to the aluminum. Heat and time do a number on the insulation that eventually fails, causing the wire to fail.

If you get confirmation it is the field circuit, check all the external components first. If it seems to be a coil (the 4 are usually wired in series) you might get lucky taking the field housing off. The armature will hang ok on the flywheel plate. Replace the lead wires by crimping new wires on. Make sure each coil is wired with the correct polarity. Repair any breaks in the insulation, get it all back together and cross your fingers.

Seriously, not as bad as it sounds, but make sure the field is the issue before digging in. And make sure its not some simple fuse or diode block in the field circuit.
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Old 10-17-2013, 01:14 AM   #3
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Quote:
Originally Posted by dach side View Post
Started my genny to warm up for oil change. Switched panel to generator power, nothing. Checked system, found I'm getting only 8v output. Started going down the trouble tree: all 3 fuses good, no loose connections found. Checked output at gen mounted breaker, still 8v. It's a northern lights 4.5 kW, about 24 years old. Has worked flawlessly last 3 years. Last used 1 week ago, perfectly normal at that time. What to look for before calling tech?

Could be anything in the voltage regulator circuit.

Regulator
field winding
Rotating Rectifier

Here's a article I wrote up for my parts website that explains how brushless generators work.

Customers often ask, just what does a generator voltage regulator do, how does it work? How does a brushless generator work?

A voltage regulator does, just what it's name implies, it regulates the output voltage of the generator. It does this using a very small portion of the generators output, and converting that AC voltage into a DC current that is inversely proportional to the generators output voltage (once it reaches full voltage). Basically, the more voltage output of the generator, the less DC current the voltage regulator produces.

A brushless generator consists of a part that spins called an armature, this is most often connected to your engines flywheel, and a part that doesn't spin, this is called the stator. When the engine starts to spin the armature, residual magnetism in the armature induces a small voltage in the output windings of the stator, most often over 10 volts, but not allot more.

This voltage is converted to a DC current by the voltage regulator, which is connected to a second set of windings in the stator, called the exciter windings. This DC current in the exciter windings forms an electro magnet, which induces an ac current in the matching exciter windings in the armature. The exciter windings in the armature are connected to units called rotating rectifiers which convert (rectify) the AC current into DC current.

The DC output of the rotating rectifiers is connected to the main windings in the armature. This current creates an electro magnet in the armature, which induces a larger voltage into the output windings of the stator. The voltage regulator uses this increased voltage to produce more DC current, and the cycle continues until the generator reaches full operating voltage.

When the generator output reaches full operating voltage, the generator voltage regulator reduces the amount of DC current that it produces, thus in effect lowering the output voltage of the generator. At the correct output voltage, with a non changing load on the generator, the voltage regulator comes into a state of equilibrium where it produces just enough current to keep the generator producing the correct output voltage.

If you add load to the generator, the first thing that happens is that the output voltage drops a little. The generator voltage regulator increases the amount of current it produces, raising the voltage back to it's proper level. If you reduce the load on the generator, just the opposite occurs. The output voltage goes up, and the voltage regulator reduces the amount of DC current that it produces, and the voltage drops.
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Old 10-19-2013, 09:58 AM   #4
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Islanders: this genset has brushes. I replaced all 3 fuses and checked all of the fine wires to the avr all seem intact. I did not check the brushes cause: a, it will require a lot of disassembly to get to them, and b, I'm thinking if it's the brushes I would expect to see some variations of the voltage prior to failing. As it is now it's producing a steady 8 volts. Also, the manual recommends brush replacement @ 3000 hrs., this has only 799 hrs.
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Old 10-19-2013, 10:27 AM   #5
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Originally Posted by dach side View Post
Islanders: this genset has brushes. I replaced all 3 fuses and checked all of the fine wires to the avr all seem intact. I did not check the brushes cause: a, it will require a lot of disassembly to get to them, and b, I'm thinking if it's the brushes I would expect to see some variations of the voltage prior to failing. As it is now it's producing a steady 8 volts. Also, the manual recommends brush replacement @ 3000 hrs., this has only 799 hrs.
Wow! Brushes!

I started working on generators in the 1980's.

Brush type generators were obsolete then.

You know, if you ever get inclined, you can replace that generator end with a new one.
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