# Posted: 29 Oct 2018 19:48
My trusty generator that I use just for power tools went kuputnik today. I ripped a few boards, turned it off, went to fetch more boards. When I tried to start it again it kicked back hard, tore the handle outa my hand. Gave it another pull, fired right up but no juice. Well, 4vac. Shaft is spinning, brushes and rings ok, no loose wiring.
Before I came crying to you guys (my usual mo), I found this great write up on gen operation and troubleshooting. Followed ol Hanks steps and got same results when I jumpered 12v to the brushes. So it looks like I need a regulator. Odd that it would happen due to a kickback on startup but that's what it appears to be.
Anyway here is the write up complete hopefully, I'm using my phone. If not, a link
my electric generator will only produce 10-12 volts sould be 230volts any ideas
The exciter wires going to the AVR are only half the equation.
There should be 2 wires coming out of the AVR going to the brushes. These wires will carry DC voltage. The outer brush will be the positive brush.
How much voltage are you getting to the brushes?
I took the reading from the brushes
Then your AVR is doing it's job.
Disconnect one of the brush leads and set your meter to ohms.
Test across the brush terminals. What reading do you get?
Remove the brush block and inspect the brushes. They should be worn into an even arch pattern. They should not be chipped or cracked. They should slide freely into and out of the block. If they stick or bind, clean the block with electrical contact cleaner.
Now inspect the slip rings. They are the 2 metal bands that the brushes ride on. They are made of copper and should be shiny. A slight black patina is normal, but they should not have a dull black buildup on them.
They should be smooth, not scratched or pitted.
If they are dirty, you can clean them with a piece of scotch brite or 400 grit sandpaper attached to the end of a small stick.
Start the engine and press the scotch brite to the rings.
When they are clean, use your ohmmeter and test across the rings. What do they read?
rings seem ok brushes seem ok I tested across the brush terminals with the meter set on 2K I got .057 not sure what you mean by across the rings? when I tested across the brushes while it was running it produced 13.7 volt hope this helps
Place one lead to each ring. This is across the rings.
Testing for voltage across the brushes only tells us if voltage is going to the brushes. It does not tell us whether voltage is going through the brushes, as the negative brush is grounded externally.
You will also need to test from one ring to a good ground. It should show no continuity.
Hank there is no continuity across either ring to ground
What does it read from ring to ring?
.046 set on 2k
This is not near enough. It should read 30 ohms.
I would highly suggest retesting it at a lower scale.
If it still does not read about 30 ohms, you are looking at a shorted rotor, and it must be replaced.
If you did not clean the rings, I would also suggest doing that. If there is a film on them, the current will not be able to flow through the film.
the rings have been cleaned brushes ok, could you tell me why i a getting about 10 volts being generated
There are actually 2 reasons. Yours may be one or both.
The first reason is that in it's most basic form, the rotor is a giant electromagnet. Even when there is no power going to the brushes, the iron core of the rotor will still hold a tiny charge of magnetism. This is called residual magnetism. RM has enough power to produce between 5 and 10 volts of electricity without external excitement.
The second reason is almost the same, but the strength of the magnetic field is dependent on 3 things - the diameter and amount of wiring in the rotor (the windings), the amount of voltage applied to the windings, and the resistance of the windings. Too little resistance will cause the voltage to flow too freely (fast) through the windings, and not be able to create a strong enough magnetic field.
The strength of this magnetic field is the biggest factor in determining the output voltage of the set.
Here is an overview of how your set works:
A genset is composed of 2 major components - an engine and a generator, commonly referred to as an alternator. hf
A generator is composed of 2 major components - a rotor, commonly referred to as an armature, and a stator. The stator typically has 2 or more windings - 1 or more power windings, and a smaller exciter winding.
There are 3 things required for the production of electricity - a magnetic field, a conductor (wire), and movement between the field and conductor. Since the field has no physical mass, it is much easier to move it than to move the conductor. We move the field by spinning it with the engine. This is why most gensets are known as revolving field gensets.hf
When you start the engine, the rotor starts spinning (it is connected directly to the crankshaft of the engine). DC voltage is applied to the rotor via the brushes and slip rings. This turns the rotor into an electromagnet. As it spins, the magnetic field around the rotor is passed through the windings of the stator (conductor). The magnetic field aligns the electrons in the wire and makes them move. This flow of electrons is electricity.
Remember, a magnet has 2 poles - north and south, or positive and negative. As the positive pole passes the windings, it moves the electrons in one direction (the positive pulse). As the negative pole passes by, it moves the electrons in the opposite direction (the negative pulse). One positive pulse and one negative pulse are one cycle, or Hertz. Since US power is 60 Hz, this process must happen 60 times per second (50 times per second (50 Hz) in much of the world).hf
We now have nominal voltage flowing (120 V in the US).
When a load is applied to the genset, this voltage drops correspondingly to the size of the load.
The voltage regulator senses this power drop from the exciter winding and says ‘Hey, I've got a load on and the power is dropping. I'd better make more power'. It does this by increasing the DC voltage to the rotor, which creates a stronger magnetic field, which pushes even more electrons into movement.
The VR constantly monitors this voltage and adjusts the field accordingly.
We now have electricity.hf
Brilliant answer after reading this I have realised I havn't checked for a voltage coming out of the avr to the brushes I think I am right to say I should have a voltage there?
Yes, it should be a minimum of 12VDC.
But you have already said you got 13.6 at the brushes.
no that was with the wires disconnected and I put meter on the brush terminals so I was reading what was coming from the brushes no wires connected
There is no voltage that comes out of the brushes.
The voltage goes in to the brushes from the AVR.
We already know the rotor has a low resistance reading. but let's check the output of the AVR.
Connect both brush leads to the brushes.
Set your meter to VDC and connect the negative lead to a good engine ground.
Start the engine and touch the meter's positive lead to the positive (outer) brush.
How much voltage is being applied to the brush?
it will have to be tomorrow as it is dark, I hope you are on line tomorrow, if so give me a time (BST) cheers John
I will be on line tomorrow between noon and 2, and then from 11:30PM to about 1AM EST (5 or 6 hours behind you).
You do not need to wait until I am online. You can simply reply, and I will see it when I get online.
not sure this went first time but the reading was 0.96 volts from the pos. trem on brushes to a good neutral
If the wires were connected to the brushes, this is a problem.
It will most likely be the AVR that is bad, but let's test the integrity of the entire generator.
We are going to manually excite the field to check the integrity of the generator.
Disconnect the brush wires.
Make up 2 jumper wires that will attach to the brushes.
Connect one jumper to the positive (outer) brush and to the positive terminal of a 12V battery.
Connect the other jumper to the negative (inner) brush, but do not connect it to the battery at this time.
Gain access to the AVR.
There are 4 wires - 2 go to the brushes, and the other 2 come from the exciter winding. Gain access to the exciter wires.
Start the set, and connect the negative jumper to the negative terminal of the battery.
Set your meter to VAC and measure the AC output at the receptacle of the set. It should be a minimum of 60 volts.
Test the voltage across the 2 exciter wires.
How much voltage is there?
Set your meter to VDC and test the voltage at the brush wires that come from the AVR. Make sure you connect the positive lead to the positive wire.
How much voltage is there?
Disconnect the jumpers from the battery and shut the set down.
Hi Hank my AVR has 4 wires at the bottom and 2 at the top the 2 at the top goto the brushes 2 of the 4 at the bottom go the main winding and 2 to the excitation winding
Measure them both. The key here is that we need to know if there is ACV going into the AVR, but