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Question DetailsAsked on 2/12/2018

Portable generator not producing the right frequency rpm and voltage good

Powermate generator I tested the AVR and brushes. I disconnected the AVR and got the following readings across the brushes 14.5 v, L1 to L2= 3.53v, R1toR2=3.4v,R1toL1 = 3.56 v Brushes did not look worn evenly across brush. When running and measured with meter set on Hz =1.7k not 60 Hz Thanks

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Don't deal with toy size generators like Powermates (Colemans), so I don't have a wiring diagram so don't know what the voltage between those legs should be - but they sound like one of two thing based on other generator experience. I presume you are talking normal small generator with 110/120V outlets on it, and maybe with some models 220V and/or maybe 12 or 24V.

1) either you are measuring the voltage between the input and output leads on the various sectors of the alternator, not the difference between the sector and ground, so you are just measuring the voltage loss across the field - lead to ground (try measuring at the output receptables) should be 115-220V if engine is running correct rpm (commonly 3600 for many makes of gas driven generators).

2) the magnetic field has collapsed and needs to be recharged. Many small portable generators have induced magnetic fields (created by the motor turning, not permanent fixed stator magnets), which dies off after a few months or so and have to be recharged. Some have a recharge system which you set to ON and then plug into house outlet power to reenergize the electromagnet - others you have to turn the motor over with an electric drill - with a load attached, as I recall, to reenergize the field. I have seen several people with small Hondas have to do that to get it working again. Check operating instructions because do it wrong and it is fried.

Here are links to some web blogs on Coleman generator issues (though more about frequency control than output voltage) - but with those low readings, unless connecting the VOM to the wrong places, I would say pretty sure to be either electromagnetic field collapse (so the rotor sectors are not seeing magnetic field which cause the electricity to be generated), or possibly something like diode pack has failed. Or maybe a short in the windings or grounded armature or windings, or enough brush and armature dust in the armature to short between the poles (sectors) of the armature. Of enough burnt-on junk on the armature to prevent power from passing from the brushes - the contact part of the rotor should be visible (though usually discolored) copper, not black or burnt brown.

On the brushes - the leading edge of the brushes, in generators and motors with cheap sheet metal brush guides, tend to wear more than the leading edge (leading being the "incoming" side as the armature turns against the brush) because the brushes tilt a bit in the holder as the rotor tries to drap them along with it as it turns - commonly maybe 1/32-1/16" difference in length of brush across the leading and trailing edges of the brush - not a dramatic amount. Normal, as long as the brush is not melting or heavily pitted heavily grooved, or wearing at a slant relative to the axis (from end to end direction) of the armature. Brush face will of course be concave. And of course it has to be long enough brush for the spring keeps a good pressure on it against the armature so it does not skip or bounce (which would usually lead to blackened, pitted, burnt surface on armature and brush). If brush gets worn too short the spring does not hold it in good contact so performance will be erratic - but more sparking and intermittent power than a consistent very low voltage.

Can't thing what effect the 1.7Khz versus 60Hz setting would have (sounds like this is an electronics, not electrical VOM) but I would think should still show the same RMS AC voltage of 115-120V on the 120V outlets.

OK - if you read 14.5V across the brushes, sounds like this is a battery charging generator - and if it produces 120V it does it using an inverter - basically same as a car cn produce 120V power through an invertor connected to the battery. If that is the case - that the basic power from the unit is 12V nominal, then failure to get 120V would have to be because of an inverter circuit failure.

Answered 2 years ago by LCD

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