AC generator problem - nasty output on scope

J

John Jackson

Guest
I bought a Hailin HL2500CL 2500 watt diesel generator last week. It's
a brushless, self exciting, 2 poles, single phase design.

When I hooked a 100 watt lightbulb to it, I noticed it was kind of
dim. I then hooked my computer's UPS to it and it kept switching to
the backup mode. I checked the generator voltage with my meter and
measured 106 volts RMS and 60.1 Hz. I adjusted the RPMs of the engine
up a bit and now have 115 volts at 62.8 Hz. The UPS still won't work.

I hooked my oscilloscope up to it (powered off the house mains) and
the waveform has an 80 volt dip between 45 to 80 degrees and between
280 to 315 degrees. It's about 345 volts peak-to-peak. The dip each
half cycle would explain the low RMS voltage at 3600 RPM and the UPS
problems.

So what's likely wrong? A shorted or open winding? I popped the
generator cover off and noticed what looks like two little bridge
rectifiers mounted opposite of each other on the rotor shaft. I'm
guessing they rectify the field current? Could one of those be bad?

There are also lots of harmonics when the generator is unloaded. Is
this normal? They start to go away with a 100 watt load and are nearly
gone with 1000 watts (used a heater). I also tested the UPS with the
1000 watt load connected to the generator and it made no difference.

I'm not trying to fix it, as my dealer has agreed to exchange the
unit, but I'm curious as to the cause of the problem. I searched
google (groups and web) and could find nothing on these types of
generators- like schematics, theory of operation, troubleshooting,
etc. Hailin's website is sparse and has no contact info for support.

Does anyone have any links or books to recommend?

Thanks for any insight,
John Jackson
 
I don't know if they all do it, but I have seen horrendous waveforms like
that from many small generators. Yours sounds really bad though. It was a
challenge making the UPSs work well with such generators. As you found out,
the speed controls the frequency. To adjust the voltage requires adjusting
field excitation level.


"John Jackson" <reply@this_newsgroup_please.com> wrote in message
news:3f18db56.92772921@theworldsnet.com...
I bought a Hailin HL2500CL 2500 watt diesel generator last week. It's
a brushless, self exciting, 2 poles, single phase design.

When I hooked a 100 watt lightbulb to it, I noticed it was kind of
dim. I then hooked my computer's UPS to it and it kept switching to
the backup mode. I checked the generator voltage with my meter and
measured 106 volts RMS and 60.1 Hz. I adjusted the RPMs of the engine
up a bit and now have 115 volts at 62.8 Hz. The UPS still won't work.

I hooked my oscilloscope up to it (powered off the house mains) and
the waveform has an 80 volt dip between 45 to 80 degrees and between
280 to 315 degrees. It's about 345 volts peak-to-peak. The dip each
half cycle would explain the low RMS voltage at 3600 RPM and the UPS
problems.

So what's likely wrong? A shorted or open winding? I popped the
generator cover off and noticed what looks like two little bridge
rectifiers mounted opposite of each other on the rotor shaft. I'm
guessing they rectify the field current? Could one of those be bad?

There are also lots of harmonics when the generator is unloaded. Is
this normal? They start to go away with a 100 watt load and are nearly
gone with 1000 watts (used a heater). I also tested the UPS with the
1000 watt load connected to the generator and it made no difference.

I'm not trying to fix it, as my dealer has agreed to exchange the
unit, but I'm curious as to the cause of the problem. I searched
google (groups and web) and could find nothing on these types of
generators- like schematics, theory of operation, troubleshooting,
etc. Hailin's website is sparse and has no contact info for support.

Does anyone have any links or books to recommend?

Thanks for any insight,
John Jackson
Click to expand...
 
On Thu, 17 Jul 2003 03:03:26 GMT, "Peter Gottlieb" <178048316@icq.net>
wrote:

I don't know if they all do it, but I have seen horrendous waveforms like
that from many small generators. Yours sounds really bad though. It was a
challenge making the UPSs work well with such generators.
Click to expand...
Yeah, it's been a challenge so far. :(

Here are the waveform pics from the generator:
http://www.geocities.com/john4839503/pics.html

I certainly hope the dips are a manufacturing defect and not a design
defect. The low RMS voltage at 3600 RPM leads me to think it's a
manufacturing one. The harmonics do seem to clean up nicely with a
load.

I'm going to exchange the unit on Friday. It's a haul to the dealer so
I hope the next one's good. I'm bringing my scope..
John
 
"To adjust the voltage requires adjusting field excitation level."

On many of these smaller generators the field excitation is a permanent
magnet, (no brushes) I hear that the magnet looses its magnetism over
time and has to be remagnetized to maintain voltage

John Jackson wrote:
On Thu, 17 Jul 2003 03:03:26 GMT, "Peter Gottlieb" <178048316@icq.net
wrote:


I don't know if they all do it, but I have seen horrendous waveforms like
that from many small generators. Yours sounds really bad though. It was a
challenge making the UPSs work well with such generators.


Yeah, it's been a challenge so far. :(

Here are the waveform pics from the generator:
http://www.geocities.com/john4839503/pics.html

I certainly hope the dips are a manufacturing defect and not a design
defect. The low RMS voltage at 3600 RPM leads me to think it's a
manufacturing one. The harmonics do seem to clean up nicely with a
load.

I'm going to exchange the unit on Friday. It's a haul to the dealer so
I hope the next one's good. I'm bringing my scope..
John
Click to expand...
 
that's why I like those Honda inverter generators. Nice clean output.


"John Jackson" <reply@this_newsgroup_please.com> wrote in message
news:3f1e475b.120426015@theworldsnet.com...
On Thu, 17 Jul 2003 03:03:26 GMT, "Peter Gottlieb" <178048316@icq.net
wrote:

I don't know if they all do it, but I have seen horrendous waveforms like
that from many small generators. Yours sounds really bad though. It was
a
challenge making the UPSs work well with such generators.

Yeah, it's been a challenge so far. :(

Here are the waveform pics from the generator:
http://www.geocities.com/john4839503/pics.html

I certainly hope the dips are a manufacturing defect and not a design
defect. The low RMS voltage at 3600 RPM leads me to think it's a
manufacturing one. The harmonics do seem to clean up nicely with a
load.

I'm going to exchange the unit on Friday. It's a haul to the dealer so
I hope the next one's good. I'm bringing my scope..
John
Click to expand...
 
That hasn't been the case with ours.

Peter Gottlieb wrote:

that's why I like those Honda inverter generators. Nice clean output.
Click to expand...
 
I suspect that this generator is a variable-speed constant-frequency (VSCF)
unit.
If that is the case then the waveform is synthesized by a bunch of SCR's
that switch into the output to artificially manufacture a 60 Hz sine wave.
You look like one or more of the SCR's are not getting their switch-on
command or they have burned out. The waveform would then not be sinusoidal
any longer. It looks like this is the problem after studying your waveform
pictures. Contact me for more info.

Marvin
 
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