Small generator over-voltage...

[George Herold]

On Saturday, May 16, 2020 at 11:07:29 AM UTC-4, Bob Engelhardt wrote:

If there\'s a better site/forum for this question, please let me know.

I have an old (mid 80\'s) Sears Craftsman generator - 4 cycle B&S engine
& 120v, 1350W rated output. (Jeff - model 580.328172)

I haven\'t used it in decades so I cleaned it up & checked it out with
the intent to donate it to the Habitat ReStore.

Imagine my surprise when I measured the no-load output voltage at 134v
(with Fluke 36 True RMS meter). That dropped to 117v with a 10A load.

The no-load frequency is 62Hz, which is what the manual says it should
be (3720 RPM). That drops to 59Hz at 10A load.

The manual also claims a +-5% voltage regulation.

Seemingly unrelated, but ... the DC output is only 7v. Also, there is
1500Hz+-, 20v+- PP superimposed on the 120v 60hz output.

Note that I never before checked the voltage and I\'ve never had a
problem with it damaging loads (refrigerator, freezer, ??). So either
it\'s always been over-voltage & no-matter, or it\'s changed while sitting
idle.

Any ideas about what\'s going on here? And to diagnose & fix?

Thanks, Bob

Those numbers seem fine to me. What\'s the voltage with a 100W
incandescent as load? (Or even a 10-20W resistor?)

George H.
who gave his old Sears gen. to his brother when he got a new one
with a much bigger muffler!

The manual spec page:
https://imgur.com/phBAUpM
The circuit schematic:
https://imgur.com/vA6RIsa

 

[Ralph Mowery]

In article <ra6sin0235u@news2.newsguy.com>, BobEngelhardt@comcast.net
says...

...
Imagine my surprise when I measured the no-load output voltage at 134v
(with Fluke 36 True RMS meter).
...

My Fluke lies!! I put a scope on the generator & got 210v p-p (or 150v
p-p depending upon what the peak is with the superimposed 1500Hz),
that\'s 71v (or 50v)RMS ... assuming sine wave, which it is, kind of.

https://imgur.com/AQlOpmA (2ms & 50v per)

I had it on the scope before, but I must have been in a fog to misread
it so badly, or I didn\'t read the p-p at all, IDR.

So I was 180* out of phase with the problem: it\'s way, way under voltage
instead of way over voltage. Which is easier to understand possible
causes - basically there\'s too little excitation current. I couldn\'t
understand how it could possibly be over voltage/too much excitation
current.

The diodes check OK with a DMM, so I\'ll look at the slip rings. Or for
a poor connection.

Is that a digital or analog scope ?

You need to just hang a good old filiment light bulb across the
generator and see how it looks and measure the voltage with one of the
old analog meters. That digital crap often gets confused on oddball
waveforms.

I don\'t recall exectally the way it works, but in the old days you put a
piece of greased paper between 2 light bulbs. One bulb on the generator
and the other on a good sine wave from the power company and a meter and
variack and adjusted the voltage so the bulbs were the same brightness
and then you could read the voltage.

 

[danny burstein]

In <MPG.3930cb7c1c82e84989ec7@news.east.earthlink.net> Ralph Mowery <rmowery28146@earthlink.net> writes:

[snip]

Is that a digital or analog scope ?

You need to just hang a good old filiment light bulb across the
generator and see how it looks and measure the voltage with one of the
old analog meters. That digital crap often gets confused on oddball
waveforms.

I don\'t recall exectally the way it works, but in the old days you put a
piece of greased paper between 2 light bulbs. One bulb on the generator
and the other on a good sine wave from the power company and a meter and
variack and adjusted the voltage so the bulbs were the same brightness
and then you could read the voltage.

It gives you a simple and crude way of comparing the
relative brightnesses of both sides of the paper..

Similar techniques have been used in photography:

The \"Polaroid Swinger [tm]\" camera, 1960\'s, used
a variant of this for its manually operated
light meter:

http://camera-wiki.org/wiki/Exposure_meter#Extinction_meters


--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

 

[Phil Hobbs]

On 2020-05-21 22:13, danny burstein wrote:

In <MPG.3930cb7c1c82e84989ec7@news.east.earthlink.net> Ralph Mowery <rmowery28146@earthlink.net> writes:

[snip]

Is that a digital or analog scope ?

You need to just hang a good old filiment light bulb across the
generator and see how it looks and measure the voltage with one of the
old analog meters. That digital crap often gets confused on oddball
waveforms.

I don\'t recall exectally the way it works, but in the old days you put a
piece of greased paper between 2 light bulbs. One bulb on the generator
and the other on a good sine wave from the power company and a meter and
variack and adjusted the voltage so the bulbs were the same brightness
and then you could read the voltage.

It gives you a simple and crude way of comparing the
relative brightnesses of both sides of the paper..

Similar techniques have been used in photography:

The \"Polaroid Swinger [tm]\" camera, 1960\'s, used
a variant of this for its manually operated
light meter:

http://camera-wiki.org/wiki/Exposure_meter#Extinction_meters


That\'s called the \"half shade\" method, and is actually pretty good.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[default]

On Mon, 18 May 2020 23:36:52 -0700 (PDT), Michael Terrell
<terrell.michael.a@gmail.com> wrote:

On Monday, May 18, 2020 at 6:43:19 PM UTC-4, default wrote:

On Mon, 18 May 2020 05:02:35 -0700 (PDT), Michael Terrell wrote:

Metal polish (EG: Brasso), or a large in eraser is better than sandpaper. It leaves a highly polished surface that only removes the oxides.

Small generators are intended for lighting, or power tools where you only have to be close. Also, without a load the output isn\'t a clean sine wave. Any inductive load helps to clean up their output.

Those old-school ink erasers were the best IMO. Don\'t see them
anymore...

Fine abrasives have the advantage of cleaning off the brush surfaces
and reseating brushes, so it may be more advantageous in a generator
that has been in storage for awhile. Otherwise I concur, a pencil
eraser is a good choice.


I used to rebuild vacuum clean motors as a sideline. The customer kept asking to see my armature lathe, since they commutators all looked brand new. These were made by Lamb, and 120VAC. I would connect them to my 24V DC power supply and polish the commutator with the motor running at a reduced speed. He gave me all his bad motors. I sold them back to him at half the wholesale price, with over a 50% recover rate. Many didn\'t run because the commutator was so nasty. I reground a blade for my Exacto knife to undercut the mica spacers. A lot of the time it only took five minutes to revive a motor. He never did figure it out, but he never brought back any of my repaired motors. Other had bad bearings or burnt windings so they were stripped and the good parts were used to make a good fan. I ended up with scrap aluminum and copper from the scrap parts, as well.

Ink erasers are still available, but you might have to go o an office supply store or buy them online.

Way back, I worked a part time job repairing consumer and commercial
electronics while going to school. One of the sidelines of the
business was installing custom stereos in vehicles. For that there
were high school kids with a mechanical bent that would do all the
work. None of them could afford decent cars themselves so there were
a fleet of high-mileage junkers parked outside the building.

There was also this place \"Ben\'s Armature,\" who\'d built a reputation
for repairing car alternators. Everyone in town swore by them being
the best, but they\'d always diagnose a bad field winding (which they
called the armature) and the cure was always to \"rewind the armature.\"
at a cost of $50-150. This old Land Cruiser I used to haul my boat
around succumbed one day and I went there and listened to the
estimate.

I decided to rewind it myself and save a buck. How hard could it be?
I took it apart and there was nothing left of the brushes. $4 for a
set of brushes (with springs and holder) and it could have been fixed
without even taking the alternator off the truck.

One by one the junkers the high schoolers used also went to Ben\'s.
(120-200K/Mi the brushes fail) In no time the business had another
sideline. We\'d charge $20 labor and $4-15 for brushes (seldom had to
do more than remove a few screws and replace the brushes)

I did get to \"rewind the armature\" one day on an old 750 Honda
motorcycle. The only hard part of doing it was in fabricating a
bobbin to hold the wire \'till the epoxy set - they used a \"self
supporting coil\" in the original alternator.

 

[Ralph Mowery]

In article <ra6sin0235u@news2.newsguy.com>, BobEngelhardt@comcast.net
says...

...
Imagine my surprise when I measured the no-load output voltage at 134v
(with Fluke 36 True RMS meter).
...

My Fluke lies!! I put a scope on the generator & got 210v p-p (or 150v
p-p depending upon what the peak is with the superimposed 1500Hz),
that\'s 71v (or 50v)RMS ... assuming sine wave, which it is, kind of.

https://imgur.com/AQlOpmA (2ms & 50v per)

I had it on the scope before, but I must have been in a fog to misread
it so badly, or I didn\'t read the p-p at all, IDR.

So I was 180* out of phase with the problem: it\'s way, way under voltage
instead of way over voltage. Which is easier to understand possible
causes - basically there\'s too little excitation current. I couldn\'t
understand how it could possibly be over voltage/too much excitation
current.

The diodes check OK with a DMM, so I\'ll look at the slip rings. Or for
a poor connection.

Is that a digital or analog scope ?

You need to just hang a good old filiment light bulb across the
generator and see how it looks and measure the voltage with one of the
old analog meters. That digital crap often gets confused on oddball
waveforms.

I don\'t recall exectally the way it works, but in the old days you put a
piece of greased paper between 2 light bulbs. One bulb on the generator
and the other on a good sine wave from the power company and a meter and
variack and adjusted the voltage so the bulbs were the same brightness
and then you could read the voltage.

 

[Bob Engelhardt]

On 5/21/2020 5:41 PM, Bob Engelhardt wrote:
> My Fluke lies!!  I put a scope on the generator & got 210v p-p ...

It doesn\'t lie - I\'m an idiot. The scope probe was bad ... a lot of my
equipment is iffy, but the probe was junk.

So, I\'m back where I started (and a little dizzy from the go-round).
Going back to the fundamentals of the situation:
- the output really is 135v
- it has always been that way or it\'s changed & I can\'t see what could
have changed
- there is no regulation. The schematic had the stator & rotor
reversed, here\'s the correct one:
https://imgur.com/REKKgHL
- the specs claim +-5% voltage - how can that be without regulation?
They lie. Maybe they mean +-5% at full load.

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

 

[Bob Engelhardt]

On 5/21/2020 5:41 PM, Bob Engelhardt wrote:
> My Fluke lies!!  I put a scope on the generator & got 210v p-p ...

It doesn\'t lie - I\'m an idiot. The scope probe was bad ... a lot of my
equipment is iffy, but the probe was junk.

So, I\'m back where I started (and a little dizzy from the go-round).
Going back to the fundamentals of the situation:
- the output really is 135v
- it has always been that way or it\'s changed & I can\'t see what could
have changed
- there is no regulation. The schematic had the stator & rotor
reversed, here\'s the correct one:
https://imgur.com/REKKgHL
- the specs claim +-5% voltage - how can that be without regulation?
They lie. Maybe they mean +-5% at full load.

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

 

[Bob Engelhardt]

On 5/21/2020 5:41 PM, Bob Engelhardt wrote:
> My Fluke lies!!  I put a scope on the generator & got 210v p-p ...

It doesn\'t lie - I\'m an idiot. The scope probe was bad ... a lot of my
equipment is iffy, but the probe was junk.

So, I\'m back where I started (and a little dizzy from the go-round).
Going back to the fundamentals of the situation:
- the output really is 135v
- it has always been that way or it\'s changed & I can\'t see what could
have changed
- there is no regulation. The schematic had the stator & rotor
reversed, here\'s the correct one:
https://imgur.com/REKKgHL
- the specs claim +-5% voltage - how can that be without regulation?
They lie. Maybe they mean +-5% at full load.

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

 

[Ralph Mowery]

In article <rah01s08j8@news4.newsguy.com>, BobEngelhardt@comcast.net
says...

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

With the 5% that is about 6 volts so the generator could put out from
around 120 to 130 volts if set to 125 volts. I have an old viberating
reed frequency meter to use with my generator. Hard to fool that thing
frequency wise. The best way for me with an old generator I have is
just to monitor the frequency to see if the engine speed is correct.

The factory may set it high in voltage to allow for the wiring drop and
internal impedance.

 

[Ralph Mowery]

In article <rah01s08j8@news4.newsguy.com>, BobEngelhardt@comcast.net
says...

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

With the 5% that is about 6 volts so the generator could put out from
around 120 to 130 volts if set to 125 volts. I have an old viberating
reed frequency meter to use with my generator. Hard to fool that thing
frequency wise. The best way for me with an old generator I have is
just to monitor the frequency to see if the engine speed is correct.

The factory may set it high in voltage to allow for the wiring drop and
internal impedance.

 

[Ralph Mowery]

In article <rah01s08j8@news4.newsguy.com>, BobEngelhardt@comcast.net
says...

I found this at http://portable.generatorguide.net/avr.html
\"Most cheap portable generators have fixed excitation. In such machines,
when an alternator is loaded, its terminal voltage drops due to its
internal impedance.\"

This is a low end generator from the mid 80\'s, so electronic regulation
wouldn\'t have been as common as it is now.

Conclusion: I don\'t have a problem with my generator - I have a shitty
generator

With the 5% that is about 6 volts so the generator could put out from
around 120 to 130 volts if set to 125 volts. I have an old viberating
reed frequency meter to use with my generator. Hard to fool that thing
frequency wise. The best way for me with an old generator I have is
just to monitor the frequency to see if the engine speed is correct.

The factory may set it high in voltage to allow for the wiring drop and
internal impedance.