Small generator over-voltage

Not familiar with USA products but a lot of the early ones were pretty basic and that sounds like normal to me :-) So I don't think I'd worry about tinkering with the control circuitry, perhaps a quick check of any diodes or caps if any would be about it.

From the schematic... it appears as if the battery would be an integral part of the alternator regulation, Do you have a good, fully charged battery connected to the 12V terminals? That, diodes and brushes are pretty much all that can go wrong.

If it has been sitting awhile, you may want to check that the brushes move freely in the holders and the slip rings are free of corrosion. The rings should be shiny and may be dark colored, that's normal but you don't want any encrustations, green stuff, white flaky stuff, etc.. If you sand them use very fine sandpaper, avoid Silicon Carbide abrasives, and blow out the dust it creates.

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.

I noticed on a 5 KW generator I have that the generator engine would tend to hunt around for speed unless I had a load of around 500 or more watts connected to it. Then it smoothed out some and got better with a 1 kw load. Using fresh gas without the ethanol in it seemed to help some too.

This is a generator about 20 years old, but does not have very many hours on it. I don't worry about the waveform. It does not have any voltage regulator circuit in it and just relies on the governor of the engine to hold it constnt.

There used to be a big thing about the generators not suited for electronics in hte past. I don't buy that for the general home electronics unless maybe some high end sterio equipment. The computer supplies are designed for wide ranges of power and the digital TV sets do not depend on the frequency being 60 HZ. Most electronics for the home now use switching power supplies and those things generate very dirty power theirsleves.

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!

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.

. It leaves a highly polished surface that only removes the oxides.

y 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.

I used to rebuild vacuum clean motors as a sideline. The customer kept a sking 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 po wer supply and polish the commutator with the motor running at a reduced sp eed. He gave me all his bad motors. I sold them back to him at half the who lesale price, with over a 50% recover rate. Many didn't run because the com mutator was so nasty. I reground a blade for my Exacto knife to undercut th e mica spacers. A lot of the time it only took five minutes to revive a mot or. He never did figure it out, but he never brought back any of my repaire d motors. Other had bad bearings or burnt windings so they were stripped an d the good parts were used to make a good fan. I ended up with scrap alumin um and copper from the scrap parts, as well. :)

Ink erasers are still available, but you might have to go o an office su pply 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.

per. It leaves a highly polished surface that only removes the oxides.

only have to be close. Also, without a load the output isn't a clean sine w ave. Any inductive load helps to clean up their output.

t 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 repa ired 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 alu minum and copper from the scrap parts, as well. :)

supply store or buy them online.

I've replaced a lot of brushes in Alternators and Starters. I had to junk o ne Alternator because a weld was broken where a wire was attached to a slip ring. Solder wouldn't hold and I couldn't get it welded. I bought another alternator at a junkyard for $20. The owner read the GM markings and said i t was a low current model. He as wrong.it was the highest current version.

I installed and repaired car radios right after I graduated. My first car w as a '63 Pontiac Catalina convertable. It was seven yeas old, but some peop le thought anything over two years old was junk.

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.

(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.

Thanks for the replies.

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.

[snip]

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:

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

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

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:

- the specs claim +-5% voltage - how can that be without regulation? They lie. Maybe they mean +-5% at full load.

I found this at

"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.