Any generator mechanics out there?

[cmdan]

This is a Mi-T-M Gen-3000-0mH0 Generator, I picked up. The Honda 5.5 hp engine runs good, the gen is only putting our 3.6 volts ac. Pulled the back cover, and checked all 4 wires to ground and none are grounded. I did notice, there are .7 ohm from the bottom left whit wire to the top right black wire and the same right top to bottom left wire. No reading side to side or top to bottom (same sides) there are 2 black wires and 2 white wires going to the connector out the back of the gen. I was thinking it may be the brushes, but just found out, some gens don't have brushes. Thought I'd post here to see if anyone has run across this before.
Also:
I just removed the generator part and there are no brushes. has a little rust on commutator or what ever the winding that spins, is called.

Another thing that seems odd, is nothing is magnetic. Seems like the stationary windings should have magnets around them.

[Curbie]

Well I'm not a generator mechanic but it sounds like your generator needs "flashing", basically it sound like your generator is an excited field (electro-magnet) type, not a permanent magnet type. What can happen with these excited field type generators is that the iron core that serves as a magnet when electrically excited looses charge over time and since there is no magnet to produce electricity, there no electricity to excite the field.

I've never tried this, but it comes from Briggs & Stratton Customer Education Department.

http://www.perr.com/tip16.html

Now, there another way to flash generator's with a 12V battery but if it's done wrong it can harm the exciter coil, I'd try the link first, it doesn't look harmful to the generator.

Good luck and be careful.

Curbie

[cmdan]

Thanks, I went to that site, which looks to have a lot of info. I try'd applying power, like it said, but that is for a system with brushes, mine is brushless. Found another guy who said to max out the throttle for 2-3 seconds and see it that worked, but it didn't. I'm still broken

[Curbie]

Well you can try Googling "flashing generator field", but word of warning first; you can burn out your generator's field coil by applying some of the direct battery to field coil fixes, so be careful and safe.

Hope this is even the problem, my only other thought would be the diodes because there is just not that much to these modern generators.

You didn't say how and when this generator died? If it was fine when it last ran and sat for a while, then the issue popped up when it was next started, I would think it's a "Flashing" issue. If it was something that happened while running, overloading, shorting, or something, I can't say what the fix would be, too many variables.

Good Luck.

Curbie

[cmdan]

I bought the generator not working. I thought I might be able to change the brushes and get it going, but it is a brushless type. I pulled off the housing to take a better look and found a crack in the plastic the windings go around. I guess I'm looking for a new gen head assy.

http://c2.ac-images.myspacecdn.com/images02/73/l_fb57c68b32164443938fa7ff87071c89.jpg

http://c3.ac-images.myspacecdn.com/images02/100/l_29591b89adb2418da0eac4fcb6c4816a.jpg

[backlash]

Maybe you can get the windings rewound.
Should be a place in Seattle that can do that cheaper than a new one.
backlash

[Curbie]

I bought the generator not working. I thought I might be able to change the brushes and get it going, but it is a brushless type. I pulled off the housing to take a better look and found a crack in the plastic the windings go around. I guess I'm looking for a new gen head assy.

I'm guessing the generator head was over-heated under load, the heat weakened the plastic and the load fractured it. I'd be a bit concerned about spending money to rewinding weakened (over-heated) plastic, but that's your call.

I hoping you got a good enough deal on the original purchase to to make all this worth while.

Good try, bad roll of the dice.

Curbie

[cmdan]

Ya, you just never know. I picked the gen up for 50.00. I figured the engine was worth more than that. We'll see.

Thanks everyone, I'll keep checking ebay and such for a while, maybe I'll find something.

[Curbie]

A good running Honda 5.5 hp engine is worth way more than 50, keep an eye on craigs list too, maybe find something a little closer. (shipping)

Good luck.

Curbie

[cmdan]

I just talked to my bro, who is an electrician, he said my ohm readings are good, and the crack may not be an issue. He said to check the diodes, since there is only two of them and it is apart, I'll check them tomorrow. If all else fails, I found this one:

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200395476_200395476

but mine looks like this one, which is a 4K instead of a 3K.

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200395477_200395477

[Curbie]

For future reference, what were the the ohm readings?

Were you able to check both rotor and stator coil?

Curbie

[cmdan]

Stator is the outer windings, right? Then the stator measured .7 ohms on each side. I removed the diodes and tested them, I don't have a needle type meeter here, but in diode setting, I get a beep one way but not the other, so I guess they were ok. Didn't think to measure the rotor. I will do that, later. I heading to the dentist to get two temp crowns....thought about skipping that. :(

[Curbie]

The stator is the the part that's stationary (hence the word), the rotor is the part that rotates (hence the word), generally speaking, all that is needed to produce electricity is a magnetic field, a wire, and motion. It doesn't matter whether the magnet or wire moves, as long as one of the two are in motion the magnetic field induces electricity on the wire.

I'm more familiar with Permanent Magnet Alternators (PMA) than Electro Magnet
Alternators (EMA), as in wind turbines and such, but the magnetic field, wire, and motion principles are the same for both, although EMA's typically use a lot more electronics some of which is used to control the current to the rotor to produce the electro magnet and some even have built-in inverters which I have no experience with.

*** Gain of salt time because my experience is with wind-turbines and such ***
When the rotor coil is charged it turns the rotor into a single (form the looks of the photo) North and South pole electro magnet which is spun by the motor inside (at least) one PAIR of stator coils, one for positive induction and one negative induction (alternating current) depending the relative (remember it's spinning) position of the now magnetic rotor.

About the only way to stop a PMA from producing electricity is to stop the motion or smoke the coils, since your EMA show no real signs visual damage, I'm guessing control electronic, either excitement current, or output frequency or load control all of which I have no experience with.

I started out fixing computers, and my experience their says start with the easiest stuff. If you've run the generator and the rotor was getting excited, it should still be magnetic, it takes months for them to demagnetize. Which brings me back to "Flashing" which is the most common solution for this which sound like a very common problem.

The Briggs & Stratton link wasn't right for your generator, did you try the 12v battery type flashing?

Curbie

[cmdan]

Thanks,

yes, the 12 volt battery was the first thing I try'd. I momentarily supplied 12 volts to the outlet with the engine off. I did it twice and got a small spark each time.

Well, the diodes checked out good, I checked the windings on the rotor, with the diodes removed and both sides had the same reading. Under the diodes there is a little blue thing with two wires coming out, one to each side of the diode. Don't know what they are, I'm thinking some kind of regulator of something. There is a capasitor, that I haven't looked at yet, don't know how to check it.

I also noticed a small darker spot on the stator in the back, I could get resistance (.006 ohms) if I test from the dark spot to one of the terminals on the plug. I couldn't get a reading anywhere else, so I'm thinking that is a short.......

[cmdan]

I just found this site and was able to test my capacitor.

http://www.desatech.com/pdf/113034-01.pdf

If I can't get it running, I found the genset head I'm going with, looks just like the old on and should bolt right up, but I haven't given up on the old one yet! It is too easy to just give up and buy a new one:

http://www.blastwholesale.com/proddetail.php?prod=GSH10543

The old genhead is peak 3K and constant 2450 watt, this one is peak 3625 and costant 2900 watt.....might be a better deal.

This is the generator new.
http://www.everygenerator.com/Mi-T-M-GEN-3000-0MH0-MTM1025.html

[Curbie]

Most folks (I've talk to) flash WITH the engine running, but it should work either way. Dark spots are the first thing I look for on PMAs and almost always indicate a short with PMAs.

If your "Flashing" is creating even the slightest magnetism in the rotor that should get current flow started and there should also be residual magnetism remaining.

If you've got residual magnetism the problem has to be in the stator coils or control electronics, and if your seeing dark (burned) spots on the stator coils, you're probably right about the shorted stator.

Curbie

[Bones]

How about a generator that the power kicks in and then kicks off kicks in and kicks off.

This started when I lived in Bermuda 1991 and after a huricane I let a Neighbor tap into an outlet to keep his fridge running but he had to put fuel in during the day when I was at work. He ran it out of gas I am sure several times under load. I have kept it because the engine still runs and figured some day I would find out what was wrong with it.

[Curbie]

As I said in a previous post I'm not a generator mechanic, but from my experience fixing things cmdan took a pretty systematic approach to diagnosing his generator's problem.

There's just not much to the concept of generating electricity as laid out in this thread; magnets, coils, motion and control.

You have something going for your diagnostic efforts the cmdan didn't; a partially functioning machine, I would devise a systematic approach to diagnosing your generator's problem. Note obvious burns or damage, next meter the field excitement power and output power for what's fluctuating, then back-trace to the cause.

Good luck, and be careful.

Curbie