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Old Generator power low

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Ongoing fiddling continues. I've pulled each contact from the connector that connects the bell to the windings and flowed solder into the crimped connections. The ohmeter says I have zero resistance through the power windings. I have 3 ohms through the control winding with 1.3 ohms on each side to the center tap. I have zero ohms at the rotor winding.

I understand that I may have a short in a winding, but with all of the wraps there are in a winding wouldn't a short in a winding just make the voltage a bit low? Whatever it is takes my field voltage to half of normal. The problem appeared to be temperature related. I have done tests outdoors - below freezing. Today I have all of the coils indoors at 70°F. Maybe I'll put it all in the oven and take it to 100°F and check it again. It seems that something should change value but not fully fail.
 
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I would have bet 10:1 it was the diodes. I was sold on that. The same darn problem returns and now the capacitor and diodes have been replaced. I have never seen a winding fail, granted they can fail and do but the other parts are the more common failure items I have seen.

I am not sure what you should be seeing for resistances. You could take a few readings from your known good unit and maybe get an idea, a rough idea anyway.

Ron
 
Ron, I'm thinking a few readings from the good unit is my next step. Yesterday I was convinced that the connections in this unit are all soldered because everything in the bell is soldered. But I started pulling the terminals out of the connector body and found that they are all crimped. I keep what's left of a very old roll of solder because it dates back to when the core was a very aggressive flux and the solder was 60/40 lead. And I used my big solder gun to get enough heat to boil out the corrosion. The new joints wick solder in nicely and may have tightened a bad joint. Today I'll give it a run and if I get the same low output, I'll dig into my Generac and get readings.

Thanks for staying with me on this. It's lonely out here in wierdo land. Mark
 
Ron, I took the end off my Generac to see what I could learn. I expected the Generac to be similar to the Aggie - same size, same output. Ya know? But there's a reason why the Generac company is growing and Coleman Powermate is out of business.
The Generac uses one primary AC output coil - the Aggie uses a pair per the diagram. The Generac uses a full wave rectifier - the Aggie uses a half wave. All of the wires on the Aggie run through a connector plug to the removable front panel (bell) so there are plenty of potential connection problems. The Generac is wired inside the bell. Lots harder to work on, but there are only 4 connections inside - two spade terminals at the rectifier pc board and a pair of bullet connectors leading to the 120v outlet on the faceplate of the Generac.
I did take a reading inside the Generac. Just like the Aggie, I read 0 ohms at the primary output winding and 3 ohms at the exciter winding. The Aggie reads 1.5 ohms from the center tap to each side. The Generac has no center tap.
One thing has changed on the Aggie. I used to get 2 1/2 minutes of good power. Now I don't it's always in 'Failed' mode. And I'm still stumped.
 
I don't know what the heck is kicking our butts on this. I actually have a 4 KW Powermate in the shed and run it every now and then as it is a backup to the backup. :)

I have a natural gas 18 KW Generac in the yard which could likely power a few houses on my street. Every Saturday at 1:30 PM it exercises itself.

I don't get the resistance readings. We are missing something and damned if I know what it is. Now it won't work at all so what the hell are we not seeing in this?

Ron
 
Sorry about the cheap shot a PowerMate. There's nothing inherently wrong with the design of the PowerMate. They get the job done with very few components. And I've learned to field strip it in two minutes flat! I have the Generac as a back-up to the back-up. If we have a long duration outage, it will carry me in emergency mode with half the fuel usage of the larger unit.

Back on subject - It would be far easier to troubleshoot if it would just FAIL!! But it's only half failed. It has two legs in the control winding and they are exactly the same. There are two windings at the AC output - and they both read fine. The issue is certainly on the field creation side.

TCMTECH had the interesting idea of removing the half wave and installing a full wave rectifier on one side of the primary. That should get me the dc voltage I need for the rotor windings. Anyhow, if I used a full wave rectifier on one leg of the primary circuit and it will create the proper output in the generator, at that point I'm done. So . . . what am I missing with that plan? TCMTECH - feel free to jump in and give me some direction. I think all the components in a full wave are Radio Shack items??
And as he suggested, IF I had a 60 - 70 volt supply I'd try externally powering the rotor. No doubt the output would be fine. When the primary side hits 65 - 70vdc the AC out is perfect.
This Aggie isn't a customer piece in for repair. I don't depend on it for anything. Unless someone who really wants this generator shows up with some cash I think I'm in for the long haul on this problem. IF I find an old PowerMate, the parts are interchangable.
Mark
 
Given that the rotor field normally runs on around 65 -70 volts It seems that it should have roughly around 40 - 60 ohms of resistance. The field on a smaller generator does not take much power. I have many high amp alternators that are 28 volt 100 amp rated that would be a rough equivalent to a 2500 -3000 watt generator. Their fields at maximum output only take around 60 watts on average.
So assuming that your generator rotor used between 60 and 120 watts at 65 volts DC the resistance should read around 30 - 60 ohms give or take. The fact you seem to be getting a near zero reading seems suspicious at this point.

It would be interesting to see if there is an amps draw jump in the rotor when the voltage goes down. If the system voltage goes down but the amps draw going to the rotor went up instead that would be a solid indicator of a partial short.
Its also the only logical place a generator such as this could develop a shorted winding without having anything burn up. Any short in the exciter windings would be carrying an AC current and would quickly burn itself up.
However being the rotor works on DC a shorted coil only creates less resistance and does not induce a circulating short circuit current in the shorted section of the winding so it doesn't burn up from it.

You could try powering the rotor externally with a battery charger or two in series to get a higher voltage and see if the amps go up at some point as it warms up. Normally the winding resistance on a rotor coil will give a steady decrease in current as it warms up. This test could be done outside of the generator as well.
 
I like tcmtech's thinking. It would be nice if you could externally power the field and see what you get. I still have those 35 Amp 400V full wave bridges if you want one. If you have a variac even a 5 amp one you could drive the bridge and the field with a varying voltage and work up slowly. Unloaded the system shouldn't need much field current.

I would definitely try some of tcmtech's suggestions.

Ron
 
tcmtech - I'm not ignoring your input in areas where I don't respond. I simply don't have the resources to take the measurements.

I've read of 'flashing' the output by flicking a 120vac wire across a pair of wires leading from the 120v outlets. It's just a flick to induce a current.
Or I could flash a 24v pulse on the rotor using my small power supply. I have a power supply made from an old computer power supply but I don't get more than 24vdc from that.

Here's one for tcmtech - my Generac has 3 ohms on the rotor windings with the bridge rectifier circuit removed. It gives me a full 20 amps at 109vac any time I ask for it. 3 ohms on that winding is just fine. I don't think you're wrong - It's far more likely that I don't understand part of this. What am I missing?

Another question;
I have 4 older 12volt batteries available. That's 48 volts to run the field. I can add in my charger at 12 volts and get 60 volts. Fresh 12v batteries put out 13volts. That would give me 60+ volts. To make this work, do I simply clip the 60 volts to the brushes? Seems like I'm gonna glow a wire somewhere in the circuit. The generator is creating 38 volts of rectified dc on its own. If I throw in pure DC that's gotta mess something up. It seems like I should be removing the diodes so it doesn't make any dc on its own. I'm running in uncharted waters here. Some navigational aid would be appreciated. I don't want to kill the generator. Or me either . . . YIKES!!

Ron, you mentioned putting your full bridge on one leg of my rotor winding. Assuming that one leg is good (even though both legs measure the same) I should get full dc voltage from that one leg. Right? If one side doesn't work, I could try the other side. If either side gives me the dc voltage I need, that should run the primary side of the generator and it'll work that way. Right? Don't lose that full wave bridge.

Wow - way more questions than answers on this end!
 
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Because I'm running out of ideas, I put a WANTED ad on craislist. I put out a call for a used,
cheap Ag-Tronics generator. I noted that I wouldn't pay much and it doesn't have to work. I need
it for parts. And I got an email this morning from a lady who says she has an Ag-Tronic to get rid
of. She got a new generator and wants the old one gone. And she did seem to know what an
Ag-Tronic is. I'll get an email later today with a photo. Stay tuned.
 
Sounds like the beginnings of an AG Tronic family. :)

I will hopefully have a few answers for you later as I am at work right now. Monday's really suck!

Ron
 
I have an answer to the generator problem. If I can find someone who will figure out which winding is bad, rewind it for free, and give me $37 I'll be all set.
So Simple! Why didn't I think of that before?
Gotta be a winding. Which winding doesn't really matter. I have $187 in a $150 generator. My bad. If I get lucky and find a non-working PowerMate for parts I'll be fine. Otherwise, I invested in my education and I'm way better armed with generator functionality! I'm no smarter, but I'm certainly better informed than I was.
 
Ron - laugh out loud now if you like. I just found a Coleman Powermate 2200 watt with a blown engine. It's even the same color as my Ag Tronic. Same castings - same part. The one I found has a broken rod. Probably ran out of oil and seized the rod bearing. It didn't break the crank so the genny rotor should be fine. And it was generating when it blew the engine. Just what I'm looking for. $30 and 20 miles away. I get it tomorrow afternoon.
Har Har Har.
 
That is incredible. Like a giant parts locker for the cheap. This is really getting good as well as funny. :)

Ron
 
The timing is perfect. My father in law was over today to try 'just one more time'. He was convinced the I had missed a connection or there was a corroded terminal or something. He used the lighted magnifier and checked for proper wicking at each solder connection and bright metal on each contact terminal. I told him "I've been driving for a month and I can't find it. You drive". So he worked all the angles until he was satisfied that the only thing left is a winding. Somewhere.
And with that we were both done. He wished me luck and went home for a nap. And my first search today found my donor genny. Now we hope it works and I can get the rotor off the engine crankshaft. I still have an opportunity to break it.
 
As far as powering the rotor externally as long as you have the same or less voltage it doesn't mater how you get it. DC is DC for the most part in this aplication. Basically all you are doing is eliminating the possibility that the short is in the exciter coils on the stator. If you power the rotor externally and the output voltage does not change the shorted exciter coils will eventually burn themselves out and show up.
For the external power test all you need to do is unhook the exciter coils and make sure you have the correct polarity going the rotor and capacitor.

On another note I have found that the old portable generators either have a tapered engine crankshaft and the rotor is held in place by a long bolt or a screw that goes through the rotor shaft. The the other version I have seen is where the rotor is threaded and just screws onto the engine crankshaft. Its threaded so the when the engine is turning it would be screwing itself on tighter so keep that in mind as to which direction you have to unscrew it if you have that design.
 
I'm committed now. I broke the old rotor. That's the rotor for the generator head that doesn't work anyhow. Good news is that I bought a new(er) generator head for $30. It's a 2003 powermate 2500 head - the same rating as the Ag Tronic. The engine code for the Powermate Briggs and Stratton and the Briggs mounted to the Ag Tronics is a perfect match, so I'll assume that the shaft is a taper with a center bolt. I got the PowerMate generator head off with no difficulty at all. The engine is broken - oil starved and stuck the rod to the crank from the look of the crank. I have to get the gen head off the Aggie and I'll be ready to make the switch.
The PowerMate is new enough that it has the plastic bell. Bummer. And where the old Aggie had a pair of windings for the AC output, the new one has a single winding. I could probably rewire the connector and use the old aluminum head and no one would know. Swap diodes, rewire and be good to go. I'll look into that.
Is there any special trick to mounting the new armature on the engine taper? Just dry mount it and let it rust or . . . ?
 
Just dry mount it and let it rust or . . . ?

Thats about all there is to it. push it together and tighten the bolt.
 
I am finally to the "Dry mount it and let it rust" part of this. I did purchase a donor unit - I noted that a couple of days ago. The donor is a 1989 - I misread the date code. The treat was getting the junk genny extracted from the good engine. There is no doubt as to the disposition of the old rotor. I cut the windings off with a hacksaw, punched the wire pack out of the winding frame, tore the winding frame off the center shaft 6 plates at a time after I 'loosened things up' with a sawzall, then took the center shaft off with a torch and hammer. I have amassed quite a pile of crap. The good news is that the new genny mounts right up to the engine.

I may dry fit the original field winding unit and head over the new rotor just to see if it all aligns. If it does, I may even give it a test run. If the problem was my in my rotor, I'll have a repaired Ag Tronic.
QUESTION: The old Aggie used a pair of windings for the AC output. The PowerMate uses a single winding. They both have a center tap. If the original center section (windings) and the head end of the generator physically fit together, is there anything about the new rotor that might mess things up? I sure don't want to break it or overheat anything. My choice is to sell either a newer PowerMate or an old classic Ag Tronic.
Now let's hope that the new generator head does work. It was running a heavy load when the connecting rod in the engine blew. It should be fine. So I'm told.
 
The new generator is on the old engine. I swapped engine shrouds and such to the old engine so it looks more consistent. And it all works perfectly! I haven't done a stress test so I can advertise the results, but it handles the loads I've given it just fine. !0 minutes and it's sounding great.
A million thanks to everyone who jumped in here with help, advice or just interest in the subject. I really learned a bunch and that was the purpose of this whole deal.
Mark
 
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