Coleman Powermate low voltage

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Well,the OP mentioned "inverters" and MY post questioned why an inverter was used when the generator already makes a sine wave output. Then someone else mentioned Honda,and I researched that to answer my own question.

generating a sine wave from a DC supply requires switching large currents.the switchuing generates harmonics.
Now,the sine wave output may be very clean and right on freq,but the inverter's switching circuitry may radiate those harmonics,that could be picked up by other instruments. It takes very careful design to minimize radiated noise.
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Jim Yanik
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I have a similar problem with my 1850 but the output voltage drops at about 1100 watts load. The diodes appear ok, but I have no way to test the varistors in parallel with them. The problem started with a snapped governor lever which would have caused very high engine speed. That would have created a very high output voltage which I suspect could have damaged the diodes and/or varistors causing them to fail as the load increases. I hope to replace both and see what happens. Any thoughts?
I've put together a small page showing the repairs. http://members.rennlist.org/warren/1850.html
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You have simply got to be an engineer. No one else puts that much detail and work into repairing something.
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Probably a good thing you didn't visit my home page... :)
Stormin Mormon wrote:

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wrote:

Well, I never understood why, but, in automobile terms, I thought alternators had higher output at low speeds than generators did, but lower output at high speeds. Or that the voltage woudln't increase that much. A) Does your Powermate use an alternator? B) Am I right about what I thought. C) Would that make you wrong?

Did the load increase? Or did the load stay the same and output voltage increase? But I guess the second would make the voltage across both the dioades and the varistors increase, which is what you had in mind. Still, would that be enough to make them fail? I guess if they were not much better than the expected output one or both would.

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The generator operates at a constant speed of 3600RPM in order to produce a 60Hz output.
Under no load the output is about 120VAC. It remains relatively constant up to about 1100 watts load. After that as the load increases it drops considerably, down to about 90VAC with a 1300 watt load. It should be capable of 1500 watts output continuously at 120VAC.
The governor in the engine failed and would have caused it to rev very high at full throttle. During this time the output voltage would have gone very high, and possibly caused damage to the diodes and/or the varistors. These components are on the rotor, and somehow connect with the field coils. I'm still trying to understand better how a brushless output generator somewhat self regulates its output voltage.
I've repaired the governor problem, and the engine works well now. However the next step is to ensure all components on the generator side are good in order to produce the proper power output.

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Pumbaa wrote:

The frequency of the AC power is determined by the number of poles the genset has in relation to the speed. A two pole generator runs at 3600rpm whereas a four pole generator runs at 1800rpm. The output voltage is determined by the field voltage supplied by the voltage regulator. The field voltage may only be 12 volts DC to get the generator to output 120VAC. A small change in field voltage produces a large change in output.
TDD
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WOW, Thanks for all the response folks! Just to clear up some stuff, it is a two pole rotor so I believe I need 3600 RPM. Second, (unless I am really up in the night) there is NO inverter in this baby, it generates AC. It sounds like (particularly from people who have owned them) that there may be NOTHING wrong with it which is kinda' sad. Well, I am going to go out and tinker with it some more...
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Just one question: are you measuring the voltage under load, or under no load?
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On this gen, you don't get ANY voltage unless there is some sort of load... I have been using a 300 Watt shop light (just 'cause it was handy)
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Latest and Greatest.
Okay, I un-soldered the diodes and checked them one more time, good to go. Put the whole thing back together, and fired it up. Same problems, If I want 60Hz I get about 90 volts. If I want 120 Volts I get about 70Hz. (In my house for comparison the Kill A Watt shows 59.9Hz and 122.0 Volts) Just to see what would work, I tried hooking up my table saw, it took a second but it did spin up and I am sure that baby pulls some amps! I then tried my battery charger, no luck it would not even turn on (which is kind of the reason I want this gen anyway). And on the 12 Volt socket I get 24 Volts!!! I'm not out any money here, just time. But, after I burned my thumb on the exhaust trying to tweek the rpm's I decided enough is enough. If I had a shotgun I would end this units pain and suffering...
Thanks to everyone who posted Craig
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I actually bought a new engine for mine (the first one didn't last very long) and it just never seemed to have enough output. I even tried connecting it to a 4 HP Honda engine. I broke the cooling fan on the rotor when I connected it to a 10 HP engine, just to see if the low output was due to not enough engine power. I found another use for that Honda engine and I'm looking for another use for the replacement engine (compressor perhaps?). I replaced all the diodes, checked the resistors, checked the coils, and I just can't find anything wrong with it. Come to think of it, you may have a bad capacitor. That might cause the low frequency. Make sure you get one with the exact same value. It should at least get a battery charger to come on (assuming it's a high-frequency smart charger type). Your DC voltage seems a bit high but I wouldn't be surprised to see 17 or 18 volts. For emergency battery charging only.
BTW Coleman gets about $250 for a new rotor. The cooling fan on my cheap Chinese generator starting falling apart (at 3000 hours) and they only want $25 for a new rotor. The whole generator usually sells for about $250 (or less on sale). My Coleman engine only lasted about 300 hours.
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