24kw AC generator frequency problem

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dburlesn
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24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 6:24 am

Based on what I have read in Nuts and Volts, I know you guys will know what is wrong.<p>!Important!
Supporting Documents & wiring diagrams:
http://www.utterpower.com/ST.htm
http://www.utterpower.com/ST_manual.pdf
!Important!<p>I'm using a fluke multimeter for measurments
and four RPM meters. so I am sure of the RPM!<p>HELP !!<p>
I purchased a single phase 24KW 60 hz 120vac/240vac 208Amp/104Amp 4 pole 1800rpm Generator to make my plasma cutter portable.
When I finally got it hooked up I got some strange readings when reading frequency.
Here are my readings:<p>U1 (Stator winding 1) to Neutral (U5-U6) 120vac 60 Hz @ 1800 RPM<p>U2 (Stator winding 2) to Neutral (U5-U6) 120vac 120 Hz @ 1800 RPM<p>U1 to U2 240vac 180 Hz @ 1800 RPM<p>Could it be the Rectifier?<p>Thanks
David<p>[email protected]

Dean Huster
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Re: 24kw AC generator frequency problem

Post by Dean Huster » Mon Jun 20, 2005 6:32 am

Because of the funny, yet harmonic numbers you have there, I'd slap an oscilloscope on the various outputs to see what the waveform looks like. Simple frequency counters, such as those built in as a DMM function, may be triggering on multiple crossover events supplied by a nasty-looking waveform vs. a nice sine wave.<p>What rectifier are you talking about here?<p>Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 7:01 am

Dean,<p>Look at the owners manual for a circuit diagram.
http://www.utterpower.com/ST_manual.pdf
and http://www.utterpower.com/ST.htm
for a good look at it's design, and slip rings.<p>If it is a nasty waveform, how can I clean it up?
A Cap on the DC output side?
and why is it only on winding #2?
Also as the brushes "wear in" will the wave form get better.
I've only run it for 15 min or so.

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Chris Smith
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Re: 24kw AC generator frequency problem

Post by Chris Smith » Mon Jun 20, 2005 10:57 am

Does Your plasma cutter involve any high frequency/ Fets/IGFets/ Etc?<p>Does Your generator operate fine on its own?

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 11:08 am

Chris,<p>No the Plasma does not use a high frequency start circuit. It is a Lincoln Procut 55<p>Generator, This is the 1st time I have ever started it.
Prior to hooking anything up, I checked the voltage and frequency.
Thats when I discovered this abnormality.<p>If it is just noise fooling my DMM how can I clean it up?

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philba
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Re: 24kw AC generator frequency problem

Post by philba » Mon Jun 20, 2005 1:51 pm

replace the DMM?<p>seriously, my guess is that you are fine. Most AC circuits have to deal with noise anyway. In most cases it just wont matter as the power either goes into a motor or resistive circuit that wont care or gets rectified and filtered (and doesn't care). <p>I'd be more worried about the shape of the "AC" wave form. Transformers, in particular, are most finicky about that. But, I bet you are ok there as well.<p>as said before, a scope will reveal all, though I'd use a resistive divider to protect the scope (or a 100X probe).<p>edit: sheesh, have you actually read the docs you linked to? this generator is as simple as they get. The only way you're going to get 120 hz is by running this beast at twice the speed - which I doubt is happening. Maybe you've misconfigured it but the doc shows the jumper configurations and they are bone head simple. Heck, I think I could service one of those puppies and I'm all thumbs.<p>[ June 20, 2005: Message edited by: philba ]</p>

upsmaster
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Re: 24kw AC generator frequency problem

Post by upsmaster » Mon Jun 20, 2005 2:11 pm

This is normal for a small AC generator just load it with some light bulbs, space heaters , and you will see the wave form smooth into a fairly nice sine wave... un loaded it will be very rough.. the more load the better...
joe

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 4:49 pm

It's a China special.LOL<p>My concern was THEY misconfigured it.
It just throws me off that one winding is 60 hz, and the other is 120hz
The Plasma cost $2,600.00
So you can see my aaaaaaa!!!!
When the DMM read 60hz, and 120hz and 180hz<p>I hooked up an old scope (hard to remember how to use it)to house current, got it to look right and took it outside.
I'll post the pictures as soon as I can, like 10 min. or so.

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 5:16 pm

OK, here are the pictures.
I did not shrink incase you need to zoom in on something.<p>Generator scope pictures<p>If you read the docs. then is this sine wave jaggedness caused by the rough (new) surface of the brushes, and slip rings?
or is it a poor rectifier?
or both?<p>Thanks for all your input!!!!!

Gorgon
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Re: 24kw AC generator frequency problem

Post by Gorgon » Mon Jun 20, 2005 5:18 pm

Hi David,
Correct me if I'm wrong, bur you never told us the voltage/frequency you wanted out of this generator. From your first posting I deduce that you want 230v/60Hz. Is that so?
I would have thought it to be 115v/60Hz. If so, U5 and U6 should not be connected together, but U1 to U6 and U2 to U5.
To measure anything useful you neeed to load the output with some minimum load. If not loaded, you will measure all sorts of funny harmonics and aliasing frequencies.<p>But first, connect the output either in serial (230v) or parallel (115v) mode. Load it with a lamp or something mostly resistive and then take your measurement.<p>TOK ;)
Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 5:41 pm

Well I'll have to think about what to load it with.
Any suggestions?
Lights seem too , well lite.
As for use. I want both 120 and 240 @60hz.
If you think about how your home panel box is wired.
L1, L2, and neutral
L1 120,
L2 120
L1-L2 240
I intend on wiring an outdoor main breaker panel (Square D) mounted above the generator.
From that I will wire outlets:
240v 50amp Plasma
240v 50amp Stick welder
120v 15amp Grinder
120v 15amp Drill
120v 15amp ????<p>Yes it totals more but like a house not all will be used at the same time.<p>The generator is rated 120vac 208amps, 240vac 104amps.<p>
Thanks
David

gerty
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Re: 24kw AC generator frequency problem

Post by gerty » Mon Jun 20, 2005 6:07 pm

Try an electric heater for a load. It'll suck the power and not put any 'noise' on your waveform.
Are you going to put some sort of cover over the generator, it doesn't look weatherproof...

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 6:13 pm

LOL,
Yes.<p>Right now I just cover it with a tarp.
After I get some more done I will have an idea of how it should be shaped and air flow.
The air compressor is in the way.
So it will probably be in two parts.
It really is a long work in progress.<p>I have several gauges, a contactor, E-Stop etc. still to mount.<p>Thanks
David

upsmaster
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Re: 24kw AC generator frequency problem

Post by upsmaster » Mon Jun 20, 2005 6:46 pm

wave form looks better than i would expect. your scope shows each leg 180 degrees apart normal for 120 to neutral the zero crossing are the same for both legs showing that they are the same hz if they were 60/120 the zero crossings would not match

joe

dburlesn
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Re: 24kw AC generator frequency problem

Post by dburlesn » Mon Jun 20, 2005 6:52 pm

would you say the distortion is caused by the brushes introducing noise into the DC excition field?<p>If so, normal wear would help?<p>David

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