[Milsurplus] multi phase AC power

[Dr. William J. Schmidt, II]

Just reading the mail.  All of this is true.  My rotary converter is just a 
simple 3-phase motor (Delta inductor set) and sets of phase shifting/ 
compensating capacitors to generate the additional phases.  The twist in 
mine is the ability to shift in and out additional capacitance to adjust the 
phase errors on the fly.  The starter capacitor goes in series with the LINE 
to overcome the 90 degree lag on "switch on".  It is true that this system 
is load sensitive (sort of makes sense if you think about it... 
coil-cap-resistor networks).  But then it was only $250 to get 100 amps of 
3-phase power.  I found 40 mf 600V AC caps where I found the motor... got 
them with the motor (anyone need one?).  I've had VFDs over the years (in 
industrial settings)... big commercial ones like the Asea's... very very 
nice, but never been able to keep them functioning through line spikes...

Sincerely,

Dr. William J. Schmidt, II  K9HZ
Trustee of the North American QRO - Central Division Club - K9ZC

Email: bill at wjschmidt.com
WebPage: www.wjschmidt.com

"It's not what you take with you... but what you leave behind that counts. 
Live each day as if it were your last."


----- Original Message ----- 
From: "Mike Hanz" <AAF-Radio-1 at cox.net>
To: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
Cc: <Milsurplus at mailman.qth.net>; "Richard Brunner" <rbrunner at gis.net>
Sent: Monday, March 13, 2006 6:29 PM
Subject: Re: [Milsurplus] multi phase AC power


> It's a common workaround for small shops that cannot get three phase power 
> delivered to the doorstep.  I made one of the idler motor converters for 
> my shop and used it about a year before switching to a VFD system.  Bill 
> Schmidt's approach is essentially one of overpowering the tuning effects 
> with an order of magnitude sized idler.  It works fairly well, though 
> there are some drawbacks.  The size of capacitors to tune the "wild leg" 
> with a 30hp motor gets /really/ expensive unless you find some that are 
> surplus, and the waveform on the output is anything but a sine wave. 
> That's not much of an issue with another motor.  With smaller idler 
> motors, you will notice considerable growling noises from the frame 
> because of harmonic currents, and it doesn't adapt well to significantly 
> varying loads - the rule of thumb is an idler motor with a minimum of 
> 150% the load capacity of the driven load, and you have to derate the 
> driven motor capacity by a third.  The noise is what bothered me the most, 
> not to mention that a VFD has the ability to enormously pamper the motor 
> with its CPU based design (not a trivial consideration when my Hardinge 
> drive motor fetches $5K) and the ability to adjust frequency between 30 
> and 400Hz gives you a whole new dimension of usefulness.
>
> Just another data point.  You will find religious wars between the rotary 
> converter folks and VFD folks on the machining newsgroups.  :-)
>
> Best 73,
> Mike
>
> Kenneth G. Gordon wrote:
>
>>On 13 Mar 2006 at 16:26, Richard Brunner wrote:
>>
>>
>>>Dr. William J. Schmidt, II wrote:
>>>   My generator is a 30hp 3-phase motor with cap start and caps used to 
>>> correct the phase shift
>>>
>>>>for the second and third legs of the (generated) phase.  ....
>>>Do you mean you excite one phase single-phase, using a capacitor to the 
>>>third terminal for capacitive starting?  This is an interesting concept. 
>>>Normally when a three-phase motor is single-phased it quickly overheats 
>>>and burns up.  Of course you have no mechanical load on it, but I have 
>>>seen three-phase motors overheat and fail with little load on them. 
>>>Because the excited winding heats up eight times faster than normal, 
>>>normal overload protection is ineffective.
>>>
>>
>>I don't know for sure, but I am pretty certain that you and Doc. Schmidt 
>>are talking about two different things.
>>
>> I have several articles here on making three phase power from single 
>> phase, and the one that provides almost commercial quality three-
>>phase power from a single-phase uses an "idler" motor to do the 
>>conversion.
>>I think this is what Dr. Schmidt is talking about.
>>
>>No power is drawn from the motor using this method. It just sits there and 
>>runs. You have to size the motor to the load, and as I remember it, the 
>>motor has to be at least twice the size the anticipated load would 
>>indicate.
>>
>>I'll try to get some URLs together on it. I was fascinated when I read it. 
>>I had never heard of this method before about a year ago, but apparently 
>>it is being used successfully in many small machine shops around the U.S.
>>
>>Ken Gordon W7EKB
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>>
>>
>
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