[AZ-Observing] Re: MSW inverters

Dan,

As Gene has already stated a power inverter would  work as is, but you would 
not have much control  over the frequency output.
A number of years ago (a big number of years ago) I built a variable 
frequency converter to power a 5 watt synchronous motor on my Cave mount. If 
you have access to old issues of Sky and Telescope there was a neat and 
simple circuit  to run the motor that was frequency adjustable. I looked in 
the Sky and Telescope index and the article was in the December 1978 issue 
page 566. Yes I know this goes back away, but so do I . I looked for my 
copy, but cannot  find it at this time. Maybe Lloyd Horton has the issue if 
you don't ( yes Lloyd and I go back a ways also)

Hope this helps
Ken Sikes




----- Original Message ----- 
From: "Dan Heim" <dan@xxxxxxxxxxxxx>
To: <az-observing@xxxxxxxxxxxxx>
Sent: Monday, October 27, 2008 3:10 PM
Subject: [AZ-Observing] Re: MSW inverters


Gene,

Yeah, I figured I'd be ok, but wanted to run the idea by the experts on this
forum first.  The unit I'm looking at is this one:

http://www.boatandrvaccessories.com/852-2071.htm

DFAC is going to be setting up for some public solar observing in Anthem
after the Veterans Day parade, and I could haul along my extension cord like
I usually do, but that's always a tripping hazard (especially at 100 feet
plus and little kids running around).  This unit is WAY more power than I
need for the scope, but would be handy to have around for other purposes.  I
don't need this for astrophotography ... just visual, so I'm sure the
tracking will be just fine.  Thanks for the info!

Dan Heim

----- Original Message ----- 
From: "gene lucas" <geneluca@xxxxxxxxxxxxx>
To: <az-observing@xxxxxxxxxxxxx>
Sent: Monday, October 27, 2008 2:08 PM
Subject: [AZ-Observing] Re: MSW inverters


> Hi Dan,
> I believe the little clock motors in the older synchronous motor drives
> can be successfully operated from just about any of the small DC to AC
> power inverters.  No need for one of the monster capacity ones, either.
> One of the small 50 watt units designed to plug into your cigarette
> lighter should work.
> Although those small inverters don't typically output pure sine wave AC,
> the issue is mainly the >frequency< of the AC.  That is, whether or not
> the unit is adjusted to give exactly 60 Hz output.  Now, most of those
> older telescope clock drives will run at a >solar< rate from "wall
> current", that is, exactly 60 Hz.  The older separate drive inverters
> had controls to change the frequency appropriately to give an exact
>  >sidereal< rate, by adjusting the output frequency to a bit less than
> 60 Hz.
> So IF you were electronically enabled (or know someone who is), it is
> possible to go inside the power inverter and make an adjustment for that
> -- (voiding the warranty on the inverter, of course).  Then the clock
> drive could be operated at sidearal rate.
> The non- pure sine wave AC will result in a bit of extra "heat" from the
> clock drive motor, (should not be any problem, as the clock motor only
> draws a couple of watts of electricity), and the exact 60 Hz output from
> the inverter will mean that the telescope will track a bit fast, that
> is, at a rate exact for the sun instead of the stars.  For visual
> observing, this should not be a problem.
>
> For reference, I have "reverse-engineered" my old Orion drive inverter
> (I re-packaged it many years ago) -- the circuit is pretty simple, and
>  >>could<< be duplicated pretty easily at moderate cost by an
> electronics tech.  (In fact, that unit does NOT put out a "pure sine
> wave" -- rather, pretty much a square wave AC, and operates synchronous
> clock drives just fine.)  Also, there are several web pages that show
> circuits for such units, some more involved than others.  For instance,
> look at Dr. Michael Covington's web pages on his modern "ALCOR" inverter
> design:
> http://www.ai.uga.edu/~mc/alcor/alcor.pdf
>
> Cheers,
>
> Gene Lucas
> (17250)
> Dan Heim wrote:
> > Fellow Stargazers,
> > I trying to find a way to power my old (ca. 1985) Orion drive system
remotely and lose the need for an extension cord.  It's a single RA drive,
with a synchronous 120 VAC motor.  What I'm wondering is, has anyone used a
modified sine wave inverter to power these things?  True sine wave inverters
are prohibitively expensive.  I'm concerned about tracking accuracy, of
course, and possible damage to the motor.  My online search provided
conflicting advice.
> >
> > Dan Heim
> >
>
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>

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