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 > -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list.