Author Topic: Sine wave power supply vs. stepped  (Read 336 times)

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Offline tony3d

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Sine wave power supply vs. stepped
« on: September 15, 2019, 08:38:39 pm »
Hi All,

Just wondering your thoughts on this. I bought a new Jackery 160 Lithium power Station. It’s very high quality build, but I elected not to buy the pure sign wave version because I intended to use it just for my Dew Heaters on my telescope. Now I’d like to also power the drive motors. Since this produces a stepped sine wave would there be a possibility of wacky mount tracking, or worse damage to the drive system?

Offline MagicSmoker

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Re: Sine wave power supply vs. stepped
« Reply #1 on: September 16, 2019, 02:34:19 pm »
Who knows... In fact, it is likely that even the telescope manufacturer can't advise you here.

If the telescope relies on the AC mains frequency for sidereal tracking then your battery + inverter system should work fine, as the frequency will be divided down from a crystal oscillator and so will have almost negligible drift/error from 60Hz (or 50Hz, for that matter). The "modified sine" waveform is really just a square wave with a peak value the same as the AC mains (e.g. - ~160-170V for 120VAC RMS) but a duty cycle of less than 50% so it has the same RMS value. Some power supplies - and certain kinds of AC motors* - really dislike this bit of chicanery, but there's no good way to predict that unless you have considerably more detail than the pictures you posted.

* - in particular, permanent split capacitor, induction and hysteresis motors really need to be supplied by a sinusoidal voltage

Offline Seekonk

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Re: Sine wave power supply vs. stepped
« Reply #2 on: September 16, 2019, 02:39:30 pm »
I would suspect that many adjustable heater controls are phase angle SCR type.  These would have problems with MSW. Or it just might not matter the exact temp as this is just to get mirror hotter than ambient. 

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