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Registered Member #4014
Joined: Wed Jul 20 2011, 05:31PM
Location: SE Michigan
Posts: 25
I saw this on ebay
It seems like a simple solution to an expensive variac. I have a few questions though. Would the output still be 50/60Hz? This would be cool to mess around with my ZVS using a power transformer as a ballast. Any ideas? Thanks
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
That is basically a light dimmer, and while it will work great for resistive loads (lightbubs, heaters) I suspect that if you try to drive a transformer from it it won't last very long. it is possible to drive transformers using a triac like that, but you need to add an additional snubber network to keep from killing the triac.
He does say it works for motors, so I suppose it is worth a try...
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Definitely worth a try, seeing as its only $10...I doubt its very robust, and I highly doubt it can drive an inductive load at 3.8KW (the 40A is probably the absolute limit of the thyristor it uses).
Registered Member #4014
Joined: Wed Jul 20 2011, 05:31PM
Location: SE Michigan
Posts: 25
Okay, when some money, I will buy one and make a review on it. I figure 20A to be more of a suitable max. If it is a triac, it cannot power a normal 60HZ transformer as I tried it with a light dimmer. Although, I did not use a capacitor in series with the transformer and triac, I should.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Could you use a light dimmer circuit as a DC power supply? Since the SCR cuts off certain parts of the wave, then you could vary the voltage accordingly, and then smooth it out with a capacitor giving a nice variable DC power supply.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I have seen these used for inductive loads such as MOTs and they seem to work just fine. I wouldn't try to use them at their max rated current with an inductive load though, it might work but then it might not.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
A much more stable approach to this is getting a Variable Frequency Drive and connect a 3 phased transformer instead of a motor, it will also need some capacitors to insure proper operation.
The transformer will make strange and often mechanical stress sounds, but it works like a charm for generating all the voltages you want. At a former workplace we had one that could give 3 phased 200-230-380-400-440-480-690 Volts from a 3x400 Volt input.
A VFD is built for inductive loads in difference to the dimmer circuits, a VFD is also a great build quality and have many protective circuits to insure a long life.
Gettting a used 1kW VFD should be no significant expense unless you want one right away, find the right places to look and they come cheap :)
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Inducktion wrote ...
Could you use a light dimmer circuit as a DC power supply? Since the SCR cuts off certain parts of the wave, then you could vary the voltage accordingly, and then smooth it out with a capacitor giving a nice variable DC power supply.
Hrm... that's an idea. DC variac, unregulated but meh.
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
I'd suggest putting a certain amount of inductance in series with that capacitor otherwise you could get a fairly large current spike when the thyristor turns on.
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3.8KW 40A 220V Power Adjustable Thyristo
