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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Possibly yes, but if it fires irreguarly (which most of the cheap ones do with inductive load), it might cause DC saturation of the cores and damage to the dimmer / popped breaker.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Do not use a light dimmer, they are designed for resistive, not inductive loads. If you insist on using a dimmer, use a fan motor speed control, they are more pricey but their heatsinked and should be able to take some load.
Don't forget to ballast your MOT otherwise it will draw more than enough current to pop your shiny speed controller.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Variacs are a little expensive here on Brazil to use them :P a 10A one we pay something around US$560...
A long time ago I think about a mosfet in series with the primary and Gate voltage control to control the resistence, but it only works for DC, for AC I dont know what it can be used.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I designed these to drive SCRs for DC bus voltage control of solid-state coils. However, they seem to work fine with everything from vacuum cleaner motors to NSTs. Here is the Mk2 circuit dimming a neon sign:
A few other people here have built these, search the forum archives for more details. The main difference is that the Mk1 is controlled by a variable resistor, the Mk2 by a voltage, which makes it easier to drive remotely over a long cable.
Also, the component values are set for 50Hz mains frequency.
Variacs are always expensive new. But you can often pick up a used one cheap or even free.
Registered Member #989
Joined: Sat Sept 08 2007, 02:15AM
Location: São Paulo, Brazil
Posts: 476
Hmm interesting circuits Steve! I will try to adapt it to 60Hz to Alexandre use (I have a low power variac, 5A 220V as Alexandre (I gave one for him), but for MOT's its a bit underpowered :P), buying on ebay is not a good think when you are on Brazil. But sometimes we find someone who is selling a variac at Mercado Livre (eBay from Brazil, actually, its from ebay group)
But for SCR's, we can find a lot of it for cheap prices here, and for a mot (Maybe 50A at 220VAC?) they are small ones.
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Control of Voltage
