Re: Control of Voltage
Dr. Dark Current, Sun Feb 15 2009, 06:50PM

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.

Re: Control of Voltage
Hon1nbo, Sun Feb 15 2009, 07:13PM

Have you considered using a variac?

Re: Control of Voltage
aonomus, Sun Feb 15 2009, 09:03PM

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.

Re: Control of Voltage
Alexandre, Sun Feb 15 2009, 09:53PM

Any scheme would have an electronic controller for transformers?
similar to a dimmer

Re: Control of Voltage
MRacerxdl, Sun Feb 15 2009, 10:27PM

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.

Re: Control of Voltage
Steve Conner, Mon Feb 16 2009, 10:40AM




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.

Re: Control of Voltage
MRacerxdl, Mon Feb 16 2009, 12:47PM

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.

Let me see what I can do :D

Re: Control of Voltage
Alexandre, Mon Feb 16 2009, 04:37PM

Interesting circuit, I will talk with Master racerxdl to see if we can adapt the circuits to 60Hz, which is not difficult.

We can even increase the power to control anything ..

Thanks Steve