automated variac 0-220Vac

[missk]

Hi

I need to use an Atmega MCU to vary the voltage from 0-220Vac on the primary of a 220V//2000V transformer. I was looking into using a stepper motor to control a variac using a pulley/belt system. But considering that this is only a part of the bigger picture, it seems complex as I need to take into account torque considerations and such.Any chance that somebody may have a better or different idea?

 

[Reloadron]

You want a motor driven varible transformer. You don't mention the load current? Transformers of this type are generally direct drive or gear (no belt or pulley) and driven by a synchronous AC motor. They come in various speeds. You mnay want to get some ideas from this link. Paying attention to motor driven and controllers. That should give you some ideas. I assume you are working from 220 V mains? The load current will determine the KVA rating you need. Most al;so have max and min limit switches so you can't overtravel.

Ron

 

[ronsimpson]

I used a motor driven transformer years ago. It moved slow. There was two voltage set points. Two voltage compareitors. If the voltage was below the low level then turn clockwise. If voltage above high level turn down direction. If the voltage is in range = motor off. No Atmega MCU. No stepper motor. 12V dc reversible motor. two relays

 

[missk]

hi guys

Thanks for the response. Good ideas,but What If I were to use my microcontroller and a digital to analogue converter to create a variable AC waveform. Then I will use a high power op amp, which will feed into a step up transformer to enable me to go from 0-220V ac. Do you think the idea has any merit?

Also it keeps cost quite a bit lower.

 

[alec_t]

That would certainly work in principle. Whether or not it would be cost-effective would depend mainly on how much current you expect to get out of the tranny.

 

[Reloadron]

Yeah, it would work in principal and is done commercially. However, per Alec keep in mind that if you want any substantial current you will need a really large driver on the low end. Next generating a nice clean sine wave using A/D is not quite as easy as it may look on the surface. The more bits the better. You may want to give this a read to get some ideas as to one way of going about it. One amp at 200 V will require over 20 amps at 10 volts of drive. Commercial units that are designed to do this are large and expensive if you want high secondary current.

Ron