switch load voltage from 220VAC to 170VAC and vice verca

Hi!

I need to drive a load with two different sine waves, 220V/50Hz or 170V/50Hz.
A first thought would be to use a transformer and switch the power supply from the secondary between 230V and 170V, using relays.
Is this a good way to do it? Are there better ways?
Any references or circuitry would be appreciated.

Thanks.

Relays are certainly an option; you don't say what your load is, though. If you've got a high-current, inductive load, you'll need a pretty robust relay. A zero-crossing SSR might be a good option.

Hi Barry!

The load is not inductive. Sorry, I don't have more info right now about the power rating of the load. Let's assume that the relays are capable of driving this load.
So I had this in mind. S1 (NO) and S2 (NC) switches will be controlled by uC. They will change their state simultaneously. When one of them is on, the other will be off.
Do I need something more, like an extra protection during switching? The switching will be taking place every 10 hours or so



Thanks.

use spdt relay having no & nc conection.

Instead of a transformer you could use an autoformer. It does not cost so much.

It has one winding. It still has a metal core, however.



You would need to find one with a tap at exactly the right position, to obtain the reduced voltage you want.

Another solution is a variac. Aka, variable transformer or autoformer.

BradtheRad said:

Instead of a transformer you could use an autoformer. It does not cost so much.

It has one winding. It still has a metal core, however.



You would need to find one with a tap at exactly the right position, to obtain the reduced voltage you want.

Another solution is a variac. Aka, variable transformer or autoformer.

Click to expand...

I think BradtheRad you mean autotransformer.

Do you know where i can buy autotransformer?

For the mains voltage regulators, I use triacs at the primary side to lower the cost of the transformer instead of regulating the output voltage at the secondary side. Obviously I produce the transformer as an autotransformer to reduce even more its cost (also its weight and volume) for the same rated power. But perhaps all this is irrelevant to the project here.

What I like pointing out is that using triacs smoothes the transition of current when switching from one terminal of the transformer to another. Naturally, in this case the MCU is interrupted by a zero-crossing detector and it turns on the next triac when necessary after a delay of about 3ms (for 50Hz mains) to ensure that the previous one turned off (that is; its current returned back to zero in case of inductive loads including the magnetic current of the transformer). This method avoids the interruption of any of the consecutive half cycles at transitions.

xxtigerxx said:

I think BradtheRad you mean autotransformer.

Do you know where i can buy autotransformer?

Click to expand...

A variac the easiest method for you to obtain the exact voltage you wish. A variac is adjustable.

If you are willing to try a used one, they are often available on Ebay. That's where I got a 2.5A variac for under $10.

The higher the amp rating, the higher the price, of course.

Thank you BradtheRad.

I want just 0.2A to 170VAC i do not want to change the voltage so i rely need a variac.
i will look at Ebay. but i want to use it in a project, so i want new ones.
If you now any distirbuter or manufactores it will be nice.