Taps on Primary or Secondary?

we've seen this movie

Is this the one about the guy who asked the same question over and over.

Kinda like a cheep "Groundhog Day" of CR4?

Now, that OT is a cheep shot.

Sound like you should start a new thread and complain to the cr4 administration, " somebody is giving out free OT's!!

"

Or it's this guy........Fundacion

Re: Pressurizing Non Refillable Cylinders - Rigid Foam

but puzzle on one single question

Just the one?

I CANNOT recommend you attempt this due to the safety concerns, and designing and building a transformer of this size should NOT be undertaken unless you have proper electrical training and experience.

The fact that you don't know which side to put the additional turns on (and no I am not going in good conscience to tell you) indicates you shouldn't be attempting this yourself. I am assuming you mean turns to increase the output voltage not taps to add input or output voltage selection.

a variac is expensive in my country

A 12kW variac is going to be expensive anywhere.

Consider purchasing cheap UPS (uninterruptible power supplies) for appliances that don't like the voltage drop.

How can you make a transformer with out knowing where to put the tap changer weather in primary or secondry winding. 12000 watts means 12 kilowat quite a big transformer for an amature to make. Get the help of a trained and experienced and qualified Engineer and experienced winder to make it. It is not an ameture's job to make a transformer .

If you were building a two winding transformer, then the primary is the best location for the taps. Main reason is that the primary winding is normally on the outside and it is much easier to run the taps from there rather than from the inside.

With an auto transformer, there will be only one winding, so you would design it with taps either side of the 110v point to allow for input voltage variables. you could design it with extra taps out past the 240v point, but this would be a waste of resources.

Be aware that the auto transformer does not provide electrical isolation as does a two winding transformer, it also has lower input surge protection and, in the event of a winding insulation failure, can deliver full mains voltage to the load.

You must be careful to get the active and neutral connections right as any discrepancy can cause a safety hazard with the rest of the installation.

he can put taps on the side, inside outside etc. until he corrects his line voltage its a waste, transformers are not a substitute for poor supply voltage.

A servo voltage stabiliser is the solution for your problem. That will provide constant output voltage what ever is your input voltage. That is what is used in locations where there is constant voltage fluctuation . A 10 step tap changer ( even if it is auto controlled ) will not give constant output voltage as the correction is in steps. Servo motor voltage stabilisers are available both in single phase and three phase. The cost is also reasonable. If you are still bent upon making a transformer then make an auto transformer and auto controller and a servomotor which you can locally purchase and assemble the unit.