Hi, I have been doing some research on best way to get isolated high power sine wave 120-220v (3kW - 5kW)

1) Auto transformer (high power, not isolated, cheap, relatively small footprint)
2) Isolated transformer (High power, isolated, expensive, big footprint)
3) Pure sine wave inverter (High power, isolated, expensive car batteries, big footprint)
4) Modified multiple MOTs in parallel with 12 v output rectified then fed to pure sine wave inverter (High power, isolated, relatively cheap)

What are your thoughts. Any other options ?

Thank you very much

 

What is your power source?

 

What is your power source?

AC mains. I have both 120v and 220v

 

AC mains. I have both 120v and 220v

Buy an isolating transformer.

 

Buy an isolating transformer.

I'll second this approach. It may be expensive and have a big footprint, but there is no better alternative that I can see. Maybe you were expecting some sort of practical magic.

 

One big transformer always beats several small ones. It is always smaller, lighter, more efficient and cheaper than several small ones; and it will be much more reliable than anything with semiconductors in it.
I curve-fitted my local supplier’s price list and his price varies as √VA.

 

The "practical Magic" method of getting that level of isolated good quality sine wave power is indeed with a transformer, which could be a used industrial surplus transformer that you may only pay scrap copper prices for. You will need to know what you are seeing and you would need to understand the connection schemes, but you may be able to save several hundred dollars worth.

 

A 5kVA toroid is 240mm diameter x 110mm high, which is probably more compact than any inverter of comparable power, though at 22kg is is probably heavier.
At £376 it is comparable with the prices of inverters of reputable makes.

 

Certainly a toroid transformer is another option, and as stated, smaller. But just like other transformers, design rules apply, and so building one yourself will require a fair amount of research.

 

A 5kVA toroid is 240mm diameter x 110mm high, which is probably more compact than any inverter of comparable power, though at 22kg is is probably heavier.
At £376 it is comparable with the prices of inverters of reputable makes.

Yea I was looking at toroid transformers too. I have to look some manufacturer in Canada because shipping from China is alot

 

The "practical Magic" method of getting that level of isolated good quality sine wave power is indeed with a transformer, which could be a used industrial surplus transformer that you may only pay scrap copper prices for. You will need to know what you are seeing and you would need to understand the connection schemes, but you may be able to save several hundred dollars worth.

I can't find any surplus transformers supplier in Canada or least near where I live. The reason I stated modified MOTs was because I can probably buy a used microwave for cad$30. But then again I have wire them manually and also buy the wire, make an inverter.

 

I have wondered about rewinding a large VARIAC core as a high voltage transformer for a linear amplifier. What I see as the challenge is how to pass all of that wire thru the center. The primary, with perhaps 200 turns of #14 wire will be quite a challenge, while the secondary with 2500 to 3000 turns of #28 wire will also be rather tedious, at best. avoiding huge tangles will be the challenge.

I suggest using a FREE scrapped MWO and rescuing the transformer, although they are sized for at most 1200 to 1500 watts with a fairly short duty cycle. I am guessing that the application would be for more than a few minutes of operation. I have not yet seen a failed transformer in a microwave oven. The failure is either the magnetron tube or the timer module.

 

I can't find any surplus transformers supplier in Canada or least near where I live. The reason I stated modified MOTs was because I can probably buy a used microwave for cad$30. But then again I have wire them manually and also buy the wire, make an inverter.

I have a few high Kva linear I may be getting rid of, what part of Canada are you in?

 

AC mains. I have both 120v and 220v

BTW that would be 120v/240v !

 

I have a few high Kva linear I may be getting rid of, what part of Canada are you in?

Ajax, Ontario

 

OK, I am in MB.

 

OK, I am in MB.

Do you think it would be possible to ship ? I'm guessing they are very heavy. Shipping would be a lot.

 

Most likely, I could weigh them to find out.
BTW, what secondary voltage do you need?

 

Most likely, I could weigh them to find out.
BTW, what secondary voltage do you need?

I would take 220/240v cuz I have a variac and a autotransformer. I can reduce it if needed.

 

They are mostly low to medium LV secondary's.