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transformer auto 0-240-415 step up

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dlmcs

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Hi I am building a a sigle to three phase rotary inverter to power large machines in my garage from a single phase supply .
I bought plans to build and have built the rotary inverter to get it working correctley I need a transformer 0-240-415 I have broke down an old ark welder with adjustable amprage . I took out secondary winding and amprage adjuster just leaving primary which is very substantial my question is my rotary motor is 10 hp three pahse so that will be what i running so what size wire do I wind the transformer with and how many turns and lenght of wire needed and how to wind .
 

Diver300

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Firstly, usual precautions about lethal voltages, suitable fuses etc etc.

Put a single turn of wire where the secondary winding was. Connect the primary to the mains. It may take a lot of current for 1/4 cycle of the mains. After that it should take very little current. Measure the voltage on the secondary winding.

It would be useful to know what the original welder voltage was.

If it was 415 V, you really want a tapping part way along the existing winding. If it was 240 V, you want to wind around 185 V of winding.

Many motors are 415 V when wired in star and 240 V when wired in delta, so you might save yourself a lot of trouble if you can just change the motor connections.

There are some companies that will make custom transformers quite cheaply. I used one about 10 years ago but I can't remember who it was. Here are a couple I've just searched for:-
http://www.custom-transformers.co.uk/
http://www.transformers.co.uk/
 

dlmcs

New Member
Hi thanks for your reply after measuring the turn of wire do i just devide the wanted voltage by the voltage of the sigle turn of wire and the welder is 240 v i wish it was 415 as i could of just rewired it to use the 415 side of it .
 

dlmcs

New Member
Also I dont know what you mean 180 volts on which side primary or secondary please could you just explaine what you mean many thanks for your help iv just spent a lot of money and time building this rotory inverter this is just the last thing also what size cable ie enamelled wire
 

Diver300

Well-Known Member
Most Helpful Member
The idea is to make a 175 V secondary, and connect that in series with the primary, so when have 240 V on the primary, and 175 V on the secondary, when they are in series you get about 415 V. (185 V was a mistake, sorry)
I don't know what gauge of wire you would need. If you work out how large you can fit in the space for the secondary, that would be a good start.

The secondary will have to take the full motor current. The primary will have to take 175/240 of the full motor current. From those figures, and the sizes of the windings, you can work out the resistive losses. They should be less than about 3% of the power.
 

RODALCO

Well-Known Member
I have used a three phase motor successfully to step up the voltage from 230 to 400 Volts. need to do it the opposite way as normal practise.
Start 3 phase motor in delta at 230 volts, then switch to star to get 400 Volts. you need capacitors to stabilize the voltages. I have a couple of video's up on my YouTube channel.
 

RODALCO

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tcmtech

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dr pepper

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Another way to do it if you choose is electronically, if you get hold of an inverter that operates from a single supply and generates 3 phase this will also work and you'll have a speed control, second hand ones turn up on ebay now & again.
This would only work on motors that are star 415v and delta 220v, which tends to be those under 2.2kw.
 
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