3 phase rotary converter

[tigerjoe]

constution plans

[ChuckFickens]

really...

and the question is?

[beso]

There are two types of converter. Tigerjoe is probably asking about a single phase to three phase rotary converter. Essentially it is a three phase generator being driven by one of its phases from a single phase source.

It can be done with a three phase induction motor. These motors will run on a single phase one it starts turning. The other phases are generated by the magnetic field interactions.

The motor need to be much more powerful than the motor to be driven because the entire load is carried on one phase. The low power factor due to the inuctance of the large motor running underloaded is usually corrected with capacitors. This resonant circuit helps reduce the problems normally associated with low power factor loads depressing the voltage of the system.

Of course the single phase supply voltage also dictates the output voltage so the three phase loads need to be wired in delta to run. This is only usually possible with motors below 2 KW.

Another way to run three phase motors from a single phase source is to use an inverter. These can run the motor at any speed without stalling or burning out. You also need load motors that runs on the single phase voltage.

[beso]

An DC/AC rotary converter is a much more facinating piece of electrical machinery. It has a single rotating armature in a stationary magnetic field. One end has a commutator just like common motors used in most small appliances.

When fed with DC it runs just like a motor. However the opposite end of the armature is fitted with sliprings. AC appears on these connections. Once running, energy can be converted in either direction.

They have a very good sinewave output. Seventy percent of the power flows directly from the commutator to the sliprings without interacting with the magnetics so converters can be very powerful for their size.

They were commonplace when the AC system took over from earlier DC grid systems and allowed for a smooth transition in technology. However they were of little use once AC became the norm and very few survive.

Many years ago I found a small 24 volt converter on the rubbish tip. It was designed to work from batteries and the AC was passed through a transformer to normal mains voltage.

These devices should not be confused with the crude motor generator sets used to make AC power from batteries.