American rotary (or other) vs DIY?

CBudz said:

So yet another phase converter discussion...

Up front: are these cheap phase converters like American Rotary reliable? Vs buying a reliable motor and building my own

I've got some 3 phase equipment; Bridgeport, Colchester, band saw, speedaire compressor (has a new single phase motor but I got the 3 phase motor too). I've accumulated over the years but never had the power. I've been traveling for work the last few years and now the itch to run them is irresistible.

This is at the hobbyist level and my house only has 100 amp service, for now.

Thoughts?

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n2zon said:

My new American Rotary (AR-20) RPC came with a Baldor idler motor, a brand I'd always considered pretty good. Not sure I'd call it cheap at $1,320. The old smaller one, also an AR, has served me for several years without a bobble, running two 2HP 3-phase motors for a lathe and a mill. YMMV.

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n2zon said:

My old one was a 5HP, but they have changed the rating designations since that one was built. It would and often did run both 2HP machines at the same time, and was rated to start a 5HP motor if it was not under load and run a total of 5HP.

The biggest problem is motor start current. They will likely advise you to get a 10HP RPC to be sure you can start the 3HP motor, although it might start on a 5HP one. If it doesn't, though, you'll have to arrange to ship it back or sell it (not sure what they'd do for you here) and get the bigger one. In my case, the price differential (from 15 to 20) was smaller than it would be for you going from 5 to 10, so it's worth some discussion with them. I'd suggest giving them a call. Their support is really good.

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dalmatiangirl61 said:

I think your biggest problem would be cost of shipping to the Aland Islands

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Jim Kennedy said:

Hi C Budz
What is your supply voltage? and what voltages do your various machines 3 phase motors operate from?
If this is your hobby and you have the ability to build, I think you should build it your self.

Jim

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CBudz said:

Has anybody used the unique3phase transformer method?

Someone posted years ago using it for their lathe, but the book itself says it's method is no good for lathes, Mills, welders etc.

Reference thread: using the transformer method to make 3 phase?


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dalmatiangirl61 said:

I've read that book, don't remember the comment about it not being good for lathe, and not sure why it would even matter. Have not tried it, still considering it, my new shop is all concrete and any sound gets amplified, might just try a sound attenuating box over my rpc.

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Jim Kennedy said:

Hi C Budz,
I am going to assume that the network supply voltage in your part of the world is 230v/400v so I also assume your machines that require 3 phase are 400v/415v.I realise some smaller 3 phase motors can be re-connected to operate from 230v/240v but then other considerations in machine wiring to be done. So I think you would need something that outputs 415v 3 phase. Would this be correct?
I have built many converters using this higher voltage method. I think a Rotary has many advantages but a higher voltage method most certainly has some advantages over a rotary.
I am very sure that Unique 3phase would never have said or written that this method was not suitable for Lathes & Mills.I can tell you that the higher voltage method requires the load to be more constant.
So something like an air compressor, you size the single run capacitor for the area of load (between Cut In and Cut Out). One of the best advantages of this type of converter is it's ability to start under load,which is opposite when using a rotary.
Now if using a lathe, quite often people say there rotary won't start the motor in High Range. With the higher voltage method you could just simply have a switch to switch in another run capacitor, you could even put a current sensing relay to do the same job automatically.
As for running more than one 3phase motor from a single transformer, a lot of people get this wrong. I think this is because there was a paper written and sold for a long time and I think they would still be selling them now and it says this method the autotransformer will only run one motor. This paper never stated who wrote it (maybe Donald Duck) but it is wrong.
and of course the total amount of motor load can not exceed the transformer output.
I would like to hear from anybody that has built this method and where it didn't work. But I will re-say the rotary has many more advantages.
In your case my thoughts are, you need 3 phase 415v so you will need a transformer single phase 240v to 415v can be simply done using an old electric welder with the sliding choke.
A big advantage of doing things like this is you plug and play the machine.

Jim

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