Three phase to one | MACHINIST CORNER | Forum

The easiest way to convert three phase to single phase is just use two of the three legs if its 200-240V..

(what you ask, not what you wanted to know) however to convert single phase to three phase the cheapest is a static phase converter... you will loose about 30% of rated HP this way but its cheap and easy... next is rotary which can be quite good and quite reasonable.. using a secondary motor started with capacitors or a pony to generate the third leg.... next would be inverters which give very clean power but have a high cost..

Now keep in mind none of those things change voltage.... you can make 208 three phase out of 208 single phase by any of those means but to get 480V three phase from 220V single phase you need to first add the leg and then use a transformer to boost it to the required voltage...

I'm pretty sure some of the inverters can change voltage. Might make them a more attractive option if you need to do that.

Hmm,

I've seen plenty of VFD drives listed with 120V input and 230V output. I'd assumed that was true in the higher voltages as well, but it looks like I was wrong. Maybe the small ones have transformers for some reason?

Dave;5452 wrote: I 've been looking at a used 3 phase cold saws. I only have single phase at the shop. What is the easiest and cheapest way to convert the 3 phase to single phase? Would the saw still work in a reasonable manner? I am not versed in electrical matters. Would it be better to get a single phase cold saw?

If you can find a single phase cold saw, it would simplify things. If you can't find a single phase unit that compares to what you are looking at (or want), you can easily create an environment for the 3-phase saw to work in.

In general, three phase motors are not converted to single phase. I would guess that would be extremely expensive, if even possible. If you want to use a three phase machine, you can easily generate three phase power from a single phase power source (220 volts). Others have mentioned using a static converter, which is the least expensive option. But, unless the tool is grossly overpowered, a rotary converter is much better and actually doesn't cost a lot more. It the tool is, or can be wired for, 220 (or 240) 3-phase power, it can be run directly off a rotary converter. The rotary converter is supplied power from a single phase electrical panel and generates the third hot wire (thus 3-phase power) using an idler motor as the generator. You can either buy a complete rotary converter (which includes a panel and an idler motor), or you can buy just the panel and furnish your own 3-phase motor to be used as the idler.

If the cold saw cannot run on 220 or 240 3-phase, you would need a transformer to take the power up to the needed voltage. Personally, I would look for a different saw if it would not run on 220 or 240 3-phase power.

The rotary converter will need to have an idler motor at least as large as the motor on the cold saw. If you have a source, or can find a good 1725 RPM 220 (or 240) three phase motor you can order a panel from a manufacturer (like Anderson Converters) for a very reasonable price. Wiring in your idler motor is extremely simple and you can run any 3-phase motor up to the HP of the idler motor (with some exceptions). I would expect a cold saw is NOT in that list of exceptions. The exceptions include 3-phase application motors that involve electronics (like some welders, etc) or those that would have to be started under a heavy load (not your case).

If you are NOT comfortable with doing some electrical work (or have a friend that will do it for you), I would recommend that you buy a complete rotary converter.

You could consider trying a static converter to keep the cost down, but I would advise against it unless the cold saw is at least 3 HP. As has been previously advised, a static converter must be rated for the exact HP of the cold saw.