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tonygretton 05-26-2007 09:00 AM

De-rating a 3-phase appliance
I recently acquired an industrial sewing machine, bought as seen, but never thought to check the power supply. It takes a 3-phase supply. I have heard of appliance being "de-rated" to accept a standard 230V/ 13A supply. Is this an option, and can it be done easily? Thanks.

jwhite 05-26-2007 09:30 AM

Sometimes the appliance is multi-tap, and you can re-wire it internally, but these are rare. Sometimes you can find out what parts inside the appliance require 3 phase and replace them with compatabe single phase parts. Usually this is just the motor. For either of these solutions you would need to contact the equipment mfg for the details of what you need and how to install it.

You can also buy phase converters. They are very expensive to buy, and expensive to operate.

joed 05-26-2007 08:36 PM

About the only thing in a sewing machine that would be 3 phase would be the motor. probably the cheapest thing is a new motor.

tonygretton 05-27-2007 12:23 PM

Thanks for the comments. I agree that the main electrical element is the motor, but it is old, large and German. Finding out whether there are internal taps might be problematical, and replacing it would probably cost well in excess of what I paid for the machine. We do have a 3-phase supply in the property but, as far as I know it extends no further than the meter. Presumably I could get an electrician to run a radial three-phase circuit from the meter? Thanks.

NateHanson 05-27-2007 12:44 PM

Having a 3-phase drop to the house is a real luxury! I'd use that, especially if you ever want to get more machinery. Finding old 3-phase machinery is often easier than finding single phase, and 3-phase motors last longer and are easier to repair than single phase. Also more powerful since they get three "pushes" per turn of the rotor, instead of two.

You can get a small phase converter to run this thing, and it maybe cheaper than having an electrician put in a 3-phase panel. Your options are a solid-state (electronic) phase converter, which allows your 3-phase motor to run on 220 single-phase, but you lose the power advantages of a 3-phase motor, since the motor is just running on 2/3 of it's guts. The solid state converter just creates a sort of dummy leg for the third phase, to get the motor started. It's basically the same as using a rip-cord to jump start a 3-phase motor. Once it's turning, it'll run on regular 220V. These solid state converters are a few hundred dollars, but are limited in size, and reduce the power of the machinery.

If you want the power advantages of the 3-phase motor you've got, you need a rotary phase converter. That's basically a big 3-phase motor (at least as big as all the motors combined that you want to run with it), that runs with no load on 220V single-phase power, and as it turns, it generates 3-phase power. Electronics inside the converter balance that generated 3-phase power into nice stable 3-phase, and that power is as good as 3-phase that comes off the electrical poles. There is a small amount of electricity consumed by the rotary phase converter, but it's only about 5% if I recall, so they really don't use much power at all. The downside is that the rotary phase converters are quite expensive.

I have a 10hp rotary phase converter that is US made, by a reputable company, and it cost me about $1100 5 years ago. I use it to run a 2 hp lathe, and a 5 hp jointer. I expect I'll someday run a 5 hp planer from it as well.


jwhite 05-27-2007 01:35 PM

Why would anyone have a three phase drop to the meter and then put in a single phase power.

I think you are confusing the three wires feeding the meter as meaning you have three phase. If you do have a three phase service you will have four wires comming from the utility to your meter.

tonygretton 05-27-2007 02:42 PM

I don't think phase converters are an option - too expensive for just this one machine, and no plans to get any more. The supply is definitely 3-phase, 4-wire, 'sez so on the front. A bit of background might clarify the situation. we are a residential outdoor activity centre in Scotland. In the past, the building forming the residential bit was a B&B, and before that a hostel for school boarders. The power demand might therefore have been higher in the past (electric oven, deep fat fryer, etc) (don't know if that makes sense). Regards.

NateHanson 05-27-2007 03:18 PM

I don't think three phase is used for resistance heaters like that, but maybe they had huge industrial washing machines or something else with a big motor.

Anyways, if you've got three phase, then cool. No matter the origin.

If you don't want to pay a hundred bucks for a solid-state phase converter, then I think your only option would be to try to find a replacement motor. Go to a motor repair shop, and see if they've got something that could fit. If it's a belt-driven machine, and the motor is sort of external, it might not be hard to make something else fit the mounts.

Hiring an electrician for new service, I would think, would be the most expensive solution of all.

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