Run 230 V AC motor in the US using a transformer?

Question

I will move to the US soon and plan on bringing some power tools (e.g. a lathe) with me that are designed to run on 230 V/50 Hz (actually, 220 V, some are old). I would like to use a transformer such as this one that would provide 240 V, at 60 Hz.

I found similar questions, but they don't cover the two points I'm worried about:

• Single-phase AC motors running at 60 Hz instead of 50 Hz. Could this cause any problems (overheating)? I don't care whether things run a little faster, but some answers suggest U/f needs to remain constant (=> 264 V?).
• Inductive load (e.g. lathe, drill) as opposed to resistive (toaster - which I'm not bringing ;-): can this cause problems with the transformer?

Answer 1

The typical North American wiring scheme is to have two wires going into the house that have 240V across them, but balanced to ground. A typical wall socket supplies a 120V "hot" wire and a pretty-close-to-zero "neutral" wire.

But stoves and dryers are 240V. So the house has 240V, 60Hz already.

Wiring your shop for 240V should be easy enough. If you're not going to be using the lathe all day every day, you may want to just run the thing on 240V and see if the motor gets hot. Start with very brief runs (half a minute) and work up. If it doesn't get hot -- job done!

If it does get hot, before you go buying transformers price out the cost of new motors, the cost of having your motors rewound, and the cost of variable-frequency drives for the motors you have. You may find a cheaper option to a transformer.

Answer 2

Transformers are big and expensive. If you have 15% excess power and torque when you use it for <3Hp no problems with extra speed being your main issue. We always get 120V dual line for oven and sometimes dryer, water heater so 240V, others 117V +/-10 x2. You’ll just need to wire up adapter outlets to use same plugs.

Add fans if you run to full load/torque at reduced V/f capacity with more than usual slip to limit temp rise. It’ll take a bit longer to get up to full speed which will add more startup heat which may stress the breaker margin time to trip if doing a lot of start stops.

Answer 3

A 50 Hz motor connected to 60 Hz should have 20% higher voltage. If you don't increase the voltage, the torque capability will be reduced to about 64% of rated torque. You can compensate by reducing rate of feeding the tool into the work piece. You will need to be careful. It will be easy to overload the motors.

I would put in or re-purpose a 240 volt circuit as suggested by @Tony Stewart. In addition, investigate using an autotransformer to increase the voltage by about 20%.

Answer 4

If the original motor was 240VAC 50Hz, this suggests it only around 3Hp as anything bigger would tend to be three phase. With the influx of low cost Chinese built motors onto the market, as TimWescott suggests, it might be cheaper just replacing the motor. The likes of HarbourFreight list a 3Hp motor for around $179 as a point of reference. Or go the upgrade and get a three phase motor and suitable single phase input variable speed drive. The various machining sites will have discussions of suitable motors etc.

Answer 5

Like the other answers have mentioned, in the US 240VAC is available everywhere. However, in houses this is generally limited to dedicated branch circuits feeding higher power appliances: stoves, water heaters, etc. So most likely you will need to have installed a separate branch from the service panel to supply your equipment.

And like the others have mentioned, 240V will be too low for the higher speed at 60Hz; flux decreases and slip increases, reducing torque and leading to overheating at load. If the loading is intermittent or reduced, and motor temp can be monitored, this may be acceptable.

If overheating is a problem, you have the options of replacing/rewinding the motors or increasing the voltage. To maintain the V/f ratio, 230V raised by 20% is 276V. The winding insulation can most likely tolerate a 20% increase in supply voltage, but be aware this is additional stress. 277VAC is a standard voltage used in commercial/industrial lighting circuits, so transformers with 277V windings are available. I won't post links; they tend to get outdated. But a search for "240V to 277V Step Up transformer" can get you started. You don't need isolation, so an autotransformer is fine, and might be less costly. Power factor should be considered for transformer sizing, and keep in mind that primary and secondary generally can be swapped.

One thing to check if you go with higher voltage is the voltage ratings of any motor starting or running capacitors. Also recommend using the proper NEMA 7 plugs and receptacles if the equipment isn't hard-wired.

One of the answers mentioned using a variable speed drive (VFD). I would be a bit hesitant; these inverters output square wave voltages that can be hard on the winding insulation. If you do go this route, locate the drive close to the motor so that the interconnection is as short as possible. A VFD, especially a cheaper one, won't be nearly as reliable as a transformer, and its power factor can be quite bad. Having said that, the ability to adjust the speed is nice to have.