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Transformer running motor?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Collin Johnson, May 22, 2019.

  1. Collin Johnson

    Collin Johnson

    May 16, 2019
    If I wanted to run a 220v motor and I only have 110v power running in my house would a transformer like this one https://www.amazon.com/dp/B000MY02LQ/ref=cm_sw_r_cp_api_i_zco5CbN7NZHSK work for what I want? I would rewire my plug for 220 but I’m only renting and the owner doesn’t want me messing with the plugs. Any help you can provide will be much appreciated.
  2. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    You have to ask, "Why isn't everyone using one of these?"
    That will increase the potential ( voltage), but it will not reproduce the sine wave of 220 volt US current. They are for running European and foreign 220V resistive devices ( heaters, irons, most electronics, etc.) on US power. Small motors will work because they aren't wound the same as the motors used on shop equipment. A 220VAC US motor needs the sine wave to match the windings or it will burn up.
  3. 3fifty7

    3fifty7 Gold Member Gold Member

    Dec 24, 2016
    I kind of hate to say it but a treadmill motor may work well in your case.
    Assuming you are putting together a grinder or something of the like.
  4. Lieblad


    Jul 24, 2015
    A transformer, Frequency output matches its input. I get the impression Mr. Johnson is in N. Amerika and simply wants to step up voltage for 240V 60Hz appliances.

    Be cautious, if desired to operate at of near its 3000W max. This appliance will need a 120V 30A supply circuit.

    Btw, Speaking of “everyone using one”. That appliance bears NSN 5950-01-541-9053 suggests its commonly used by US Military when they go anoy people in foreign lands.

    Last edited: May 22, 2019
    Ken H> likes this.
  5. ferider

    ferider Basic Member Basic Member

    Jun 20, 2018
    Should work just fine, as long as your motor uses less than 3kW. For a synchronous motor, the 50 to 60Hz move will just make it run a little faster :)

    Now, would be easier if you have 2-phase access in the house to just use that. Check your drier outlet, for instance. Of course you can't ground the motor then, so do at your own risk if you decide to go that route ....

    There are only few European appliances where the 50->60Hz transition will not work, TVs in particular.

    Just remember, getting zapped by 220v hurts more than 110v .... don't ask me how I know :) (I'm a German EE).

    Last edited: May 22, 2019
    Ken H> and Natlek like this.
  6. seanj


    Mar 1, 2010
    What's your application for the motor?
  7. Nathan the Machinist

    Nathan the Machinist KnifeMaker / Machinist / Evil Genius Moderator Knifemaker / Craftsman / Service Provider

    Feb 13, 2007
    you can run a 240 volt motor off of a 120 volt power source with a step up transformer, assuming it is rated for the power the application will require. If your transformer is sized large enough for the application there will be no problem.

    Most single phase 240V electric motors are looking for two hot lines that are 120 volts to ground and 240 volts to each other, this application will see one line that is 240 volts to ground and the other a neutral. This sounds like it would be a problem but it isn't. That said, a 240-volt to ground power source is not trivial. I'd be real careful not to touch that.

    That said, the appliance that you linked to will double the voltage but that does not necessarily mean that the amperage capacity of that line will be sufficient. For example if you are running a 3000 watt motor, that is going to draw over 20 amps on a 120 volt circuit, and your breaker may not be sized large enough for that.

    you should calculate the current draw of your setup and confirm that it does not exceed the capacity of the circuit you're putting it on. For example a 10 amp 240 volt motor will max out a 20 amp 120 volt circuit. This device only doubles your voltage but it does not actually increase the power available from a circuit. As the voltage doubles your amperage halves.
    Last edited: May 22, 2019
  8. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    I will defer to Ferider and Nathan that is will work on the motor Collin has.

    This is how I learned it:
    The 240 windings in the US are made from two 120 lines referenced to each other. This is a sine wave with a center reference. This way the windings in a 240 volt US motor are pushing and pulling in the right order.
    A 120 volt wave is only half this cycle, and is referenced to ground. It is drawn by center tapping the 240 volt winding on the power line transformer. That is why your breaker box has two incoming lines at 240 volt line referenced to each other. To get the 120 volt breakers, these lines are separated from each other and you get two 120 volt lines that are phased 180 degrees to each other and each referenced to ground. Each one is one half the sine wave of the 240 volt wave.
    That is why you have to move more than one wire when changing a motor from 120 to 240. If you just expand 120 volts to ground to 220 volts to ground, neither the 120 volt wiring setup or the 220 volt wiring setup will be right for that voltage wave. Perhaps it will turn the motor, but it should not create full power and may create heat.

    European 220 is not the same as US 220.
    European and foreign devices use 220 volts that is referenced to ground. It is twice the pressure (voltage) of our 110 volt lines. The reason they set up this system was due to the original European lines having to carry the voltage farther. The other choice was bigger wires.

    The US used to have many different voltage systems, even DC, up to the end of WW2. When the power companies and government started the GRID and the power all needed to be the same.
  9. Nathan the Machinist

    Nathan the Machinist KnifeMaker / Machinist / Evil Genius Moderator Knifemaker / Craftsman / Service Provider

    Feb 13, 2007
    I think that most homes in the US are fed a single line from the utility at the transformer that feeds your street. If I remember right, even though you have two legs in your panel, they're both somehow derived from the same line and your local ground, I don't think it's two legs all the way from the utility. The center tap on that transformer is forced to local ground and that becomes your neutral, it is midway between the two legs. You get two legs off of that transformer that are 120V to ground (and therefore neutral) and 240V to each other. It's all a full sine wave.

    Functionally, 240V and a neutral is the same as two 120V that are 180 degrees out of phase unless you also have some component that uses the neutral, like you might find in a clothes dryer. If that neutral isn't used somewhere in the circuit (and it isn't in a motor) it's the voltage potential between the legs and not the location relative to ground that matters. An electric motor doesn't use neutral and the ground doesn't carry current.

    You'll be switching multiple wires in a motor probably because there are multiple poles. I'm not sure but I expect you're taking two windings per pole and putting them in series for high voltage and in parallel for low voltage.

    True three phase systems are a different animal. Modern 208 Wye three phase has three 120V legs (to a central neutral) that only generate 208 leg to leg because they're phased 120 degrees. This does take three legs from the utility. You can run a single phase motor from two of those legs, though it may not be ideal. I don't think that delta even has a neutral. Any of this can run a 240 electric motor if you can get around 240V potential between two legs, even if the phasing is weird, but I expect a single phase motor is going to work best if the two legs are phased 180 degrees. Which they will be if you step up low voltage single phase. Which is what the OP is talking about. :thumbsup:

    The amperage capacity of the circuit is a different story. Watts are watts, there's no free lunch.
    kmf600 likes this.
  10. Natlek


    Jun 9, 2015
    You have real mess there with electricity power , didn t :) And once you have our Tesla there :D
    Last edited: May 24, 2019
  11. Nathan the Machinist

    Nathan the Machinist KnifeMaker / Machinist / Evil Genius Moderator Knifemaker / Craftsman / Service Provider

    Feb 13, 2007
    We do. and what I said, watts are Watts, is not completely true. I mean, it is true for all intents and purposes and for high-school level physics class but the reality is your power factor correction efficiency can mean that your current is not what you might expect on an inductive load like an electric motor. you can pull a lot of amps without actually consuming a lot of Watts at a particular voltage if your power factor is not good. Those of us running a rotary phase converter know what I'm talking about.
    Lieblad and Natlek like this.
  12. Lieblad


    Jul 24, 2015
    One delta configuration exists what has a neutral and its fairly common for small 3 phase services.
    Its called "hi-leg" delta where one transformer coil is center tapped and grounded to become a neutral. This furnishes multiple voltages. 240V 3 phase, 240V single splitphase (familiar to homegamers), and 208V singlephase.

    My Utility Co. has 2 phases running along my street. By way of an "open delta" configuration on primary side of transformer it provides that above described 3 phase service for a sewage lift at the end of street.

    Since it already is on my street, Were I willing to pay for it, I could have 3 phase at my house also.
    Many US neighborhoods have similar ability to easily serve 3 phase to houses. Paying for it another matter.
    Last edited: May 25, 2019
  13. Nathan the Machinist

    Nathan the Machinist KnifeMaker / Machinist / Evil Genius Moderator Knifemaker / Craftsman / Service Provider

    Feb 13, 2007
    On that system are the two legs 180 degrees and the high leg 90° and 208V to ground? I've been wondering about this.
  14. Lieblad


    Jul 24, 2015
    Yes, If I understand you right.
    You might Google Images ”hi leg delta”, you probably find dozens examples.
  15. 12345678910


    Jul 13, 2009
    Probably not

    do you have an electric stove or electric clothes dryer ?
  16. Drew Riley

    Drew Riley

    Oct 17, 2007
    If your service panel has any double pole breakers, then you have 220VAC. If you have a well pump, central air conditioner, electric stove and/or clothes dryer, etc... then you'll likely have 220VAC running in your house. Now, whether any of this is close enough to where you're gonna be running your motor, is another question.

    If you have two circuits fed from breakers on BOTH legs of your service panel, you could theoretically run two different extension cords from an outlet on each circuit to run your motor. It's not recommended for a number of reasons, safety being one of the main concerns, but it is an option IF you know what you're doing and take the proper precautions. This would be an absolute last resort for me personally.

    As for running a 220VAC motor with a step up transformer, it can be done, but as has been pointed out (and this is a BIG factor), you need a 110VAC circuit that's built to handle the load you'll be throwing at it. While 220VAC motors NORMALLY draw around 1/2 the current of a 110VAC motor of the same HP, they do so because they are running on dual phase voltage (110VAC per leg). When you implement a step up tranformer, instead of halving the current across two legs, you're actually doubling your current onto one leg. So if you have a 2 HP motor, for instance, instead of 12 amps across each leg, you're actually running at least 24 amps, and possibly a little more due to inefficiency in the transformer.

    Reading the Amazon description of the transformer, the manufacturer recommends sizing your max wattage at a minimum of 1.5x whatever you'll be running through the transformer. So going back to our 24A motor on 110VAC, that's roughly 3kw already (2880W), so you'd actually want closer to a 4.5kw transformer.

    That's also assuming you have an outlet, wiring AND breaker that can handle 25 to 30 amps.

    These are all numbers for a 2hp/1.5kw motor. If it's a smaller motor, you might get away with a 15 or 20 amp circuit, though you'll still probably be pushing it, depending on what you have.

    Stacy was right about at least one thing: There's a reason you don't see too many people running motors on step up transformers.
  17. seanj


    Mar 1, 2010
    Maybe I'm missing something here, but in an earlier post I asked what the application was. I didn't see a response to that. However, if the OP is wanting to use a motor for knife work why not get a KBAC VFD or similar and be done? I know it's more expensive but there's a lot of if's, in some cases big if's, using the intended setup. A VFD would be much simpler.

    Maybe I'm missing the point but that's my two cents.
  18. Drew Riley

    Drew Riley

    Oct 17, 2007
    It would certainly help to know what the machine (and the motor) specifically is. That said, I can see wanting to try to use a transformer IF it would work, as it's going to be much cheaper than a kbac VFD and replacing the existing motor with a 3 phase. Also, he may not need variable speed.

    OTOH, getting a different motor for the machine may be a better option to begin with, and if doing that, a VFD and 1.5hp 3 phase motor may also make the most sense.
    seanj likes this.

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