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Find kW of 3-Phase Motor Without Nameplate & Select Capacitor for Single Phase Connection

maly123a 9579 12
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How can I determine the power of a three-phase motor without a nameplate so I can choose the right capacitor for single-phase operation?

Without a nameplate, the practical approach is to estimate the motor from its physical dimensions and, if possible, check the terminal-box cover for any capacitor value or other data [#16517531][#16517486][#16518083] Measuring no-load current alone is not enough; to estimate power you need current under load and the temperature rise, and one reply says the easiest way is still by comparing dimensions with known motors [#16517463][#16519706] Suggested measurements were shaft diameter, mounting-hole spacing, height to shaft center, and total weight [#16518083] The thread does not reach a single agreed rating: guesses ranged from about 1.5–1.7 kW with 100 µF to 4 kW at 960 rpm [#16517743][#16518859][#16517779][#16519706]
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  • #1 16517459
    maly123a
    Level 11  
    Posts: 87
    Rate: 31
    Hello,

    As in the subject, I do not know how to check the engine power because I do not have a nameplate, is there any way to check it? I need this knowledge in order to buy a capacitor so that this motor can be connected to one phase. I am asking for a quick answer.
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    #2 16517463
    karolark
    Level 42  
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    The simplest measurement is I.
  • #3 16517486
    retrofood
    VIP Meritorious for electroda.pl  
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    maly123a wrote:
    Hello,

    As in the subject, I do not know how to check the engine power because I do not have a nameplate, is there any way to check it? I need this knowledge in order to buy a capacitor so that this motor can be connected to one phase. I am asking for a quick answer.

    You can take a ruler, measure a bit and compare the dimensions with the data of other engines from those years. Everything can be found on the net.
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  • #4 16517491
    maly123a
    Level 11  
    Posts: 87
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    So how can you write how to do it because I don't know much about it as much as you can?
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  • #5 16517531
    Anonymous
    Level 1  
  • #6 16517709
    maly123a
    Level 11  
    Posts: 87
    Rate: 31
    The diameter of the struggle is 25 mm
    The engine brews over 40kg
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  • #7 16517743
    Anonymous
    Level 1  
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  • #8 16517774
    maly123a
    Level 11  
    Posts: 87
    Rate: 31
    I will wait for the opinions of other people, now I was thinking about a capacitor of this capacity, if there is no way out, I will buy it in the dark and try it.
  • #9 16517779
    Strumien swiadomosci swia
    Level 43  
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    It won't work for you, it's a 4kW 960 rpm engine.
  • #10 16517795
    maly123a
    Level 11  
    Posts: 87
    Rate: 31
    So what can't be changed into one phase like this? I read that it can only be up to 3 kw?
  • #11 16518083
    Krzysztof Reszka
    VIP Meritorious for electroda.pl  
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    maly123a wrote:
    The diameter of the struggle is 25 mm
    The engine brews over 40kg

    Nothing fits here. The diameter would have to be 24 or 28 mm and the weight probably too large.
    Measure the height to the center of the shaft, the spacing of the holes on the paws and exactly the weight and diameter of the shaft.
  • #12 16518859
    vcc
    Level 35  
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    This is not the case with 1.7kW or 2.8kW, I used to have such a block, it can be 25mm for a shaft because old engines had different dimensions, e.g. 4.5kW has a 35mm shaft
  • #13 16519706
    supchem
    Level 21  
    Posts: 1070
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    I think it's 1.7 kW. I have such an engine.
    karolark wrote:
    The simplest measurement is I.

    Yes, but you will measure it idle and it won't help you much. You would have to load it, measure current and temperature rise, but the easiest way will be by dimensions.
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Topic summary

✨ The discussion revolves around determining the kW rating of a 3-phase motor without a nameplate and selecting an appropriate capacitor for single-phase operation. Users suggest measuring the motor's dimensions and weight to estimate its power, with estimates ranging from 1.5 kW to 4 kW based on physical characteristics. Some recommend checking the terminal board for capacitor values and emphasize that motors above 3 kW may not easily convert to single-phase. The importance of measuring current under load for accurate power assessment is also highlighted.
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