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    tandemsforus's Avatar
    tandemsforus Posts: 24, Reputation: 3
    New Member
    		  
    #1

    Jul 23, 2008, 06:24 AM
    What size motor will converter run
    Hi
    I have a rotary converter that turns single phase into three phase. The motor on the converter says it is 5 hp. How can I tell what size 3 phase motor it will run
    Thanks
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #2

    Jul 23, 2008, 11:08 AM
    Best to consult the manufactuer of your specific unit.

    Here is a link to one of the more popular ones, look for Rotary Converter Sizing Chart link at the bottom.

    3 Phase Converter Info- Sales- rotary phase converter, static 3 phase rotary converters.

    If this is not your manufacturer, Google "Rotary Phase Converter".
    tandemsforus's Avatar
    tandemsforus Posts: 24, Reputation: 3
    New Member
    		  
    #3

    Jul 24, 2008, 06:40 AM
    Thanks tk
    I got the 5 hp converter used with a band saw I bought. It was used and has no manufacture named.
    I looked at the site you recommended. Very informative.
    Here is the rest of my question. Maybe I should have asked it from the start. I also have a planer that has a 7.5 hp 3 phase motor. Per the information I read, from the site, it says I need a 20 hp, 15kw converter for hard start applications. Does that sound right to you? It takes a 20 hp , 15 kw converter motor to run a 7.5 hp 3 phase motor? The cost of the converter is $1495, I can buy a single phase 7.5 hp motor for $5-600 dollars. As I read the info it would be 1/3-1/2 the price just to replace the 3 phase with a single phase.
    KISS's Avatar
    KISS Posts: 12,510, Reputation: 839
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    #4

    Jul 24, 2008, 08:32 AM
    See if there is a code letter on the nameplate. Motors can draw 300-600% of their rating upon starting. See: motorsanddrives.com - Locked Rotor Code Letters

    Taking 7.5 HP * 746 W/HP =~ 5,6 KVA (some conversions thrown in)

    15 KVA / 5.6 is about 2.7 X, so it's a reasonable assumption.

    Don't forget to consider the wiring requirements which includes capacity and breaker space and disconnects, labor and inspections in your calculations.
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