Testing 3 phase motors

I am testing a couple of 3 phase motors I have acquired. I have a single phase to 3 phase 3/4 hp rotary converter that generates the 3 phase field. I have checked a couple motors but when I tested 2 Baldor motors I tripped my fused switches. The first heated my switch red hot and the second turned slowly then killed my FRS 5 fuses in my converter set up. Both were 2-3 hp but I checked a different manufacturer 3 hp motor and it ran fine. So at this point I need to get more fuses. I had the motors wired for low voltage to match my 240 supply. I checked these wiring configurations thoroughly.

How do I test these 3 phase motors? I checked resistance between a 3 leads and measured a couple of ohms each. No spikes.

Also, I am looking to use these 3 phase motors for an idler in a separate rotary phase converter. I have read about getting a balanced voltage. Would this be just measuring the 3 voltages from the 3 different combinations of leads? What is a decent balanced voltage supply - say for mills or lathes?

Thanks Pal

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Delta connected motors can have an open winding and still have a good resistance. So can 2-Y connected motors, which is the most common type of connection of 3-phase motors in the 2-3 hp range. It is very possible that you have mis-connected motors or open windings. If the motors are identical and from the same source, mis-connections are the likely culprit. Typically for 240 volt dual voltage Y connected motors, 1&7 connect to power, as do 2&8, and 3&9. Leads 4,5,&6 are just tied together.

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Johnny Walker

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