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440 Three Phase

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catmechanic47

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#1
I just came across a old Stanley 1/2 hp, cast iron bench grinder. It didn't have a cord on it, but was marked 3 phase 440 volt. I wired it up and tried it on my rotary phase converter, which is of course 220v. I ran it for just a few seconds, maybe a minute. It started and ran about 3000 rpm at first and then started pulling down so shut it off. upon disassembly found a dry dragging bearing which might account for the slowing down issue, but I suspect the voltage issue is the real problem. There are only 3 leads coming from field windings so I assume it is 440 only. It is a neat old grinder and I would like to salvage it, but don't know of an option,except ask you guys. any ideas?
 

John Hasler

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#2
I just came across a old Stanley 1/2 hp, cast iron bench grinder. It didn't have a cord on it, but was marked 3 phase 440 volt. I wired it up and tried it on my rotary phase converter, which is of course 220v. I ran it for just a few seconds, maybe a minute. It started and ran about 3000 rpm at first and then started pulling down so shut it off. upon disassembly found a dry dragging bearing which might account for the slowing down issue, but I suspect the voltage issue is the real problem. There are only 3 leads coming from field windings so I assume it is 440 only. It is a neat old grinder and I would like to salvage it, but don't know of an option,except ask you guys. any ideas?
You can't use it on 220. Rewind it.
 

Chipper5783

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#4
John is right, you can't use it on 220. However, you can run it. Motor shops very commonly test run motors on reduced voltage. The issue is that you can't exceed the nameplate current. Get an ampmeter on one leg and try it. If the current is above name plate FLA, then shut it off. If it is below name plate FLA then you can play as long as you want.
 

British Steel

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#5
If it's currently star connected (a little Y like a Mercedes badge on the motor plate) you *could*, if brave enough, find the point where the three coils are connected on the stator windings, bring the three previously-joined ends out as the other connection of each winding on added wires and convert to 220-240v Delta, not for the faint hearted but do-able!

Dave H. (the other one)
 

Tony Wells

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#6
Since it's relatively small, I'd look for a dry type step up transformer and adapt it. It would be a cost comparison issue to having it rewound or at least having the leads pulled by a motor shop. There aren't many, but a few options.
 

catmechanic47

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#7
Thanks again to all. Have a line on transformer that may put her back on line.
 
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