# Static Converter



## Jim (May 5, 2012)

I used a relatively inexpensive static converter to poer my Bridgeport and it seems to be working well for the light use it receives in my shop.  I realize it uses a capacitor to start the motor and then runs it on single phase power at I think 2/3 the rated horsepower.  Is this going to destroy my motor or will it be ok to use indefinitely?
Jim


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## Tony Wells (May 5, 2012)

I know of some static converters that have been used 8 hrs+ a day for 20 years without damage. I think the key is recognizing the reduced hp you get. You already acknowledged that, so IMO, you are good for a long time, as long as you don't push the machine.


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## 8ntsane (May 5, 2012)

This very same question does come up evey now and then, on several different forums.  Alot of people have claimed damage to the motors used with them, and many will say its because the static unit only delivers 2 thirds power.

Really, I dont see any problem using one, unless your running the machine hard, and need the full HP rating of the motor, and using a static converter you simply wont have. If its a mill you have powered with this converter, then I wouldnt think you would hurt the motor. Milling machines seldom see full load to the point they use all the name plate HP.

I have also read others claim the static converter causes the motor not to run as smooth. I can not comment on that, as Ive never used one. I guess its that old argument that your running on 2 of the 3 phases. 

When its all said and done, motors can crap out when ever. Regardless if run on 3 phase off the pole, RPC, or VFD. Many do claim the motor life on a static converter is shorter, but its allways a hear say thing most of the time. If the motor your running is just a run of the mill motor, nothing special or exotic, then I would just continue on running it. If you have a failure, then have it rebuilt, or replace it, and then decide if you want to change your ways of powering a 3 phase motor.


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## Jim (May 7, 2012)

Thank you for the replies.  I guess I have used the static converter for two years now without problem.  Obviously, I don't run it everyday nor do it do eight hour shifts.  I'll keep it for now.
Jim


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## CharlieW (May 7, 2012)

Jim said:


> I used a relatively inexpensive static converter to poer my Bridgeport and it seems to be working well for the light use it receives in my shop.  I realize it uses a capacitor to start the motor and then runs it on single phase power at I think 2/3 the rated horsepower.  Is this going to destroy my motor or will it be ok to use indefinitely?
> Jim



I bought my 1960's bridgeport about 10 years ago.  It was apart in a man's home garage.  He had used it in some sort of repair shop, he owned, before he retired.  He ran it off of a static convertor for the 20 years he owned it.  I took it all apart repainted it and replaced worn parts.   Upon turning it on the first time, it had a terrible knock in the head.  I tracked it down to the motor.  I imagined a pulley or bearing problem.  I removed the motor and discovered the armature core was loose on the shaft.  It was so loose that it was banging the laminations in the case as it turned.  

I thought I would have to find another motor.  I then remembered an article I read a few years back.  It talked about converting a BP to a single phase motor.  One thing that was done was to press out the shaft and make a new longer shaft to accomodate the step pulley.  This made me think that I could bore out the laminations to true them up and press in a new shaft that I made.  I'm still using that mill today.

My feeling is that running a 3 phase motor on 2 single phase leggs, causes an unbalanced condition and that vibration eventually shakes the shaft loose from the armature core.  I run a 5 hp rotary phase convertor.  Like a dummy, I mounted it to a wood wall.  When I start it up, it vibrates the wall making a loud annoying sound.  As soon as I start running equipment off of it and it goes from running like a 3phase motor being run on 2 single phase leggs, to a balanced motor, when it starts generating the 3rd leg of the 3 phase, it quites right down.

I would never run a 3 phase motor off of a static converter unless the motor was cheap and easy to replace.  A BP motor is not an off the shelf motor.  I run several machine off of the RPC but if it was just the mill, I would go with a VFD.

Charlie W.


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## Old Iron (May 7, 2012)

I don't know what HP your motor is in your mill, But you could use the static converter and another 3 phase motor to make a RPC.

Paul


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## Kevinb71 (May 7, 2012)

1+ on Paul's response. Just use it as is right now and keep your eye out for a 3ph motor and then make a RPC.


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## 8ntsane (May 7, 2012)

Charlie W 
Had commented on the 3 phase motor being imbalanced when feeding 2 legs out of three. I myself have noticed the same thing with more than a few of the RPC Ive built over the yrs.

I noticed with the RPC just idleing on its own, not as smooth as I would like. But switch on a machine a load it, then the RPC would tend to smoothen out.

I suppose over time damage would be found with a static running this way all the time. I personally have ditched all the RPC for VFDs on both Lathe and Mill. I have never run a static converter to notice any long term effects either. What Charlie has mentioned does make sense though.


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## randyjaco (May 8, 2012)

The static converter may not be damaging to the electrics of the motor, but when I switched from static to RPC , I noticed that the bearings in my Sharp mill stopped clacking and  the machine ran noticeably smoother. I haven't used a static converter since. I have one you can have cheap 8^)

Randy


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## 8ntsane (May 8, 2012)

randyjaco said:


> The static converter may not be damaging to the electrics of the motor, but when I switched from static to RPC , I noticed that the bearings in my Sharp mill stopped clacking and the machine ran noticeably smoother. I haven't used a static converter since. I have one you can have cheap 8^)
> 
> Randy



Well, I guess thats another static user that has found ill effects from there use. The imbalance must be very real. Interesting comments so far. Id like to hear of others that have run these, with ,or with out problems over the long haul.


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