Unbalanced Phase Converters and Power Loss
 

I use a 7.5HP rotary phase converter to run my 2HP Sheldon Lathe. I was
taking a medium cut in some 1020 steel in backgear and after a couple
of passes it seemed that the lathe was losing power. I opened the
cabinet up and the motor was very hot. If I disengaged the power feed
and retracted the tool the lathe would come back up to speed.

The motor is the original and it is wired properly at 220v.

Is it possible that the converter not being balanced or tuned is
causing this power loss. Bob Swinney sent me an article on balancing so
it will not be a problem to do so as I have ordered some run
capacitors.

I do not have the voltages right now on the 3 legs. Should I measure
these with the lathe running with no load?

Thanks, Steve

For all practical purposes a 7.5 HP RPC running a 2 HP machine should not
require much in the way of balancing. I suggest as a first test:

1. Run the RPC with the lathe turned off. Does it overheat?

2. Run the lathe unloaded (no cutting). Does it overheat?

If the answer to either is "yes", then the respective motor is probably
defective.

Bob Swinney
wrote in message
ups.com...
I use a 7.5HP rotary phase converter to run my 2HP Sheldon Lathe. I was
taking a medium cut in some 1020 steel in backgear and after a couple
of passes it seemed that the lathe was losing power. I opened the
cabinet up and the motor was very hot. If I disengaged the power feed
and retracted the tool the lathe would come back up to speed.

The motor is the original and it is wired properly at 220v.

Is it possible that the converter not being balanced or tuned is
causing this power loss. Bob Swinney sent me an article on balancing so
it will not be a problem to do so as I have ordered some run
capacitors.

I do not have the voltages right now on the 3 legs. Should I measure
these with the lathe running with no load?

Thanks, Steve

On 12 Dec 2004 07:17:02 -0800, wrote:

I use a 7.5HP rotary phase converter to run my 2HP Sheldon Lathe. I was
taking a medium cut in some 1020 steel in backgear and after a couple
of passes it seemed that the lathe was losing power. I opened the
cabinet up and the motor was very hot. If I disengaged the power feed
and retracted the tool the lathe would come back up to speed.

The motor is the original and it is wired properly at 220v.

Is it possible that the converter not being balanced or tuned is
causing this power loss. Bob Swinney sent me an article on balancing so
it will not be a problem to do so as I have ordered some run
capacitors.

I do not have the voltages right now on the 3 legs. Should I measure
these with the lathe running with no load?

Thanks, Steve

Actually..it sounds like you have lost one leg completly. Might check
the voltages at the motor and then see if the motor will run from any
other 3ph source. It could be you have lost a winding in the motor as
another cause.

Gunner

"To be civilized is to restrain the ability to commit mayhem.
To be incapable of committing mayhem is not the mark of the civilized,
merely the domesticated." - Trefor Thomas

wrote:

I use a 7.5HP rotary phase converter to run my 2HP Sheldon Lathe. I was
taking a medium cut in some 1020 steel in backgear and after a couple
of passes it seemed that the lathe was losing power. I opened the
cabinet up and the motor was very hot. If I disengaged the power feed
and retracted the tool the lathe would come back up to speed.

The motor is the original and it is wired properly at 220v.

Is it possible that the converter not being balanced or tuned is
causing this power loss. Bob Swinney sent me an article on balancing so
it will not be a problem to do so as I have ordered some run
capacitors.

I do not have the voltages right now on the 3 legs. Should I measure
these with the lathe running with no load?

Thanks, Steve


Install three 220 volt low wattage light bulbs across the phases. It is
the simplest way to monitor the voltages. You can easily tell a 10
percent difference in voltages at a distance. Remember that your phase
shift from the converter is only 120 degrees at one power loading unless
you can vary the reactance between the phases.

John

That sounds like the motor might
not be properly wires for 220.Check it again and check the ohms .