Single to three phase.

You can also just install a Run Capacitor between L2 and T3 and the motor will fire up if the MFD rating is high enough on the Capacitor.....

Soooo like this...... I have my surface grinder wired like this.....
1PH TO 3PH MOTOR.jpg
 
It’s an interesting fact that you should not connect a lower HP motor if it’s below the lowest HP rating of the phase converter. So a 3/4 hp motor on a 1 to 3 hp converter can be a problem. I did this with my surface grinder...it runs seemingly normally for about 2 minutes then trips the breaker. The reason is technical and dull and I don’t know it.
 
BGHansen said:
I can't imagine stalling a bench grinder with a 1/3 reduction in power.

Bruce
Click to expand...

That depends on how much power the grinder starts off with.

Edited as I had my grinder HP numbers wrong.

I grind tool steel regularly on a 1hp Baldor and can slow it down enough to notice it, but certainly not stall it. My 1/2hp Baldor I can really slow down to the point I don't even bother trying to use it for the tool steel. I'm certain I could either stall the 1/2hp model, or slow it so much as to be a major issue, if it was derated to only 1/3hp.

I also have a 3/4hp 8" Central Machinery grinder from HF that was given to me. That one I can stall with a wire wheel on it, but to be fair a wire wheel doesn't have the inertia that a grinding wheel does, so it's not exactly a fair comparison.
 
Last edited:
Seems to me that shoving a piece of work into a grinder hard enough to slow it down is just asking for trouble. If the grinder is a 1/4 HP, grinding a piece of 3/4 inch steel plate is too much. If you do big work, get a big grinder. Or mill it down and deburr on the grinder. I've seen (big) grinders come apart and it ain't pretty, even on a good day.

.
 
Me either, I think its a none issue for this application. When I get it, I'll post the results.
.
 
As an FYI my Black Diamond drill grinder has aa 240 volt 3 phase 1/3 hp motor. It's been running on a static converter for over 2 years and sharpened well over 1,000 drills ranging in size from 1/16" to 3/4". It has plenty of power for this application and never slows down regardless of the size drill being sharpened.
 
I am thinking of replacing the single-phase motor on my lathe with a 3-phase in order to eliminate the torque pulses. I do not have 3-phase service in my shop. From this discussion I gather that a static converter would not eliminate torque pulses and I would need to go with a VFD. Is this correct?
 
JPMacG said:
I am thinking of replacing the single-phase motor on my lathe with a 3-phase in order to eliminate the torque pulses. I do not have 3-phase service in my shop. From this discussion I gather that a static converter would not eliminate torque pulses and I would need to go with a VFD. Is this correct?
Click to expand...
A VFD or a RPC will do it.
 
JPMacG said:
I am thinking of replacing the single-phase motor on my lathe with a 3-phase in order to eliminate the torque pulses. I do not have 3-phase service in my shop. From this discussion I gather that a static converter would not eliminate torque pulses and I would need to go with a VFD. Is this correct?
Click to expand...

I keep hearing these types of comments about torque spikes, and somewhat erratic running speeds with machines being powered by single phase motors, or 3 phase motors energized by static converters. I don't have 3 phase in the shop, and have several machines running on static converters. The machines include a tool grinder, milling machine, and lathe where finish is certainly important. I have never run into these problems with these machines. I also have another lathe, a horizontal mill, and surface grinder with single phase motors. Again, any and all of them are capable of mirror finishes with the proper speeds, feeds, and lubricants. I have on occasions even put tachometers on the machines to see if there are erratic running speeds. In a 30minute+ time span none seems to vary more than 5 rpm.

It would be interesting to know the age, size, and brands of the motors that people are having problems with. Most of the motors on my machines are originals dating from as far back as the early 1940's through the mid 1980's. There are various brands including, Emerson, Baldor, Peerless, US Motors, Century, and Leland.
 
You must log in or register to reply here.
Back
Top