What Did You Buy Today?

I am no expert, but I have been told you can run the single phase motor with a VFD and control the speed. Not all VFDs convert from single phase to three phase.
But I have some more research to do.

In the first place, an "expert" being divided into two distinct sounds, that being "ex" and "spert" yields the following definitions. "Ex" as in a 'has been' and ""Spert" being a 'drip under pressure'. Which definitely fits my opinion of "expert" opinions.

That being said, I have worked in the industrial side of electricity and electronics far longer than small computers have been around. Am I then an "expert"? See the definition above. . . I specifically deny being an expert. Take my word with that in mind.

In answer to your question:
It is possible but not very practical to overspeed. The "overhead" cost of such an operation would far exceed that of replacing the motor with a 3 phase one. Running above base speed would not be too much of a problem. No more than a 3 phase motor not designed for such use. But I don't see much use for running above base. Most times we are trying to reduce speed.

In running below base speed however there are several factors to consider. First and foremost is the centrifugal switch and starting capacitor. The entire starting network would need to be switched out of service when the motor was running. It would be possible to do externally with a "speed switch" adjusted to low enough speed. Or with a timer, or even by hand if you watched close and operated it fast enough.

Another factor is that while a 3 phase motor creates a "rotating magnetic field" inside the stator, a single phase motor does not. A single phase motor has a magnetic field that flip-flops back and forth and depends in the inertia of the rotor speed to get any practical use from the field. The start winding and capacitor provide, temporarily, a second phase to allow starting. I will refer you to the following posting to give some insight there.


Consider that while the 3 phase motor has their rotating magnetic field being slowed down, the single phase motor is simply flip-flopping back and forth at lower speed. The 3 phase motor can maintain its' torque down to near zero speed by altering the curve of current flow. Railroad locomotive AC power is an extreme example of this. But no amount of current alteration will make up for that single phase flip-flopping. The slowest I ran a single phase motor "reliably" in my experiments was at 50 cycles. And that caused significant heating. One might go to 40 cycles with sufficient cooling air flow. I didn't try it. . . An external fan was necessary at 50 cycles. I didn't have the capacity to "force feed" cooling air.

Then there is the loss of power. At low speed, a single phase motor has no usable torque. I don't have a "prony brake" as such, but simulating one with a cobbled together mish mash of wood I was able to stall the 2 pole motor used in my experiments. Not for long though, the motor is still usable at 60 cycles. But enough to convince me that such experiments were a dead end.

I will ask that you keep in mind that my experiments were not scientific, there were no measurements made and no records kept. Just an old man scratching an itch. Unsuccessfully, I might add.

Bill Hudson​
 
In the first place, an "expert" being divided into two distinct sounds, that being "ex" and "spert" yields the following definitions. "Ex" as in a 'has been' and ""Spert" being a 'drip under pressure'. Which definitely fits my opinion of "expert" opinions.

That being said, I have worked in the industrial side of electricity and electronics far longer than small computers have been around. Am I then an "expert"? See the definition above. . . I specifically deny being an expert. Take my word with that in mind.

In answer to your question:
It is possible but not very practical to overspeed. The "overhead" cost of such an operation would far exceed that of replacing the motor with a 3 phase one. Running above base speed would not be too much of a problem. No more than a 3 phase motor not designed for such use. But I don't see much use for running above base. Most times we are trying to reduce speed.

In running below base speed however there are several factors to consider. First and foremost is the centrifugal switch and starting capacitor. The entire starting network would need to be switched out of service when the motor was running. It would be possible to do externally with a "speed switch" adjusted to low enough speed. Or with a timer, or even by hand if you watched close and operated it fast enough.

Another factor is that while a 3 phase motor creates a "rotating magnetic field" inside the stator, a single phase motor does not. A single phase motor has a magnetic field that flip-flops back and forth and depends in the inertia of the rotor speed to get any practical use from the field. The start winding and capacitor provide, temporarily, a second phase to allow starting. I will refer you to the following posting to give some insight there.


Consider that while the 3 phase motor has their rotating magnetic field being slowed down, the single phase motor is simply flip-flopping back and forth at lower speed. The 3 phase motor can maintain its' torque down to near zero speed by altering the curve of current flow. Railroad locomotive AC power is an extreme example of this. But no amount of current alteration will make up for that single phase flip-flopping. The slowest I ran a single phase motor "reliably" in my experiments was at 50 cycles. And that caused significant heating. One might go to 40 cycles with sufficient cooling air flow. I didn't try it. . . An external fan was necessary at 50 cycles. I didn't have the capacity to "force feed" cooling air.

Then there is the loss of power. At low speed, a single phase motor has no usable torque. I don't have a "prony brake" as such, but simulating one with a cobbled together mish mash of wood I was able to stall the 2 pole motor used in my experiments. Not for long though, the motor is still usable at 60 cycles. But enough to convince me that such experiments were a dead end.

I will ask that you keep in mind that my experiments were not scientific, there were no measurements made and no records kept. Just an old man scratching an itch. Unsuccessfully, I might add.

Bill Hudson​

Thank you for the detailed and well written explanation.

You are confirming what I have read, following some of the links provided above. I was misinformed and glad that I got the right info before I wasted any money or time on it. I had one belt sander year ago that I installed an industrial DC Perminant Magnet motor from an industrial sewing machine with a speed control on it. It was great and had good torque the entire range of speeds. I may keep my eye out for another one but for now, I am good with it the way it is.
 
Picked up this medical instrument cabinet yesterday that fits perfectly between my roll-away toolboxes. The guy had it listed for months and finally dropped his price, I paid $40 :grin:

medcab.jpeg
00O0O_33n5jQ1HmBh_1200x900.jpg

I figure the medical grade isolation transformer is worth that alone....

John
 
I pulled my stuff out of storage and moved it into my new shop this weekend. A lot of my tools were looking pretty sad, including my trusty old Jackson auto-darkening hood. I've wanted to replace it, since it is 1st gen technology and I've had it since the 1990s.

Lots of people have said good things about the Lincoln Viking 3350 4C, so that's what I ordered. It was less than half of the cost of Optrel, and the current Jackson and Miller offerings seem to have fallen behind the curve. I guess I can live with myself for buying from stinkin' Lincoln, so long as I can cover the badges with stickers of my choosing.
 
I pulled my stuff out of storage and moved it into my new shop this weekend. A lot of my tools were looking pretty sad, including my trusty old Jackson auto-darkening hood. I've wanted to replace it, since it is 1st gen technology and I've had it since the 1990s.

Lots of people have said good things about the Lincoln Viking 3350 4C, so that's what I ordered. It was less than half of the cost of Optrel, and the current Jackson and Miller offerings seem to have fallen behind the curve. I guess I can live with myself for buying from stinkin' Lincoln, so long as I can cover the badges with stickers of my choosing.
You're going to love it. I replaced my Jackson with the Lincoln - night and day difference.
 
I pulled my stuff out of storage and moved it into my new shop this weekend. A lot of my tools were looking pretty sad, including my trusty old Jackson auto-darkening hood. I've wanted to replace it, since it is 1st gen technology and I've had it since the 1990s.

Lots of people have said good things about the Lincoln Viking 3350 4C, so that's what I ordered. It was less than half of the cost of Optrel, and the current Jackson and Miller offerings seem to have fallen behind the curve. I guess I can live with myself for buying from stinkin' Lincoln, so long as I can cover the badges with stickers of my choosing.

I've been looking at a Lincoln 3350 too, I've got an ok generic auto darkening helmet but seeing better has to help my meager skills. I'd love one of the Optrels but can't convince myself to spend the $450, $220 is a lot easier to swallow.

I've had the 3350 in my cart half a dozen times over the past couple months, but I keep waffling. Using a Lincoln helmet with a Miller welder just seems like it is tempting the welding gods. :grin:
 
I've been looking at a Lincoln 3350 too, I've got an ok generic auto darkening helmet but seeing better has to help my meager skills. I'd love one of the Optrels but can't convince myself to spend the $450, $220 is a lot easier to swallow.

I've had the 3350 in my cart half a dozen times over the past couple months, but I keep waffling. Using a Lincoln helmet with a Miller welder just seems like it is tempting the welding gods. :grin:
If you don't want to upset the welding gods try an Esab. I'm really happy with my Savage A40.
 
It's worth mentioning that I ordered my new hood from Baker's Gas and Welding Supplies. I had a coupon plus free ship, so the 3350 cost $200 delivered. This was after ordering tig rod storage tubes at $100 for 10 including shipping, making them cheaper than Amazon and eBay by a margin of 4 extra tubes!
 
Back
Top