Tool Gloat

I hate you (in a good way). If you want to sell it cheaply, let me know.

Check out

Thanks, but I have that manual. It has nothing on operation.

BTW, the mach> I hate you (in a good way). If you want to sell it cheaply, let me > know.

I am afraid that 3 phase motors have less vibration and offer better grinding quality than single phase motors, due to better balance.

You can simply make a phase converter for it from a 1 HP motor. You do not need any capacitors, just spin the rotor by hand and then apply electricity.

For the person to whom I sold my previous Bridgeport, I made a phase converter just like that, he spins the shaft by hand and applies power after it is spinning. Works just fine.

I can sell you a 1 HP 3 phase motor for $10. It is new, never been wired.

Thanks, but I'll probably just buy a VFD. I like VFDs, I use one on my

And I'm hunting since years to get one for below $500 ...

Nick

I contacted Deckel (I'm from Germany) and got the manuals for free. Don't know wether they have English manuals.

Nick

David wrote in article ...

If it is THAT simple, why don't licensed electricians do this on a more regular basis instead of going with phase converters?

Could such a hookup be a violation of electrical code?

Your apparent success notwithstanding, I have to wonder if there is some sort of danger involved in such a setup.

You don't get full HP with a static phase converter.

Best regards, Spehro Pefhany

Hi Spehro

I have read enough of your posts to have great respect for your knowledge. So, I wonder if you have any data related to the "full HP" of electrical motors. Specifically, I wonder how the "HP" rating that is marked on an electrical motor is determined.

I have made several measurements of HP from 3 phase motors with single phase feeding them. They all deliver full rated HP, but at a lower RPM than listed on their name plate. I recognize that there is danger of stalling a 3 phase motor when it is connected to single phase.

My question about HP is related to wondering how industry establishes "HP". Is it RPM? Is it heat of the wire? Is it heat of the case?

Jerry

You can run a three phase motor with a start and run cap, just like you do with a single phase motor. The problem is that you have to figure the run cap for a fixed hp load. Anythng less or more than the computed load will change the phase shift of the third phase cap. Using a rotary converter gives you a wider range of operating conditions for the motor. A variation of the load on the motor is swamped by the idler motor.

John

I believe that manufacturers establish the HP rating of their motors based on the HP they can deliver in continuous use ( or in case of non- continuous usage motors based on what they can deliver at the duty cycle listed ). If you tested three phase motors with three phase feeding them I would expect they would deliver more than the full rated HP when loaded enough to lower the rpm below the listed rpm. The temperature of the wire and case would be higher and the life of the motor shorted.

Dan

Hi Dan

I agree with your suggestion that motor's temperature is what the manufacturer actually uses to then identify "max" HP. The RPM listed on the name plate is actually their way of telling us that, when the motor is "fully loaded", it will be running at That RPM.

When I tried to investigate what HP the 3 phase motor would deliver when fed single phase, I was surprised that all the motors *I* tested would deliver full power with single phase. My original assumption was that the power would begin to drop off slightly after some HP value around 2/3 name plate rated HP. That didnt happen. And, I was (am still) too impatient to run a temperature/time test on the fully loaded 3 phase motor. A large factor involved with motor cooling is the heat transferred from the copper to the case. I assume the "2/3 HP" is somewhat low. I suspect that when properly supervised, a 3 phase motor can deliver alot more than 2/3 name plate rated HP, continuously.

Jerry

Check with the engineers at Sears.. They can tell you how to get a lot of HP out of a little motor.

John

two points:

1. motor ratings for HP can vary, some quote "peak hp", others quote continuous duty with a specified temperature environment - the first are nearly meaningless. But in all cases, at least in theory, it's power deliverd to the shaft that is to be specified.

1. electricians don't do electronic work, that's why they don't design and install static phase converters

Full power, or full torque?

Three phase motors are rated do deliver rated mechanical HP at the rated maximum ambient temperature. If you are running at less than that temperature, you can somewhat exceed rated HP. That said, running a motor at its max does limit its life.

The temperature test is fairly easy: one measures the DC resistance of the motor after a long soak at a known temperature, run the motor in its setup for a while, and then disconnect motor from power and immediately measure its DC resistance again. The increase in resistance will be proportional to the increase in temperature of the motor core, assuming a pure copper resistance thermometer element.

The main problem with this method for home users with large motors is availability of an ohmeter that can accurately measure resistances in the ohms or tenths of an ohm. One can get digital multimeters (DMMs) that will do this (especially ones with 4-wire (kelvin) connections), or one can build a kelvin double bridge (a kind of wheatstone bridge), using an ordinary DMM as the null detector.

Or, one can build a slidewire wheatstone bridge: .

Joe Gwinn

Hi Joe

My investigation of the HP delivering capability of 3 phase motors when supplied with single phase has been limited to measuring shaft HP for relatively short periods. The data *I* acquired shows that a 3 phase motor can deliver considerably more than 2/3 of its name plate rated HP when connected to single phase. I can only guess about the time required to rise the motor's temperature to some damaging value. But, it would take alot more time than I'd be able to run my dyno. And, the temperature of the motor can easily be managed by some external cooling if that became a problem (in home/hobby use). My question to Spehro ( for whom I have respect) was related to how the motor design engineers relate HP and Temperature and RPM. But, if you have information about the design considerations used by motor engineers, I'd sure like to know more.

Jerry

It's because when one drives a 3-phase motor with single phase, only one winding is handling all the electrical power, so it will be hotter than the other two. That said, iron and copper are not bad heat conductors, so it tends to even out. To a degree. Especially if the motor is well designed thermally, and most industrial motors are.

The issue is to ensure that the hottest spot isn't too hot.

One could measure all three windings separately.

It's hard to give a more precise answer, so back-of-the-envelop computations plus a temperature test may be the fastest way home.

There are also textbooks on motors, such as "Electric Machinery", 6th edition, Fitzgerald et al, McGraw-Hill 2003.

Joe Gwinn

Hi Joe

I see that I am a little short on research. I figured that 2 of the motor's winding were doing the work. I even figured the windings were distributed evenly throughout the motor circumference and therefore the heat in the core might be fairly uniform. I can see where the winding (copper) could get too hot, too quickly if vast amounts of current is drawn. But, I monitored the line current and saw that it didnt increase excessively as the load was increased to full name plate rating. Also, I was content to load the 3 phase motors to no more than their name plate rated HP. I did notice that a fully loaded 3 phase motor will run at a lower than name plate rated RPM when connected to single phase. My question about 3 phase motors running with single phase was (is) related to the data behind the "2/3 HP" limit. Text books that deal with running 3 phase motors on single phase have been hard for me to find. Does Fitzgerald deal with single phasing 3 phase motors?

Jerry