I have been offered an industrial pedestal grinder that has a 3 hp, 220 3 phase motor. The grinder has been in a garage hidden away for many years. The machine looks to be in reasonable shape and the wheels seem to turn easy enough. Question is there a way to test the motor to see if it still works. The original owner bought the machine to put in his shop many years ago and has now passed away. The family found the grinder when they went through some storage areas. The family has offered the machine to me for a very good price, mainly just to get it out of the garage. The grinder was never put into service. Before I go and purchase a phase convertor is there a way to test it on a single phase line to see it the motor is still good or if it is shot. No one in the family knows if the grinder worked or not. gear
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Testing a 3 phase motor.
- Thread starter gearhead
- Start date
- Replies 13
- Views 8,494
Matthew Kinsman
Aluminum
- Joined
- Sep 29, 2007
- Location
- Hamilton Ontario
Its tough to test a three phase motor without three phase power. You can eliminate a few questions with a multimeter by checking all three phases to ground should not conduct and between each phase should be the same. Setting up a phase converter seems like alot of investment for a pedestal grinder. And if you intend to set up a phase converter then do it whether the grinder is gonna work or not. If you are really concerned you could take it to a motor shop and usually the will fire it up for a cup of coffee and a couple doughnuts.
Forrest Addy
Diamond
- Joined
- Dec 20, 2000
- Location
- Bremerton WA USA
I would think a regular procedure is indicated where you have a long neglected mystery motor.
It would make sense to take it to to a motor shop but you could save a minimum charge if you DIY.
First a general clean-up and inspection. Open it up and look inside. Look at the bearings, inspect the leads, etc then fix what needs attention. If the motor is dry you might still give it a bake in a 200 degree F oven for a day or so. The next step is to megger it: apply a high voltage to measure the insulation strength but a good second best is to run some tests with a light bulb and a plug in cord.
You might still take the motor stator to the shop for a quick check. If they don't have to take the motor apart you could save a few bucks.
The price of low end VFD's have come to the point where they are competitive with even home brew phase converters. You might consider a VFD. If the motor is 1 HP or less they make them with 115 Volt input. They step up the voltage with a trick circuit inside.
It would make sense to take it to to a motor shop but you could save a minimum charge if you DIY.
First a general clean-up and inspection. Open it up and look inside. Look at the bearings, inspect the leads, etc then fix what needs attention. If the motor is dry you might still give it a bake in a 200 degree F oven for a day or so. The next step is to megger it: apply a high voltage to measure the insulation strength but a good second best is to run some tests with a light bulb and a plug in cord.
You might still take the motor stator to the shop for a quick check. If they don't have to take the motor apart you could save a few bucks.
The price of low end VFD's have come to the point where they are competitive with even home brew phase converters. You might consider a VFD. If the motor is 1 HP or less they make them with 115 Volt input. They step up the voltage with a trick circuit inside.
johnoder
Diamond
- Joined
- Jul 16, 2004
- Location
- Houston, TX USA
They are more apt to be good than old single phase motors with starting capacitors and centrifugal switches maybe.
Here is how I run a 15HP three phase on single phase.
http://www.practicalmachinist.com/vb/showthread.php?t=158528
Here is how I run a 15HP three phase on single phase.
http://www.practicalmachinist.com/vb/showthread.php?t=158528
Pierce Butler
Hot Rolled
- Joined
- Jun 28, 2007
- Location
- Texas
Forget the static converter. In the end the VFD will be cheaper.
A VFD will cost no more than one or two good grinding wheels.
A VFD will cost no more than one or two good grinding wheels.
Pierce Butler
Hot Rolled
- Joined
- Jun 28, 2007
- Location
- Texas
The "trick" is called a voltage doubler which is the addition of a cap and a diode or two. Pretty reliable stuff actually.
Lloyd H
Aluminum
- Joined
- Feb 11, 2008
- Location
- Chester, IL
motor test
Hook up 240 to two leads and 35 or 40 mfd run capacitor from an old AC unit from the third motor lead to one of the 240 leads and it should run. It will start most likely and if you can live with 2 HP your done. If it runs backward move the cap lead to the other 240 lead. I just did a 3/4 HP grinder with 15 mfd about 2 weeks ago for a guy.
Hook up 240 to two leads and 35 or 40 mfd run capacitor from an old AC unit from the third motor lead to one of the 240 leads and it should run. It will start most likely and if you can live with 2 HP your done. If it runs backward move the cap lead to the other 240 lead. I just did a 3/4 HP grinder with 15 mfd about 2 weeks ago for a guy.
peterh5322
Diamond
- Joined
- Dec 15, 2002
- Location
- Monterey Bay, California
"I just did a 3/4 HP grinder with 15 mfd about 2 weeks ago for a guy"
That's 20 µF per HP, and the normally recommended value is 30 to 35 µF per HP, so you're in the ballpark.
You want a large enough capacitance to start within 1 to 2 seconds (1 is better than 2), yet not so much capacitance that the voltage on the manufactured phase is significantly over 264 (10 percent high).
That's 20 µF per HP, and the normally recommended value is 30 to 35 µF per HP, so you're in the ballpark.
You want a large enough capacitance to start within 1 to 2 seconds (1 is better than 2), yet not so much capacitance that the voltage on the manufactured phase is significantly over 264 (10 percent high).
Pierce Butler
Hot Rolled
- Joined
- Jun 28, 2007
- Location
- Texas
For a grinder a common VFD would be fine. It is a wire-n-go VFD. There are a few parameters that you may want to set, but they are few and simple.
I like Teco VFDs - their 2 year warranty is tough to beat.
Here is a 1hp VFD that produces 230 volts 3ph from 120 volts 1ph.
http://www.factorymation.com/s.nl/it.A/id.193/.f?category=30
Here is a VFD that take 230 volts 1ph input and produces 230 volt 3 ph output.
http://www.factorymation.com/s.nl/it.A/id.197/.f?category=32
I like Teco VFDs - their 2 year warranty is tough to beat.
Here is a 1hp VFD that produces 230 volts 3ph from 120 volts 1ph.
http://www.factorymation.com/s.nl/it.A/id.193/.f?category=30
Here is a VFD that take 230 volts 1ph input and produces 230 volt 3 ph output.
http://www.factorymation.com/s.nl/it.A/id.197/.f?category=32
Hooked up the grinder tonight using a factorymation.com VFD. Very easy to wire up. Question is the numerical display supposed to stay on and blink when the VFD is in the off mode. Grinding wheels are turning the wrong way but I'm told that is just a wire change on the grinders side. I can notice a slight wine in the VFD, but my hearing is shot so it does not bother me. The wife noticed it right away. Gear
Pierce Butler
Hot Rolled
- Joined
- Jun 28, 2007
- Location
- Texas
Glad to hear the FM50 is working for you. They are easy to wire up and the manual is better than average.
Yes the LEDS flash when it is not powering the motor. That prolongs the life of the LEDS.
Turning the wrong way? Swap any two output wires. Alternatively you could set F_04 to 1.
The whine can be eliminated by raising the carrier frequency. Try setting F_12 to 6 or 7,
