Disc grinder motor

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Craig Daniel

Joined
Feb 17, 2016
Messages
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Does a 3 phase motor have to be inverter duty to be operated by a vfd? The motor I am looking at has "Reconn" listed beside rotation, Does this mean I will be able to use it in forward and reverse with a vfd? Do you need a vfd with a rating of more power than the motor? I'm sorry for all the questions lately but I need some guidance here.
 
Reconn likely means it's been reconditioned (rebuilt). Your best bet is a footed 56C frame 3phase TEFC enclosure. Get a 1725 RPM. The VFD will likely have multiple HP settings. Make sure you get a VFD rated for your HP. I think a 2hp VFD will run a 1hp motor, but not positive.
 
Craig Daniel said:
Does a 3 phase motor have to be inverter duty to be operated by a vfd?
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No. Many of us us VFD's with loads of non-Inverter Duty motors. No problem. The long answer is that 'Inverter Duty' means more insulation to handle voltage spikes that can accrue with VFD's. Insulation is always good, but I wouldn't worry about it in a non-critical/non-production environment.

Craig Daniel said:
The motor I am looking at has "Reconn" listed beside rotation, Does this mean I will be able to use it in forward and reverse with a vfd?
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VFD's can do forward/reverse with ANY standard 3-phase motor. 3-phase is simple...swap any pair of leads and you get reverse. VFD's do this. (I don't know what Reconn means and it doesn't matter to your question). (note, some odd VFD's like the KBAC may require you to buy the optional switch on your VFD to switch to reverse...most other vfd's let you select direction as an option on the screen).

Craig Daniel said:
Do you need a vfd with a rating of more power than the motor? I'm sorry for all the questions lately but I need some guidance here.
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To answer this we need to know what exactly you want to do AND which VFD model you are looking at. VFD's were originally designed for people to control the speed on motors -- NOT to change phase or voltage. Nowadays, we all use them to take our 110v or 220v 1-phase household power and turn it into 3-phase 220v power in addition to variable speed.

Older VFD's often needed to be de-rated (you need a bigger VFD) if you wanted to use them to generate 3-phase power from your 1-phase power. HOWEVER, the KBAC and TECO VFD's that many of us use do NOT have to be de-rated. Just choose one that will take whatever household power you want to use (probably 220v 1-phase) and outputs 220v 3-phase, and use the rating it suggests for motor hp (so if it says it's rated for 1.5hp, then you can use it with ANY motor UP TO 1.5hp).

Technically, a good VFD nowadays can actually be used with a larger hp motor than it's rated for, and it will use its electronics to only give you the rated power. So if you buy a 1.5hp VFD and use it on a 3hp motor, this will work, but your 3hp motor will only output 1.5hp.

If some of this doesn't make sense, then just ask. Some of the explanation above was a simplification... tell us exactly what power you have in your shop and what you want to do and we can be more specific.
 
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I have 220v power here in the shop, I am looking at a 1 hp 3 phase , 208-240 volt, FLA 3.5, 1750 rpm. I have not bought the motor yet but was wanting to make sure it would work for a variable speed disc grinder set up. I was told by a local guy that DC motors are better at variable speed and for reversing qualities, I have searched all weekend for answers as to which way to go so I wanted the answers from you guys. I just want to buy the right stuff first so I don't have headaches later. What vfd would be a good choice for this motor? Thanks so much guys for all the help!
 
The teco fm50-202 is what I use. It's running a 2 hp 2x72, a 1 HP disc, and a surface grinder.
It's 220 single phase in, 3 phase out. Some guys use the 3hp teco as well.
The downside is it's not nema 4 rated. I had to build an enclosure to keep the dust out otherwise it will crap out on me.
 
Craig Daniel said:
I have 220v power here in the shop, I am looking at a 1 hp 3 phase , 208-240 volt, FLA 3.5, 1750 rpm. I have not bought the motor yet but was wanting to make sure it would work for a variable speed disc grinder set up. I was told by a local guy that DC motors are better at variable speed and for reversing qualities, I have searched all weekend for answers as to which way to go so I wanted the answers from you guys. I just want to buy the right stuff first so I don't have headaches later. What vfd would be a good choice for this motor? Thanks so much guys for all the help!
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Craig, You are looking for the right motor but be sure to buy a motor that is listed as TEFC ( totally enclosed fan cooled) . It will have a shroud at one end with cooling slots in it. You need this because of dust in the shop that will ruin a normal motor. Here is a photo of a 2 hp tefc 208 volt 3 phase motor for illustration. Check out the shroud at the rear of the motor. This is what you want only in a 1 hp motor instead of 2 hp. 1 hp is plenty for a disc grinder. When you get your drive (VFD) most will have a space for a reverse switch which you need to install. A lot of guys use the Teco drives and are happy with them. I use KBAC drives which are dustproof and have a great reputation for reliability. They can be bought at a good price if you shop hard. Some of he knife makers here have found good places to buy drives for a good price and maybe they can help. If you want to make knives then a good disc grinder is a must in my opinion. Good luck with this. Larry P.S. This motor is a 56c mount as well as having a foot so it can mounted on it's foot or mounted directly to a grinder for direct drive. This is good because you probably will mount youir motor to a plate or some thick plywood but will need a "face mount" to install a work rest. LL

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Can someone address the DC motor , I was told they are a better choice for a vfd drive but in a DC contoller?
 
DC motors can vary speed through pulse width modulation or through variable voltage. Variable voltage speed controls reduce the amount of torque a DC motor puts out because of the reduced potential. PWMs give constant voltage and vary the frequency essentially turning the motor on and off many times per second, and varying that pulse frequency changes the speed.

DC motors in the size and configurations we typically need for our equipment are either generally unavailable, overly expensive, or of incorrect HP. They're mostly used in complex systems where you feed a machine 480 volts and through transformers and inverters in the equipment, use a low voltage DC system to power stepper and servo motors.

They're really not terribly useful for us, although I'm sure there is an example or two of people using them, it's likely because they found them cheap in special circumstances.

They're not a better choice for a Variable Frequency Drive. The smaller ones are easier/cheaper to control speed than an AC motor.

I'm curious who you're getting advice from, since 99% of people here will be using a 120/240 3ph AC motor on their disc sanders or a 120/240/480 3ph AC motor on their belt sanders with a modern VFD. The reason is because it's the best solution currently available to having a variable speed tool in the HP ranges we use, in a motor with the form to fit our equipment, and run on typical wiring available to the majority of us with typical residential wiring.
 
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With the most common vfd's dicussed here you don't need to do anything special selecting them. I recently found that ABB has a single phase input drive for machinery now, ACS355 line. And if I recall correctly some manufacturers will allow for single phase input on a (normally) three phase drive but only if you double the horsepower of the drive compared to the motor, that may be where you heard about changing the drive rating other than matching it to the motor.
 
There is a local guy who said DC motors are better than AC, I am looking at buying the motor and controller as a pair. I really appreciate all the help.
 
3 phase AC motors with a vfd work perfect for our purposes.
No reason to overthink it. Unless you have been given a free dc motor with speed control, go with ac.
 
hello.....if you wanted to use them to generate 3-phase power from your 1-phase power. HOWEVER, the KBAC and TECO VFD's that many of us use do NOT have to be de-rated. Just choose one that will take whatever household power you want to use and outputs 220v 3-phase, and use the rating it suggests for motor hp.

assemblage PCB
 
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