Why don't more people use DC motors for grinders?

REK Knives

REK Knives

Moderator
Knifemaker / Craftsman / Service Provider
Joined
Apr 3, 2011
Messages
5,682
For example... if I were to want to get set up with a variable speed disc sander, I would basically need a DC motor, a Nema 4 DC vfd, and the discs (nielsen)... From what I've heard DC motors have a lot more torque at low speed. For that matter, why don't people use it on a regular grinder more often? Just curious... Seems like a cheaper/better option that AC but maybe I'm missing something.
 
dc motors just aren't as common as 3 phase AC motors. i found two 90vdc 1/2hp DC motors and 120v 1 hp DC drives on Ebay and 8" disc from lapidary supplier. cost was about $125 per grinder. but you got to shop
 
Willie71 said:
Cost and availability are the biggest hurdles.
Click to expand...
Buying new it looks like to me that a 1.5hp tefc DC motor and nema 4 vfd would run around $400 whereas the same thing in AC would run about $600.
 
razor-edge-knives said:
Ahhhh that makes sense ok so basically most people don't want to mess w/ this, is it complicated or something?
Click to expand...

A rectifier that can handle the current is all that is needed. You should be able to get an all in one unit. It is similar to running a foredom flex shaft, the foot pedal is an all in one unit.
 
Last edited:
Bill DeShivs said:
You have to convert your AC to DC before you can use DC motors.
Click to expand...

The DC drive does the conversion. It isn't a VFD like AC three phase.

It runs off 120/240AC and delivers the necessary DC field and DC armature voltages. By varying the armature voltage, it varies the speed.

I like DC motors. Bader uses them. The new high quality lathes, drill presses, mills, and similar equipment use direct drive DC motors. No belts anymore.
 
razor-edge-knives said:
Buying new it looks like to me that a 1.5hp tefc DC motor and nema 4 vfd would run around $400 whereas the same thing in AC would run about $600.
Click to expand...

I couldn’t find a dc motor under $500.00 a few years back when I built my grinder. Got the 2hp ac 3ph for $150.00 shipped.
 
Willie71 said:
I couldn’t find a dc motor under $500.00 a few years back when I built my grinder. Got the 2hp ac 3ph for $150.00 shipped.
Click to expand...
Gotcha, well prices must have come down a bit as more people are using them.
 
I have a 1HP 180VDC motor running my grinder. It was expedient and free surplus for me so why not. I have a DC speed controller from KB and it plugs into my 220VAC outlet and works great. Actually got 2 motors so it made sense.

If I was buying new I would go 3ph AC though.
 
The opposite has happened to ebay and auction DC motors. They used to sell for little over scrap. I bought NIB 1HP motors for less than $50, fractional HP for $10-30, and a honking 100# 3HP one for $100. Many times I was the only bidder. The controllers used to be cheap too.

I think the newfound popularity has run the price up.

Things to do with a 3/4 to 1HP DC motor and drive.
1) Take an old drill press and convert it to VS DC.
2) Take an old bandsaw and convert to VS DC.
3) Take an old 4X36 Craftsman belt sander and covert to VS DC.
4) Rebuild an old 2X72 grinder to VS DC.
5) VS DC disc grinder.
6)VS DC blower for forge
7) VS DC buffer
8) VS DC Roof/wall fan
9) VS DC dedicated slow speed sharpening belt grinder. Mine uses 2.5X48 belts on an Ickler grinder.
10) So many ther things
 
DC is speed controlled by varying voltage or pulse width what somewhat resembles varying voltage. But traditional DC motors require brushes what create more heat and nobody likes to mess with their dust and changing especially in enclosed housings.
What really shines for torque nowdays is brushless DC. Thanks to cheap microprocessors and rare earth magnets. What btw, could be argued that brushless DC motors, like ALL motors are AC motors afterall.
 
I had one of the early Hardcore billet grinders which came with a white painted Baldor DC motor,
The new ones are Baldor 3 ph AC
I don't know why Hardcore doesn't use the DC anymore.
 
I'm running two DC VS motors & three AC VFD motors. I honestly cant tell any diff in using them.
When I got the first VS grinder, DC was the only VS option. Now it seems VFD is the norm. I did buy a 1.5hp DC motor and controller brand new on ebay a few years ago for $300 shipped.
 
I'm using Baldor DC motors and KB drives. They were the best I could find on eBay; moon's ago and are still working. Probably paid about $270 for each motor/drive setup since I knew what to look for at the time. DC drives were supposed to have the most constant torque output throughout the rpm/load range.

My two motors are Emerson or Baldor 2HP DC Motor, TEFC, 1750 rpm, 180V armature, 145TC frames (totally sealed). One part number is CDP3585 motor with tachometer. Bought as surplus.

It sounds like AC vs DC doesn't matter much now for belt driving motors with variable speed. Most people tended towards AC about 10 years ago but I went DC due to what I thought was a better chance at more torque at lower speeds.
 
I have a 1.5 hp dc motor w/tc something or another "face/mounting". If I wanted to get a drive for it, where would I start? what capacity of a drive should I look for/buy? Can someone please post me a pic or a link, ebay or otherwise for such?
And... can you run (w/said driver) the motor in reverse? Cuz if so, then you could use a 10" wheel for the drive AND walk around to the other side of the grinder and have a huge 10" contact wheel w/a rest of it's own w/o changing anything. A free standing machine of course. Or one on a slim bench in the middle of the shop.
 
anvilring said:
I have a 1.5 hp dc motor w/tc something or another "face/mounting". If I wanted to get a drive for it, where would I start? what capacity of a drive should I look for/buy? Can someone please post me a pic or a link, ebay or otherwise for such?
And... can you run (w/said driver) the motor in reverse? Cuz if so, then you could use a 10" wheel for the drive AND walk around to the other side of the grinder and have a huge 10" contact wheel w/a rest of it's own w/o changing anything. A free standing machine of course. Or one on a slim bench in the middle of the shop.
Click to expand...
Firstly, you will need to know manufacturer & model to find what sort of drive controller it needs.

As far as running in reverse, thats specific to motor design.
Brushless DC motors typically can reverse. Thats a function of its controller.
Brushed motors, Some can reverse, some cant. (Those what cant may be able to 'run' in reverse, But will at reduced power and extreme brushes wearing)

Btw, Be careful messing around with DC motors.
Lashing them up to homemade grinders and such. Some designs will quickly overspeed and self destruct if unloaded. A belt breaking for example.
 
Last edited:
You must log in or register to reply here.
Back
Top