intermittent use motor for grinder?

Stan Wilson

Stan Wilson

Joined
Apr 26, 2000
Messages
94
I've found a new 2.5 horse d/c variable speed motor with controller from a surplus supply house For $49.95 plus shipping.But it's rated for intermittent use.would this be a waste of money to try to use this for a grinder?I spent all my extra cash on a new grinder,so now I've got a grinder with no motor and no money left to spend on a motor.
 
Rebos,

Do you have anymore info on the motor and controller? Hopefully, the rating may be a max power rating for some duration....say 2 1/2 HP for 30 min, and a lesser power continously like... 2 hp continous.... From my experience, I found that most manufactures of motors and controllers are very helpful if you call them with these types of questions. Is there anyway to get the maunufacturer and a model/serial number? What is the speed?

Heck, reliance electric has the owners manuals online for thier DC controllers. Maybe it will be as simple as adding a heatsink to the controller for continous duty at the rated power.

At that price, it is certainly worth looking into to. Are there more available or is this a one time deal...?

Be glad to help if you need it,
Sincerely,
Rob Frink


 
Intermittant use "usually" means that the motor is designed for such uses as MOVs (motor operated valves). These motors only operate when either opening or closing a valve. For the most part, once the valve is positioned, they just sit there. These are usually high torgue motors.

This isn't to say it will not work but a friend of mine has one on a home built grinder and it gets hotter than a pistol. He can only operate it for no more than 10 minutes or so.

C Wilkins
 
I called and asked them to fax me the spec sheets.According the specs for the controller it's rated for continuous duty at 1.5 hp.RPM is 0-6750,reversable,permanent magnet,115 volts to controller.The motor is made by Argord the controller by KB electronics.They have nearly 3000 of these to sell off.
 
Good info....

I have a few thoughts to share. I think you'll be happiest with your grinder if the drive shaft runs about 3000-3500 rpm max for rough grinding. So for a 6750 rpm motor you could do a 2:1 pulley reduction and that would give you 3375 rpm at the drive shaft....that yields about 3500ft/minute belt speed. At this belt speed you'll have 1.5 continous HP available. From there you simply turn the speed down to match your task at hand. If you find that you are low on torque in the intermediate speed ranges the you could further reduce the drive shaft ratio from 2:1 to say, 3:1. That would be a 2" pulley on the motor and a 6" pulley on the grinder or 1.5" to 4.5"...respectively.

I have a KB controller that I picked surplus....never used it but it appears to be of high quality. I don't think you can go wrong at $49....especially if everything is enclosed and dust tight!

If you go with the motor and find that your grinder is too fast, another option is to reduce the diameter of the drive roller to get the belt speed in a useable range.

Good luck with it,

Rob
 
Rebos,This motor sounds like the ones that Surplus Supply Center is selling.It is almost the same thing as the tread mill motors that they sell.I have two of these running in my shop at the present.One I have on my metal cutting bandsaw and the other on my main grinder.The only problem that I have had from these motors in the last year has been that I had to re-solder a couple of the connections on the board as they were not soldered very good and came loose,and made the motor act up,This was a small inconvenience to have to pay for the price difference.
The shaft is a metric size so I couldn't just order a drive wheel for the one on my grinder but the guy at the local machine shop was happy to make the wheel for me for $15.00.This motor has seen allot of hard use in the last year and I am not sorry that I put it on my grinder,If it went out today it has paid for itself more than once.
The other suggestion I have about them is to do away with the inline circuit breaker.The first of the two motors I have was giving me fits.When it was warm outside and I was trying to grind for any length of time.It would keep throwing the in-line breaker and the motor would heat up very quickly.I decided one day to bypass the breaker as I was wanting to get a blade ground in a timely fashion.And I figured that if I burnt it up,it would just be a lesson learned.After doing this the motor has run cooler and doesn't stop all the time.Like I said I have run it hard for a year with no problems.It has seen days of 6 hours or more of grinding.
They will work great for you untill you can get a bigger and better notor for the grinder and then you can make a disc grinder out of it or run some other piece of equipment in the shop.
Hope this helps out some.
Bruce

------------------
Bruce Evans Handcrafted Knives
The soul of the Knife begins in the Fire!!!!!
Member of,AKTI#A000223 and The American Bladesmith Society
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I found them at Surplus Center,no web site but heres the phone #. 1-800-488-3407. item number 10-1806
 
I bought one of the motors from Surplus. I read about the problems with the motor not being sealed and grinder dust killing it. I built a box around the motor and used AC filter material in an attempt to make it clean running. When I built the box I was worried about the motor getting enough air to cool so I put one of the Surplus blowers in the box.
I am still having problems with finding pullys for the 17 mm shaft. I drilled out a 1/2" pully, leaving a quarter inch the 1/2" diameter to lock it with a nut. Next step is to grind a small piece of the shaft to accept the locking bolt on the pully.
I realize that I've probally over engeneered this. My wife keeps saying that she is going to post a sign on my shop saying "Overbuilt by Lynn". I'll post again after running for a while.
Still trying, Lynn
 
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