Thoughts on a motor

Daniel Macina

Well-Known Member
#1
So I have been looking around for a motor for my grinder build. Not in any hurry just want to find a good motor at a good price. One will pop up eventually. I am looking for a 1.5 hp, 1700 rpm, TEFC, 3 phase motor. I happened to run across a Baldor motor that I can get for $100 that meets all the specs, the only catch is it has 4,500 hrs on it. That is to many correct? Probably on the end of its life? Don't really know how long one should last but at $100 even if it doesn't last long it might be worth it. I know Baldor makes some great motors. Sorry for the dumb question don't know a ton about motors.
 
#3
Daniel...if that baldor is like any I've ever used it should be good. We used the small 1hp baldors with 3m wheels on them for deburring parts in a production job shop. We'd flip 'em on in the morning and leave 'em running all day...there were about 30 of 'em in that shop.

I don't ever remember replacing one in the 12 years I worked there...fixed some cords and switches but that was it. Also...they tend to be expensive due to their reputation. I would probably jump on it...
 

Daniel Macina

Well-Known Member
#4
Daniel...if that baldor is like any I've ever used it should be good. We used the small 1hp baldors with 3m wheels on them for deburring parts in a production job shop. We'd flip 'em on in the morning and leave 'em running all day...there were about 30 of 'em in that shop.

I don't ever remember replacing one in the 12 years I worked there...fixed some cords and switches but that was it. Also...they tend to be expensive due to their reputation. I would probably jump on it...
Would you mind if I messaged you with the listing so you can see what you think? If it's no trouble?
 

John Wilson

Well-Known Member
#7
4500 hours is less than one year of production time in a factory environment. (8,000 hours is the round number for one year of production.) That is nothing on a quality motor, so long as the motor was on a machine indoors. If you get to inspect the motor, try to wiggle the shaft. If there's no shake or slop, shaft spins smoothly by hand, and no signs that she got too warm once upon a time I'd call it good to go.

FYI, a grinder is not anything close to "hard use" for a motor. You can pick up an inexpensive IronHorse motor brand new for a just a little more than the cost of that used Baldor. There's no question that the Baldor is a better motor, but in reality anything below 5HP is considered disposable. I've been running a 2HP 3600rpm Ironhorse for about four years. Every now and again I lay my hand on it while it's running to see if she's getting hot. Nothing. Doing just fine.

You didn't ask, but a 1700rpm motor is fine for grinding. However, there will be times when you're going to want more speed, such as profiling blanks. When I'm really in the groove grinding bevels I will crank her up to about 80% of max speed, which is roughly 3000 rpm.
 

Daniel Macina

Well-Known Member
#8
4500 hours is less than one year of production time in a factory environment. (8,000 hours is the round number for one year of production.) That is nothing on a quality motor, so long as the motor was on a machine indoors. If you get to inspect the motor, try to wiggle the shaft. If there's no shake or slop, shaft spins smoothly by hand, and no signs that she got too warm once upon a time I'd call it good to go.

FYI, a grinder is not anything close to "hard use" for a motor. You can pick up an inexpensive IronHorse motor brand new for a just a little more than the cost of that used Baldor. There's no question that the Baldor is a better motor, but in reality anything below 5HP is considered disposable. I've been running a 2HP 3600rpm Ironhorse for about four years. Every now and again I lay my hand on it while it's running to see if she's getting hot. Nothing. Doing just fine.

You didn't ask, but a 1700rpm motor is fine for grinding. However, there will be times when you're going to want more speed, such as profiling blanks. When I'm really in the groove grinding bevels I will crank her up to about 80% of max speed, which is roughly 3000 rpm.
I have looked at the iron horse motors and was going to pull the trigger then I saw the Baldor and I got to be honest got hypnotized at the thought of having a Baldor motor.

As for the rpm's if I understand righ (I am getting a VFD) the KBEC 27d VFD has a deal the allows the motor to run at x2 speed. So say you have a 1700 rpm motor it would run at 3,400 rpm with that setting on the VFD. I was under the impression that 1,700 rpm was the thing to get. I could be completely wrong.
 

ARCustomKnives

Well-Known Member
#9
4500 hours really isn’t bad at all, though it’s probably not the best metric to go by. It really depends on a number of factors: was it sized appropriately for the job it performed for those hours? Was it within design specs? Was it in a rough environment? Was it abused? Etc...

If a motor is just turning a light load in a clean, relatively cool environment, it may last for well over 100k hours.
On the other hand, if it’s driving a trash pump with bad bearings in a 150 degree boiler room and being short cycled all day long, you’re probably not going to get full life expectancy.

As long as the bearings still turn smoothly and the wires don’t look like they’ve been baking (discolored, insulation brittle or cracking), I’d say you’ll probably be fine with the Baldor.
 

KenH

Well-Known Member
#10
Daniel, there has been much discussion of 1800 vs 3600 rpm motors. The discussion for 1800 rpm motors is the 1800 rpm motor will have a slight bit more torque at low rpm than will the 3600 rpm motor. The motor can be ran at 120 hz (doubling jumper) to get the high rpm, and use a 5" or 6" diameter drive wheel to get the high belt speeds desired for profiling (hogging metal).

The above is true, but the amount of torque required at low rpms is very small. At low speeds you're not using much pressure, but a light touch so the torque isn't an issue. My view on the 3600 rpm motor (I've been using an Iron Horse 3600 rpm motor for a few yrs) are positive. I've got VFD set for a max of 70 hz which gives around 3800 rpm for a belt speed of 4,000 SFPM which is all I desire for profiling. The 3600 rpm motor is only 2 poles vs 4 poles for the 1800 rpm motor. This allows for a less expensive motor, and saves a good bit of weight.

As folks have said, 4500 hrs isn't a big deal on a well maintained motor. About the only thing that will go wrong is the bearings and they are easy replaced. Overheating the motor can cause a breakdown in the insulation of windings, then using on a VFD can possibly be problematic.

I'm getting ready to order another Iron Horse motor for a horizontal grinder project and expect I'll order another 3600 rpm to save around $50 on cost for same hp.
 

John Wilson

Well-Known Member
#12
Ken makes a key point: the 3600rpm motors are two pole motors. While you do get an increase of top end, at slow speeds the motors get "coggy." At less than 20% speed the vfd/motor can't really regulate speed very well, not smoothly anyway. If you have an application where you want to run at an absolute crawl, you probably want the 1700rpm motor. Conversely, running a 1700rpm motor at twice the rated speed is fine for a while but will cause it to overheat after some time, which is why they make 3600rpm motors. As with all things in life, it's a compromise. But at least this isn't one to lose sleep over. You'll be fine either way you go.
 

ARCustomKnives

Well-Known Member
#14
I always understood that the risk of overheating was more for low speeds than high speeds, due to the speed of the cooling fan. At 2x you should be moving twice as much air across the motor to help regulate heat, though running at any speed for extended periods will likely make the motor warmer as it runs, especially if bogging it down for long intervals.
 

John Wilson

Well-Known Member
#16
I always understood that the risk of overheating was more for low speeds than high speeds, due to the speed of the cooling fan. At 2x you should be moving twice as much air across the motor to help regulate heat, though running at any speed for extended periods will likely make the motor warmer as it runs, especially if bogging it down for long intervals.

Great point. Low speeds are definitely more detrimental. The high speed heat is not from lack of air flow, as you correctly say. The issue is carrier frequency from the VFD and I suspect, hysteresis and eddy currents from it. I suspect hysteresis because just as you said there is no reason to expect the motor to get hot, but they do, and it led me to suspect induced current. Many of the motor failures I've seen in the past 15 years or so were intermittent trips on a motor that would pass a Megger test. The insulation is the culprit. Eventually the insulation will break down and you get a hard ground that you can find with a simple ground test. But in the intermittent stage I found you can take that motor and put it in directly across the line installation and it would never even hiccup but it can't run reliably off the VFD anymore.
 

John Wilson

Well-Known Member
#17
Well I just ordered it. Even if it just last a year or two it will be worth it to me. And if it's absolute crap at least I'm only out $100. We'll see. I'll let ya know how it turns out. Thank y'all for the help. Learning lots!
That's a very good motor. I wouldn't pass it up, either. If one day you decide you need more speed you can repurpose the motor to just about anything. A disc grinder would be perfect.
 

KenH

Well-Known Member
#19
I've not had a problem with my cheap Chinese VFD causing a "coggy" feel, even at 10% speed which I do run from time to time. I guess I'm happy with the 3600 rpm motor, I just placed an order for an IronHouse 3600 motor along with a $79.50 shipped Chinese VFD that's rated at 3hp. It's the same model I've been running for the last 3 yrs or so. I'm gonna build that horizontal grinder that's been topic of discussion.

Daniel, I think you'll be VERY happy with the used motor - I suspect it'll give years of good service. Have you decided what VFD are you ordering?

Ken H>
 
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