All,
I recently acquired, for free, a new 1.5 HP motor which I intend to use to replace the underpowered motor on my old Craftsman Bandsaw (circa 1980). It’s a GE NEMA 56 frame general purpose farm duty motor.
The problem is it’s not the right motor on a number of dimensions (but, hey, it’s free). I want to use it without getting myself in trouble. I know there are a lot of electricians on Knots and thought you guys could help.
Problem #1: It’s a 3450 RPM motor while the one I’m replacing is a 1725 RPM. I plan to solve this problem simply by replacing the belt sheaves so as to make the bandsaw wheels spin at the same speed they would if I had a 1725 RPM motor running. I’m replacing the 2.5″ OD motor sheave and the 5″ OD lower wheel sheave with 1.75″ and 7″ respectively. According to the specs in the Grainger catalog, this should get me within 10% of the original blade speed. Any problems there?
Problem #2: It’s a 1.5HP motor replacing a 0.5 HP motor. I know this is way more power than I need, but the motor was free so I want to use it if I can. Is there anything dangerous about having a motor that’s too big? What can I do to mitigate?
Problem #3: It draws 17 amps at full load and my garage is wired for 15 amps. It starts up just fine, but I have access to 220V as an alternative. Two questions: 1) will it blow the fuse even if I don’t load the motor to the full 1.5HP, and 2) can someone point me to directions on the web to re-wire the motor to 22V (again, GE general purpose, NEMA 56 frame, single phase 1.5 HP, capacitor start)
Thanks,
Eric
Replies
17 amps seems awfully high for a 1.5 hp motor, it's either horribly inefficient or possibly you are looking at locked rotor current. With that heavy a current draw Crapsman would be claiming 15 hp! If you hook a 17 amp motor to a 15 amp circuit and the breaker fails and burns down your shop the insurance company will rightfully balk at paying your claim. Would need a model # not just a frame # to tell if it can be configured for 220v.
"17 amps seems awfully high for a 1.5 hp motor" My Jet motor states 18 amps on the motor plate, 1.5HP original equipment motor.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Thats what I get for going with gut instincts! GE's specs say 16.4 amps for their 1.5 hp farm motor. 18 amps puts the efficiency down near 50 percent, just seems low, at 100 pct. eff. that would be 2.8 hp. I thought modern motors would'nt lose so much. I stand corrected and surprised.
It also sounds funny, if you're used to 220 motors. My 5 HP TS has a FLA of 21A, but 220v. If it could run on 110 that'd be 42A.My goal is for my work to outlast me. Expect my joinery to get simpler as time goes by.
I was taking that into account, I'm still surprised at 50 pct. efficiency in a modern motor. No wonder the power companys like us.
I don't have much understanding about motors and electricity, but I think the 18 amps isn't what it draws continuously. More like on start-up and if it gets pushed (say the blade binds up, or feeding too hard too fast). Also, I suppose a higher quality motor, say a Baldor, might not draw as many amps? The Jet motors are Taiwanese made.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 5/15/2006 1:08 am by forestgirl
Yes I'm sure thats at full load, it just seemed awfully high to me . I went out and looked at my 1.5 hp Baldor and its 16A. Sheesh you'd think in 200 years of making them they would have gotten the efficiency up higher than that. Internal combustion engines do better than that ! No I'm not going to put a Briggs and Stratton on my bandsaw !! :)
Up awfully late aren't you?? Full of Mothers Day cheer??
"Full of Mothers Day cheer??" I've got my puppies right here next to me, LOL. No children in the world on my part, but I have a grandchild-by-marriage whom I love very much. forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Rated amps. Because no real motor specialist has stepped in to help us, I'll try. I don't think rated amperage is at full load, but rather at continuous load at a given temperature rise. Full load to me is what some companies would have you believe when the motor is strangling and giving up the ghost. A good motor delivering it's rated HP will run quite hot to the feel. It's operating efficiently and can run continuously for years.
A motor when starting can take twice or more of its rated amperage momentarily. A motor should not take more than eighty percent of rated amperage of the circuit breaker because the breaker just isn't that accurate. Most breakers are of the slo-blow type so can take the extra surge momentarily before blowing, or tripping.
As a side note, and as I recall from a class about sixty years ago, a gasoline engine, I think, is about eight percent efficient. Electric motors are way more efficient than that.
Time to trade in your Model T.http://world.honda.com/news/2002/p020718.html
Actually, 17 full load amps would be pretty typical for a 1 1/2hp, 120vac motor. The FLI should be noted on the motor ID plate, as well as if the motor can be used on 120 or 240vac.
http://woodworking-woodworking.com/pulleys.html
This will help with problem #1.
All,
Thanks for the interest.
The model number of the motor is 5KC49NN2419Y. The nameplate says 13.2/6.6 AMPS (I had guessed 17 from the fact that my 0.5 draws 5.6A). I'd still like to know how to (not if I can) convert it to 220V. I googled without much luck.
Do I assume from the posts so far that nobody sees a problem with a 1.5HP motor spinning at 3450 so long as I sheave it down so that the blade moves per spec?
Cheers,
Eric
Icoul'nt find that # on GE's motor site, I'll paste the web address at the end. Have you taken the wiring cover off to see if there's a diagram inside? There are several motors with #s close to yours and they are all dual voltage.http://catalog.geindustrial.com/stepSearch.jsp?FAM=ac_motors&Lang=EN&CC=MA&Profile=&sNode=261
That 13.2/6.6 AMPS indicates it is a dual voltage motor (13.2 amps at 120vac, 6.6 amps at 240vac) so it should just be a matter of figuring out how to make the connections. If you're lucky, there's a little diagram on the motor someplace that shows how to do it - it may be on the motor plate, or possibly on the inside of the access plate over the wiring terminations. If you go to the GE website posted above, maybe you could pull up the connection diagram for a similar motor and see how it's wired up.
The label lists two amperage ratings, so the motor should be dual voltage. Typically under the cover where the wire goes into the motor you'll find wiring connections for 110 or 220 VAC set up.
As for using a 3450 rpm motor in place of 1750 rpm motor; you're on your own with that one.
1: You've got the ratio right, but you will need the extra flexibility of a cogged belt to run around a small radius pulley. You can get them from Mcmaster (http://www.mcmaster.com). Most likely your pulleys want an A section belt, but check before you order.
2: That's a lot of HP to run this machine, but as long as you don't get stupid with it, you should be ok. You should try and avoid situations that could bind up the band (e.g. sawing logs).
3: You shouldn't try to start/run a 1.5HP motor on a 15A 110 circuit. If you have 220, that's the path of least resistance (literally).
Pete
Eric,
First of all, if the motor is capable of being wired for 220 it will say so on the spec plate, listing amperage draw for both 110 volts and 220 volts for instance, or the voltage as 110/220. If there is no mention of 220 volt on the plate, then the motor can't be converted.
If the motor can be wired for 220, the information for the proper hook up should be right on the motor, either on the spec plate or on a label inside of the wiring box, often times on the inside of the box cover. While the basics of rewiring are the same for all motors, how the leads are marked will vary a lot so you won't be able to get generic rewiring information from the net, and I'd be surprised if GE posts the information, given the thousands of motors they manufacture. If all else fails, take the motor to a motor repair shop they should be able to set it up in just a few minutes.
If you wire for 220 you will most likely need a different switch since you will have two hot leads that need to be switched versus the single hot lead on a 110 motor. If you do need a new switch a magnetic switch would be a good upgrade, Grizzly has them at a reasonable price.
1.75 for a pulley is very small, the belt will run a bit rough on such a small pulley, I would go to a 2.5" to 10" or 3" to 12". You can safely increase the blade speed a bit and may find that the saw cuts better by going to a 3" to 10" combination or 3 1/2" to 12".
The additional power available won't do any damage to the machine unless you severely jam the blade or the wheels which is almost impossible to do.
If the motor starts and runs well on the 15 amp breaker, you can continue to run on the 15 amp circuit, since, unless you push the motor quite hard, it won't draw anywhere near its maximum. If the motor does pop the breaker, even occasionally, you should upgrade the circuitry since breakers wear out and become erratic after repeatedly tripping.
John White, Shop Manager, Fine Woodworking Magazine
John,
With a 2 to 1 ratio on the pullys, doesn't that slow the output of the motor from 1725 to 862.5rpm and increas the HP from 1.5 to 3? Or is there somthing wrong with my logic?
Jack
Off the top of my head (in case your listening FG) :), I believe the hp, stays the same and the torque doubles.
Thanks, I could remember that when you half one thing you doubled the other, but couldn't remember which.
Jack
Talking of torque, I believe the motor turning power remains unchanged. The use of pulleys (gearing) simply alters the leverage but the available force is unchanged. Thus an underpowered tool remains so no matter the speed of operation.
Anyone please put me right if appropiate!
You can increase the torque by lowering the speed through gearing or pulleys, but the available power remains the same.
John White, Shop Manager, Fine Woodworking Magazine
Thanks! I just did not wish anyone to conclude that gearing would solve power problems.
You ought to re-think your definition of 'free.'
"You pay a great deal too dear for what's given freely" ;-)
Ain't that the truth.
If you go by what the big industrial machines run at, it should ease your mind. About one HP per each two inches of cutting depth between the guides is normal. My blade travels at 60 MPH, and the wheels are cast iron.
I would do as John suggested and go with a larger motor pulley, and maybe a larger drive pulley although you will have plenty power with a little higher speed.
Don't worry about a hazard from the extra power. The worst that will happen if you snag, is that the blade will break, which happens to band-saw blades all of the time.
> About one HP per each two inches of cutting depth...This sounds pretty high unless you're talking about overrated import motors. My "medium industrial" BS will cut 13" with a 1 HP motor. Even if you allow for the fact that motors got a conservative rating in the 40s, there's typically still no need for that kind of HP.Pete
Hi Pete, I am talking about 3 ph. motors, on big industrial tools, and manufactures like Tannowitz don't use a lot of smoke and mirrors to rate the motors on their tools.I know you can cut 13" with a 1 hp. I have a small BS with a small motor too, but I have a 36" saw with a 7.5 HP motor, and it will cut that 13" about 7 times faster than yours, or about as fast as yours will cut 2" of thickness.Another side benefit of having more power on a BS is that the blades will last longer with more power, in that it will take a larger chip per tooth. When any saw is under-powered, the feed-rate has to be too slow to keep from burning the motor, which leads to too small a chip > more friction > High heat > out-gassing of moisture, melting resins> condensing and depositing back on the side of the blade, > which causes more heat, > ruined blade.When there is enough power for the tooth to take a larger chip, the chips take the heat with them.
OK everyone,
Thanks for the help. The question certainly generated some interesting conversation.
Here's my plan:
1) I'm going to try to see if a motor shop will trade me or charge me a small amount to switch to the right motor, as it's a brand new GE motor
2) If not, I'm going to go with the 1.75" x 7" pulley set up. It's only 20 bucks for the pullies, 30 if I get the special belt to go around small pullies. I don't have enough room to go with the 2.5" x 10" combo -- the pulley will hit the table beveling mechanism.
BTW -- it's the small pully that spins fast, not the big one. So, precision balanced pullies (which are about 2 x the price) are not what I'm going with.
Cheers,
Eric
Actually that big pulley will be spinning the same RPMs as the origional, and it will weigh twice as much with much more centrifugal force. If you are lucky it wont be too bad, but there will be more vibrations than before. Adding sand bags to the cabinet will help.
Mike
Vibration is caused by imbalance, not weight. A high-quality machined pulley should be fine.
Pete
A good machined pully and a link belt. With a pulley the small, deforming of the belt is more likely.
Jack
Right but he said he wasn't going to buy high quality dynamicly ballanced pulleys. And the increased weight alone is not an issue. However, I would assume that if a large and small pulley were made to the same tollerences (+- X%), the larger one would be off by more. And I have never tried what he is doing so I really don't know. I do know the increadibly small imballances can cause huge problems with a band saw. Mostly my issues with this were related to the wheels and tires, but I have heard tale on this site that belts and pulleys are also importaint. I hope it all works out, I am just helping find potiential hangups.
Mike
I certainly wouldn't argue that a Tanny would match a light or even medium-duty machine. It was built from the ground up for a big motor and high feed rates. I just wanted to point out that stats from machines in the 3000 lb weight class should not necessarily be taken as rules of thumb for lightly built hobbyist machines. Your comment to the original poster (who already has a motor he got for free) was on the mark.Pete
Edited 5/16/2006 10:25 pm ET by PeteBradley
I am not sure but I suspect that spinning such a very large pulley at such a high speed will cause all kinds of vibrations. Better get the best darn machines and ballanced pulleys out there.
Mike
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