1.5 HP 3Ph Motor Questions

KnuckleDownKnives

KnuckleDownKnives

Time to make the doughnuts..
Joined
Feb 12, 2015
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Hi all. I asked about this motor quite a while back and now that i have a 3hp VFD running one of my grinders, and in the process of running power in my new shop, I'm thinking of using this motor if it's rated for what I'd like to use it for. I know it's not a TEFC, but an internally cooled motor, and I think i have a way so that isn't an issue. If i use my grinder VFD to run this is this motor ok to use at lower RPM's so I don't burn out the wiring? I want to use it to make a disc grinder. For the cooling, my plan would be to mount it to my work bench, build an enclosure around the motor with a hole cut into the bench top and large PVC piping under the bench going to a "clean" area of the shop for clean air for it to cool itself. I know this isn't ideal, but I have everything I need to do this except the disc and rest.

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It will probably cost you more to do that modification than just buying a 1.5HP 3Ph motor from one of the popular sites.

However, there is a plus to your mod - it will have the same cooling at slow speeds as at full speed. Regular TEFC motors have greatly decreased cooling at slow speed with a VFD, because the fan turns at the same speed as the shaft.
 
Stacy E. Apelt - Bladesmith said:
It will probably cost you more to do that modification than just buying a 1.5HP 3Ph motor from one of the popular sites.

However, there is a plus to your mod - it will have the same cooling at slow speeds as at full speed. Regular TEFC motors have greatly decreased cooling at slow speed with a VFD, because the fan turns at the same speed as the shaft.
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It won't cost me a dime as I have everything needed, except a disc and tool rest. . So it sounds as if the wiring will not overheat at lower RPM's. Plywood for the shroud, 4" PVC pipe for the air vent, and some caulking to seal it. I even have extra wire from when I did my grinder to run it to the VFD.
 
Are you asking if you can power a 3hp motor and a 1.5hp motor from the same VFD? If so, I don't think that's advisable, at least not with the KBAC line of VFDs, they have jumper configurations specific to motor HP, and while I don't think it's a problem running a higher hp motor short term at a lower setting, I do think running a lower hp motor with the 3hp setting can damage the motor and/or the VFD.

I guess you could set it to 1.5hp to run both, but you'll be hurting the longevity and the power of the 3hp motor significantly. The bigger the variance, the worse it is.


Running at a lower rpm wont help anything, it's liable to hurt, as the motors rely on their fans that turn with the shaft to cool them, in fact, most of the motors we're using are suffering from having insufficient cooling while being run at less than their rated RPM, except for certain VFD optimized motors that compensate for this.
 
javand said:
Are you asking if you can power a 3hp motor and a 1.5hp motor from the same VFD? If so, I don't think that's advisable, at least not with the KBAC line of VFDs, they have jumper configurations specific to motor HP, and while I don't think it's a problem running a higher hp motor short term at a lower setting, I do think running a lower hp motor with the 3hp setting can damage the motor and/or the VFD.

I guess you could set it to 1.5hp to run both, but you'll be hurting the longevity and the power of the 3hp motor significantly. The bigger the variance, the worse it is.


Running at a lower rpm wont help anything, it's liable to hurt, as the motors rely on their fans that turn with the shaft to cool them, in fact, most of the motors we're using are suffering from having insufficient cooling while being run at less than their rated RPM, except for certain VFD optimized motors that compensate for this.
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Ok, I forgot about the HP jumper. I could actually solve this problem fairly easy and cheap. About $15. A standard wire to din board connector and a 2 pole rotary selector switch with enough positions for each jumper setting and I could make a selector switch I can select any HP setting. Wire/solder it all up and would pretty much be a plug and play other than drilling a hole for the switch.

Think I'll give it a shot. Motor was free, so I'll I think I'll run it till it burns up...
 
you can safely run a 1.5hp motor with any VFD that delivers 1.5hp or more. read thru your owner's manual and you should find a programming function that sets maximum current the VFD will produce and other functions that will protect your motor and the VFD. for this particular motor, set it for 6 amps and you are in business. again, check the VFD manual, most recommend a direct connection from VFD to motor with no switches in the line.
if you try to run a 1.5hp motor with a 1hp VFD, you probably will not hurt anything, but the VFD will probably turn off for overcurrent, especially if the motor is overloaded(read as HOGGIN)
 
scott.livesey said:
you can safely run a 1.5hp motor with any VFD that delivers 1.5hp or more. read thru your owner's manual and you should find a programming function that sets maximum current the VFD will produce and other functions that will protect your motor and the VFD. for this particular motor, set it for 6 amps and you are in business. again, check the VFD manual, most recommend a direct connection from VFD to motor with no switches in the line.
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The issue is my grinder is a 3hp motor and this is a 1.5 hp motor. So running both of them off of the same VFD I would need to change the jumper in the HP settings inside the controller (KBAC-29). the motor would have a direct connection to the VFD the switch would be to change the HP setting without having to open the controller.

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you still won't hurt the 1.5hp motor unless you really overload it. the drill you plug in the wall is rated for 1hp, the wall can deliver 2hp. the drill runs just fine. the rating on the VFD is what the VFD can deliver, that why you hear the phrase, the motor draws 6 amps. in your case, the motor would draw 5.0 amps from 6.7 amps available. I don't understand the 3hp motor run off a 2hp VFD. the motor will never develop more than 2hp. to achieve full power, the motor wants 9 to 10 amps. the most the VFD will output is 6.7 amps.
 
scott.livesey said:
you still won't hurt the 1.5hp motor unless you really overload it. the drill you plug in the wall is rated for 1hp, the wall can deliver 2hp. the drill runs just fine. the rating on the VFD is what the VFD can deliver, that why you hear the phrase, the motor draws 6 amps. in your case, the motor would draw 5.0 amps from 6.7 amps available. I don't understand the 3hp motor run off a 2hp VFD. the motor will never develop more than 2hp. to achieve full power, the motor wants 9 to 10 amps. the most the VFD will output is 6.7 amps.
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KBAC-29 is a 3hp VFD. I understand everything you are saying. I know I could run a 5.0 amp drill plugged straight into my meter with 200+ amps available and it's only going to draw what it needs to work. Maybe you know more about VFD's than I do and probably so. The book just shows the KBAC-27 illustration for locating purposes. The KBAC-29 is labeled differently it's just not shown in the illustration. The book says nothing about what the jumper for the HP setting does. It just says to change it depending on what HP motor you are running. I don't think making a switch to run my 3hp motor so the setting is on 3hp is going to hurt my 3hp motor, and running the 1.5hp motor with the setting on 1.5hp is going to hurt the 1.5hp motor.
 
if you read the fine print, the KBAC-29 delivers 2 hp when supplied with 240v single phase and only delivers 3hp when supplied with 240v three phase. The KBAC VFDs are simplified units and use jumpers and potentiometers to do what other units do with programming. I have a 3hp Leeson VFD and use it to drive motors from 3/4hp to 3hp and have had no issues. this shows all KBAC VFDs and how to set them up http://www.kbelectronics.com/manuals/kbac_manual.pdf
 
Yes, I have the manual, my understanding is the 29 (IP) model outputs for 3hp. I should have been more clear as to which 29 model I have.

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However I think you may be misunderstanding my original question. I know the drive will run the motor, that is not my question I know it will. My question was pertaining to as far the the motor plate that shows the rating of the motor insulation class: B for the 1.5 hp motor. My big 3hp iron horse motor is an insulation class F. What I was asking is if I run the motor with the VFD am I going to chance burning the wiring up inside the motor running it at lower RPM with the VFD due to its lower insulation class. I'd rather not burn the wiring up and chance a fire if it's not rated good enough by running it at lower RPM's.

I went with the 3hp VFD as my first choice as a VFD so that I could run anything from 3hp down and not need a bigger one to be able to run a 3hp motor.
 
scott.livesey said:
for what we do with motors, it should not matter. the maximum life of your B class motor is when you keep max motor temperature below 266F, the F class below 311F (http://www.engineeringtoolbox.com/nema-insulation-classes-d_734.html) not something we would see grinding knives
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Great, thank you Scott. I asked because I have seen others comment on here on motors others have asked about and they said on some of those posts they may have an issue with wiring overheating issues. I don't really anticipate using it hours on end, but at the same time I wouldn't want have issues from the get go.
 
Listen to Scott - he's got the right ideas on VFD. Just think of it this way, the VFD is jumpered to provide 3hp, the 1.5 hp motor just won't pull near all the 3hp will provide. The 3 HP VFD "could" provide enough power to really overload the 1.5 motor, but with a disk grinder you're not going to be overloading it at all - heck, 1hp is enough for disk grinders.

On your ducting - sure looks like overkill, but that's better than not doing enough. Just a filter box built around the intake end of motor would suffice just fine, but with your duct, I'd be sure to mount a fan blowing in to be sure there will be suffice air flow at low rpm. I'll bet LOTS of your disk grinder use will be at lower rpm where the extra cooling could be nice.

Ken H>
 
I explain it like this:

A VDF set for 3 HP is internally "fused" (not exactly a fuse, but that will do for the explanation) for the current draw of a 3 HP 3Ph motor. Let's say it is 12 amps per leg. If the motor jams or gets heavily loaded, the internal "fuse" will break the circuit at 12 amps on any leg. It can't deliver more than 12 amps per leg no matter what.
A 1.5 HP motor draws about 6 amps per leg. If run on the 3 HP VFD, the internal "fuse" monitor circuit won't shut off power until it reaches 12 amps/leg. If the motor was jammed or locked up, the motor would burn up with the excess current.

This would be a big deal on a motor that ran a conveyer belt or a swing gate, but a motor running a disc or belt sander would be very unlikely to get jammed to the degree to overcurrent by a factor of 200%.
 
Thanks Ken and Stacey. I really didn't know what the jumper really did. So guessing off of your comments it just limits the amperage. :thumbsup:

Ken, as far as the duct I'd rather use duct and not use a filter. I have one on my first grinder with the treadmill motor and cleaning is a pain. I'd rather get clean air to it and not have to worry about it. I have to clean the one on the grinder as it gets clogged up and doesn't get good air and I can tell it when the motor doesn't have all its power. I actually found some 6" pipe and some fittings to make some turns if necessary. A small fan on the inlet will be good to. I have a small desk fan I don't use will work perfect.
 
Ducted motor cooling in industry is basically stove pipe fittings with the last piece stuck on the end of the motor. 4" duct is plenty. Increase the end piece with a 6" adapter to fit the motor end. Some rubber foam will close any gap as well as cut down on rattle.

The airflow is provided by an inline duct fan. Ebay has lots, and you can find them in hardware stores and yard sales.. Here is one for $19 with free shipping:
http://www.ebay.com/itm/4-6-8-Inch-...hash=item2a2d0c4a0e:m:mIiPhrKCYqD-2utlMb2IbWw

Wire the fan to a switch at the grinder, or connect it to the lighting circuit and let it run all the time the lights are on.
Remember that you won't do much good if the air entering the duct is dusty shop air. ERither put a good filter on the intake, or bring in outside air.
 
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