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Home Model Engine Machinist > The Tools and Tips > Tools > Low power - motor or VFD?

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Old 03-19-2018, 03:08 AM   #21
Aries37
 
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On all of my installs I donít use wire nuts on the motor connections, but instead use ring terminals crimped to the wires then attached together with appropriately sized machine screws and nuts. Itís more work and requires taping the finished connections but insures a solid trouble free installation. Most motor junction boxes are always too small and when you bend the wires to put them in place the wire nut connections tend to come apart. All wiring should be stranded conductors and not solid.


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Old 03-19-2018, 07:47 PM   #22
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Success! I think anyway...Parameter 13 ďtorque compensation with rangeĒ. I couldnít find much info on this parameter and the vfd uses a range of 0.0-4.0 on this parameter. So I really wasnít sure where to go with this one.IMG_2025.jpg


It gives that warning that this setting could cause damage to the motor so I was hesitant to try. It turns out the factory setting was zero. I increased it to 1.0 and there is a world of difference. I think Iím going to reinstall the motor and see how it does with the belt on. Maybe 1.0 will be sufficient. I donít want to push it to far....if I even knew what too far is. It doesnít specify what the numbers in the adjustment range mean so Iím not sure


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Old 03-19-2018, 08:28 PM   #23
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It sounds like some sort of current compensation to maintain torque.
Good to hear you've got a potential solution.
If you run the motor for a good while and it doesn't get overly warm you're not driving it with too much current
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Old 03-19-2018, 10:31 PM   #24
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Well done finding the fault. I've got a KOC100 series VFD which came with a 172 page manual and it took me ages to reset all the parameters to get my three phase 2 hp motor to run correctly.
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Old 03-19-2018, 11:24 PM   #25
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Quote:
Originally Posted by Herbiev View Post
Well done finding the fault. I've got a KOC100 series VFD which came with a 172 page manual and it took me ages to reset all the parameters to get my three phase 2 hp motor to run correctly.


They gave the opposite problem lol....I donít know why the manual only goes to parameter #35....unless of course, thatís all the parameters adjustable in this vfd
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Old 03-20-2018, 02:19 AM   #26
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Great to hear that you may have solved the problem. I would agree with Nick that this setting is internal compensation for current/torque. Also noted the HZ settings available are way above 60 Hz. Older motors like you are using need to be at the 60 Hz settings, otherwise you run the risk of over current and motor burn out. Further you should have a voltmeter to check voltages between phases at the motor. They should be close to the input line voltage. The current draw on each phase should be measured with an Amprobe, close to the FLA rating on the motor. These readings will vary depending on how the VFD is set, meaning at what HZ the motor is operating at. Motors not rated for VFD use will overheat and draw more current when operated in the 20-30 HZ settings for long periods of time so itís a matter of striking a balance by some extensive testing while under load on your mill.
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Old 03-20-2018, 05:04 AM   #27
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Now that it seems to be running better Iím gonna check the output voltages again and check the current draw. What do you guys recommend as safe minimum and maximum hz? I wonít hold it against anyone if the motor gets fried lol. Aries, are you saying to not exceed 60hz at all and to keep the minimum above 30?
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Old 03-20-2018, 01:00 PM   #28
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My previous post stated the reasons for holding close to those parameters.
Older motors, like you are using, were designed for 60 Hz and not rated for VFD use, however most of them will work OK if they are wired and set up correctly.
I would further suggest using line and load reactors, referred to in one of my previous posts. The design and function of VFDís puts stress and loads on the copper windings and insulation. Frequencies beyond the 60 HZ settings makes things worse. If you were to purchase a new motor rated for VFD use, the manufacturer has accommodated these requirements in the design of that motor, therefore they cost more.
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Old 03-20-2018, 02:12 PM   #29
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That sounds reasonable. The main reason I went with the vfd to begin with was to be able to use the 3 phase motor in my garage, I was looking at speed control as a fringe benefit. I think Iím gonna use the setup as is and see how this old motor does. If it some point down the road the motor starts giving me trouble, Iíll upgrade to a newer motor and utilize the speed control at that point.
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Old 03-23-2018, 01:27 AM   #30
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One big issue with VFD is knowing the maximum rotor speed a motor can handle. With modern motors you can reference the motors data sheet, with older motors you might never be able to find out because the assumption was they would run on 60 Hz. So you do run the risk, when going past 60 HZ, of over speeding the rotor and grenading it. How far beyond 60Hz that would be is unknown but with drives that can do 400 Hz it is a real possibility.

Another issue that you will run into is the winding insulation on old motors is subject to punch through form high voltage spikes as a result of the fast switching the drive does. This is compounded buy older motors often having degraded insulation to begin with. You can reference the drives manual to see if they have any suggestions for remediation of this electrical noise but in the end it just means your (actually the motors) life span won't be as long as a modern motor.

In the end I wouldn't worry about motor life as long as you don't get excessive with speeds over 60 Hz. In the end you are operating an old motor with an unknown number of years left in its lifespan. I'd enjoy it for as long as possible as in a hobby shop it might last decades longer. Or it could die tomorrow.

By the way you will enjoy having variable speed. It is surprising how nice it is to have even if you have to shift gears from time to time to get more torque for low speed operations.


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