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Ok thanks well it has cost me $3 to learn something
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[How do I?] Speed Control.
- Thread starter Downunder Bob
- Start date
Ok thanks well it has cost me $3 to learn something
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It will cost you a lot more than $3 if your PWM controller experiment results in a baked motor. As it is, your single phase motor still has value. You could sell it and put the money toward a 3ph motor. Or use it in another single speed application.
Running the motor at less than rated voltage (effectively how the PWM controller will alter the speed) without changing the frequency will cause a rise in current, which will manifest as an increase in heat. On top of that, (assuming the PWM controller proves to be effective at altering speed at all), your RPMs will be less, your motor fan will spin slower, and cooling capacity will be decreased. It's a recipe for a bad day. I won't go on record saying it won't work, but I advise against it.
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Thanks, I guess good advice, I thought $3 was too good to be true. What I really want to do is reduce my lathe to about half speed using the lowest headstock gear of 60 RPM to get about 30 RPM for the occasional tricky screwcutting operation, as this would be very low load on the motor. For general turning I would be quite happy to just use the headstock gears and run the motor at full speed. I could of course add a smaller pulley to the motor. I may never have to use it. It was just a thought and at $3 it appeared attractive but if I risk burning out the motor I will have to give it up.
I could have ordered this lathe with a 3 phase motor, but I really don't want to go to 3 phase as I would have to get an electrician to bring the 3 phase to my shop.
Thanks again.
Bob.
I could have ordered this lathe with a 3 phase motor, but I really don't want to go to 3 phase as I would have to get an electrician to bring the 3 phase to my shop.
Thanks again.
Bob.
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If the load is very light and if you have a way to monitor motor temp (ex: RTD embedded in the motor windings) then it might be OK to try. just be mindful of latent heat; if you're watching temperature climbing and you shut it down before overheat, the heat will probably continue to climb after you shut it down. Also don't use a voltage-based temp probe (thermocouple or LM35) as these will give distorted readings from all the EMI in the motor.
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I have a 1.5HP 3 phase motor on my lathe. I power it with a small VFD . The VFD is intended for 3 phase input but I input single phase 240V; there is a parameter you can set to disable phase loss detection. Some small VFDs (like some TECO units I believe already mentioned) are designed specifically for single phase input and 3 phase output.
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Are you saying you can use a VFD to run a 3 phase motor with speed control; fro a single phase input. that might be worth looking at.
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I can and will monitor Amps, I had intended to anyway, just so that I don't overload the motor. doubt if the motor will have a temp probe within the windings. I can easily monitor outside casing temperature, but if the temp. rise is very rapid it probably won't give me sufficient warning. I will do a few experiments, watch for temp. rise after a short run, then try longer runs and see how it goes, providing the magic smoke does not escape as soon as I turn it on, should be fun.
life is one big learning curve. I have every intention as posted elsewhere to set this lathe up with both horizontal and vertical milling capabilities, because I do not have the s[pace to locate even a small milling machine, I'm so tight on space I've had to settle for a short bed lathe only 16" between centers. And I have some projects that will definately require milling abilities.
As I've always said don't tell me what can't be done, show me how.
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You can run it off single phase. You need to make sure you get a 240v 3 phase motor. You can run that motor from a suitable vfd but you can't create 400v from a 240v power supply. Well that's my understanding.
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Yes sir, that's what I'm saying. There are two options for doing this;
1. you buy a VFD specifically designed to operate on single phase input/ 3 phase output
2. you buy a VFD specifically designed to operate on 3 phase input/ 3 phase output, and with some slight of hand you coerce it into accepting single phase input.
I highly recommend going with the first option unless you just happen to have a 3in/3out VFD laying around with no greater purpose.
The first one I linked to (Omron/Yaskawa VFD, what I have)...
...is a unit made for 3-phase input, but I am only feeding it single phase, and I've disabled the phase loss detection to allow it to run in this condition. This is acceptable but the drive must be derated by almost 50%. I only used this VFD because I already had it sitting on a shelf collecting dust. If I were to buy a VFD for this purpose, I would have bought a single phase input drive like the ones I listed below.