Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Graham Waterworth on August 05, 2006, 07:09:11 PM
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Hi All,
I am looking for A VFD unit to drive a .75HP DC motor. Any recommendations for use with Mach3.
Graham.
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I have a baldor 5 hp H2 on my knee mill, It has been totally rock solid, it also has a nice open loop vector mode that keeps a pretty constant torque or speed.
Chad
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I am probably showing my ignorance here, but I have plenty of it to give away ;) , are VFD's not just for AC motors.
Hood
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Hi Hood,
not according to the drives warehouse web site, they list VFD's for both AC and DC motors.
driveswarehouse.com/index.php?prop_3=1&osCsid=957229ca83b9a9a30bc0d6706ec3cd49&cPath=149&filter=1
Graham.
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told you i would show my ignorance ;) always thought DC speed controllers were called variators or something along these lines. Always thought frequency was an AC thing.
As they say every day is a school day and I think I need to attend more frequently.
Hood
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Is that attend more frequently or with more varied frequency ;)
Graham.
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lol
probably with more frequency rather than just varying it ;) Actually just had a look at your link and I think I may be correct. VFD are for AC and vary the frequency to achieve speed control, think DC varies the voltage but will do some more reading so I dont make a total plonker out of myself the next time.
Hood
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You may be correct, I think they are just listing the two types under one heading, I just clicked the VFD link and thats the page it gave me.
The range is so vast that I don't know what I want or need to give me the best results.
All I want is to drive the unit from mach3 with as little extra gubbins as possible.
The motor I have is 180 VDC, 850 watt, 5000 rpm, 5.2 adc
Any ideas on what I need.
Graham.
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Sorry dont have any experience with DC motors :(
Finding a speed controller that will power your motor per your specs should be easy enough but finding the most suitable is beyond me.
There is a good section for VFD, Phase converters etc on http://www.practicalmachinist.com/ubb/ultimatebb.php/forum/3.html lots of knowledeable guys there.
Hood
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HI Graham,
I didn't read your post very well ( it was late), VFD is usually associated with AC motors. My baldor vfd won't do anything for you. I think it is going to be hard to find what you want. I did a little digging and most of the DC drives i can find in that voltage and hp rating are intended to run motors with field coils. I haven't personally dealt with these but from what i have been reading it looks like the filed coils are basically replacing the magnets in a permanent magnet brush motor. I don't think these will work for your motor.
Can i ask what you are using these on? My guess is is a lathe. So based on that guess i am going assume you want to do some CSS , perhaps some ridgid tapping, or maybe just get better results with thread cutting. Again just guessing.
If you are primarily going after CSS then i would suggest you find a VFD with pwm input, open loop vector control and single to three phase converter built in and replace your dc motor with a different 3 phase AC motor.
Tell me a little more about what this motor is on. How many wires coming off this motor , is there a variable speed control on it now?
Is it an Asian mini mill or lathe with a speed control? if so this might work for you ..
http://www.homanndesigns.com/DigiSpeedXLDeal.html
Chad
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Hi Chad,
the application is a lathe, After reading up on all this I think I am going to go down the AC route, I have a homann digispeed on the machine now but the setup is not as good as it could be. This is not the fault of the digispeed, its the crap motor and controller. Its gutless at low speed so my threads go out of pitch when the motor starts to stall. Also the thing will only run at about half speed in reverse.
When I use CSS with very light cuts (.025") on a 5" dia steel billet the motor struggles to accelerate.
This could all be down to me expecting too much from a 6" chuck lathe, I am used to using lathes with 36Kw spindle motors. I don't stall them very often, but it has been known ;D
Graham.
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Look at the post that I made about the compact 5 lathe that I am working on... That Drive seems to be working very well!
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Many of the VFD that are for 3 phase(single phase or 3 phase input power) actually output some form of a pulse width modulated wave form that runs a 3 phase AC motor quite well. They might run a universal dc motor, but the wave forms I have seen wouldn't run most of common dc series or permanent magnet type motors. They also don't work well to power 3 phase electronics on older machines. Most of these usually pull one phase of AC and rectify it for the electronics.
Surplus Supply out of Omaha, Nebraska usually has some dc motor controllers that use a potentiometer to vary the motor speed.
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You might try Beel Industrial Controls Ltd. (www.beel.ca) They do a SMC motor controller that might suit you. I am converting/updating
a Boxford TCL 124 lathe and it is fitted with a 180 Volt Lenze PM DC motor. They have been very helpful. Not up and running yet but tests out OK.
I am using Xylotex driver, CNC4PC isolating board and Mach3 but have a long way to go yet!
Ian
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Hi Ian,
do you have any part numbers for the unit you are using.
Thanks
Graham.
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Graham,
Part number was SMC-00. I had to upgrade (with help from BEEL)two on-board resistors to cope with UK mains 240 volts.
Their website (www.beel.ca), from the products tab, has a picture, specifications and a pdf manual
Ian
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try yaskawa V7 seri VFD. it had Frequency input