| | |
When I bought the 8X12, I knew that a VFD was on the must-do list. Found a 1/2 HP Hitachi drive on eBay and also a new 1/2 HP, 4-pole, 3-phase motor.
I think someone was a bit generous in bestowing a 3/4 HP rating on the OEM motor that came on the lathe. There is a considerable difference in size between the original and the one I installed to work with the VFD.
Pics are of the original motor and the new one. My quick-change reverse arm is also visible in those shots. The other pics are of the drive mounting. Notice how far the motor protrudes from the protective housing on the spindle side.
The Hitachi drive is a sensorless vector, self tuning device. Slow speed performance is great.
Ed B
Those motors only had 750 watt rating that really means they are around 1/2 hp, (yes I know 746 electrical watts = 1 HP) but they are never are that efficient. I used to test motors, for leeson electric, I would be impressed if they actually were even 1/2 hp.Originally Posted by Ed Boysun
What model drive did you end up getting?
chris
Hi Chris,
I found a bunch of Hitachi SJ100DN on eBay. They were brand new in unopened boxes and the price was really right on them. They had the DeviceNet interface built in and I guess I'd rather not had that, but they still work well and the DN part really only affects the ability to use an external control to reverse the motor. As it is, I need to use the keypad to do that but it isn't a big deal.
Ed B
So you cannot hook up external switchs and a pot? I cannot say that I have worked with that particular drive but almost everyone I have can go to external hook ups.
chris
I'd never known about the DeviceNet interface until I saw these drives offered for sale. By using a computer, I take it, that the drive is completely controllable over the network.
If you bought the drive without the network interface, there is an analog interface for controlling the speed with a pot. When they put the DN on, you lost some of the terminals and the pot speed control is one of those. You still retain the ability to turn the motor on and off with external switches. Digging through the books that came with the Hitachi, I also just discovered that you can use an external switch to change direction of the motor and a momentary contact switch is capable of controlling the Start/Stop of the motor. Looks like I can re-wire and eliminate the relays I'm now using.
Yep exactly, thats what i was getting at, many you can use one switch to start and another for direction. Some are 3 wire setups(momentary on) some are 2 wire(maintained on) some can do both. I have alot of exeperince with Mitsbuishi drives and they can do it all even with a network card. I don't know if you are planning to go to full cnc but that drive would more then likely be compatable with mach lathe etc.
chris
do you think you'll have any issues with swarf on the VFD with an open housing? i have a similar hitachi drive although mine is 1 hp and i just bought my 3450 RPM 3 phase motor for my 9x20.
I have never run a drive outside of enclosure, my geuess would be yes. The smart thing would be to get it into a box and cut vents or add a fan. For the $18-25 its worth all the work, I don't work in the metal working industry, my industrial experince has been either testing, or priniting presses. I can tell you they don't like hot, humidty, and even though they are not on(running) they are hot at all times when energized so don't touch untill you see that screen/led go blank. In addtion there alot chances to short out, chips tend to get everywhere.
So how fast can the bearings on the 9x20 take, if you run that drive up to 120Hz you will be at maybe 5500 rpm or there abouts(more windage the slower it will go)input rpm. Also watch your motor bearings they don't always like high speeds. Just so you know if you do take it above 3450 your torque will flatline so the closer you get the high end the less power you will have. You may also have issues on the low end motor design depending, as 2 pole motors like to heat quickly at slow speeds.
chris
I thought I'd try the shield now in place for a while and see if it is enough. I have a chunk of clear Lexan and a piece of piano hinge that I've reserved for making a front door with, if the swarf turns out to be a problem. I don't see a need to close off the left side and I'm sure that will provide adequate ventilation so I shouldn't need a fan. I worked on an adapter plate for a 4-jaw chuck the other day. Making an interrupted cut on a 3/4' thick plate that I had sawed into an octagon and was turning to a circle, I had the lathe running pretty much continuously for a couple hours. The drive heat-sink was barely warm, and so was the motor. Motor was much cooler than it would have been if I was running it at full speed instead of the 15Hz I was using.
Chris, I agree on the 2-pole motor for a drive. I don't turn anything real tiny and have no need for the top end of speeds. In actuality, a 6-pole motor would get a guy to 2,000 RPM for a top speed, if you bumped the upper freq limit up a bit. Three times the torque of a 2-pole motor too.
Ed B
i'm also gearing down 2:1. so my peak rpm should be about half of what you quoted. i also then get a boost in torque from the setup. i have a second pulley set i bought to get me closer to 1:1 which will raise my upper rpm speed if i have to machine something really small.
Motor torque = 5252 X HP / RPM
A 1/2HP 4-pole motor develops 1.5 lbs/Ft of torque.
A 1/2HP 2-pole motor develops .75 lbs/Ft of torque.
Of course with your 2:1 reduction setup you'll double your torque to 1.5 lbs/Ft, minus any losses associated with your pulley setup.
Hmmm! No free lunch.
Ed B
Ed I have played with many drives and never had one run more then 120Hz, most barely make it to 90Hz on smaller motors like these esp if they have a fan. I have actually had one motor that I had on a pot adjustment for speed stop at 95Hz it would run at 94(barely) and 95 it just plane stopped and locked up-granted this was a retro-fit on a belt. I would stick with 4 poles, and gearing/belting after that.
Its my limited but general experience that 6 pole motors would be useless in a lathe they create a NASTY vibration at certain speeds and loads, haveing to do with the way that they are constructed(the thru bolts actually ring)-I tested probably around 8-10 six pole motors at leeson, they were not real popular, one was on a drive and it was to say the least unpleasant night at work. You do not get more torque with more speed, its at best flat line and I should have stated this often declining over rated rpm.(that is really motor specfic) so you would still preform best at 1200 rpm(or name plate). The more poles you have on a motor the better that motor will pullup to nameplate and the tighter that motor will hold name plate across the line. With drives it can be kinda a crap shoot, we ran torque curve on one standard model motor, for customer at leeson and it was way off the wall. the motor would hold(if memory serves) its peak torque at 660 rpm with a 4 pole motor on a drive with a certain carrier(that drive had 5 or 6 i think). On another carrier it lost power(it was less HP) to across the line(nameplate), and a third it held highest torque at around 1200 rpm. Now I could dial those dynes in very tight, and do things you could not do in the real world down to the rpm but you get mixed results out of drives thats for sure. A three phase curve is normally a quick rise then a shallow approach to full rpms these looked like carrots( <) it was very odd to say the least. My time spent at leeson was not wasted, too bad I still don't work there.
Heating is also motor and use specfic, I would imagine its hard to over heat the motors at slow speeds unless you are swinging some serious material. Vector/sensorless seem to do much better at keeping the cores running cool. When you run torque boost that will also start bring the temp up although I am not entirely sure that they would implement that on a vector you would have to enlighten me.
chris
Posting Permissions
| | |
LinkBack URL
About LinkBacks
