I don't have the three phase power turned on, the tenant doesn't need it. I could use all the three-phase machine tools a few hours a month but it's just not worth the bill and deposit for power. I do have a VFD that's good for three hp. Rather than hook up the VFD to each tool as I need it, could I hook up all the building up to the output of the VFD and just use one tool at a time? The lathe is 5hp but if I use it for light work, will it be OK?
Because of the mass of the chuck and spindle the starting current of the lathe could very well be too much for the VFD. ( likely? ) Polyspede makes bigger single to 3 rated VFDs.
Not sure what you mean hook up all the building.
I've only read a few VFD manuals, but I seem to recall most said that the motor should be within a certain distance of the VFD. How about a cart option?
The cart was the original idea and probably the best option.
They also typically warn against putting any sort of switching between the VFD and the motor.
It is generally bad news to have switches between the VFD and the motor (as would normally be the case with the setup you are proposing). The switching can produce HV sparks which can zap the output transistors.
Now -- if you replaced each switch on the machines with a remote FWD/OFF/REV switch, and added a rotary switch *at* the VFD to change which tool is fed, you could probably do it with no problems. (Make sure that the output is off before switching the VFD to the next machine).
Now -- if you have an extremely over-rated VFD, you can probably get away with switching between the VFD and the motor. I did with a 1 HP motor on a Nichols horizontal mill, and a 7-1/2 HP VFD. Once that VFD got cooked by the heat from a fire in the shop, and I had to move to a smaller one, I set it up so the machine's switch commanded the VFD for FORWARD/STOP/REV, and added a pot for setting the speed, so I don't need to switch belts as often.
Good Luck, DoN.
No, it sill not work as it the controls ill be inoperative if powered from a VFD. You need a phase converter, which is very easy to make or buy.
iGunner Asch fired this volley in news: snipped-for-privacy@4ax.com:
Ayup! I can do a "slam reverse" with mine (using the VFD's input signals), and have never had a problem, but I've seen guys blow up even bigger ones on smaller motors by switching the outputs, instead of using the functions almost all VFDs offer natively.
FWIW, doing a slam reverse with a VFD isn't quite as 'instant' as with a switch on a 3-phase line, but still pretty quick.
Lloyd
Gunner Asch fired this volley in news: snipped-for-privacy@4ax.com:
Of COURSE it does, but you avoided addressing my statement in order to make your own rules, Gunner!
A VFD (unless VASTLY oversized) won't slam-reverse a motor at ANY setting that won't blow it up as fast as a reversing switch on essentially unlimited-current 3-phase house power!
I _wholly_ approve of using VFDs, and they perform just fine (including with [about] 0.5 second reverses on my 14" Chicom lathe). But it's silly to say they'll perform like a 'zero-impedance' power line! (quoted, because nothing's _really_ zero impedance/resistance/fusing/whatever)
Lloyd
Some practical numbers:
Don't they just throw juice to windings in both directions at once, essentially freezing up the motor magnetically? That's a little safer and easier on the hardware than what SawStop does, huh?
- To change one's self is sufficient. It's the idiots who want to change the world who are causing all the trouble. --Anonymous
Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:
Since a switched 'slam reverse' is just reversing the relationship of two of the phases, that's exactly what they do on most VFDs, with the exception that some can also impose some DC, or connect-in some braking resistors to make the slowdown quicker; and all of them worth a penny limit the current to what is safe for the VFD.
A simple DPDT switch on a line-fed setup can't do either of those things, and it works fine, too (if the breaker doesn't pop). All it does is swap two legs on the motor, and you have to deal with the other issues.
Lloyd
I know you were saying "slam reverse", but I read that as a judicious application of power by the crafty and knowledgeable VFD to stop the spindle, taking into account all the above. Toggles don't do that, let alone "right", but I've seen it done on other machinery over the years in long-past garages.
- To change one's self is sufficient. It's the idiots who want to change the world who are causing all the trouble. --Anonymous
On a bunch of my 3-phase machines, I used what is called a plugging switch that was controlled with a V-belt coming off a main shaft to stop the motor.
Huh? How does a switch (electrical) controlled by a belt (mechanical) stop a motor (electrical)? Ya lost me there, Tawmmy me boy. Are you running a steam engine and mainshaft in yer shoppe?
Zis you?
There are still overhead shafts throughout the building and were used up until the '50s. The shaft was run by a 1-cylinder natural gas engine. All the babbited bearings are smooth as silk,
A Plugging switch stops a motor quickly. A speed switch with normally open contacts is used in conjunction with a contactor or starter wired to reverse the field windings of a squirrel cage motor. In plugging applications, the device, when properly adjusted to given conditions, will provide the control circuit logic to apply reverse energy to the motor to reach zero speed. The motor, electrical power distribution, and machine must be designed to handle sudden stopping.
Very interesting, I learned something new today, thanks a lot.
Yeah, they're cool old tech. The only one I've seen in action was powered by a steam engine (Vista museum) 30' away and it ran the power hammer. I'd love to see one where I didn't have to listen to the engine and hammer. OSHA doesn't like them much, though, wot?
OK, I get all that, but how does it relate to the v-belted mainshaft?
The v-belt tells the switch if the machine is going forward, revrse or stopped. In a brush machine (like a BIG sewing machine) when it reaches the "end of the brush" switch or the operator hits the "STOP" switch, the plugging switch switches two legs of the 3-phase power to the motor for as long as the shaft is moving and electrically brakes the motor. When the shaft stops turning, the contacts open and the motor/machine can start again in forward.
Old tech but it works just fine.
How often do they reverse and how long do the motors last?
The cycle is typically 30 to 40 seconds and pluggs for Less than a second and I can't remember ever replacing a motor. The motors are typically 3/4hp and could probably replaced with a 1/4hp. Excessive plugging like when the machine is being repaired or tested and the motor gets rather warm.
I just started installing VFD's on machines and would have put one on every machine just for the speed control and ramp-up.
Now, I'll be using s VFD just for power conversion. I should build a rotary, I'll see if there are some good motors laying around.
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