Uninterruptable Power Supply (UPS) with CNC?

[j ferguson]

My shop is in South Florida where electrical outages are common. It occurs to me that if I suffered an interruption while a CNC part was being made, the machine would stop, maybe without any damage to the work-piece or tooling, I could turn everything off, but then would have no way of knowing where I was in the cycle.

Since I'm going to have small equipment (Sherline CNC Mill), the cost of an UPS to keep running for say 5 minutes would not be excessive. I would think that the benefit would be that I could interrupt the process at a known point, shut everything down and when power returns, restart 15 or 20 steps before the quit point. Does this make sense?

Has anyone else dealt with this or is this just another outbreak of craziness on my part?

 

[Tony Wells]

It's generally not so much of a risk on a mill, unless you are interpolating threads. The steppers or servo motors simply stop quickly, since they are relatively low speed. The spindle will coast to a stop while the table has already quit moving. Naturally, a UPS will help, but depending on the HP and load, it may take a pretty fair sized one to actually keep cutting as normal for any length of time.

On a lathe, threading in particular, I have seen many, many parts scrapped because of a simple power blink. The control stops, the servos stop, the spindle coasts down, grooving the thread and sometimes (most of) breaking the insert. Simple turning/facing/boring ops are not quite as bad.

 

[John Hasler]

My shop is in South Florida where electrical outages are common. It occurs to me that if I suffered an interruption while a CNC part was being made, the machine would stop, maybe without any damage to the work-piece or tooling, I could turn everything off, but then would not have no way of knowing specifically where I was in the cycle.

Since I'm going to have small equipment (Sherline CNC Mill), the cost of an UPS to keep running for say 5 minutes would not be excessive. I would think that the benefit would be that I could interrupt the process at a known point, shut everything down and when power returns, restart 15 or 20 steps before the quit point. Does this make sense?

Sure. I would suggest a very short duration UPS (perhaps 1 minute) and an automatic shutdown procedure in software that would save the state of the machine to disk and shut everything down in an orderly, non-destructive fashion. It's going to take a lot of power to keep the motors running at all, though.

 

[Marco Bernardini]

It is possible to have an UPS which can power a whole shop… since there is one powering an entire town.
In 2003 the town of Fairbanks, Alaska, got an UPS (actually a BESS, battery energy storage system) with 13,670 batteries (1,300 metric tons), giving 27 MW (yes, MegaWatts!) for 24 minutes. Pretty useful when you live at -50°F.
A whole article about that UPS is here: http://www.power-eng.com/articles/p...ge-system-marks-second-year-of-operation.html

 

[awander]

You might be surprised how little power is actually needed to run a small machine, especially one as small as a Sherline.

Medium-size NEMA23 steppers only pull about 12-18 watts each.

A Sherline spindle is about 180W Maximum.

 

[countryguy]

My first thought was a Battery UPS for say 60 to 120 seconds and a Diesel or Gas Generator which kicks in w/ an auto cut-over switch. Those are not too expensive. The expensive part will be a smooth auto-cutover. For that part I think you could possibly put up something else in the line??? Not my area of expertise. Are your motors VFD controlled w/ a phase output coming from the VFD unit?
Our Liebert at work is in the loop and keeps all the phases in check, even if the power cuts out. You can get a Nice 5-10K generator used (or new) anymore for a fraction on some of the US Govt. liquidation sites. There are about 30 there now. anyway, Not keen on battery's as we need to cycle them out every 5 years and the Fire Depts wants to inspect and know about it should they arrive on site and need to use Water. Not good on a live circuit they know nothing about.

Enjoy the weekend
CG

 

[John Hasler]

You might be surprised how little power is actually needed to run a small machine, especially one as small as a Sherline.

Medium-size NEMA23 steppers only pull about 12-18 watts each.

A Sherline spindle is about 180W Maximum.

In that case just get a 500W UPS and be happy.

 

[JimDawson]

I have been thinking about this problem also. I am going to buy a 6KW inverter, I already have 4 heavy truck batteries, and a battery charger that will run the system.

This is electrically inefficient, but not out of reason. My mill will not even see the power fail, and should actually continue to run for some time, at least 30 minutes or so.

I have power fails often enough that I have emergency lighting in my shop. Scared the he!! out of me one night when the power failed. No flashlight handy, and large pieces of sharp, hot metal around at waist height. Fortunately, I had the cutting torch right beside me so I fired that off to use as a light. I installed the emergency lights the next day.

 

[Ray C]

I have been thinking about this problem also. I am going to buy a 6KW inverter, I already have 4 heavy truck batteries, and a battery charger that will run the system.

This is electrically inefficient, but not out of reason. My mill will not even see the power fail, and should actually continue to run for some time, at least 30 minutes or so.

I have power fails often enough that I have emergency lighting in my shop. Scared the he!! out of me one night when the power failed. No flashlight handy, and large pieces of sharp, hot metal around at waist height. Fortunately, I had the cutting torch right beside me so I fired that off to use as a light. I installed the emergency lights the next day.

Scary situation, Jim, with the lights going out...

As far as inverters go, try looking at inverters intended for yacht/marine use -maybe a used one. I see these things every day and some are enormously powerful. -Not cheap either because they're intended to run some fairly heavy loads. Also, the 24V units pack more punch and tend to cost less per watt than 12V units. Most of the bigger yachts are running with 24V mains. Also, AGM-type batteries are preferred. Really good deep-cycle characteristics. I see people all the time who try to use normal automotive quality for the main house batteries and they won't last more than a year or so. Just today, I installed some huge AGMs... Good grief they were heavy!


Ray

 

[j ferguson]

In that case just get a 500W UPS and be happy.

There's also the computer and as someone up-thread suggested, a light bulb. So maybe for me 750 watts for five minutes would be enough with the software tweak to write present position to file for the restart. I suppose there's also nothing wrong with skipping all this except the light bulb and going back to the beginning since I'd be cutting air until i got to the place I was when the lights went out.

FWIW, the neatest UPS I ever saw was a system sold to hospitals. It had a motor with alternator windings which when land-power was on, turned a very large flywheel at a synchronous speed. There was a magnetic clutch (very big) and a Cat diesel engine which was kept warm by heating the coolant. the clutch popped on an outage and the engine started close to instantly and picked up the slight drop in flywheel rpm and now the motor generated such that the ripple in power seen in the hospital was low enough not to bother any of their equipment. it worked too.