# Uninterruptable Power Supply (UPS) with CNC?



## j ferguson (Jul 18, 2014)

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?


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## Tony Wells (Jul 18, 2014)

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.


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## John Hasler (Jul 18, 2014)

j ferguson said:


> 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.


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## Marco Bernardini (Jul 18, 2014)

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


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## awander (Jul 18, 2014)

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.


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## countryguy (Jul 18, 2014)

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


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## John Hasler (Jul 18, 2014)

awander said:


> 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.


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## JimDawson (Jul 18, 2014)

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.


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## Ray C (Jul 19, 2014)

JimDawson said:


> 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


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## j ferguson (Jul 19, 2014)

John Hasler said:


> 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.


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## John Hasler (Jul 19, 2014)

j ferguson said:


> 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.



A No-Break.  AT&T used them at their microwave relay sites in the sixties.  An elegant design.


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## countryguy (Jul 19, 2014)

Some safety practices anbd battery URLS Gents,    Just be safe and realize there is a maintenance cycle here that you must adhere too.   I had to keep our large Lieberts in-check for about a decade.  They came in every month or two.  Often a battery would be pulled due to internal this or some diagnostic that.    A 24V DC high current capable system is a potential is all I'm saying.   Myself, I like a small battery setup w/ a generator cutover.    both are a worthwhile system if you've spent days on a complex part and the wind blows down the power.   I get that! 

http://www.hse.gov.uk/pubns/indg139.pdf

http://www.generatorjoe.net/html/whataboutsws.html

http://www.batteryequaliser.com/products/product_battery_maintenance.htm


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## Ray C (Jul 19, 2014)

countryguy said:


> Some safety practices anbd battery URLS Gents,    Just be safe and realize there is a maintenance cycle here that you must adhere too.   I had to keep our large Lieberts in-check for about a decade.  They came in every month or two.  Often a battery would be pulled due to internal this or some diagnostic that.    A 24V DC high current capable system is a potential is all I'm saying.   Myself, I like a small battery setup w/ a generator cutover.    both are a worthwhile system if you've spent days on a complex part and the wind blows down the power.   I get that!
> 
> http://www.hse.gov.uk/pubns/indg139.pdf
> 
> ...




You are indeed correct, batteries are nothing to play with and they need to be used within their means and proper charge cycles.  I've come to like the sealed batteries (AGM type) because they don't leak acid all over the place.  When the "sealed" batteries first came out, they had some issues but the technology is improved now and they outlast most other types.

On a technical note, the current draw on a 24V battery is only 1/2 of a 12V battery.  They tend to last longer because of the reduced internal current and you don't need to use triple zero (000) gauge cables to jumper several together.

FYI:  Automotive batteries are not well suited for UPS systems.  They prefer to be kept at full charge.  Deep cycle batteries are rated for their number of charge cycles down to 20% of full charge.  Usually, it's something like 800 to 1500 cycles depending on the quality/warranty on it.   If you do that with an automotive battery, it will be toast after a handful of times.



Ray


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## D.C.Clark (Jul 24, 2014)

I've got this one:

https://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BX1300G&tab=documentation

It will run my Sherline 4 Axis CNC, PC and monitor for 20 minutes, long enough to finish most any job.

David Clark in Southern Maryland, USA


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## middle.road (Jul 25, 2014)

D.C.Clark said:


> I've got this one:
> 
> https://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BX1300G&tab=documentation
> 
> ...



This might not need saying but... 
With it hooked up to the PC, use the utility program to manually check the battery periodically. Don't rely on their automatic 'self-test'.
You may also want to verify how the automatic shutdown mode is setup if the PC is tied to the Sherline at all.
I would take the 20 minutes and cut it by half to be safe. I've used these and similar ones for eons and it is hit or miss in
regards to the length of time it provides power.
I have a couple down in the store room that are less than two years old that I've pulled out of service that behaved erratically and that
I need to (someday) go over them and diagnose their problems.

The batteries - at times - start to go after only a year, just when you're counting on 20 minutes you're lucky to get 5.
Beware of the 'Asian' counterfeits when buying replacement batteries. I had one client who found a 'better' deal on the batteries
and they somehow fried the UPS.

-=-

Another possible source for commercial grade units would be the on-line liquidator auctions, especially when they're doing a data center
of a failed biz. The rack mounted UPSs used for servers and network equipment are very heavy duty. I've used those in racks powering
multiple servers. And you get the added benefit of cleaner power to your equipment.
One such site that I use to buy equipment from back in the day: http://www.go-dove.com/en/index

_Dan


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## j ferguson (Jul 25, 2014)

D.C.Clark said:


> I've got this one:
> 
> https://www.apc.com/products/resource/include/techspec_index.cfm?base_sku=BX1300G&tab=documentation
> 
> ...



This was the sort of thing I had in mind.  I had a pretty good hunch that someone else would already thought of it.  

Thanks David,

John


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## woodguy (Jul 26, 2014)

Consumer quality UPS equipment does not produce a true sine wave output. It is possible that some things in a shop environment might be damaged or not work correctly when powered directly from such a system. Computer systems contain switching power supplies which are unaffected by the difference in the input waveform, but some other things could be. My cnc equipment would not be a problem and that is probably the case for most people's equipment. The concern is that powering an entire shop with a consumer quality UPS might have some unattended consequences.


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## John Hasler (Jul 26, 2014)

woodguy said:


> Consumer quality UPS equipment does not produce a true sine wave output.



Neither does your power company much of the time.  Take a look at what comes out of the wall with a scope.


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