I've been trying to convince the boss we need a CNC mill. We are located in the Ozarks in Arkansas and have unreliable power in our area(that would be Arkansas). My boss's big complaint against CNC's is this power supply problem A fella down the road with a CNC mill is constantly having problems because of the unreliable power. I want to know can what the power company sends us be filtered or backeup somehow to give us reliable, clean AC? Backuped would be for the numerous blimps and short power outages. Not the day after day without power we get out here.
First determine how much power (including peaks) you will require and for how long. Talk to the CNC vendor to determine power requirements and if the controller power can be split off from the motors; doubtful, but worth asking. Then contact UPS vendors. It's doable, but it wouldn't be cheap and don't forget to include the UPS upkeep (batteries, etc.).
You should be more specific. In what regard? The controllers, the servos, and the machine spindle would all be separate power consumers with increasing expense to back up.
A lot of electronics failures are blamed on bad power, when they're just poorly made to start with. Convenient excuse for the manufacturer facing a warranty claim. This has been going on since the early 80s when the phony power filtering racket got its start as an add-on to PC sales when margins started to shrink after the initial IBM PC blitz. Lots of propaganda.
Richard J Kinch wrote in news:Xns9552DFC7739B2someconundrum@216.196.97.131:
I'll have to disagree here. I have a considerable amount of experience with CNC equipment. There is not a machine that I know of that could not benefit from supply power filtering, especially if you have more than one piece of equipment in the shop. The facility I am currently employed with has over 1000 CNC machines, among other types of equipment, some of them huge power users. You would probably be amazed at the transients and other power problems present. The machines we have filters/conditioners/suppressors on have dramatically reduced electrical problems compared to non-conditioned machines. This includes drive failures, power supply failures, and sensor failures. In the process of adding conditioners to the rest, on a worst-machine basis.
snipped-for-privacy@yahoo.com (ken) wrote in news:2f646325.0408271543.44358cb9 @posting.google.com:
To answer your question, CNC equipment likes clean power. They especially do not like sudden power drops and the spikes and other trash associated with those events. From experience....out of 1000+ machines, when the power does go out unexpectedly (fortunately, a rare event at our facility), you can about bet on ~0.5% of them with major electrical problems when the power comes back on, another 1-5% will have some minor problems.
If the problems are really coming from the power utility and are not just glitches in the computer that are being conveniently blamed on the power - in other words, you can see the lights flickering often and frequently - a UPS system isn't going to help.
It doesn't matter if you keep the CNC computer running with a UPS for the controls if the big motors doing the work stop. You still just made scrap out of that chunk of metal.
If the power at your shop is really that bad, I would work with the power utility to get you on a better circuit - they often have special circuits set up for hospitals and public buildings where they take special pains to avoid switching glitches and blackouts, you might be able to get switched over to one of those.
Otherwise you might have to install your own primary engine generator plant (Diesel, Gasoline, Natural Gas, Propane) to run the CNC mill from, to get the reliability you need to never stop in the middle of a cut - that way the power will be rock steady unless the generator breaks down, or the fuel tank runs dry.
For electronics, we used (I forget the term), an "in line" or "on line" generator. Its a very heavy motor/generator combination with desel drive. The idea is that the power comes from the generator, but it is driven by a power line motor. The inertia of the large motor/generator rotors smooth the power out through dips in the line, and also will give enough time for the desel engine to start up if the power fails completely.
Where I worked at Cisco, we had generators in their own separate buildings outside. During the year that California had bad blackouts, the lights would go out, and we would go outside, where, of course it was broad daylight (air conditioning loads usually caused the outtages). There was a huge noise, and there were these generators going full tilt, in a line as far as the eye could see, literally several city blocks. It was really cool.
Hi, I work for a power company, and in one of my earlier roles worked in the test section, the section where all the difficult power quality issues ended up. One that I recall involved a CNC machine shop, the owner was very angy that we were supplying him with poor quality power and damaging his machinery. We installed a dranetz power line analyser, and boy was there some crap in his power systems, it was a wonder anything worked at all.
The thing is though, we don't supply crap power, well mostly anyway. By crap power, I mean power that is still on, but full of dips and spikes. We do on occasion fail to supply any power, but it's excellent quality We can on occasion, have failures in our voltage regulation equipment , and supply the wrong voltage, and while low voltages can cause motors to burn, it's still very rare on our network. It's also very rare for our equipment to mess up the quality of the power supply. The only thing we can do to pollute the nice clean stuff we get from the generators is burning connections, and they dont usually last very long once they begin to burn. Where 99 percent of the crap comes from is customer loads, either the customer themselves is doing it, or a close neighbor.
In the case of the cnc shop above, he was doing it to himself. One of his lathes was causing such a disturbance that was destroying his other machines. Putting in filter/conditioners/suppressors as Anthony suggests is good advice, but don't do it thinking that it's the power companies fault, because a Richard said, it's the crap circuitry in your expensive CNC stuff thats really caused you to part with the green stuff.
The exception to that is if the crap is spewing out of your neighbors shed, thats were the power companies real role comes in, protecting customers from other customers. So Ken, have a look at what is around that machine that's having all the problems, it might be obvious where it's coming from. Anyone in the area making concrete reinforcing mesh? How about an arc furnace, or induction furnace?
"john johnson" wrote in news:41303a45$0$29950$ snipped-for-privacy@news.optusnet.com.au:
Wholeheartedly agree John....It isn't the power company's fault in our case, and we know it. It's all the crap we generate in-house. Induction furnaces, huge 400 hp air compressors (4x), big-assed anodizing operations (some serious power use there), all the CNC machines, etc. We pull enough power in our facility to run a small city.
"So Ken, have a look at what is around that machine that's having all the problems, it might be obvious where it's coming from. Anyone in the area making concrete reinforcing mesh? How about an arc furnace, or induction furnace?"
I am getting al this 2nd hand but we are 20 miles from town. Besides our shop and the one with the CNC lathe and mill the is nothing but cows, bears, and trees. Ozarks in Arkansas
Is your CNC equipment fed directly from the main switchgear where the power company feeds the facility? If it isn't, you might be plesantly surpirsed at the improvement you would get by setting up a separate distribution AND GROUNDING system inside your building just for the CNC equipment; feed it right off the main power switchgear. Yse larger wire than code requires; keep the non-CNC equipment on the old feeds.
Another thing you cand try almost for free is to trace the lines from the CNC equipment all the way back to the main building feed and check that every connection is properly tightened. Over time this stuff WILL WORK LOOSE. Several years ago I was in charge of powering a major computing facility. Every Christmas we shut the whole place down for a day and tightened connections. We always found one or two 8o(. It is truly amazing the stunts some industrial electricians will pull; especially with grounds. Ever see 50 volts of trash between neutral and green on a 120 circuit? It does WONDERS for networked computers. In this case the ground was connected to a different transformer than the one feeding the power.
Sounds a bit like the case I ran into several years ago, as the installation project manager, where the operating branch kept insisting that the supplied voltage was excessively high. On my own, I showed up at the site with my own voltmeter and found that my readings agreed with the supply authority readings. Turns out, the operating tech. didn't want to admit that he was guilty of mistreating his equipment, as soon as his supervisor showed up with HIS voltmeter the problem was solved. Gerry :-)} London, Canada
I was going to bring those up, but they might not be the best answer to power a large CNC operation - there is always some frequency slip in an electric motor, so the output frequency will always be a bit off. And when the power fails and they change over, there will be a serious voltage sag and frequency drop as it flywheels until the Diesel gets started, clutched in, and the generator gets spun back up to speed.
For mainframe computers or other devices that aren't dependent on the line frequency for clocking (or anything else), this isn't a problem - everything gets converted to 5V/12V DC and internally clocked, so let the incoming power sag. As long as the power supplies can deal with it and the Air Conditioning stays on, it's all good.
But for a CNC mill trying to spin the work and synchronously move the tools around it in a repeatable pattern, a frequency sag could cause some major problems unless the whole mess is servo-locked together to always stay in sync, and the computer can follow the changes.
And has been brought up elsewhere in the thread, a lot of the dirt in the power is from your own shop or your neighbors. The utility can have problems like switching dropouts, too, but it's just as often a local thing. Get someone in who deals with power quality problems - I don't, I just keep the lights on and know when to call an expert.
Then again, I have a SmartUPS 2200 for my PC - serious overkill. ;-) (Hey, it was free - dead batteries included, and a set of new gel-cell batteries was $50.)
keith bowers wrote in news: snipped-for-privacy@corp.supernews.com:
Keith, There are 3 buildings being fed off of two 13.8K feeds a primary feed and a secondary, the secondary feeds a limited area of the plant, unless the primary has issues. There are 4 substations within the plant. Almost all the equipment is fed from busways, and they are load-balanced through the substations. The equipment not busway'd would be the very high power users (induction furnaces, holding pots, the compressors and anodizers). There is *no* way to segregate the CNC equipment from the rest of the stuff, since the CNC equipment makes up probably 80% of the equipment in the plants, and is located within all three buildings. There is over 1000 CNC machines at our facility. The cost would be prohibitive to re- configure the entire facility. However, as it stands now, we are basically maxed out on the in-plant infrastructure. If we add much more, a new sub will have to be installed, along with upsizing the incoming transformers, etc to handle the additional load. This may be a time to segregate some equipment.
All connections for infrastructure are checked regularly on a PM basis, all the way to the machines.
this was a big concern for problems we encountered on an earl cnc project we did at work
one solution we never applied was a motor-generator -- actually a motor-alternator, if you will.
the thought was, in the event of a power fluctuation (not actual loss of power), the power would come from the alternator side of the unit, and the flywheel action would smooth out any minor variations.
Hmm ... there was a emergency power backup for a building in which I used to work. The primary reason for its existence was to make sure that the fume hoods in the chem lab continued to work, as they were sometimes working with some rather nasty gasses. (Nothing intended as weapons, but simply as stages in creating experimental IR detectors.)
Anyway -- the backup system consisted of a big synchronous three-phase motor spinning a flywheel (about 4' diameter by about 8" thick, IIRC) monted in a pair of self-aligning roller bearing races in pillowblocks.
Beyond that was a flexible coupling made of stacks of steel shims as flexible links, a magnetic clutch made from the electro-magnetic landing-gear brake from a B-58 (IIRC), followed by a big healthy diesel.
There was a cabinet of electronics against the right-hand wall as you entered the shed in which it lived.
The electronics monitored both the power line voltage and its frequency -- and if either went out of spec, it would engage the mag clutch, instantly spinning up the diesel, and that would generate power by continuing to spin the synchronous motor at the same speed (1800 RPM, IIRC).
Circuit breakers to this were 400 A three phase. One at the synchronous motor, and three back in the nearby room where the air conditioning and heating equipment lived.
If well maintained, it worked perfectly, even kicking in to add support when the hydraulic freight elevator would start up in hot weather during near brownouts. It supplied power to about half of the building.
However -- there are still things which could go wrong. And when they did go wrong, they tended to be spectacular.
First -- remember the big dual-row self-aligning roller bearings which I mentioned? They were mounted in pillow blocks, fed oil from individual tanks on the side rails of the machine. There was a rubber hose from each tank to the corresponding pillow block. There was also a temperature sensor screwed into the pillow block to monitor the oil temperature, to shut things down gracefully if the bearing starts to overheat.
Well ... the hoses got old and brittle, and one broke from vibration -- apparently late on Friday of a three-day weekend. This drained the oil out of the tank -- and out of the pillow block. After a while, the bearing started to overheat, and generate interesting noises, which got the attention of the guard force. However, they did not have a key to the shed where it lived, and somehow had lost the home phone number of the person whose responsibility it was -- so it was allowed to continue to run.
Remember the temperature sensor? Well, it monitored the *oil* temperature, and since the oil was on the floor in a puddle, there was nothing to monitor, so the sensor thought that things were fine.
On Tuesday (remember the three-day weekend?), when the fellow in charge came in and heard the noise, he went into the shed, and saw the bearing spitting bright yellow sparks, so he shut it down and bypassed it. If things had gone a bit longer, it might have seized and ripped the pillow blocks loose from the frame and gone galloping across the lawn to the next building -- about 150 feet away.
It was out of service for a couple of months while the replacement bearings were procured (through an Army procurement system), and the one fellow who maintained these around the country (and in Alaska for sure, since that is where he was just before coming to our place one time when I talked to him.) (We were in Virginia.)
Both bearings were replaced as a precaution, though there was no doubt that one of them was beyond hope. It had rollers about the size of 35mm fill cassettes. At least one of the rollers came out of it
*looking* like a film cassette, as it had metal smeared to form the lip where the film exits. :-)
The second time involved the shims used as a flexible coupling. The fellow who did maintenance said "The shims are starting to fail, it is time to order some more. Here is the part number and a source. It should cost about $90.00. I'll install them in six months when I am back.
Well ... remember that I said that this was a US Army site? (A R&D lab, actually.) There are always priorities, and some other things took all the money during that period, so they were not ordered.
End of next six months -- same situation.
Sometime before the next six months runs out, someone presses the call button on the freight elevator, and there is a horrendous noise from outside. It turns out that the final shim in one of the three stacks broke, applying a serious side load to the magnetic brake. It was destroyed beyond repair.
Another several months of downtime -- more than six, this time, as those brake assemblies are hard to find.
Money saved: $90.00
Cost of new brake assembly: $30K+
This is how the Army saves money. :-)
Final one involved someone testing the backup system. Remember me mentioning that there were three 400 A three phase breakers? They took enough force to set so there was a moulded phenolic helper handle to slip on over the normal toggle.
Anyway -- testing involved turning off the breaker controlling input to the backup generator. As expected, it took up the load without a glitch. Now -- when power returns, the controller drifts the power frequency until the local power is in phase with the power line before switching back.
There were three breakers there. One disconnects power from the input. One disconnects the building load from the output. The third bypasses the backup unit, accepting power directly from the line. The person doing the testing switched the wrong breaker back on -- the one which connected the line directly to the building -- and the backup unit was about 180 degrees out of phase with the line power. Result was that the motor/generator was instantly stalled (with a loud grunt), and at least two (and I think all three) of the fuses at the power pig cluster on the pole blew -- blacking out not just that building, but several others nearby as well. (It may have taken out some fuses upstream as well -- I only know what I saw. :-)
Oh yes -- the backup system survived, but there was no way to re-start it until the line power came back. :-)
And as it turned out -- nobody was using any of the nasty gasses during any of those failures.
However -- something like this would probably be an excellent way to assure clean uninterrupted power for a few CNC machines. Just make sure that nobody short-cuts the maintenance. :-)
Sounds like someone put some thought into the original layout With stuff intermixed like that there's not much you can do other than clean up MANY small areas which would cost a fortune 8o(.
Perhaps many are sold on the basis of propaganda, but a machine shop is a very different situation to most homes and offices. Big motors and other bits of kit starting and stopping can put all kinds of crap on the line.
I saw in "Communication News" that Active Power has a UPS that contains a 600 lb steel flywheel instead of batteries. Units up to 130kw. Operating temps of 0-40C. Maybe you could drop one of these beside the CNC machine.
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