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gunsmither
10-21-2013, 06:28 PM
Being without power for an extended period could be hazardous to my business.

I would like to have a back up generator for 240 volt single phase power for my home and shop.

The largest machine I would like to power with it is my 2007 TM-1, which takes a 40 amp circuit on single phase 240 volt.

My concern is the quality of power put out by a back up generator.

Has anyone here ever used a single phase generator for CNC machine power?

If so, can you recommend a brand, or a style of gen that has CNC quality power? Is there such an animal available?

I have seen some whole house gens that say they are good for electronics, computers, etc.

Any suggestions would be most appreciated. Thanks! Joe

sch
10-21-2013, 06:55 PM
Generator outputs are very close to sinewave, but flutter a bit on frequency, which should not be a problem. Freq variance when at speed will be maybe a herz or so, most are rated at less variance.
They take 5-10 seconds to crank up so the electronics should be on a battery backup that can hold things up til the generator fires up. You would need upwards of 14-20kw to power lights, and an
HVAC, in addition to the machine. Propane/natural gas generators with automatic switch over will run $4-8k plus install, depending on size. If you are worried about electrical noise, noise filters on the output are available. Figure 20 to 35 amps to run an AC or heat pump per unit, whole lot less to run gas furnace. Hope you are not "all electric". What happens with the Haas if power goes off while
running a job? Does it have a seizure? Does the controller die gracefully or with loss of program? If the controller keeps going under battery backup but the machine shuts down, how soon does the
controller become aware of this?

lakeside53
10-21-2013, 07:29 PM
Typical home generators of 4-12kw put out a terrible waveform - it's a very "square" looking sine wave with a lots of noise. If you want a decent waveform "Gillette" makes a quality generator head. You can find them paired with many different motors under several brands, and they sell their own.

http://www.gillettegenerators.com/categories

The Artful Bodger
10-21-2013, 07:38 PM
Typical home generators of 4-12kw put out a terrible waveform - it's a very "square" looking sine wave with a lots of noise.

They do? I wonder how they make alternators that can do that.:rolleyes:

Dr Stan
10-21-2013, 07:38 PM
Being without power for an extended period could be hazardous to my business.

I'd first define "extended period" and also look at the history of power outages in your area. Only then can you make a rational decision on a backup generator.

If you conclude a generator is essential as others have pointed out not all generators are equal nor do they tend to produce an adequate wave form for computers and the like. I would find a local reputable electrical contractor (preferably at least 2 or 3) and sit down with them and ask for quotes. Make sure they understand your needs are not the same as the typical residential customer, but more like those of a police station, fire station, or medical clinic. Then get ready for sticker shock.

Jaakko Fagerlund
10-21-2013, 10:16 PM
Typical home generators of 4-12kw put out a terrible waveform - it's a very "square" looking sine wave with a lots of noise. If you want a decent waveform "Gillette" makes a quality generator head. You can find them paired with many different motors under several brands, and they sell their own.

http://www.gillettegenerators.com/categories
Haven't yet seen or heard of a generator producing modified sine wave, inverters yes. Though in the same breath haven't seen 4-12 kW inverter for home use, as that sort of power is usually not pulled out from a battery.

kf2qd
10-21-2013, 10:27 PM
The best generators will be an inverter style generator. The output will be better suited and cleaner for electronics. They are the more expensive units. Honda makes several. And yes, they make larger generators with inverters for use with electronics.

Load variation should be handled better by the inverter type unit. Plain alternator type units can get off frequency in both directions with variable loads.

lakeside53
10-21-2013, 10:48 PM
I've looked at many "smaller" (less then 20kw) generator outputs and most are horrible. If you don't have a scope or distortion analyzer, one easy test is how well light dimmer works -on a typical lower cost home generator they have a very small range from low to bright - characteristic of the very steep sides of the "sine wave". Another is the weird singing noises you get from small fans/motors - that's the multiple peaks on the top of the waveform. Harmonic distortion is very high - 10-20%. "Good" generators will have less than 5-7% distortion, and the best with electronic control and inverter output, maybe 2-3.


Many UPS will not accept a generator input without filtering.

In my neighborhood alone (56 of us) almost everyone has a generator - we get 7-15 days a year without power! They range from 4kw junk to 25kw Natural gas powered "whole house" standby units. There are a few Honda EU6500i - these are pretty good, but 3X the cost of a typical (non-Honda) non-inverter generator. Mine's a 10KVA, 9KW 16hp from the mid 90's. Decent motor (B&S vanguard), crappy generator, and.. its "spec" is "less than 5%" - not however in the "real world".

Here's a manf's glimpse into the issues.
http://www.enrg-generators.com/klnpower/kpower01.html

Something not covered is the ability of the generator to produce low distortion power when connected to other than purely resistive or power factor corrected loads.

Sure... most manf say "less than 5%" or 3-6% or whatever, but they don't specify the test methodology. Just draw a lot more current from one side of the 120-0-120 generator and see what happens, and you can be certain they tested with a resistive bank.


Here's a good real world article. The waveform on the bottom of page 2 is somewhat similar to what I see (mine has more spikes and is steeper), and Fluke calls it 12.8% :
http://support.fluke.com/find-sales/Download/Asset/3497420_6112_ENG_A_W.PDF

lakeside53
10-22-2013, 12:03 AM
Haven't yet seen or heard of a generator producing modified sine wave, inverters yes. Though in the same breath haven't seen 4-12 kW inverter for home use, as that sort of power is usually not pulled out from a battery.

No, not "modified" as in cheap inverters - just a lousy attempt at a generated sine wave :)


See above post example.

The Artful Bodger
10-22-2013, 12:23 AM
Haven't yet seen or heard of a generator producing modified sine wave, inverters yes. Though in the same breath haven't seen 4-12 kW inverter for home use, as that sort of power is usually not pulled out from a battery.

I believe there is a class of generator called an 'inverter generator' where the output of a motor driven alternator is rectified and is passed to an inverter.

PStechPaul
10-22-2013, 12:25 AM
I think the waveform distortion is caused largely by the automatic voltage regulator (AVR) which I think feeds a rectified but unfiltered voltage to the field and it cuts the field current abruptly when the voltage limit is reached. If a smooth DC current is applied to the field, the waveform should be much better. The waveform is probably best when the generator is loaded with a resistive load at the rated maximum power. At lower power levels, the output voltage would tend to be higher, and regulation is accomplished by "clipping" the peaks which results in the waveform shown in the Fluke app note. I found a discussion that claimed a simple capacitor on the output of the bridge rectifier driving the field can correct much of the distortion:

http://www.microcogen.info/index.php?topic=1833.45

Here is an article about a more sophisticated AVR which may help explain this:

https://www.cumminsgeneratortechnologies.com/www/en/common/pdfs/avr/TD_SX460.GB_04.05_05_GB.pdf

and

http://www.electricneutron.com/generator-2/automatic-voltage-regulator-for-generator/
http://store.gedigitalenergy.com/manuals/Documents/General/GEK-12510.pdf

dp
10-22-2013, 01:01 AM
I've always worked in IT and have been responsible for some very well-known dot com data centers. These sites always run on inverters and those inverters (aka power scrubbers) alternately run on city power or batteries, depending on city power reliability. Now, any time city power fails the local generators come on line, of course, but regardless, that only effects where the batteries are charged from. The data center runs on battery powered inverters, period.

That means the wave form never changes, and the inverters don't care where the input power comes from. This provides a remarkably stable and predictable power source. The one thing it can't do, obviously, is charge its own batteries. The fail-over from city power to battery power is invisible in this configuration. There is 60 to 90 minutes of on-battery power time to restart the gennies if they run out of fuel. That, btw, is the most threatening possibility in the entire enterprise. It is the last thing anyone thinks of. Axe me how I know.

Quick clarification - when the batteries are being charged the inverters are running on charger power.

Paul Alciatore
10-22-2013, 01:30 AM
One more thing about generators: if you do not run them UNDER LOAD on a regular basis, they WILL fail when you need them. This is a more basic law of nature than gravity. Do give them an hour or two of real use every week or two.

I would talk to at least two generator suppliers in your area before buying anything. You can also find some good used generator places in most areas. Be prepared for sticker shock.

PStechPaul
10-22-2013, 02:39 AM
I tried to post a reply to this thread but for some reason it was held for moderator approval. Maybe because I had a lot of links?

Basically, I found that many generators use a crude automatic voltage regulator (AVR) which shuts down the field supply to limit the voltage, and causes clipping distortion especially at light loads. The waveform should improve at full rated load. And it may be possible to add a capacitor on the output of the rectifier which supplies the field current, and it may improve the waveform a lot.

vincemulhollon
10-22-2013, 08:35 AM
One more thing about generators: if you do not run them UNDER LOAD on a regular basis, they WILL fail when you need them. This is a more basic law of nature than gravity. Do give them an hour or two of real use every week or two.

I agree completely and extend your remarks with the cost of maintenance, both fuel, parts, and most importantly labor, needs to be properly estimated. If you spend an hour a week fooling with a generator either running it or maintaining it, the total of labor and parts and substantial fuel costs equal about a hundred hours of production time annually, or in other words you need to use the thing to save a hundred hours of production per year in order to just break even.

Also to extend Paul's remarks a stereotypical generator fail is the way most people discover their gen has had a partially clogged fuel filter is they just idle the thing for a minute every week and under load the clogged filter can't flow enough. Ditto air filters. And nothing rusts like an engine not run up to full temp for awhile. Oh and another classic I've run into, the coolant pump/fan/thermostat is broke, no problemo in the winter if you only run two minutes at idle but under load that engine is done for in five minutes.

There are exceptions to the economics, if you wisely buy a trailer generator you can loan it to people for money and it's always cheaper to take the generator to the repairman than to take the repairman to the generator. Of course that makes it easier to steal, and you get to license trailers (depends on state, I guess). Then again if you loan it to the ham radio guys for field day you'll get infinite "free" beer in exchange. And you could tow it to your house or someone elses house if the shop didn't need it. So its more complicated than just dollars and cents.

Finally as telecom guy who's been in the biz in one form or another since analog microwave was in use, I assure you that crazy as it probably sounds, transfer switches are more reliable than "hurricane alley" commercial power but less reliable than say, urban underground feeder Wisconsin power. So if you install a UPS / generator system in an area where plain old commercial power is excellent, that means you'll have less reliable power because the xfer switch will fail more often than commercial power will fail. I cannot tell you how many outages we had that were basically self inflicted where the xfer switch or the generator was the root cause, but lets just say it happened a lot more than commercial power failed by maybe an order of magnitude... Generator / xfer switch is however perfectly effective for CYA purposes and you'll always get a pass when a xfer switch failure causes a problem, even if it happens 10 times as often as a commercial power failure would cause a problem. Customers are always thrilled to have ten outages because the backup emergency generator switch broke, but they'll go insane if you tell them commercial power is out and you have no gen just once, they're weird that way.

lakeside53
10-22-2013, 11:28 AM
Two years ago I put in a 600kw genset. It feeds a small data center and a 100 person 24x7 call center. The generator coolant/oil is continuously heated to operating temp so it's ready to go to full load in a few seconds from starting. All top quality components and installation ($$$$). It starts automatically every 7 days and runs for 30 minutes, twice a year its run up to full load with an external load bank, and twice a year we simulate a power failure to exercise the transfer switch.

So far we've had a major coolant leak (CAT took care of it...) and a transfer switch failure! The $12,000 switch fried its brain... but "failed safe" so it decided to transfer power and switch the genset on late one Sunday pm. Nobody thought much of it so it ran for a few hours before someone thought that might be excessive considering all the lights were on the area. lol... but the worst part - couldn't shut it off because the transfer switch wouldn't switch back. Great... Finally figured out how to kill the power and get it switched back... but there was some pucker-factor associated with bypassing the transfer switch and remaining on City power for the 3 days it took to fix.

CCWKen
10-22-2013, 05:18 PM
The inverter generators are becoming more popular now. They produce as good a quality of electric as any utility company. The problem is they're still limited on the high end output but they keep building them larger and larger. If they can build a 200+A welder, bigger generators aren't too far behind. You need to decide what is critical and how deep you'll dig into the pockets. "Normal" gensets won't give you power for several minutes. I run a 7Kw UPS system. As soon as I get a round-tuit, the UPS will be backed up by a generator. The UPS switches almost instantly so there's no problem with computer/electronic equipment.

gunsmither
10-22-2013, 07:19 PM
Thanks for all the input gentlemen. Lots of good info. I think I will contact Haas and see what they have to say also. Thanks again! Joe