120V/240V AC Output Quality Of Welders

Has anyone hooked up an oscilloscope to the AC outlets of an engine
driven welder? How clean is the output? Could you run a computer,
radio, television, or laser printer off it?
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N38.6 W121.4
Reply to
Barry S.
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I have a Miller Bobcat. The scope says the output is as pure a sinewave as I see from the utility company. That's to be expected since it is an alternator, what else could it be? The frequency varies around a bit (function of engine RPM), but only things like electric clocks and old phonograph turntables care much about the frequency being precisely 60 Hz. Voltage regulation is pretty decent at light to moderate loads, about +/- 5%. With a heavy switched load, I've seen voltage momentarily drop as much as 15%. All of that is acceptable, and comparable to what you'd get from the utility with a slightly undersized service drop.
Computers all use switching power supplies, so they don't much care if the power is clean, exactly on frequency, or well regulated (within reason). They convert the AC directly to DC, chop it at a high frequency, step it down, and rectify and regulate it again at the 5 and 12 volts the computer's electronics actually need. Sinewave, square wave, or even DC is acceptable as input power as long as the voltage is relatively close to nominal (+/- 20% or so).
CRT monitors can be a different story. Some aren't regulated very well, so line voltage variations can cause the picture to expand or collapse, or go out of convergence. You may also get traveling hum bars if the frequency is off. The amount of regulation they have isn't always a function of price either. I've seen some expensive monitors show these problems, and some cheap ones which didn't. It is just a matter of how the designer of the particular model felt about good power supply design. In general, LCD monitors don't suffer these problems, and are much less power hogs too.
Laser printers generally use switching power supplies, so the comments above about computers apply to them too. They do require a lot of power compared to a computer or monitor, so there could be problems with a marginal generator.
Ink jet printers usually use a wall wart power supply, which while it is a switcher too, is generally not a very classy switcher, and may not produce good results if the frequency or voltage is too far off nominal (I haven't had any problems with my Canon and HP ink jets running on the Bobcat, though).
The same sorts of comments apply to radios and TVs too. Tape players may wow a bit with changes in line frequency. CD players generally don't care.
I use my Bobcat as backup power for the house. It runs all my computers, TVs, TiVos, satellite receivers, ham radio gear, etc, as well as some lights, refrigerator, freezer, furnace blower, and central air conditioning. The voltage dips a little when one of the bigger loads switches on, but not enough to cause any problems.
If several of the bigger loads switched on at once there might be a problem, but that hasn't happened to my knowledge while I've been running on the generator. For sure none of the computers has ever rebooted, nor has one of the TiVos lost a program it was recording, while I was running on the generator. I do try to practice power management, and don't try to run everything at the same time.
I was a little concerned that the central air might be asking too much from the generator since its starting surge is right at the full rated output of the generator, but it has handled it without complaint. I suspect Miller's ratings are a bit on the conservative side. It sure is nice to be able to sit in air conditioned comfort watching TV while all the neighbors swelter in the dark.
Gary
Reply to
Gary Coffman
Barry:
I have been researching the same thing for almost a year and all the info I can find says the quality just isn't there to run sensitive equipment. From everthing I have read if you need clean power to run the more sensitive newer appliance/computers etc. you need a good quality inverter style generator. I'm sure there are some good quality very expensive construction grade engine driven welders out there that would do the job nicely but they are out of my price range.
I have an old Miller Big 20 engine welder with a single outlet and a Coleman 5000 watt generator and I was looking to replace them with one single unit but look s like it's not that easy if clean power is required.
Jimbo
Reply to
Jimbo
That's why I have * 2 * UPSes.
Actually I have my answering machine on one of them.
I don't know what you're doin' but that oughta solve the problem.
- "Jimbo" - spluttered in news: snipped-for-privacy@golden.net:
Reply to
Greg M
Earlier this winter we had a huge storm in the Seattle metropolitan area which knocked out power in many places. My son had a major school paper due the next morning, and it (about 40 pages) only resided on the hard drive of my PC. Our first step in coping with the impending disaster which would have ensued had he failed to turn in his paper on time was to unplug my PC and drive it to a job site where we used the power of a generator/welder unit on the back of a truck to bring up my PC and copy the paper to a floppy. The generator, which brand I don't recall but it was a lot like a Miller Legend, powered my computer perfectly. Don't forget, your computer doesn't actually *use* AC, everything is transformed and rectified to +/-12VDC and 5VDC.
(He took the floppy to the city library where we did the final edits and printed the paper out. Feeling tremendous, he took it to school the next day only to find that the teacher had granted extra days due to the storm and he just couldn't face working on it any more. He ended up barely passing, which is much more a reflection on his school than his paper - I know, I read it very carefully indeed.)
I suspect a printer would work fine. Anything with an AC supply in it like a radio or TV I would wonder about.
Grant Erwin Kirkland, Washington
Barry S. wrote:
Reply to
Grant Erwin
One could put a protection UPS unit between generator and a computer. Most are small and would be good to protect from spikes or surges.
I have a 1KW one under my desk now - shares were my feet would kick around. :-)
Martin
Grant Erw> Earlier this winter we had a huge storm in the Seattle metropolitan area
Reply to
Martin H. Eastburn
We have a house and shop full of stuff that runs off two different types of inverters and occasionally from two different generators, one of which is an 8kW Hobart welder/generator. Very few problems. X10 (sensitive) is only happy with the best inverter output, but OK on both of our generators. Some clocks might not be happy if your generator isn't well governed, especially if the load fluctuates. No problem with computers, they're quite happy to run off even cheapy square-wave inverters by most reports. You might search the archives of alt.energy.homepower, lots of discussion of the topic.
List of our loads etc. at
formatting link
Wayne
Reply to
wmbjkremovethis
- Gary Coffman - spluttered in news: snipped-for-privacy@4ax.com:
Nice post Gary.
Thanks.
Reply to
Greg M
After reading Gary's post I'm beginning to think this clean power thing isn't as critical as I have been led to believe.
Jimbo
Reply to
Jimbo
I think so too. Many of the ATX power supplies available today will run on 90 to 240 volts with no adjustment.
Reply to
Jim Stewart
How loud is the Bobcat? Too loud to sleep at night with it on?
__________________ Note: To reply, replace the word 'spam' embedded in return address with 'mail'. N38.6 W121.4
Reply to
Barry S.
That sounds good - but was the sine wave there if you struck an arc ? The surge or HV strike might have induced a peak on the sine or maybe a sag. They might be conditioned very well just for off site computers.
Martin
Gary Coffman wrote:
Reply to
Martin H. Eastburn
Those welder/generators are not optimized for fuel efficiency or for low noise. They would make poor backup domestic power sources for this reason. But they undeniably work. I had a Miller Legend AEAD for a couple of years, had a big Onan gas engine. I *loved* stick welding with that machine. Really well engineered. Sold it for more than I paid. - GWE
Reply to
Grant Erwin
I haven't seen a CRT monitor made since the mid-1980s that didn't contain a fairly decent switching power supply, and I do mean the main supply, not just the scan-derived supply. They also seem to be tolerant of voltage down to 90V. And since displays often don't scan at 60 Hz, monitors have to be resistant to hum interference, and I've never seen any unless a bad ground loop cropped up.
Reply to
do_not_spam_me
Depends how thick your walls are. If you're thinking about using that machine for home power, it's a bad idea. It's only suitable in that role for temporary use. Very inefficient, and the hours will add up quickly. Combined with a modest inverter/charger and some batteries you could cut the gen run time in half easily enough though. Even better, scale up the inverter/battery setup and cut the gen time to a couple hours per day.
Wayne
Reply to
wmbjkremovethis
Gary, as always I found your post to be most informative -- many thanks. However, I did want to clarify one point. Can a switching power supply really be fed a DC input? I was under the impression that it required an alternating input -- not at any particular frequency, but that it did use a step-down transformer to lower the voltage into something closer to the required range. Of course, my impression is based on what I vaguely remember from the schematics for an Apple II power supply back in the early 80's, so it may be that my memory is at fault, or that switching power supply design has evolved a wee bit since then!
Reply to
Andy Wakefield
I may be the wrong person to ask that question, I can sleep virtually anywhere at virtually any time. With the welder on the truck in the driveway, and the house closed up to run the AC, I can *hear* the generator running, but it isn't particularly loud or obnoxious in the house.
The Bobcat isn't a particularly quiet unit, you do have to raise your voice to carry on a conversation when standing right next to it. But through the walls of a well insulated house, it isn't very loud at all.
Gary
Reply to
Gary Coffman
Didn't try that. I don't normally expect to be welding with it while using it as emergency house power. According to Miller, you get reduced power output from the auxillary generator when welding (there's a chart in the manual). That's never concerned me, since I don't do that.
Gary
Reply to
Gary Coffman
Not every switcher can operate from DC, but many of them can. In particular, a PC power supply immediately rectifies the incoming AC to DC before chopping it at high frequency and using a toroid transformer to step it down to the working voltage.
Gary
Reply to
Gary Coffman
Computer power supplies are hardly sensitive. They're about as cheap a power supply as one can get.
J
Reply to
James Arnold

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