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
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
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
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:
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:
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
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
How loud is the Bobcat? Too loud to sleep at night with it on?
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N38.6 W121.4
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:
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
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.
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
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!
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
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
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
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