On 14 Feb 2004 17:30:09 -0600, Barry S. wrote:
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?

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