Re: Generator
- From: etpm@xxxxxxxxxxx
- Date: Mon, 18 Aug 2008 03:45:04 GMT
On Sun, 17 Aug 2008 20:04:46 -0600, "Private" <please@xxxxxxxxxxx>
wrote:
I dunno about the greater knowledge, but I do know that a DC motor
<etpm@xxxxxxxxxxx> wrote in message
news:48a7ea92.48839136@xxxxxxxxxxxxxxxxxxx
On Sun, 17 Aug 2008 14:41:12 -0600, "Private" <please@xxxxxxxxxxx>
wrote:
Greetings Private,
"SteveB" <toquerville@zionvistas> wrote in message
news:cpvln5-ab21.ln1@xxxxxxxxxxxxxxxxxxxx
I need to power my Lincoln SP 175+ in a remote location without bringing
in
a line off the pole. ($$$) It calls for 220v and 22 amp in. What would
be a good size generator to look for that would run the unit, not get
over
heated, yet not be overkill?
220volts x 22amps = 4840 watts = 4.84 kilowatts
Add a little 'for mother' to account for losses in power cords and for the
usually exagerated generator rating. Long power cords can cause voltage
drop which results in increased amperage which could overload/overheat
your
welder.
I think you have made a mistake in the above paragraph. When a motor
is running it is also acting as a generator. This generator action is
called "Back EMF". The Back EMF limits how much current the motor will
draw. Different motor types act differently when the voltage is
dropped. DC motors just slow down without drawing more current.
However, when an induction motor recieves lower voltage it will start
to slow down and draw more current. This is because the motor
produces less Back EMF when running at reduced speed and voltage and
so it will then draw more current. This higher current leads to more
heat in the windings which can burn out the windings. The welder
transformer doesn't work the same way as an induction motor and so it
doesn't draw more current as the voltage drops. When a transformer
type welder recieves less voltage it just uses fewer watts. At least,
that's how I remember it. If I'm wrong someone will surely correct me.
Cheers,
Eric
I am not an electrician or electrical engineer and defer to your obviously
greater knowledge.
With respect,
I had thought that all electrical loads would try to maintain output power
by pulling more amps whenever voltage dropped. Will a DC motor not try to
maintain output torque at the lower speed caused by reduced voltage? Does
this not increase amperage draw? I am told that low voltage (resulting from
continuing to drive with a failed alternator using rapidly discharging
battery power as long as possible) can cause automotive fuel pumps to
overheat and lead to failure. By your statement, if dropping input voltage
does not increase amperage draw of a transformer welder then ISTM the output
power must be reduced, this will likely cause the weldor to increase the
controls to compensate and ISTM that this will result in the transformer
drawing more amps.
I know just enough to keep my power cords as short as possible and as big as
I can afford.
will just slow down with lower voltage. So will a "universal motor".
The universal motor is the type used in hand drills and the like. They
have brushes and a commutator and will work on AC or DC. Variable
speed drills may not work on DC. Now a welder operating at reduced
voltage will indeed draw more amps if the operator increases the
setting. However, I don't believe the welder can be adjusted to draw
more amps than it can handle without some sort of safety device
shutting down the machine. As happens when welding too long and
exceeding the duty cycle of the machine. A good book on electric
motors is "Electric Motors and Control Techniques" It is published by
Tab Books.
Cheers,
Eric
.
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