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Posted by dave on May 21, 2008, 4:34 pm
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ol' bubba here wants to build a nice cheap DC welder, preferably that
outputs "pure DC" (not rectified AC). Lincoln used to make such
machines, essentially an AC motor driving a DC generator head. according
to numerous sites, most (maybe all?) DC motors can be 'driven' and used
as generator heads.
I have three DC motors sitting gathering dust, and -plenty- of heavy
angle iron for the frame. plus misc other components, like a nice
rheostat, and the leads. might have to break down and buy a lovejoy
coupling...
take a quick look at my DC motors here:
http://machines.freehostia.com/dc_motor_as_generator/
dc_motor_as_a_generator
which of the three would be my 'best bet' for this idea?
sure, I'd 'like' it if it put out about 300 amps (and less, too) but
I'll probably settle for what I can get...maybe 150 amps out?
this doable?
ps-please, no 'insurance adjuster' or 'fire inspector' type dire warnings
thanks, guys,
toolie :-)
- -
replies by e-mail, if any, please remove the weirdstuff from my address
before you click 'send' - thanks :-)
- -
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Posted by Winston on May 21, 2008, 4:45 pm
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dave wrote:
> ol' bubba here wants to build a nice cheap DC welder, preferably that
> outputs "pure DC" (not rectified AC).
(...)
http://www.hotrodders.com/forum/my-diy-tig-welder-77730.html
--Winston
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Posted by Spehro Pefhany on May 21, 2008, 4:53 pm
Please log in for more thread options wrote:
>ol' bubba here wants to build a nice cheap DC welder, preferably that
>outputs "pure DC" (not rectified AC). Lincoln used to make such
>machines, essentially an AC motor driving a DC generator head. according
>to numerous sites, most (maybe all?) DC motors can be 'driven' and used
>as generator heads.
>
>I have three DC motors sitting gathering dust, and -plenty- of heavy
>angle iron for the frame. plus misc other components, like a nice
>rheostat, and the leads. might have to break down and buy a lovejoy
>coupling...
>
>take a quick look at my DC motors here:
>
>http://machines.freehostia.com/dc_motor_as_generator/
>dc_motor_as_a_generator
>
>which of the three would be my 'best bet' for this idea?
>
>sure, I'd 'like' it if it put out about 300 amps (and less, too) but
>I'll probably settle for what I can get...maybe 150 amps out?
>
>this doable?
>
>ps-please, no 'insurance adjuster' or 'fire inspector' type dire warnings
>
>thanks, guys,
>
>toolie :-)
For welding you want some tens of volts at rather large current. I'd
say "none of the above" unless you're into welding very thin sheet.
As a generator, a motor will put out roughly the same voltage as the
nameplate voltage at the rated RPM, and the 100% duty cycle current
will be around the same (short circuit current will be similar to the
LRA, but proportional to RPM). Open circuit voltage is proportional to
RPM for PM motors or DC motors with a fixed field voltage run as a
generator.
What you want for a welder is something like an aircraft generator or
maybe a truck alternator (??) that will put out a lot of current at
low voltage.
Here's a guy or two who have Cheney'd around with a car alternator to
make a simple welder:
http://home.comcast.net/~t.molnar/Obwelder1.htm
http://www.hackaday.com/2005/07/16/junkyard-tig-welder/
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Posted by Richard J Kinch on May 21, 2008, 5:47 pm
Please log in for more thread options dave writes:
> which of the three would be my 'best bet' for this idea?
>
> sure, I'd 'like' it if it put out about 300 amps (and less, too) but
> I'll probably settle for what I can get...maybe 150 amps out?
You're asking for 10 times the current and 1/10 the voltage that these
motors (as generators) were designed to handle. While by virtue of DC
motor versatility you may be able to configure them to operate at that
condition, they will quickly fail from overheating, overtorquing, or other
outside-the-envelope consequence if so applied.
Not that hard to find a 5 VDC power supply putting out a regulated 200 amps
from house current.
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Posted by on May 21, 2008, 6:39 pm
Please log in for more thread options > ol' bubba here wants to build a nice cheap DC welder, preferably that
> outputs "pure DC" (not rectified AC). Lincoln used to make such
> machines, essentially an AC motor driving a DC generator head. according
> to numerous sites, most (maybe all?) DC motors can be 'driven' and used
> as generator heads.
>
> I have three DC motors sitting gathering dust, and -plenty- of heavy
> angle iron for the frame. plus misc other components, like a nice
> rheostat, and the leads. might have to break down and buy a lovejoy
> coupling...
>
> take a quick look at my DC motors here:
>
> http://machines.freehostia.com/dc_motor_as_generator/
> dc_motor_as_a_generator
>
> which of the three would be my 'best bet' for this idea?
>
> sure, I'd 'like' it if it put out about 300 amps (and less, too) but
> I'll probably settle for what I can get...maybe 150 amps out?
>
> this doable?
>
> ps-please, no 'insurance adjuster' or 'fire inspector' type dire warnings
>
> thanks, guys,
>
> toolie :-)
>
> - -
> replies by e-mail, if any, please remove the weirdstuff from my address
> before you click 'send' - thanks :-)
> - -
With the big-ass magnets you can get nowadays, is a homopolar
generator feasible for a welder?
Or is the voltage too low?
Dave
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> outputs "pure DC" (not rectified AC).