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Re: Cabbott: regulating a pig from Reinhard
From: RWB355-at-aol-dot-com
Hi Cabbott,
You wrote:
Couldnt i just put a parralel arrangement of oven elements on the output of
my arc welder? this would regulate the resistance the arc welder has. that in
turn would regulate the current that can pass thru the pig. just a thought
**Note: You donīt change the resistance (DC) your welder has. You change the
complex part (AC resistance).
You could do this, but the resistance of an oven element is way to high. A 2
kW element would have somewere around 6.5 to 7 ohms (DC resistance). This is
at least about 10 times the internal resistance of your welder, so you might
as well not connect them to your output, because the current flowing thru the
primary of your welder wonīt change much if the oven elemnts are connected or
not. The secondary of your welder has about 50 volts (open circīd) and if you
draw around 7 amps (per oven unit), your welder will just "smile" because you
arenīt loading it at all. Thatīs why I said use heavy copper or steel strips
as a ballast for the output side of your welder. You are just talking
MILLIOHMS here. To get mOhms from oven elements you would need a hell of a lot
in parallel and in your case, you donīt need this fine of an adjustment (by
dis/connecting oven elements). This is why itīs so important to have a good,
short ground connection when welding.
If I were you I would take a few oven elements (adding them in parallel as
your power hunger grows) to do the dirty work and use your welder to fine
adjust the output od your pig. You can use different metals in your welders
secondary, to adjust the loading of the welder. Stainless for example has a
higher resistance than normal steel, etc. Aluminum, Brass, anything that will
conduct and is heavy enough to take the rated 250 amps will do.
After getting your setup working, I would exchange the welder for a big variac
plus a resistive load (that limits the current to your max needs). This way
you can learn using cheap or availible parts and when you get your setup
running properly you can upgrade to a neater and better control setup, without
having to "junk" expensive parts, that are of no use anymore. The real problem
a resistor has in our cases is the voltage lost across it. An indutactance
doesnīt have this problem (Okay you 200% guys out there. It DOES have a small
drop, do to the wire resistance. But this wonīt change the voltage output of
your pig more than 100-200 volts, so FORGET it)
hope I could clear your clouds,
Coiler greets from Germany,
Reinhard