Re: MIG wire speed control problems

Thanks John, Now I have done some of what you mention and everything seems
to work ok, the pot is nice and smooth (with analog voltmeter) and the board
checks out OK. There is a nice big elecrtrolitic capacitor filtering the 24
volts that looked bad, the positive side looked black and some sort of film
on the outside, I unsoldered it and measured and it was OK too. I am
certain that the problem is in the wire feed mechanism. There is only one
active wheel that is pushing the wire and I think it is encountering
changing pressure from the wire spool when trying to spool the wire out.

I am now looking at better and more powerful mig machines and plan to
purchase a new welder in the very near future. The old Century will be
relegated to an experimental machine that I plan to modify and learn details
of the mig welding circuitry.

Thanks again for your very informative reply. I plan to use the information
to start my files on how to do the modifications.

Best Regards,

Ray


"John Crighton" <john_c@xxxxxxxxxx> wrote in message
news:44683734.854167@xxxxxxxxxxxxxxxxxxxx
On Mon, 15 May 2006 03:16:07 GMT, "Rafael Ramos"
<ramray@xxxxxxxxxxxxx> wrote:

Hi all:

I am trying to repair the wire speed control on a Century welder Model
83132. The control has a very short usable range and past position 4 is
faster than 700 IPM, so it is almost impossible to "tune it in". Is there
a
place where I can buy a pc board for this unit or get a schematic of the
pc
board with the parts values. I don't think the Century factory keeps
parts
for these old machines. Who owns Century now? I called the support
number and somebody from Lincoln answered. BTW, I know that I am going
to
get the advice to throw the Century away and get a Red or Blue machine.
Well, I am seriously considering buying the Millermatic 210 or a similar
machine. Any suggestions?

Thanks for your response

Best Regards,

Ray Ramos


Hello Ray,
Have you checked the potentiometer that controls the motor speed?
Maybe it is dirty.
Unsolder the wires to the potentiometer and use a multimeter on the
ohms range to check that the wiper contact of the potentiometer
changes resistance smoothly when the shaft is turned smoothly,
measuring between wiper and either end of pot. with the ohmmeter.
An analog meter with needle pointer is best for this test.

Look for loose and dirty connectors on the motor control board.
Tighten up/clean any connections that look dodgy.

Obtaining a schematic would be ideal, then repair would
be easy but don't give up on that idea yet, keep looking.
In the mean time you could isolate the two motor connections
and build your own speed control in a separate box for less
than $20 in parts.

Google
motor speed control
There are lots of schematics to choose from.

Here is the third hit down
http://www.solorb.com/elect/solarcirc/pwm1/
Here are details of a kit.
http://www.ozitronics.com/docs/k67v3.pdf

I prefer the first link above because it is important
to find a good quality wire wound potentiometer.
The ohmic value of potentiometer VR1 is not critical
in the solor circuit above.
You can find a good quality wire wound pot. in your
junk box (or friends junk box) or from junked equipment
and use it.
Any value between 1000 ohms and 10,000 ohms will
be fine. You just have to reduce the values of R6 and R7
accordingly. Better still, make R6 and R7 trimpots.
Having found a good quality pot for free, the rest of
the components are peanuts in dollar value.

Once you have built a speed controller and got
your welder functioning again you can take your
time finding the Century schematic and repairing
the faulty Century board.
Just a suggestion.

Regards,
John Crighton
Sydney



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