I bought one of those cheap chinese mig welders, It splatters alot and
is alittle unstable. I
removed the case to find only a transformer and two diodes. Im
thinking of adding a inductor
in the + dc line, most good dc welders have atleast this. Is there any
other improvements
i could do to stabilize the output? Would filter caps help?
Hello Mr Tucker,
I have been down a similar road, buying a cheap
welder and then trying to make it work better
by doing the sort of improvements that you are
talking about. I wasted a lot of time and effort.
My advice to you is take it back and spend
more money on a machine similar to these
in this link below
http://www.ben.com/tools/sp-175plus.html
Stay away from 115V machines. Too small.
Here is the link to the Lincoln 175T manual.
http://content.lincolnelectric.com//pdfs/products/navigator/im/IM537D.pdf
Page 54 shows the transformer and choke assembly
made with flat ribbon wire. You can see the capacitor
also. These 93,000 microfarad caps are very expensive.
About $100 as a spare part here in Australia.
Maybe cheaper in your part of the world.
Schematic is on page 43
What I like about this model, if you look at the
schematic, is the voltage taps are done on the
secondary of the transformer. A cheaper, not so
good method, is to tap the primary winding of the
transformer.
Here is a link to the Miller 185 manual
http://www.millerwelds.com/om/o1313p_mil.pdf
Page 38 shows four capacitors of 30,000 microfarads.
Four separate caps is better than one big cap.
Lower ESR
The schematic is on page 24.
From the schematics of these manuals, you may get
some ideas what to aim for if you do decide to try and
improve your cheap welder. There is also a how to
weld tutorial and problem solving pages that may
help with the spatter problem you are having.
Another option is to use your electronic repair
skills to fix a broken machine or a machine that
has been written off beyond economic repair
because some component is no longer available.
Use you skills, get round that problem and maybe
pick up a bargain on an older high quality machine.
Just for fun on your cheap welder. Try adding
a choke to the "work" lead. You don't even have
to cut the work lead. Just connect the large alligator
clip/clamp (that normally goes to the job) to
the "add on" choke and use another "work clamp"
from the choke to the job.
You can make a choke. Make two or three.
Find some old discarded microwave ovens.
Salvage the large power transformer.
Remove the "I" piece of the "E" and "I' core.
and knock the windings out of the "E" section
of the core.
To remove the "I" section in one piece.
Slightly hacksaw about 1mm into the weld.
Use a "brickies bolster" or wide blade chisel
and gently tap into the hack sawed cut.
The "I" section will come off easily in one piece.
It would be nice to use proper winding wire or
ribbon but just for fun use whatever heavy insulated
cable you can get your hands on and fill up the
window. Probably only several turns.
There has to be a gap between the "E" and "I"
pieces of your core. Start with an excessive gap
of say 2 to 3 mm and use whatever clamping method
you like to hold the "I" piece in place.
Tack weld it back on if you like, or get fancy and
make it adjustable with brackets and screws.
Make a few chokes like this and you can experiment
adding one or all three to the "work" lead and see
if your welder works better.
Later on you can adjust the gaps of your chokes
a bit nicer to get maximum inductance for the
operating current you are interested in.
No point in having a huge gap where the choke
does not saturate until 200 amps flows through it
when you are only interested in say 100 amps.
No Point in having a small gap and the choke
saturates with only 30 amps flowing through it.
So while you are just experimenting for fun, err on
the big gap side. Then close it up later.
Some time ago, I was sucking the brains of an
engineer from Lincoln Electric in regard to building
chokes and how to set the core gaps and he got
the shits with me and said,
"We make fucking welders here, not electronic
power supplies, we experiment by trial and error
until the machine welds correctly"
So from the horses mouth, experiment and have fun.
I enquired on this group years ago about setting
the gap for a particular current. There were a few
methods involving power supplies/banks of capacitors
and using an oscilloscope to look at the pulse shape
across a low value sense resistor. I didn't quite
understand what I was supposed to look for.
This was the other method suggested which I used to find the
current at which the core saturates with a particular gap.
Variac on very low setting (several volts) ? AC stick welder primary
Welder O/P --> 100 amp shunt --> choke under test --> Welder O/P
That is, across the welder output terminals connect your choke
under test in series with a 100 amp shunt.
The 100 Amp shunt acts as a sense resistor so a digital voltmeter
can indicate the current flowing. For example on my shunt 60mV
equals 100 Amps.
An oscilloscope is placed across the shunt and shows a nice sine
waveform.
Turn up the variac on the primary side AC stick welder.
Warning! Keep input voltage low, several volts only, because
the secondary has almost a dead short across it.
As the current increases through the choke and shunt you will
see the AC waveform begin to distort slightly.
Note what the current is just before distortion.
If it is around 100 amps you are laughing.
If it is only 40 amps then you will have to increase the gap
between the E and I piece and try again.
I'll bet this machine of yours does not have
a proper wire speed controller that works
independent of the output voltage settings.
This is another improvement you can make.
Pulse Width Motor Speed controller. Google for those.
Here is the one I used. It works well.
http://www.solorb.com/elect/solarcirc/pwm1/
Be warned, I spent more time experimenting/making
test welds trying to improve a cheap machine than
I did welding up proper jobs and projects.
The cheap welder improvement project takes over.
Isn't that correct Igor?
Home built Welders become an Obsession!
Regards,
John Crighton
Sydney
