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Posted by dave on August 12, 2008, 8:07 pm
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I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"
here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/5385/capacitor_closeup.jpg
here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg
and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/5385/welder%20schematic.jpg
electrically, I'm a "real slow learner", so, thanks for your help, guys :-)
toolie
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Posted by Ignoramus6985 on August 12, 2008, 8:28 pm
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I think that their purpose is suppressing high voltage from HF arc
starting subsystem, so that it would not damage the rectifiers.
i
> I just bought an old miller dialarc HF "whiteface" vintage. while
> getting ready to test it, and cleaning it out, I noticed some of the
> leads on the tiny capacitors in the main rectifier bridge are loose,
> kind of like how quarter-inch round rod would rattle around inside a
> piece of half-inch water pipe. they're "probably" bad, because of that
> alone, I'd guess, but, umm, what exactly is the electrical function of
> those four tiny things supposed to BE? like "what're they doing for me?"
>
> here'a an extreme closeup of one of the 'loose leads' capacitors, next
> to one of the four "big honkin" diodes in the bridge.
> http://www.image-upload.net/files/5385/capacitor_closeup.jpg
>
> here's a page from the owners manual, where they're descibed...
> http://www.image-upload.net/files/5385/parts_blowup.jpg
>
> and here's the parts schematic, for the same machine.
> http://www.image-upload.net/files/5385/welder%20schematic.jpg
>
> electrically, I'm a "real slow learner", so, thanks for your help, guys :-)
>
> toolie
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Posted by Jim Chandler on August 12, 2008, 8:50 pm
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dave wrote:
> I just bought an old miller dialarc HF "whiteface" vintage. while
> getting ready to test it, and cleaning it out, I noticed some of the
> leads on the tiny capacitors in the main rectifier bridge are loose,
> kind of like how quarter-inch round rod would rattle around inside a
> piece of half-inch water pipe. they're "probably" bad, because of that
> alone, I'd guess, but, umm, what exactly is the electrical function of
> those four tiny things supposed to BE? like "what're they doing for me?"
>
> here'a an extreme closeup of one of the 'loose leads' capacitors, next
> to one of the four "big honkin" diodes in the bridge.
> http://www.image-upload.net/files/5385/capacitor_closeup.jpg
>
> here's a page from the owners manual, where they're descibed...
> http://www.image-upload.net/files/5385/parts_blowup.jpg
>
> and here's the parts schematic, for the same machine.
> http://www.image-upload.net/files/5385/welder%20schematic.jpg
>
> electrically, I'm a "real slow learner", so, thanks for your help, guys :-)
>
> toolie
they're probably to provide a DC path to ground for AC spikes.
Jim
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Posted by Martin H. Eastburn on August 13, 2008, 9:21 pm
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I was in RF before retiring.
1. Notice the #10 or such wire that the cap is attached.
The large diameter has lower inductance and higher DC and AC current.
2. Since the cap is in series (and yes legs wiggle mean it is dead) Only AC
current flows. The value of the cap and the inductance of the total
lead set determines what frequency it is shunting. The inductor Z
when it turns on and turns off produces spikes. Switching hot does as well.
3. Notice the ones in parallel to the rectifiers (diodes). They keep RF
current from inside the diode which might arc on the internal die and kill
the unit. Down in the bottom right is a RF high voltage arc with a set
of arc points that are used to limit the output RF arc. If these eat back
then the voltage increases and can cause more problems. But normally,
this is a source of RF noise that can harm transistors and diodes.
4. The module below the bridge is a filter. Likely an RC but with the
'V51' that tends to indicate an AC item. So resistor for better control.
5. The resistor R2 is a minimum load.
Replace the caps - keep their leads short. Higher voltage is just fine.
Get the same value as in the spec - that is the 'frequency' it shorts...
Hope that helps.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/
Jim Chandler wrote:
> dave wrote:
>> I just bought an old miller dialarc HF "whiteface" vintage. while
>> getting ready to test it, and cleaning it out, I noticed some of the
>> leads on the tiny capacitors in the main rectifier bridge are loose,
>> kind of like how quarter-inch round rod would rattle around inside a
>> piece of half-inch water pipe. they're "probably" bad, because of that
>> alone, I'd guess, but, umm, what exactly is the electrical function of
>> those four tiny things supposed to BE? like "what're they doing for me?"
>>
>> here'a an extreme closeup of one of the 'loose leads' capacitors, next
>> to one of the four "big honkin" diodes in the bridge.
>> http://www.image-upload.net/files/5385/capacitor_closeup.jpg
>>
>> here's a page from the owners manual, where they're descibed...
>> http://www.image-upload.net/files/5385/parts_blowup.jpg
>>
>> and here's the parts schematic, for the same machine.
>> http://www.image-upload.net/files/5385/welder%20schematic.jpg
>>
>> electrically, I'm a "real slow learner", so, thanks for your help,
>> guys :-)
>>
>> toolie
>
> they're probably to provide a DC path to ground for AC spikes.
>
> Jim
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Posted by DoN. Nichols on August 14, 2008, 7:36 pm
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> I was in RF before retiring.
>
> 1. Notice the #10 or such wire that the cap is attached.
Hmm ... that looks to me (I still have the image saved locally)
like about 22 ga wire, with insulating sleeves slipped on over it.
Looks like the silicone rubber in fabric type of insulating sleeve --
something which is unlikely to go brittle over years of exposure to UV
and weather.
And if that is the case, then wiggle is perfectly normal.
> The large diameter has lower inductance and higher DC and AC current.
Yes -- it would, *if* the wire actually had a larger diameter.
I don't think that it does. It should be possible to slide the end of
the sleeve down a little away from the capacitor body to verify this.
Enjoy,
DoN.
--
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
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> getting ready to test it, and cleaning it out, I noticed some of the
> leads on the tiny capacitors in the main rectifier bridge are loose,
> kind of like how quarter-inch round rod would rattle around inside a
> piece of half-inch water pipe. they're "probably" bad, because of that
> alone, I'd guess, but, umm, what exactly is the electrical function of
> those four tiny things supposed to BE? like "what're they doing for me?"
>
> here'a an extreme closeup of one of the 'loose leads' capacitors, next
> to one of the four "big honkin" diodes in the bridge.
> http://www.image-upload.net/files/5385/capacitor_closeup.jpg
>
> here's a page from the owners manual, where they're descibed...
> http://www.image-upload.net/files/5385/parts_blowup.jpg
>
> and here's the parts schematic, for the same machine.
> http://www.image-upload.net/files/5385/welder%20schematic.jpg
>
> electrically, I'm a "real slow learner", so, thanks for your help, guys :-)
>
> toolie