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  • OK. That worked. You can get "factory original" parts from Mouser.com or Digikey.com under that part number for around 5 bucks.

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    • Or you can get them from surplus dealer MPJA.com for under two bucks each. Their part number is 31094 BR. I've bought tons of stuff from them and never got a bad part over 15+ years.

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      • Or you can get them surplus from Marlin P Jones Associates (use the first letters and add ".com") for under $2. This site will apparently not let me post their initials. Their PN is 31094 BR.

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        • I order 10 of them and some thermal grease yesterday. After tax and shipping it was less than $30.

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          • Finally got around to testing the smaller selenium bridges. Sr2 has welder output as bridge input and Sr4 has 120vac as input as wired in the welder itself. The test was with 70vac input and the bridge output into a 100ohm resistor, with the oscilloscope across the resistor.

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            Both looked good on the scope, 2nd pic has some kind of interference phenomena between scope and camera.

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            • Sr3 and Sr5 are higher current bridges but very low input voltage as wired in the welder. 15Vac for Sr5, 30Vac for Sr3. I tested both at the rated voltage, and then over the rated voltage.

              Sr3 at rated input voltage of 30Vac
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              Then Sr3 at 50Vac. It is clipping the top of the waveform, and the peak inverse voltage is exceeded, causing quite a bit of current to flow the wrong way and causing significant heating of the bridge. This test was very brief to avoid damaging the bridge

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              Sr5 at 15Vac

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              and at 30Vac. Here again, there is reverse current leakage causing bridge heating and waveform clipping

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              So, it seems the large one had almost completely failed, and the smaller ones were still functioning as they should.


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              • Far better off than than the big ones were, but it appears they are not equal in cutoff voltage at the bottom of the trace--they were on their way out.

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                • You watch funny TV.

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                  • 2 guys, both genius, even part time,,, 2 months, they be a steal at 6 grand for labor.

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                    • Originally posted by Aeronca41 View Post
                      OK. Let's do the black ones in the second picture first.

                      Looks like the black one on the left (SR4) has wire 64 going to its left and right terminals--two connections (2 wires numbered 64), but tied together by the rod at the back bottom of the rectifier. You will have to connect those two wires together somehow, and then put the single result to the MINUS (-) terminal on the new bridge. Wire 63 goes to the PLUS (+) terminal. Wires 4 and 21 go to the AC terminals, doesn't matter which one goes where on the AC terminals.

                      For the black on the right, (SR2) wire 37 to PLUS, 35 to MINUS, and wires 36 and 3 to AC.

                      For the two big orange ones:

                      First replacement (SR5):
                      Wires 44 and 43 to MINUS and PLUS, respectively.
                      Wires 42 and 41 to AC

                      Second replacement (SR3) :

                      Wires 45 and 24 to MINUS and PLUS, respectively.
                      Wires 32 and 47 to AC
                      Here's how to identify the terminals on a bridge rectifier. In the event you find a bridge with all 4 terminals oriented the same way (highly unlikely, but possible, I suppose), they will identify the positive terminal by clipping off that corner of the plastic at a 45 degree angle. All the rest of the info below is the same.

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                      • Been away from this thing for a bit, what with the heat wave here in BC. Too darn hot to do more than try and keep cool. Anyway, finally checked and double checked all the wiring and it seems to be okay. Now, the final test, connect the scope to the output leads and turn it on. No columns of smoke issuing from anywhere, so far so good.
                        Here is the AC output waveform
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                        and DC straight polarity
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                        and lastly, DC reverse polarity
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                        This was with no loading on the output terminals, as in no welding. Once we get some decent temperatures here I will try burning up some rods.

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                        • I’m getting ready to swap out my selenium doofloppies with the diode seeberdeebers, but I don’t have the flux capacitor to see their wave form on my TV, so I’ll just have to hope for no smoke leakage.

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                          • Lookin' good. Check the smoke seals before you start.

                            Ryan, I am absolutely amazed that a guy of your intellect and esteemed social standing wouldn't have a couple of extra flux capacitors in the shop! What's this world coming to?

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                            • The world is in shambles. Just take a look at Washington DC, it’s full of....”oh man....”

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                              • Is that machine choochin there, wingnut? I’m about to get started on mine and I’d prefer you be my huckleberry.

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