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OT Converting a AC driven welder

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  • OT Converting a AC driven welder

    Hello welding minded folks, I've got a 200 amp Airco welder thats of the old motor-generator type. I opened up the unit to inspect the layout and wiring. It apears the 3ph line only goes to the motor and the dc generator portion is isolated. Due to it's small size I got the thought of trying to convert it to a portable unit. With the cooling fan shield removed there is direct access to the motor shaft. Would it work to attach a gasoline engine, via a flexible coupling, to drive the generator? The name plate specifies motor rotation of 3500 RPM. All AC wires would be removed for safety reasons.

  • #2

    Are you sure it's a 3-phase powered DC generator? It's very easy to convert 3-phase to DC without using a generator so I'm wondering if it's really a single phase A/C motor/DC generator?

    Regardless if it's a 1 or 3 phase motor DC generator, you should be able to turn the motor generator with a portable power plant.. and power the welder. I can't see any reason why it won't work. Just make sure you have a strong enough engine to maintain RPMS durring load on the DC side.

    -Adrian

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    • #3
      Yes it can be done. When you seperate the motor from the generator there will have to be an endbell with a bearing to support the gen. shaft. If the gen does not have the support bearing. Some sort of endbell with a support will have to be made.

      Years ago I had a welder made this way. The gen was driven with a V belt though. I used a walkashaw 4 cylinder engine. It did work very well but a lot of work to get an portable welder.
      Don\'t ask me to do a dam thing, I\'m retired.
      http://home.earthlink.net/~kcprecision/

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      • #4
        I figure you will need at least 10 "real" horsepower and more would be better.
        Free software for calculating bolt circles and similar: Click Here

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        • #5
          <font face="Verdana, Arial" size="2">Originally posted by Evan:
          I figure you will need at least 10 "real" horsepower and more would be better. </font>
          Nonsense.... 10 "fake" horsepower is far superior.. Buying, Feeding, and maintaining 10 real horses would be costly and also very messy..

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          • #6
            Been there, done dat. I just bought a new push lawnmower. It has a very similar Briggs engine to my 25 year old one. Same size, almost identical engine. The old one is rated at 2.5 hp. The new one says 4.5 hp. Yeah sure.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              The throttle control is the bugger. Need a Real RPM ball govenor.

              I sold one like what you described for $35. It never occurred to me to convert it. I am down to 3 big rusting hulk 3phase welders in my yard. Anyone need a 400 amp welder?

              David

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              • #8


                Here is how you calculate how much HP (torque really) you need to turn your generator. For a 200amp welding rig, I'm assuming you would power it with up to 11,500 watts (or your typical 50A 230v receptical) I.E: 50A * 230V = 11,500 watts. You said your generator is 3500 RPM and that's also used to calculate how much torque you need. We'll assume you have a 11,500 watt generator.. If you know how many watts it really is, tell me.

                Torque (N.m) = (11,500 watts) / (2*Pi*3500 RPM/60)

                Equals 31.376261 Newton meters (N.m) of torque required.

                lb/ft = 31.376261 (M.n)/ 1.355818

                Equals 23.141 LB/FT of torque needed.

                Horsepower = (23.141 LB/FT * 3500 RPM) / 5252

                Equals 15.422 Horsepower...

                So, if you want to generate 11,500 watts with a super efficient DC generator, you'll need over 15 horsepower.

                -Adrian

                Code:
                /**********************************************************************/
                /*                                                                    */
                /* Created 05-11-04: Adrian Michaud                                   */
                /*                                                                    */
                /* Generator Horsepower Calculator                                    */
                /*                                                                    */
                /**********************************************************************/
                
                #include &lt;math.h&gt;
                #include &lt;stdio.h&gt;
                
                #define PI 3.1415926
                
                void main(int argc, char **argv)
                {
                double rpm, watts;
                double nm, lbft, hp;
                
                   if (argc &lt; 3)
                      {
                      printf("Usage: hpcalc rpm watts\n");
                      exit(1);
                      }
                
                   sscanf(argv[1], "%lf", &rpm);    /* RPM of the generator.      */
                   sscanf(argv[2], "%lf", &watts);  /* WATTS output on generator. */
                
                   /* Calculate how many Newton meters of torque needed at max output. */
                   nm =  watts / (2 * PI * rpm / 60.00);
                
                   printf("%lf Newton meters of torque are required to generate %lf watts\n",
                      nm, watts);
                
                   /* Convert newton meters to lb/ft. */
                   lbft = nm / 1.355818;
                
                   printf("%lf LB/FT of torque are required to generate %lf watts\n",
                      lbft, watts);
                
                   /* Calculate how much horsepower is needed to drive the torque/RPM. */
                   hp = (lbft * rpm) / 5252;
                
                   printf("%lf horsepower is needed to produce %lf watts\n", hp, watts);
                  
                }

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                • #9
                  Someone who used to work with me did that conversion . I think he used a 4 cylinder gas engine out of a wrecked car ( free).He said he had hell of a time rigging together a governor. It worked pretty good....

                  Comment


                  • #10
                    Use a 4 cyl car engine and a cruise control.
                    Free software for calculating bolt circles and similar: Click Here

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                    • #11
                      <font face="Verdana, Arial" size="2">Originally posted by Evan:
                      Use a 4 cyl car engine and a cruise control.</font>
                      This might prove impractical. As the cruise control works on vehicle speed, you would have to drive while welding. This would occupy the hand normally used to hold the cell phone, and the hood might interfere with vision.
                      Jim H.

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                      • #12
                        The aftermarket cruise control on my Ranger picks up speed from the distributor. It would work just fine.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          I thought a lot of cruise controls worked on vacuum. If there's anything wrong with the vacuum circuit the cruise won't work. IMO-HOO (In My Opinion-Humble Or Otherwise)
                          - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                          Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

                          It is true, there is nothing free about freedom, don't be so quick to give it away.

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                          • #14
                            If there's anything wrong with the vacuum circuit the engine won't work either.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              Real cruise control systems apply gas when the MPH drop below the set point, and also apply brake when the MPH increase above the set point. Cruise control systems need to maintain the driveshaft RPM, not the engine RPM.

                              The vacuum system is just a tap off the intake manafold and is used to power accessories and sometimes emmision control systems but it doesn't prevent the engine from running. In fact, we block off the vacuume port when we use the engine without the accessories.

                              Cruise control either use the vacuume system to power the throttle/brake accuators, or it uses electric power for the accuators.

                              Cruise control does not maintain RPM, it maintains MPH so using the RPM from a distributor is not cruise control. Going up a hill with an automatic transmission might cause the tranny to down shift and the RPM to jump.. RPM and MPH are only constant in ideal conditions (Driving on a perfectly consistant road in a vacuume with no stearing inputs).

                              -Adrian


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