Build A 70 Amp Welder
from microwave oven transformers!
AAAWelder is a free site where you can learn to build simple welders and other projects. If you have paid someone to access site content, you have been had. You should report the crime, with extreme prejudice, to the proper authorities. Randy Gross, aaawelder
Greetings do-it-yourselfers and thanks for the visit.
I am a veteran welder/fitter with 20+ years developing and applying my skills. I have worked in fab shops from the corn fields of Illinois to the ship yards of the deep south pitting my skills against world class welder/fitters. I recently completed a 70 amp welder built from microwave oven transformers. The experience was rewarding as well as enlightening. Few things compare to creating something that is unique, the only one like it on the planet. I take personal satisfaction in that as any do it yourselfer would. At AAAWelder, only the basics are given. Customizing the finished product is strictly your own. You are the artist, AAAWelder is the canvas, explore and create a masterpiece.
WARNING!!!!!! Proceed with the construction of this device at your own risk! If you are not sure of proper procedure and safety precautions, DON'T EVEN START! The energy produced by this unit can kill you if you allow it. Be smart. Be safe. Be aware!
How I Built My Welder
Step 1: GET THE TRANSFORMERS
There are several ways to do this. The method I chose was to call the Dept. of Sanitation and ask them to set several microwaves aside. When I told them what the project was, I got a few laughs and an O.K. Two weeks later, I had 6 microwave ovens. You will need 2 transformers for the 110v unit.
Step 2: STRIPPING THE UNITS
A word of caution here concerning the transformer: take care when removing the connectors from the primary coil (see Fig. 1). Sometimes the only thing that holds the coil ends in place is a piece of tape. Pulling or jerking could rip them free causing breakage or stress fractures in the magnet wire. Take the time to do it right. Remove the transformer. There are other things I remove as well: the cooling fan (you need 1 for the 110 unit), the power cord, the magnets from the magnetron (to be used in another project), and the wiring harness (wire from the harness can be used to run power to the transformers, cooling fan and on/off switch).
Step 3: Modify The Transformers: Phase 1
This is the make or break phase of this process. How and what you do from this point on will determine the results of your efforts. Programmers use a term that says it all: GARBAGE IN, GARBAGE OUT! Take your time. Do it right. If you feel yourself getting angry or frustrated, stop, drop everything, go and get something cold, come back later.
The secondary coil in both transformers has to be removed. I will explain my way, you may have one better. The important thing to remember is; do not remove the magnetic shunts. The transformers did not work properly; they kept tripping breakers.
The tools I used to perform this step were a common hammer and a really sharp chisel. The width of the chisel was less than the width of the core slot. Clamp the transformer to a stationary object (table, bench, etc.) as shone in Fig. 2. Place the chisel at the start point of cut # 1 (Fig. 3). Cut through the coil by striking the chisel with the hammer until you reach the stop point, which should be completely through the thickness of the coil. Cut through any remaining strands left by your first cut. Remove the clamp. Turn the transformer 180 degrees and clamp (cut # 2 should be at the top now). Repeat the cuts at cut # 2 until that section of coil is free. Remove section (Fig. 3). If you cut into the primary coil, get another transformer, that one is history. Strap yourself in, now the real fun begins.
As you can see from fig. 4 and fig. 5, the remainder of the secondary coils must be completely removed, including the 3 turn filament winding. I solved this problem by finding a steel bar that could be driven into the core slots without jamming and have enough area on the face to push the coils out in one chunk instead of thousands of strands. Good luck!
Transformer Modification: Phase 2
If you enjoyed phase 1, keep your belt buckled, you're going to love phase 2. This is where you get to rewind the secondary coils so that they will perform the way you want them to. The steps I describe in this phase are theory based on research and conclusions from my own experiments. I relate electron flow to that of water because they share the same characteristics. Everything you do to insure unimpeded current flow will get you the best performance from these transformers. With that in mind, let us proceed.
You need to determine, as best you can, the direction the primary coils are wound. Turn the transformers so that the connectors on the primaries are facing you. One will be going into the core (let's call this the in put for sake of clarity) and, the other coming out (out put). The secondaries of both transformers will be wound with respect to their primary winding. This is an attempt to keep the transformers in phase
with each other.
If you find that the primary is wound clockwise, simply reverse the procedure in Fig. 7.
The first three rows should go smoothly. The forth may jerk words out of you. I used a screwdriver with the spade taped over to pry gaps between the wire and the core. Your goal is 20 turns of #10 AWG stranded copper wire, insulated, 25 feet in length for each transformer. I reached 18 turns and my welder works fine. Once again, good luck!
Step 4: Specs and Test
Soft-wire the transformers according to this simple schematic. You can hard-wire this unit after it is working properly.
Do not apply power to the circuit yet. Locate tag ends of the filament winding and cap, as much as 13 amps can spill out. Do not include yourself in this circuit; a blast through your heart can kill you. Think safety before you flip the switch
. Tape the output wires to a non-conductive stationary object spaced a minimum of 4" apart. If you have followed the order of assembly, all that needs to be done here is to check the output voltage. With your voltmeter set to 50vac, turn the welder on, take a voltage reading, turn the welder off. If your lights are still on, you have passed the first test; no shorts. If the output read is not to specs, and reads approx. half, reverse wire the secondaries. If you hit the nail on the head, congratulations my friend, you now have a welder. Hard-wire your unit. No instruction for housing the unit is given here, that is a matter of choice, taste and individuality. I used the housing from an old radio transmitter I found at the dump. The housing from the microwaves can be cut and fashioned for the welder. The possibilities are endless.
This welder burns the 1/16" 6013 with ease. The 3/32" 6013 burns slightly cold because I did not achieve the full 20 turns each. So strive to hit the target of 20/20. I lay down a hot shining bead with the 1/16" 6013 and if I want a built-up weld, I run a 2-cap with the 3/32" 6013. This combo works just fine for me.
Keep in mind that although this welder uses a 110vac source, it is cranking out some major amps. A 20 amp breaker may not be enough for continuous use. A 30 amp breaker would be better. It seems I can weld forever with the 1/16" 6013, but the 3/32" causes trips when I weld too long. I hope this tutorial was instrumental in helping you to build a welder you will be proud of. I would like to hear about your success. If I overlooked something or did not clarify a point, I would like to hear about that too. If I can assist you at any step of the journey, please feel free to e-mail me.