Build a Microwave Transformer Homemade Stick/Arc Welder


Step 6: Wire your two transformers together

Picture of Wire your two transformers together
Why do we use two transformers?
Just one of these isn't big enough to make a really juicy welder.
If you happen to find a big enough transformer somewhere, feel free to use that.

Here's how to hook up two transformers.
First we wire both primary windings in parallel to the wall cord.
Then we wire the thick secondaries in series so they both"Push and pull" in the same direction.

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OVERLOADED3 years ago
does wiring the sec in series also give you double the voltage ?
No. Wiring in series boosts current. Wiring in parallel boosts voltage.

I know it is an old post, but wiring in series raises voltage, not current. Wiring in parallel raises current.

Also be carefull with your transformers, make sure they are the same gauge thickness and windings, preferably exactly the same transformers. That can bring you trouble both in long term and short term use.

Great project, waiting for my microwave oven to go down so I will give it a go ;)

thx wasint too sure about trans or even why i asked that question so long ago?
would the transformer out of a golfcart charger be enough to use by itself for a welder? and how would u wire it?
archer12325 years ago
Do you even hook up the green ground wire to anything on the transformer? I dont get it. :/
TimAnderson (author)  archer12325 years ago
green goes to the cabinet. It's not supposed to carry any current. It's just there so a a loose wire that touches the enclosure will blow a fuse instead of giving you shocks.
should the green be hooked up to both cabinets? and a cabinet is the transformer right? lol
It wouldnt be a bad idea to hook the green wire up to both the transformers so no madder what you do or wat happens they stay grounded.   
So basically you are just hooking up two wires to each tranformer(positive+negative)
fast400ex4 years ago
First of all, I would like to say PROPS TO YOU for this awesome project; I really want to try it. But I have a couple questions. If 10 gauge wire like, what is in an extension cord? (Bare with me, kind of a newbie) so this welder requires one outlet plugs, correct? Would it be possible to add more transformers for higher amperage? Do you strip the ten gauge down to bare solid copper? And you wrap it where the original smaller wire was right? Also, in the schematic, how are the existing primaries connected to the new 10 gauge windings? Okay, so I think I’m figuring this out a little better, connect the original windings together and connect the new windings together so it is two long lengths of wire? And connect the negative of the one outlet plug to the smaller wire guage winding and the positive to the larger? Or what? Sorry I am just slightly confused by the wiring. sorry if I sound like an idiot here, but I would appreciate a response because this is an awesome project I want to try.
also, whats the final output? and would there be a way to change it? like a large potentiometer or something?
Hubiewan4 years ago
Hubiewan asks, have you tried three transformers for use with thicker rods?
Garik_axper5 years ago
In the schematics you have 2 electric cords that plug in the wall outlets,but here you are running the primaries parallel to one wall outlet . Am I missing something ? BTW thanks for this Instructable, you guys are geniuses :)
what if the wire isn't insulated is it okay if wired it up anyways just respond somewhere above or msg me at
kekeiffer6 years ago
not to prove my ignorance here... but what would happen if you tried to beef up this design by adding two extra transformers.. 4 insted of 2? ive seen plans for an ark welder with 10 but thats too out there again there is probably a logical reason just wondering why not four
rndmnmbr7 years ago
For the next one, you might instead try making it run from 240v instead of regular 120v wall voltage. 120v breakers are usually 15 amp, and wired like this you're pretty close to throwing the breaker every time you weld. 240v has two hot lines and one neutral, each hot carrying 120v (if you look in your breaker box, you'll notice that you're getting 240v off the pole, which is split into two 120v circuits by simply splitting the wire). Just run one hot to one transformer and the second to the other, and combine them back on the neutral. 240v breakers are generally rated from anywhere between 20 and 30 amps, which is plenty, plus the cross phases of the 240v will make for a better, easier weld. For reference, the best weld with standard 1/8" 6011 welding rod is done around 90 amps, or for the slightly less standard 1/8" 7018 rod is 130 amps. Most 120v welders, even set up like this, welds 6011 moderately to poorly and can't weld 7018 at all.
MrV rndmnmbr6 years ago
You mean that he should seriewirering the transformers togheter and run them on 240v?
micojoy6 years ago
how am i going to know the number of turns in the primary? that's the only way i can solve the number of turns needed in the secondary winding because we can assigne the volts in our own need.
MrV6 years ago
If I going to use this welder on 240v, as you recommended,serie wiring it. but is it important to follow the the step above? must the transformers be wired right, or dosent it matter?
TimAnderson (author)  MrV6 years ago
if your microwaves were made for 240, put them in parallel. if they were made for 110 but you're using them on 220/240/something, then put them in series.
when wireing this you want the plus lead to connect to plus or is it minus to plus? I can never remember.