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What went wrong?

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bowdenjeffery

New Member
I am a total electronics noob and am trying to pick it up through experimentation so all help is useful. I found a microwave today during bulk pick up which i salvaged the transformer for to build an arc welder. I also decided to take out some of the other components motors, ect.. to play with.

So i decided to hook the fan into the plug cable and see what would happen... I wired the two close wires on the fan to the two voltage carrying wires on the plug and the ground to the third one. The fan says 120 volts, .3amps, so I figured it would work. I plugged it in and it spun real fast for about 15 seconds and then sparked and smoked and died..

As part of the learning process I want to know what went wrong.. Were the amps from wall too high? Would adding resistors in the circuit somehow have fixed this problem?
 

Mike_2545

Super Moderator
Hi and welcome to the forum.

If you are new to the field of electronics, its best to stick with low voltage 'experiments' at first, so as not to create hazardous situations.

The microwave you salvaged out of the trash could have any number of things wrong with it. A motor does not need resistors to limit the current so it could have been on the fritz to begin with.

I would not think that a microwave transformer would make a good arc welder, no matter how hard you try.

Stay safe
 
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Sceadwian

Banned
Makes me wonder too, from what little you said sounds like it should have worked. I know I've hot wired 'regular ac' fans before and they work fine, not sure how it was wired from the microwave though, it very well could have been in series with something else, the question is did you pay attention to what else it was wired with when you took it apart? It may have been because the motor wasn't loaded? That's a bit of a stretch but I'm not sure what else to think of, mind you I'm pretty week on the varied abilities of motors.
 

bowdenjeffery

New Member
I would not think that a microwave transformer would make a good arc welder, no matter how hard you try.
There are several guides for making them throughout the internet.
such as :
Build a Microwave Transformer Homemade Stick/Arc Welder

You just have to recoil the secondary windings to make the transformer work.

Thanks for the advice though..I will proceed cautiously. Its bulk pickup in my neighborhood so theres lots of good things to scavenge.
 

tcmtech

Banned
Most Helpful Member
Most likely what you had was a dual purpose motor. That is it has the normal line voltage winding and a second low voltage winding to power the electronics.
This is very common on cheaper stuff. The motor supplies the low voltage and works just like a step down transformer.
By combining the step down transformer and the fan motor into one unit it saves manufacturing costs.
You most likely picked the low voltage secondary and used that at full line voltage.

Dont ever try using a microwave transformer for a welder! Its output is high voltage an lower amperage. A welder uses low voltage at high amperage.
The microwave oven transformer will kill you before you ever get one weld done!

If you want to make a welder use the transformer out of a big battery charger.
 

bowdenjeffery

New Member
my other post is being moderated but basically you have to rewind part of the transformer to make the amps high enough. Search Google, lots of people have made microwave arc welders.
 

Mike_2545

Super Moderator
Yes, but they use two microwave transformers. And rewind the secondary.
Then you end up with an AC stick welder.
 
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tcmtech

Banned
Most Helpful Member
If your rewinding then your fine!
I do welder and plasma cutter repair as part of my business and you would be scared to see what little people know about electricity and welding in general. It surprises me still!
 

Sceadwian

Banned
Don't worry mike, death isn't too common, it's the horrible maiming. That being said... Have fun be safe =O
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Don't worry mike, death isn't too common, it's the horrible maiming. That being said... Have fun be safe =O
You certainly need to be VERY careful, 240V mains is really pretty 'safe', you have to work really hard to get it to kill you (or be very unlucky) - but a microwave oven transformer will almost always kill you.

I only know of one case of an engineer getting a shock from an MOT, he died - but by some lucky coincidence the paramedics were already on the same street - and they managed to bring him back to life. However, he was never quite right afterwards.
 

mneary

New Member
I think that the folks here are taking the MOT safety discussion a bit more lightly than has been customary here. It's not a toy for a beginner. Period.

If you don't have clear plans for what you're going to do with 1kVA of 3kV, there are better things to be plugging into the wall.

Maybe it's late and maybe I'm grouchy, but I had to write this.
 

jrz126

Active Member

mvs sarma

Well-Known Member
Excellent photos Bill !!!

the guys need to be seriously cautioned in their and our own interest too.
 
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