video Easiest Microwave (MOT) Salvage/Re-use Tutorial
These videos show you how to take any broken microwave and get the transformer out of it, tear it down, and rebuild it according to whatever project you have that needs one. These form the heart of many other projects, which I cover (or will cover if not out yet) in other tutorials.
Hopefully every question you might wonder is explain in detail in the videos. I give plenty of alternative options for tools and methods.
Part 2:
Part 3:
I'm a big proponent of criticism and feedback. My first video had some audio issues. I made parts 2 and 3 several months later after feedback and I think they're much better. Please leave comments if you have any suggestions for improvement, criticism, things you thought were poorly explained, etc. I read it all and it helps me make better tutorials in the future.
Hopefully every question you might wonder is explain in detail in the videos. I give plenty of alternative options for tools and methods.
Part 2:
Part 3:
I'm a big proponent of criticism and feedback. My first video had some audio issues. I made parts 2 and 3 several months later after feedback and I think they're much better. Please leave comments if you have any suggestions for improvement, criticism, things you thought were poorly explained, etc. I read it all and it helps me make better tutorials in the future.
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More turns on the primary *is* better. But the wire used must be capable of supporting the amount of current through it that will be pushed through it.
That's why transformers have size, and more power requires larger transformers. Else, you'd wrap 120 turns of 26g wire and use a much smaller core and it would be the size of a walnut rather than a softball.
If you used a 2000 turn 16g primary, note how gigantic the core would have to be to fit all those turns in. But it would be super efficient. Transformers are already 80-90% efficient, so, meh, minimal returns, close enough for me to not worry much.
I can't condone playing with high-amp sparks, but, almost everything can be done with reasonable safety if appropriate measures are taken.
High-amp sparks are mostly heat. Just be sure to avoid high-voltage, which will kill you instantly. Ignore anything you read otherwise, voltage (above 50v) is what is dangerous. And the higher it is, the more dangerous it becomes.
Technically, yes, that will work fine.
In practice, you probably will not like the limitations.
I already gave you the tools to answer this yourself, (mostly in Part 2) so, you're just missing how to work it through in your head.
What did I say happens when you reduce wire size? You reduce the amount of current (amps) it can handle without overheating. So, if you reduced the wire cross section on the input, down to about 10% of the original (16g --> 26g), you've reduced the current the primary can provide without melting the wire. BUT.. you've kept the input voltage the same (Still 120v).
So yes, you can end up with the right output voltage if you followed the turns ratio math. BUT, your current (and/or power) is still dropped to 10%.
Your bottleneck in this case is not the magnetic limit of the transformer, it will still attempt to do its job. But the wires will melt as it happens. Let's use some (guessing, but probably pretty close) numbers:
Suppose:
- 1000W-size transformer core
- 120v socket
- 16g (0.0508", 1.29mm) original primary
- 120 turn original primary
- 26g (0.0159", 0.40mm) original secondary
- 2000 turn original secondary
Now you could proceed 2 ways:
1 - Just look up what a given wire gauge can handle in terms of cooling for current (there are different ratings depending on circumstances).
2 - Figure it out based on what you've been given. You know it was designed properly in the first place, so, what was that original 16g wire rated for?
Amps = Watts / Volts
= 1000w / 120V
= 8.3 amps
And if you look up electrical tables, that's roughly in the ballpark of what 16g can withstand without overheating when packed into a small area with some fan cooling. So, let's use that number and scale it.
You now have wire with 10% the cross section, so it can withstand 10% of the current. 10% of 8.3 amps is only 0.83amps. Now, that wire can withstand 0.83 amps flowing through it whether it's given 1 volt or 1000 volts. Wire doesn't care. The only thing that might matter at some point is what voltage is so high it punches through the wire's insulation. But that doesn't matter because you haven't changed the voltage, you're still just plugging it into the wall.
Power = 0.83 amps * 120v = 100 watts.
Now, the core is still the same size, so it will still attempt to transform up to about 1000w before it starts to strangle itself. What do you suppose happens when you try to push 8.3 amps through a 26g wire that would in that circumstance typically only be rated for 0.83 amps?
Smoke. Melting. Fire.
You'll notice we haven't even started talking about the turns ratio yet. That's because it doesn't matter. If you do the math right and build the coil right you can get your output voltage right.
...
So, there's your answer. The next part is, are you asking the right questions?
Why do you want to use the secondary as the primary? Why not just use the original 16g one? Did you damage or lose it or use it for something else? What do you want to melt metal for? Is it from another project? What did those project specs say to do?
1 - MOT projects tend to trip breakers frequently, at least until you get the hang of them. In your case, this will mean buying a new fuse each time, not just flipping a switch. Might get expensive. Also, the fuses should say on them what current they're rated for before they blow.
2 - If I understand you, you're thinking of creating a ~17:1 stepdown transformer by powering the ~2000 turn secondary off the mains, and using the ~120 turn primary as your secondary, thus giving you ~6 volts?
Yes, this will work. But your input current (and thus power) will be limited to the current that that tiny secondary wire can support. The bigger 14g wire on the primary can support ~15 amps. The tiny 28g wire on the secondary can't even support 1 amp without melting. Let's say 0.75 amps.
So, 120 volts in, with wire that can only support 0.75 amps. P = I * V = 120 * 0.75 = about 90 watts.
So you've turned a 1000 watt transformer into a 90 watt transformer. But, it still works, in a desert-island scenario where you need a 6v, max 15A output.
Or, now that I re-read your comments, you want to replace the primary. Okay, your volts and amps mix will be whatever you coil them to be, but you will still be limited to 90 watts because of the input/primary side.
Normally, by re-using the primary, you dodge all these issues because the original primary was already set up to handle the same voltage and current that the primary needed.
Besides, legally, all electrical repairs or modifications must be performed by a professional electrician.
At $2.50 + tx per fuse, just trying would be quite expensive.
2- Since I'm not that good at maths, I thought you could pull any power out of the secondary provided you have enough turns / gauge.
I guess it would work if I added one breaker per transformer, but that could quickly become expensive.
You could also plug it into your kitchen instead. 30A at 120V is quite a bit of power, you would almost surely be fine plugging in any MOT to that, as long as you weren't running other heavy-draw appliances at the same time (blenders, microwave, etc).
What MOT-projects and what would you want to use them to make?
In fact, I already blew the fuse once by mistakenly starting the microwave (not a donor!) and the countertop oven. The panel door is long lost, so I had to check every plug and light to know which was which.
I mainly intend to do this project out of curiosity, learn soldering, then do quick repairs. For example, I'm sitting on a chair with a broken retainer. I repaired it once using riveted aluminum plate, but it seems too soft for the leverage applied when sitting, so I had to install steel wires joining the armrests behind the back of the chair. This doesn't look very good.
I am reasonably sure you could just plug an MOT stick welder into the kitchen circuit and be fine. It is probably worth the cost of a fuse (once) to gamble on it. If I'm wrong, you'll be out an extra $3. If I'm right, you'll save ~$12.
I'm retired from Ford Motor. Our Body Shop transformers are 50-kva to 100-kva and fed with 460-volts. The primaries are fused at 400-amps with 4/0-AWG wires. These transformers are water-cooled at 2-gal./min.
A typical 1/4" spot weld in two thicknesses of .020" sheet metal requires 20,000-amps at seven cycles (and ~4.5-volts).
The secondaries produce so much magnetism that carbon steel bolts on the jumpers are disasterous. They heat, loosen, and burn off. We must torque 1/2" stainless steel bolts, washers, and nuts very tight. They last because stainless isn't magnetic.
I realize you aren't making 1/4" buttons and that your duty cycle is very low, but still, spot welding requires a lot of power, tip pressure, and a good timer for 'squeeze', 'weld', and 'hold' times. The only way to tell if a weld is good is by destroying it. (just my 2 cents)
Spot welders do not need good timers. I have one, it works without. Most home and comercial (non-car factory) use do not timers of any sort. They have a thumbswitch for power and a lever for pressure. Braindead easy stuff.
Like many things, you can add features and complications if you are doing mass production or want to take a human element out of it. But to anyone building their own spot welder from junk, this does not apply.
Also, you can make your own timer mostly from microwave parts too.
Thanks for the feedback though, it's nice to have a frame of reference for what the big boys do.
anyway i've come across this transformer its HID ballast transformer in the picture.
the strange thing about this transformer that the primary and secondary coil is connected together, and the core shape is strange not the regular E I but I T I
anyway the third strange thing is the thinner wire coil is the smaller coil
and the thick wire coil is the larger coil.
i understand that this transformer is 480 volt but what does that mean, if the primary was 1 round per volt that means 480 round per coil if it runs off of 120v does that mean the transformer will be more efficient .
i'm trying to figure the best way to utilize this transformer either as a power supply or a spot welder.
I wish you would explain it to me
thank you
Ballasts are not transformers. As I understand, the cores are not internally continuous, there is a gap. If so, I don't think they'll work as a transformer. If you cut off the outer "I" pieces, is the "T" piece full length? There's certainly a lot more grinding to do to these to get separation but it might be possible.
The "1 turn per volt" does not apply to these, that is a rule of thumb for microwave oven transformers only and does not apply to other types and especially other sizes, like I said in the tutorial.
I can't help you on this one, since I don't know much about ballasts. I could search for schematics or cross sections and learn, but I'd have no advantage over you doing the same.
http://www.youtube.com/watch?v=dylJMpzRn5k
it's not that hard to separate the core I from the rest of the core and yes the T column goes all the way to the bottom.
I think it's doable but the only downside is that as the primary coil has about 4 turns per volt then to achieve the 2 volts needed for a spot welder i would need about 8 turns of heavy gauge wire that can handle 500 amps which about 3/4 of an inch in diameter seems unrealistic
Moving on, the rule for a spot welder isn't "1 volt", it's really more "1 turn". Even the big welders that weld car bodies are still 1 turn IIRC. So, you're not looking to add 8 turns. You should still add only 1 turn, 8x as thick as you would have.
500 amps is not a lot of current for spot welding. It's about the bare minimum for the thinnest of materials and smallest contact areas.
Figure you should fill half your transformer with the primary winding (about the same thickness as the wiring of the socket its plugged into, no point in going thicker, so, generally re-using the primary is fine). The other half, roughly should be the secondary. In a spot welder, the secondary is a gigantic single turn. It can be solid copper, stranded copper, scrap bits of pipe and sheet soldered together at the ends or hoseclamped into a bundle, doesn't matter.
A spot welder doesn't need any voltage really, since the output is a short circuit with no load. The only resistance in the circuit is the wires and metal material being welded itself, all in contact.. This yields only the tiniest fraction of an ohm, which means the tiniest voltage can cause massive amps to flow, which is what does the welding. Current = Voltage / Resistance.
Lastly, if you're looking up current carrying capacities of wire, ignore that. It's off by an order of magnitude usually. Spot welds take fractions of a second, up to about 5 seconds max. Then there's lots of time to reposition before the next weld, so your effective duty cycle is tiny. For welders with high duty cycle, the electrodes have hose/tubing nipples on them so they can be water cooled.
Look at a picture of a spot welder some time and look at how thick the arms are. 1" thick bar is quite common even on a smaller welder.
The spot welder video is scripted and half filmed, it just takes time. I think I will have to reduce the quality and thoroughness of my videos, 'cause, at this rate, 2 or 3 a year is so slow it's frustrating for me. I thought I'd get the next video out in 2-3 weeks, it's been 4 months.
I know exactly what you mean about editing videos it takes so much time but the quality of editing isn't really important as the quality of information .
so don't feel that it needs to be perfect because nothing is .
To join the wires: Separate them about 2" back. Lay them out flat and separate like a comb. Then scrape them a bit with a butter knife, wire brush, or something else. Not much, then take a thick piece of copper wire and wrap it around them tight, 3 or 4 times at the back of the 2" , very very tight, crushing them together. You could also use a hose clamp.
Then, heat it up using a blow torch, or stick it on the element on your stove. Shove solder into the copper wrap. If the wire was scraped, the solder will work its way into the wire and melt the insulation back. Alternatively, just blowtorch the wire ends completely, from every side, incinerating the enamel. Wait for it to cool, brush the comb part on all sides with a wire brush, maybe use acetone or vinegar to remove the oxidation, and then secure them all together with a hose clamp.
Another thing I like to do is then wrap the end of a copper pipe around the last 2", with an extra 2" sticking out. Bash the copper flat/rectangular and then torch that and fill it with solder. That gives you a nice heavy mounting lug that you can drill a hole in a put a bolt through.
1.There is any formulas for how much amp's will be generated for every turn made on the secondary coil?
2. Do i really need 2 MOT's to build a arc welder or just a 220V one will do the job?
Maybe ask a followup on your purpose, because asking this kind of question implies to me, that you're trying to solve a problem backwards. In almost no situation do you care about matching amps, you care about matching volts. If you're asking about a welder, set voltage to 30V, figure out how many turns, and you'll find out how many amps you'll get.
Any time you know the desired output volts, you can check the max amps from that transformer by doing Wattage / Volts = Amps. So a 10 pound transformer will be ~1000 watts short term (a few minutes), if you have 12v output... 1000/12 = 83 amps max.
But... to answer your question anyway:
First, find out the max amps on the primary side. Wattage = Volts * Amps.
Guess wattage by weight 100w/pound. Volts will be socket voltage (120, 240).
So, for example, 1000w / 120v = 8.3A max on the primary.
The amps ratio will be the inverse of the turns ratio (or volts ratio, same thing).
For example, if your volts or turns ratio is 10:1, your amps ratio will be 1:10.
So, 120V to 12V is 10:1. Max amps was 8.3A, now is 83A.
120V to 60V is 2:1. Max amps was 8.3A, now is 16.6A
There's not a formula for "each turn", since the ratio changes with each new turn you add. It drops as.. a logarithm perhaps? I forget my math terms.
2 - Primary Voltage does not matter in terms of transformer capacity. Whether starting at 120V or 240V, a 1000W transformer is still a 1000W transformer.
The only thing 240V helps is that usually they still use wiring as heavy or heavier than 120V circuits, which means more wattage is available from the socket. So you could hook up multiple transformers without blowing a breaker. Make sense?
So, probably yes you do need 2 MOTs. But it depends what you're welding. You might be able to burn 1/16" electrodes with a single MOT on thinner steel. Thicker (most cost effective) electrodes require at least 1500W, if not more.
Also, if you use two MOTs, you have twice the heatsinking ability for the same load, which means double the duty cycle which is convenient.
Nothing says you can't hook up 10,000W of transformers to a 1,800W circuit to ensure you can burn 1,800W all day and night without overheating the transformers... just know that you can't max out those transformers without tripping the breaker. Electrode size is the biggest thing that determines how many amps will actually draw. Thick sticks will try to draw more power, thin ones will be self-limiting.
Thanks again!
Let me start by saying that this is an awesome tutorial and gave me awesome ideas.
After watching your videos I decided to build a spot welder, which I did, but I'm having some problems...not being an expert in this kind of things I think that my spot welder lacks "the power" to weld.
It makes the metal sheet red hot but it takes some time and does not weld.
I'm using a 700W MOT (at least that's what it says in the microwave) and 240V.
I did 2 turns in the secondary and I have an output of 2,4V.
The wires are 1cm thick with 6mm copper core, is the insulation too big?? Is the core too thin?? Since I'm not yet finished with my design There's an extra 1m of wire from the MOT to the "claw"...problem??
For the "claw" I'm using solid metal grounding rod (that I thought to be copper but I have my doubts)
The connection between the "claw" and the wire is still improvised and it's basically the wire and the rod tied together with copper thin wire.
These are the areas where I think the problem might be....
Any help/tips would be great....
Sorry for the long post.
Pedro
Portugal
1 - Simply not enough power, no matter what, for that material thickness. Need more wattage.
2 - Not enough pressure, clamping pressure needs to be harder. Occasionally, it could also be too hard and cause this.
3 - Could have poor connections between the claw and wires. Very low voltage means connections need to be very good. Connection needs to be heavy wire everywhere, no thin parts, and lots of surface area at contact points (use washers and bolt to help).
4 - Use 1-turn secondary instead.
5 - Secondary wire is not thick enough (my guess is this one). Add more copper. Any copper is fine, use the existing stuff plus more.
6 - Could be surface corrosion/oxidation on the metal, but not in your case because it is heating red hot.
Glad to help Pedro. Let me know if any of these work.
However, you may not be limited as much as someone in North America in terms of how big of an arc welder you can power off a single circuit. You can connect more transformers in parallel.
In most homes in North America, there are 15A breakers. 120V x 15A = 1800W. I don't know what's standard wiring size in Europe, but 220V (actually closer to 240, but measure it), if it's the same wire and breaker size.. you could get 3600W.
Bottom line, this means you can hook up 3600W of transformers and with double the wattage, you can burn double the stick size as an American without tripping the breaker. Make sense?
Research where your breakers trip at first though.
Not too much though, there's no such thing. Extra capacity you don't use is fine. If you bought a nice welder that's what it would be. You just need 4-12 MOTs. I've seen welders with that many. An advantage to doing this is that you wouldn't be hampered by duty cycle. Transformer-based welders are limited to 5-20% duty cycle (30 seconds to 2 minutes on, 8-9.5 minutes cooldown). With extra capacity, you could weld thinner sticks at 100% duty cycle, never having to stop to cool down.
There's lots of upgrades you can make to a standard stick welder, right up to the point where you'd turn it into a TIG welder. I'd get into it, but, it's long to type and will appear in a future tutorial.
Or, you could connect them in "series." That is, you take however many you will hook up, and wire them for 1/x volts. So, 6 transformers would have 30/6 = 5 volts each, all connected head-to-tail, adds up to 30V. It's electrically the same in the end.
There are tricky parts to both. Mainly making sure you have the right "phase" for both input and output, or they would cancel each other out rather than add up, and possibly blow a breaker. Sorry, but until I make that tutorial, you'll have to do your own research and teach yourself. I could write it out but by that point I'd have a whole other tutorial here in the comments.
1 turn secondary? That makes a spot welder. You won't be arc welding anything with it. 24-36 turn secondary to arc weld (shoot for around 30-36V). Or if in series, half that each.
A 1 turn secondary would allow ~1200A, but air has too much resistance for the 1V for electricity to arc through the air. You start having enough voltage around 24V, but aim higher or your arc will keep going out any time you shift it. That means you'll be around 30-40A per MOT. Which is enough to arc weld.
If the "I" piece split, along the laminations? No problem. Tiny bit of epoxy or glue and you're fine. Sometimes it's hard to get glue inside to dry, so I just put glue on the outside at the seam too, sometimes with a piece of paper or cardboard to help hold tension. Bolts are better. Neither will cause any noise. You're fine.
For wattage, weigh them. 100w/pound (200w/kg) for short duty cycle use.
I think 100A @ 30V should be doable, that would be 30V * 25A = 750W each, and that would be a small/medium microwave transformer, so unless they're tiny, you should get your 100A when combined.
DO NOT drill that hole. The transformer will not work at all if you do that, all the magnetic flux will short through the copper.