microwave spot welder (help needed)

[jimmyhackers]

im half way through making my microwave transformer spot welder.

im up to the point of a single loop of high amp cable looped round once inplace of the secondary coil.
im using two screws as the contact points and the distance between them is not set yet.
the plug blew a 3amp fuse but is working on a 5amp
output voltage is 1.6ish volts and im unable to test amperage.

its working as in its making sparks and making things glow/fuse.

ive tried spot welding two relatively thin peices of metal together as you would tabs on a battery with little success

i think its a little low on power but im not sure hence asking.

anyone got any tips.

 

[circuit]

This could be useful for your project:
https://translate.google.com/translate?sl=lt&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fcircuit.lt%2F%3Fsection%3Dprojektai%26page%3Dwelder&edit-text=

 

[Syonyk]

What mains voltage?

If it's 110v and 4A, you should have ~275A, which should be plenty to spot weld. What type of electrodes are you using to weld with?

 

[jimmyhackers]

thanks for the info so far

im on 240v

the electrodes are galvanised screws screwed into the wire at the moment (bad i know)....im waiting for payday till i can afford some copper lug connectors and some heavy gauge copper wire.

i have had a look on a fair few other diy spot welders and difference i can see is the copper electrodes..so its probably that

i wasnt sure if the microwaves wattage had anything to do with transformer size....my microwave transformer was from a 700w
i get the feeling that most people that have done this have rather large 1000 - 1200w microwaves. is this the case?

im unable to get another loop on with my current gauge of wire but have noticed a few others doing 2 or 3 loops instead of my one. it seems this raises the output voltage......should i try finding some thinner wire and add a few more loops?

 

[SjwNz]

I just made a spot welder and had trouble making good welds, I tried more turns and then used two microwave transformers
with the primary's in parallel and even more turns on the secondary's with only a little better welds. One of my main problems was I was trying to
use some smaller diameter wire i got for free in the secondary and was trying to increase voltage to get more power. I ended up buying the biggest diameter wire that I could fit into the transformer. with a total of 3turns on the 2 transformers I then had a new problem, I had to much power I made a little timer circuit to set the on time of the spot welder and now I can weld 0.2mm nickle to the POS side of the A123 battery in just under 100mS or less and the welds are bloody strong. I had a quick play using Tungsten for the electrodes but they just lighted up like a light bulb so went back to copper.

 

[jimmyhackers]

thanks for the help..

ive got her working now.....was half down to my technique and half down to the electrodes.

i was turning the thing on before id made conact with the electrodes, making wastful sparks.

changing my technique had some improvement but welds were very weak.

then i replaced the electrodes with copper nails i found.

welds are good n strong now.

duty cycle of its like 10% though.

 

[markz]

Thats all it is, transformer, cut off secondary, low guage wire a couple wraps, plug primary into wall so thats 120Vac. Then need probes, so solid wire again low guage, file down to a point. Is the timing circuit easy to build, or can I buy for cheap off ebay?

Also wouldnt this type of tab welding heat up the battery more then just soldering.

 

[Ohbse]

While transformer based welding can obviously work, it's definitely not as good as a more precise microcontroller based capacitive discharge or DC battery powered welder such as the JP welder.

I've built both, in comparison the transformer welder is rubbish. As there are now better alternatives I would advise against starting a transformer based project.

 

[markz]

Yeah, I've been looking into capacitive discharge welder, pretty easy, only hard part is finding a cheap 1 or 2 farad capacitor. The other parts are all ebay. SCR, buck, dc-dc conv all pretty easy.

 

[kdog]

Hey JH
The MOT welder I built works a treat. A couple of tips that I found out along the way.
You must use copper electrodes bc the electrode-strip junction needs to have the lowest resistance, it just doesn't work otherwise. I use the wire out of single core residential power cable ( house wire). I works super well and is easy to get free/ cheap.
Aim for a voltage of btw 1.5-4 volts off the secondary
Get good copper fill and remove the shunts out of the MOT.
Play with electrode pressure till you get satisfactorily results.

Pulse timing is critical. I used a solid state relay driven by a 555 to produce a pulse between 0-300ms. 300 is wayyyyy to much but about 10-20ms does the trick. Finger on a switch is way to slow/ unpredictable
I can dig up my circuit if you're interested. I posted a pic of the finished on one of the spot welding threads bout page 4-5.
You should be able to weld up to .2 nickel strip with good results with a 1000-1200w MOT.

 

[Ohbse]

SCR Cap discharge is also rubbish, suffers many of the same issues with repeat-ability and control. Microcontroller/FET switched is the best way to go these days, with either big DC battery source (my preference and cheapest option by miles) or caps if you prefer.

Best/easiest option would be to buy a JP welder, they're a great deal and do the business with no dramas. If you really must DIY then build the same thing with an arduino, FETS and a FET driver.

 

[markz]

I am wondering if this would fit the bill for a CD welder?
Its 3.5 Farad Capacitor.
http://www.amazon.ca/gp/offer-listing/B00FU8O4NQ/ref=dp_olp_new?ie=UTF8&condition=new

I've read up on this, watched youtube and everything seems doable, the SCR, Buck converter etc. If I can build one at under $100 it would be great.
I've seen some that look like it puts a lot of heat on the battery can, hopefully those are just low farad cap builds.

 

[Gregory]

markz you are better off posting questions in the CD Welder for $100 thread, but FWIW I would consider the JP Welder if starting over.

 

[yemyint oo]

can i use 110v microwave to make a spot welder?

 

[spinningmagnets]

Read this first

https://www.electricbike.com/resistance-soldering-unit/