Thanks: 0
Needs Pictures: 0
Picture(s) thanks: 0
Results 1 to 7 of 7
-
30th December 2013, 12:51 AM #1
Transformer from a mickywave question
Hi all,
Youtube is to blame, build your own spot welder, Ah OK I could do with one of those, lets have a look, mmm OK seems all that is needed is a transformer out of a microwave, plus a few other bits, tip shop yielded a prime example for $5, thought it best not to utilize the one in the kitchen, so today I set about pulling the sec winding out and sqeezed in 3 turns of some heavy welding cable, I could have made it easier by removing the outer layer of insulation but a nice tight fit seems to be the go, I could have also removed the shunts but at this point I left them in.
Testing with 240v straight onto the primary gave me a tad over 3 volts on the secondary (no load) and I had about 5 or so amps on the primary (no load) so with an ideal tranny I should get about 400 amps which should be enough to bzzzzzt a couple sheets together, this will be about all the cable will handle anyway for 2 or 3 secs of on time.
Get to the question..... I placed a bit of thin weld wire across the output expecting it to heat up quickly or at least get a few sparks, nope nothing didn't even get warm, yep turned on, yep 240 yep 3 yep humming quietly and yet nothing, I wanted to see some hot wire at least
What could be the cause?
Maybe I completely mashed the cable as I was bashing it a bit flatter? Nah, I didn't hit it that hard, just flattened it a bit.
As I understand the shunts are there to limit current so maybe that's it,
Maybe all my flux has leaked off and not inducing anything in the secondary,
Ahh I know maybe I need to wind it the other way, it is just a basic E I type so the direction doesn't seem to matter,
at this point I after suggestions....
I still blame youtube
Cheers all
Pete
-
30th December 2013 12:51 AM # ADSGoogle Adsense Advertisement
- Join Date
- Always
- Location
- Advertising world
- Age
- 2010
- Posts
- Many
-
30th December 2013, 08:40 AM #2DISCLAIMER
No liability is accepted by UBeaut or the Wood Working Forum's administrators
or moderators for advice offered by members posting replies
or asking questions regarding electrical work.
We strongly advise contacting a Licensed Tradeperson for all electrical work.WARNING
Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
Members following such information do so at their own risk
-
30th December 2013, 05:41 PM #3
Definitely
If your transformer primary is pulling 5A at 240 V with no load on the secondary, I suspect that there is a shorted turn somewhere in the system, or there is something very odd in the transformer design. I am an electronic engineer used to designing and specifying transformers for consumer and broadcast equipment up to 5KW transmitters, but have never dealt with microwave oven transformers, but by normal standards would consider no load primary currents in excess of 100mA for a 1200VA transformer excessive. A transformer of that size would typically be used for continuous duty 400 + 400WRMS concert amps.
I have a general interest in welding technology, but no direct experience in dealing with spot welders, but understand that there is significant resistance in the contacts between the electrodes and sheets being joined, and also between the sheets themselves. In that case, I doubt that a 3V applied voltage would be sufficient to to establish significant current to form a bond.
Again, I have no knowledge of the power supply systems in microwave ovens, so could be completely barking up the wrong tree.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
-
30th December 2013, 07:38 PM #4Senior Member
- Join Date
- Sep 2011
- Location
- Northern Beaches, Sydney
- Age
- 68
- Posts
- 329
What's that glow on the horizon ?
Ahh, it's pjt trying out his spotwelder Mk II !
Stewie
-
31st December 2013, 08:47 PM #5New Member
- Join Date
- Mar 2009
- Location
- Bathurst
- Posts
- 7
Hi Pete
It should work... A humming microwave transformer is a good sign.
I have just checked the no load amps on the primary from two of my many microwave transformer (MW) projects. A spot welder came in with 4.6 amps no load. A pyrography machine i built came in with 1.2 amps no load on the primary.
A band saw blade welder that I put a MW transformer on with about two and a half turns has no trouble welding 10mm blades.
Have you tried a different bit of wire in case there is some insulation or corrosion on your welding wire? As we are using very low volts (usually only 1-3 volts) it does not take much to give you a negative outcome.
Regards Floyd
-
1st January 2014, 03:19 AM #6
After the non bzzt the other day I put it aside and then thinking about Malb's post I thought well in all probability it didn't work seeing as it was a tip shop find, I did test run the oven and it did make all the right noises but I didn't actually heat anything in the oven so maybe everything else worked but the bit I wanted, anyway I'll make up some proper ends and do a few more trials with some clean sheet.
There was one youtube guy who welded together 2 bits of 3mm thick stuff no problem, my wire might be a bit small for that.
Here's photonicinduction with his 1100+ amp MOT 1100 Amp Extreme MOT - YouTube
Pete
-
23rd February 2014, 10:33 AM #7
Backyard rewinding of microwave Transformers Oh the Horror.
I've seen a few of these things first hand
Here are a couple of the issues.
If you want it to be a normal transformer...it should not have any shunt windings.
One of the big problems with these rewinds is that mostly people do them in thermoplastic insulated wire.
This brings two problems.....
The first and dangerous one.....the plastic on the wire will only be good for 105C IF you are lucky...if it is normal plastic coated wire more like 65C......transformers can get hot, particularly the inner windings.....failure and fire are very real possibilities.
the second is that the turns are seperated by quite some distance and from the core due to the thickness of the insulation...thus inductive coupling and efficiency will be poor......heat will be generated...see above.
Seriuosly folks.......do not do this stuff......its not a good idea.
If you want a spot welder...ebay is your friend.
There are new and second hand ones on there all the time.
If I need a spot welder, I borrow one from Magic Murf.....he got his....lightly used, complete and in good nick off ebay for $100
cheersAny thing with sharp teeth eats meat.
Most powertools have sharp teeth.
People are made of meat.
Abrasives can be just as dangerous as a blade.....and 10 times more painfull.
Similar Threads
-
Suitable Transformer ????
By naijin in forum PYROGRAPHY (Woodburning Art)Replies: 3Last Post: 12th December 2013, 05:40 PM -
Step down transformer woes
By henlan77 in forum HAND TOOLS - POWEREDReplies: 18Last Post: 10th April 2012, 09:29 PM -
How do I tell which transformer I need
By Arry in forum WOODWORK - GENERALReplies: 8Last Post: 10th June 2011, 06:29 AM -
TRansformer wired incorrectly?
By .RC. in forum METALWORK FORUMReplies: 4Last Post: 24th January 2011, 05:50 PM