Author Topic: Microwave owen transformer spot welder?  (Read 18054 times)

Offline PekkaNF

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Microwave owen transformer spot welder?
« on: November 17, 2015, 08:13:49 AM »
Ten years ago I read about MOT spot welders and confiscated one MOT from korean owen that was scraped.

Fast forward 10 years: I found that MOT when I was cleaning up garage and desided to find out if it works.

Has any of you build MOT spot welder? How much power you get out of it and what V/A?

I removed secondary and noticed that there are shunts between primary/secondary. Are these shuts good to have?

I put one round of solid copper wire on secondary and got about 1,6 VAC (per round, no load current was 3A on primary). One, two or three sounds of as thick cable I can cram in?

There are estimates on transformer VA-rating vs. core area. Are those estimates any use here or are they out of whack?

Plan is to check if this transformer is any good for small jobs and lab timer circuitry with it. There is a buzz box type welding machine waiting to be butchered for real attempt.

Pekka

Offline vtsteam

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Re: Microwave owen transformer spot welder?
« Reply #1 on: November 17, 2015, 08:58:39 AM »
Wish I could help Pekka, I started to build a spot welder from a big transformer about ten years ago. Pulled out the secondary (which was a pain) and re-wound with a few turns of heavy gage cable, but never actually tried it out. It's sitting in a box upstairs. Harbor Freight offered a sale (half) priced spot welder in the mean time, and I ended up buying that. I still wonder how that first one would have worked out.  :zap:  :loco:
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Online John Rudd

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Re: Microwave owen transformer spot welder?
« Reply #2 on: November 17, 2015, 08:59:55 AM »
Pekka,
The mot you generally find are ok for use as a spot welder.....

Have a read here.....http://www.chatzones.co.uk/discus/messages/7/16416.html

You need around 2-3 turns of thickest wire you can fit giving maximum current....
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Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #3 on: November 17, 2015, 09:12:24 AM »
I've been playing around with a MW transformer making a bandsaw blade welder ( The butt weld mechanism has to be surprisingly accurate  - so far I have made two good welds from several feet of blade :LOL: )

Initially, I tried using a spot welder to power the blade welder, but the spot welder is low voltage (~1.7vac - one turn with a 230v primary) .The blade welder needs two or three turns ( I've been experimenting with more but 2-3 seemed to work best)

For a spot welder you'll need to mount the transformer as close to the jaws as possible to keep the resistance down. The current flow is huge: I measured way over 600A from a small hand-held spot welder.

Use the as much copper you can squeeze into the transformer gap (I'd use multiple strips lacquered or taped to insulate them ).
« Last Edit: November 17, 2015, 09:38:53 AM by BillTodd »
Bill

Offline vtsteam

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Re: Microwave owen transformer spot welder?
« Reply #4 on: November 17, 2015, 09:19:37 AM »
If I remember correctly I did use some solid copper sheet in the "construction"  -- I think I  did a search at the time and found that liquid styrene was a good coil dope type insulator, so I made some by dissolving large quantities of polystyrene foam in a small quantity of acetone. Not a recommendation, just an account of my madness in general.  :zap:
 
I love it when a Plan B comes together!
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #5 on: November 17, 2015, 10:37:26 AM »
Thanks.

Bill, my friend is fixing one old east german bandsaw blade welder and he got it working....problem is annealing cycle after the weld. Old transformer had leaked all smoke out. I gave him a small buzzbox welder and he sawed secondary out put there three (I think???) rounds of 95mm2 fine wire cable coaxed into soft shrink tube (all from local winding shop). It's almost finished.

I'll follow up the links&leads.

I'm still wondering the shunts between windings. Some instructions tell to leave them, but they "rob" part of the flux. i don't get it. Why they are good, unless you want to limit current....or maybe they are there to load the primary a little even when secondary is open circuit????

Pekka

Offline vtsteam

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Re: Microwave owen transformer spot welder?
« Reply #6 on: November 17, 2015, 10:41:12 AM »
I've been playing around with a MW transformer making a bandsaw blade welder ( The butt weld mechanism has to be surprisingly accurate  - so far I have made two good welds from several feet of blade :LOL: )

Initially, I tried using a spot welder to power the blade welder, but the spot welder is low voltage (~1.7vac - one turn with a 230v primary) .The blade welder needs two or three turns ( I've been experimenting with more but 2-3 seemed to work best)

That looks handy, Bill.
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Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #7 on: November 17, 2015, 10:53:45 AM »
Quote
I'm still wondering the shunts between windings. Some instructions tell to leave them, but they "rob" part of the flux. i don't get it. Why they are good, unless you want to limit current....or maybe they are there to load the primary a little even when secondary is open circuit????

I took mine out to give more room for windings. I suspect the shunts are necessary in the original, to add inductance (the MW load is mainly capacitive, so might be require to limit current in secondary) .
Bill

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #8 on: November 17, 2015, 02:16:27 PM »
Ineresting reading on shunts. Some nice anecdotes on magnetrons and radars.

Now I have to deside what to test next.

Pekka

Offline Manxmodder

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Re: Microwave owen transformer spot welder?
« Reply #9 on: November 17, 2015, 06:11:46 PM »
I've been playing around with a MW transformer making a bandsaw blade welder ( The butt weld mechanism has to be surprisingly accurate  - so far I have made two good welds from several feet of blade :LOL: )

Initially, I tried using a spot welder to power the blade welder, but the spot welder is low voltage (~1.7vac - one turn with a 230v primary) .The blade welder needs two or three turns ( I've been experimenting with more but 2-3 seemed to work best)

For a spot welder you'll need to mount the transformer as close to the jaws as possible to keep the resistance down. The current flow is huge: I measured way over 600A from a small hand-held spot welder.

Use the as much copper you can squeeze into the transformer gap (I'd use multiple strips lacquered or taped to insulate them ).

Not a specifically a spot welder but I do like Tom's techniques method and apparatus for silver soldering bandsaw blades.

Youtube video link:
https://www.youtube.com/watch?v=mzKSk_Zs0Ew

...OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #10 on: November 18, 2015, 04:17:34 AM »
Quick measurement shows core cross section area of 22cm2, which quick&dirty formula says would produce 470 VA of power....

On spot welder dirty deeds done dirt cheap....what voltage (vs. amps) I should coax it, before something starts to smell?


Pekka

Online John Rudd

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Re: Microwave owen transformer spot welder?
« Reply #11 on: November 18, 2015, 04:49:20 AM »
Pekka,
A few links to try....

http://www.giangrandi.ch/electronics/trafo/trafo.shtml

http://sound.westhost.com/articles/xfmr3.htm#s3.0

In the last link, at the bottom of the page are some zip files containing various calcs/spreadsheets/data....
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #12 on: November 18, 2015, 06:20:42 AM »
Looks like they are geared of designing continuous power. I'm trying squese every little red hot electron trough it max. two seconds....but if core saturates a lot of fireworks can happen in two seconds :zap:

Pekka

Offline Noitoen

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Re: Microwave owen transformer spot welder?
« Reply #13 on: November 18, 2015, 01:03:52 PM »
The little piece of metal core between the windings act as a current reducer. Removing them increases the output current.

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #14 on: November 20, 2015, 04:07:01 PM »
I had a spot welder for years to go with my then selection of other welding tackle. It was all sold on my present move but I bought a cheap scrap MIG for the hell of it. In another forum there was guy from Oz who had built much the same  thing but principally the arms etc were wood. Nevertheless, it was a fair idea for intermittent use. His arms went on fire.

I thought that there was a simpler and more reliable tool in a 40 arc welder and coupled with another 10 or so for a copper earthing rod, it was all quite practical  using scrap 1" square arms from an old table set of legs.

I'll let you know when I have time from doing a massive probate job following the death of my wife who had-- would you believe- a turret ( 4 heads)spot welder for orthodontic stainless steel band and wires.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #15 on: November 21, 2015, 04:11:10 AM »
When I had a Morris Marina 1,8 l TC, I was studying how to use MIG. I got the gat cheap because it had an encounter with a deer. I was able to cut out front pilars and part of a roof from othervice crubled similar car. Fair amout of fitting and welding before windshield, bonnet and doors fitted. MIG had a timer and a special nozzel for "spot" welding. Needed a lot of clamps and preparation to imitate spot welding.

I found one small industrial machine 350, but it was big. Well over 35 KVA, water cooled and all that.

I found out that just a stone throwing distance away from my work is shop/factory that stock anything you need for carbon brushes and motor/transformet winding. I bought a metre of 25 and 35 mm2 copper rope (used for carbon brush manufacture), 10 mm silicon sleve and class fibere backed adhesive tape good util 155C.

Old isulation had taken a little hit from secondry removal. Put some tape over the core.

I was able cram 2 2/3 rounds of copper rope on the MOT. That produces 2,4 VAC unloaded on secondary. I measured less that sec partial secodary shot circuit (tried to make it short, but it buzzed and arched), primary pulled 14A and voltage dropped 230->220 VAC. Looks like this will do.

I wonder if copper grounding electrodes could be used as a welding arms or electrodes.

Pekka

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #16 on: November 21, 2015, 05:12:31 AM »
I think that I can go some way to answer your Mig/Mag issues. Basically, all that was needed to create a spot weld was a modified Mig nozzle or shroud which is nothing but a nozzle with two raised lugs and a a the ability to punch a hole in one of the two sheets of body metal. The Mig nozzle was placed touching the intended join and the hole was filled with metal. As the arc was shielded there was no necessity to use a face shield.

It may interest you to know that some 30 years ago Alan Robinson the Lecturer in Motor
Vehicle Restoration at Gateshead College produced a set of notes for student use and this was subsequently made into a book both in English and Swedish.  A revised edited which adds a Mr Livesy to the authorship is still available and is obviously updated. Again, the Welding Institute in Cambridge, UK produced a series of videos for the amateur and I recall the repair of a MGB  in the Mig one being shown to students on the City and Guilds qualification course of which I was a 'manure' student.

Further digressing does suggest a Mig-Welding.co.uk series of information which may help . What must be remembered is that the actual sticking bits of metal together is the easiest learnt whereas the English Wheeling and panel beating are demabnding prior to pulling a vehicle back in correct alignment once major structural damage has been  undertaken

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #17 on: November 21, 2015, 05:43:23 AM »
Strictly speaking, if you use a MIG to 'spot weld' you are actually doing a 'plug weld' which is obviously so when you look at them. (Perfectly sound way of joining stuff though)

As I was reading Pekka's post it went though my mind that ordinary MIG copper tips could perfectly well be used as the tips for a proper 'spot welder' ie one that joins by passing an enormous current though the two metals and joins them without added extra metal by way of filler wire.
Andrew Mawson
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Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #18 on: November 21, 2015, 06:33:32 AM »
Andrew is perfectly correct in describing the joining process as a 'plug weld'.  It does get a bit pedantic when a spot welder has to melt its way through normally used galvanised body steel to create a joint and replace the anticorrosive properties of the zinc- which should- if you get it right- create an as new joint- with(( clears throat again) the same ability to be torn on impact rather than the incumbents. Its all in Thatcham, the exact number of spot welds to be replaced.

Regarding the spot welder, mine had the existing copper arms but with home turned inserts  but in order to reach more inaccessible spots, I made up a set of longer arms in copper with copper electrode tips. However, after discussion with the gurus at Gateshead College, it was suggested that the arms could have been made out of steel again with copper tips.

My present plans are inherently simpler and will utilise nothing more complicated that cheap and easily obtainable copper earth rods material which comes in 4 foot lengths which could have supplied the local Nissan factory where we obtained donor reject Nissan Primeras. Air hacksawing and stitching up almost pristine body panels  was a joy rather than a chore. I did, however, design and make welding clamps to hold the compound shapes.




Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #19 on: November 21, 2015, 07:41:43 AM »
My spot welder, which is a hand held type,  has approximately 1" diam main arms and 1/4" electrodes. I am always amazed how hot the 1" arms get in use. I cannot believe that it is directly the current flowing in the 1" bar that is causing the heat. I suspect it is the resistance of the brass coupling to the body of the machine and the tips themselves whose heat is being conducted by the fat copper bars.

Andrew Mawson
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #20 on: November 21, 2015, 12:27:30 PM »
Oh, I never have used those small spot welders, they look a little special and probably something worth imitating.

If you do the math, there must be very little of restance on every joint, therefore my goal is to minimize number of components and connections on secondary. Plan is to terminate other end of the copper rope (secondary winding) on lower (fixed) arm and the other end to pivoting upper arm.

I was toying with the idea of using steel profile/pipe as arms and put the conductor iside of them, but big current here might interfere here and my intuition tells that this might be of complication.

Thanks to Andrew, I got a bag of M6 MIG wire tips, they feel like a good candidate for this small spot welder.

I have one grounding electrode, OD is about 13 mm and it looks like copper.

Which is better, linear movement of the upper arm or pivoting arm? On my doodles looks like a over arm is the most simple solution. Long arm should have very small radial movement. I.E. lateral displacement of the tip should small enough not cause too much trouble.

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #21 on: November 21, 2015, 01:40:58 PM »
From a theoretical point of view, a straight line squash is best, but an arc should be fine, as the displacement is microscopic (or should be). I set mine up (with the power off !) to firmly nip the pieces together. Then adjust performance by varying the welding time. It often pays to do a few trials to check what time is best. In my test piece the one on the right is when I was happy with it functionally and cosmetically.

Clean electrodes help enormously  :clap:

The electrodes in mine are fixed using a tapered cotter in like the old bicycle pedals used but without the retaining nut, so they are just tapped in - rather crude but it seems to work.
Andrew Mawson
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #22 on: November 21, 2015, 02:45:19 PM »
Thanks. More doodles with arm then...

Another avenue: Which type of solid state relay to choose? I have used triacs with zero crossing switching...apparently not that great here: Highly inductive load.

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #23 on: November 21, 2015, 02:59:10 PM »
Assuming that you intend to switch the primary of your transformer (which I'm sure that you do), so long as you use a solid state relay that is very well over specified for the load you should be fine. Some useful gen here:

https://www.omron.com/ecb/products/pdf/precautions_ssr.pdf

Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #24 on: November 22, 2015, 03:41:57 AM »
Yesh...primary. And that one is chalenging eneough. Some swears on zero (voltage) crossing switching some swears at it. I tried to google answers and I got even more confused that I were before.
Like this, halfway down and not geting anywhere....
http://electronics.stackexchange.com/questions/181874/when-where-to-open-and-close-a-transformers-output


Finally I setled here:
http://www.automation.com/library/articles-white-papers/industrial-io/understanding-solid-state-relays

Transformers
In controlling transformers, the characteristics of the secondary load should be considered, because they reflect the effective load on the SSR. Voltage transients from secondary load circuits, similarly, are frequent in transformers and can be imposed on the SSR. Transformers present a problem in that, depending on the state of the transformer flux at the time of turn-off, the transformer may saturate during the first half cycle of subsequently applied voltage. This saturation can impose a very large current (10 to 100 times rated typical) on the SSR that far exceeds its half-cycle surge rating. SSRs having random turn-on may have a better chance of survival than a zero cross turn-on device, for they commonly require the transformer to support only a portion of the first half cycle of the voltage. On the other hand, a random turn-on device will frequently close at the zero cross point, and then the SSR must sustain the worst-case saturation current. A zero cross turn-on device has the advantage that it turns on in a known mode and will immediately demonstrate the worst-case condition. The use of a current shunt and an oscilloscope is recommended to verify that the half-cycle surge capability is not exceeded.

A typical approach in applying a SSR to a transformer load is to select a SSR having a half-cycle current surge rating greater than the maximum applied line voltage divided by the transformer primary resistance. The primary resistance is usually easily measured and can be relied on as minimum impedance, limiting the first half cycle of inrush current. The presence of some residual flux, plus the saturated reactance of the primary, will then further limit, in the worst case, the half-cycle surge safely within the surge rating of the SSR.

Although. I was about to give it up ans use a contactor and RC-snubber (that's hard eneoug..)

Oh, and I found this, but those rocks looks diminutive.
http://www.avdweb.nl/Article_files/Tech-tips/Spot-welder/Spot-welder-controller-circuit.jpg
http://www.avdweb.nl/arduino/hardware-interfacing/spot-welder-controller.html
Second link confirms of switching SCR:s on near maximum voltage.

Pekka

Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #25 on: November 22, 2015, 04:18:00 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

Bill

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #26 on: November 22, 2015, 04:53:58 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

I can pretty well agree.  Frankly, adequate arc welders at a give away price are available to replace the complexities of cannibalising a piece of old scrap.  As far as the spot welder is concerned, it can be a single side machine which is no more than a pressure loaded carbon arc rod tied to the arc set. Again, a couple of carbon arcs  makes what was called Limelight by Charlie Chaplin. No, it isn't a joke it is a practical  way of brazing if you have to go cheeseparing for one reason or another.

To answer the obvious question, I've done it, written about it, it was seemingly ignored and -who knows- ignored yet again.

Ah well,


Norman

 

Online John Rudd

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Re: Microwave owen transformer spot welder?
« Reply #27 on: November 22, 2015, 05:09:31 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

Exactly,
I have an Italian Cebora unit. It is completely manual in use, plug in, place over job and squeeze the handles.....job done...

In complete contrast, when serving my apprenticeship, we had to make a tool box, the spot welder we used was bench mounted with an integral timer.....took the guesswork out of holding the handles together for too long or not long enough.... :zap:
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #28 on: November 22, 2015, 05:11:12 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

I propably forget to mention that I have 90C bimetal switch that I was thinking of putting there for overheating....

I have been a bit sick last three days and haven't rush with a mechanical construction. Partly also, because I'm waiting 18 mm dia 500m long pure copper rod (eyeball figure).

Idle mind had some time to play with the control part. I agree that it would be easy to manually weld with a proper welder about 2/3 to 2 sec welds, but this small welder will be reserved for a) study and b) very thin stainless steel (and other foils/wires) and friend of mine has a bandsaw welding aparatus refurbished by my old very small welding transformer that welds well, but it is pretty hard to control annealing, therefore a control circuit would be higly desirable.

Spot welder it will be, but following test hast be done outside of the living room warmth. Direct orders from ministry of the deomestic affairs. She was not amused of test to saturate the core and current measurement of simulated spot welding. Women!

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #29 on: November 22, 2015, 05:59:46 AM »
Pekka,

I don't think you need to 'over think' the design. Just make sure that your solid state relay is well over specified. At the end of the day SSR's are cheap as chips - if you fry one it's not the end of the world. Just replace it with a bigger one :)
Andrew Mawson
East Sussex

Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #30 on: November 22, 2015, 07:54:03 AM »
Just in case you haven't already seen this:

BTW his spotwelder is very powerful so his timings are in cycles (20mS - I guess)

https://www.youtube.com/watch?v=82Iil0fFN9Y
Bill

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #31 on: November 22, 2015, 01:15:01 PM »
Thanks, I saw it. His unit is pretty ideal to him, 15KVA I think, his reasoning being that on thin steel plate you can weld well with MIG after this machine gets small.

And NO, I'm not over complicating it. I'm trying understad enough of instead of over simplifying it. Just got 400 VAC welder, single phase all out 180A...This could be tranny donor to next spot welder....but this thing first - baby steps.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #32 on: November 25, 2015, 02:02:20 PM »
Got yesterday 20 mm copper rod and big enough CU/AL connectors. They are pretty nice, all data is available down to screw torque.

I found out that grounding "copper" rods are steel rods, that are plated with copper....

Found out place that sells spot welder electrode rods by metre (or even pieces). They have 8,10 and 12 mm at the small end.

Postal service is on strike......

Pekka

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #33 on: November 27, 2015, 04:05:56 PM »
I've just found out that my earthing rod is also coated steel. Happily, I have found a possible source of small quantities of  scrap copper to cut up. I'm now looking for insulation for the welder arms. I have, like the other Atkinson cousin , a cunning plan.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #34 on: December 17, 2015, 02:51:48 AM »
Ok. Got 1 metre of 10 mm spot welding electrode rod and 1,5 metres of 12 mm diameter. Those were smalles amount (cutoffs....) from the welding supply shop that deals with individuals here.

So I must build something. Work has kept me busy, but maybe in Christmas time I can squise some time off.

Next I need to build mechanics, I think I have all in the junk er.. materials pile. Probably will use circuit board for insulation.

But my mind is in timer/counter. I want something like 2-100 mains cycles. Or from 20 ms up to sec or two. Any suggestions to ready made timer/counter that would keep the count between power up/down cycle and has PNP/NPN output. Maybe with BCD switches.

Pekka

Offline SwarfnStuff

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Re: Microwave owen transformer spot welder?
« Reply #35 on: December 18, 2015, 12:06:34 AM »
Hey Bill, Thanks for posting Dan Gelbart's spot welding tutorial. I went to check it out and recalled that he has many very good tutorials on prototyping which in a way is what we get up to in our play-pens.
Or, at least I seem to, even if I have plans I seem to adjust / modify them for the materials at hand or more often because I messed up on some part.

I have added his page to my bookmarks figuring from there I can wander off to his many other topics.
John B
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #36 on: December 25, 2015, 08:01:52 AM »
Been busy with the work and flu&other seasonal hinderaces....

I have a concept for mechanics, I was going to rocker type. Mainly because of the simplicity and I don't need high cycle time. However the pneumatic cylinder I have is too smal for normal rocker, I need to make swing arm to have eneough force and to keep the whole contraption compact.

I have two problems:
1) How to hook up the current from tranny to electrode holder
2) How to make the electode holder adjustable and I would like very much to able to adjust the holder position and to swap the holder and to turn it over (other end having 90 degree mount for electrode and other 45 degree or special).

Both would be simple if I had two big chuncks of copper. Big square piece, 20 mm bore for electrode holder and four bolt mount. Really elegant solution. Copper has excelent electrical and mechanical properties for this part. But I don't have it, nor I can easily get one!

I was considering similar construction of aluminium, I have it, easy to machine and I have a special clamps to connect copper cable to aluminium. Main problem I have is that I don't believe there is a good enough electrical contact between this aluminium bar and 20 mm copper bar (electrode holder).

I was thinking of "tinning" the 20 mm hole (for electrode holder) in this aluminium block, but I never have soldered aluminium and googling it produced mainly special fluxes and solders that seems proprietary, expensive, dubious mixtures of mainly tin and rest of it mainly zink....resulting in about 25% conductivity of the aluminium. Could aswell use steel or brass....equally bad results and wole lot cheaper.

Only way I can think of using the aluminium mount, is to make a sleeve of copper tube. Standard sixe OD22, ID 20 would be close enough and probably could get two metre piece without breaking the bank. This thin sleeve should work well when clampd between rod and split block, and still have enough of cross section area to conduct the current.

There might even be insulator material that would survive between the copper sleeve and aluminium block?

Is there a problem I don't see or would this work?

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #37 on: December 25, 2015, 08:15:02 AM »
Pekka,

Seasons greetings to you.

It's notoriously hard to get good very low resistance contacts reliably on aluminium due to the inevitable oxide film that grows. It can be done, and contact surfaces need covering with petroleum jelly or similar to exclude air as far as possible. At the currents you are probably using I would anticipate problems.

Bite the bullet and buy some copper block or find something that can be 're-purposed'
Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #38 on: December 25, 2015, 11:31:11 AM »
Thanks. Ham and turkey to you too!

I have scoured local scrappies, small shops and put some adds on local bulletinboards. I haven't got a piece of reasonably copperish copper yet.

I put two more adds on local hobby boards, but if I don't get answer on few days I'll try something else. Like copper sleeve as a conductor and aluminium or steel block as a support.

I have some AL/CU connectors and I have seen propper electricias using them/grease/torguewrench and works. Not really something I'd like to rely on low voltage/high current application.

Pekka

Pekka

Offline JHovel

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Re: Microwave owen transformer spot welder?
« Reply #39 on: December 25, 2015, 09:51:41 PM »
Merry Christmas!
It is possible to tin aluminium properly - against mine and others' 'common sense' - and I have been shown, taught and done it, all the while shaking my head in disbelief.
The process is to heat the aluminium to soldering temperature (using an oxy torch in mine case, because the aluminium moves the heat away so fast, you have to keep pushing more in fast). While it is hot, vigorously brush the surface with a stainless steel brush to remove the oxide layer. Apply ordinary tinning flux to this shiney hot layer and add solder/tinning rod. This sort of floats on the hot surface without seemingly joining the aluminium. Vigourously wirebrush the solder/tin into the aluminium surface until you see it actually 'mixing in' and suddenly it 'alloys' with the hot aluminium surface. You can then add solder/tin to that surface and it flows like ordinary soldering does. However, the last step only works for a very short time! It seems that the aluminium insists on putting an oxide layer between the pure aluminium and the alloyed layer if you keep it hot enough.....
Once you see it all happeneing in front of your eyes, you will shake your head in disbelief like I did and then use the process whenever necessary.
Cheers,
Joe

PS: I learnt about this while doing a course on leading car panels, including aluminium car panels.
Cheers,
Joe

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #40 on: December 26, 2015, 08:44:11 AM »
ONE person said that he has 30*10 mm copper buss barrs....length 2400 mm! I'm pretty sure that is pricey. But it's only 90 km (one way). Not too bad.

Now...If I would cut a 40 mm piece of that bar and make a v-groove for electrode holder. Multistrand cable is easy to attach on that coppe piece, no problem there, but would this two 40 long line contacts give enough cross sectin for the current? Probably yes.

Another idea is to make close fitting 20 hole + slit other side onto piece of this buss bar for the electrode holder and cut a little (17*10*20 mm) lug for the cable connector. This would only work as an connector and there would be a separate mechanical split holder for the arm.

Tonight I'm going to order some electrical parts for the controller.

Pekka

Offline sparky961

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Re: Microwave owen transformer spot welder?
« Reply #41 on: December 26, 2015, 09:32:12 AM »
I'm having a bit of trouble picturing your current troubles, but I've thrown in some possibly useful idea starters below.

Have you checked your local building store for a solid copper grounding rod?  No idea of the alloy or quality but you'd hope it would conduct well considering the application.  Maybe you guys use something different there?

Near the grounding rods you should also find heavy grounding cable.  Here it's used for grounding 100A and 200A electrical services.  It's not the most flexible stuff to work with but if you're considering bus bars already then flexibility doesn't seem a big concern.  You can put them in parallel if you need something with even less resistance.

Do you or any of your friends have a furnace that's hot enough to melt copper?  The melting point is almost double that of aluminum, but not outside the realm of home foundry setup.  Scrounge whatever small pieces of copper you can (plumbing, electrical, whatever) and cast your own large block whatever size you need.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #42 on: December 26, 2015, 11:49:13 AM »
I'm having a bit of trouble picturing your current troubles, but I've thrown in some possibly useful idea starters below.

I am electrical engineer and I have some experience on various systems. Therefore I'm little apprehensive when I push componenets beyond their intended use. The way low voltage circuit works on resistance spot welding machine is simple on most of the aspects, but there was very little at the university that prepared me to work few volts and thousands of amps...

Right now I'm consentrating on a bit that connects secondary coil conductor on the stationary and moving electrode holder.

The conductor has very fine multistrand braid, about 35mm2, should be fine for short pulse of 1100A.

Electrode holder is 20 mm pure copper bar used on electrical cabinet construction.

This piece has two functions:
1) To connect tranny secondary to electrode holder with minimal resistance, this is not one time operation, but must allow mechanical adjustment.
2) Mechanical: Attach mechanically bar to arm.

This is a small part, maximum linear dimenssion 40 mm, 20 mm hole trough it.

Have you checked your local building store for a solid copper grounding rod?  No idea of the alloy or quality but you'd hope it would conduct well considering the application.  Maybe you guys use something different there?

Here copper grounding rodds are steel core, copper cladding.

Near the grounding rods you should also find heavy grounding cable.  Here it's used for grounding 100A and 200A electrical services.  It's not the most flexible stuff to work with but if you're considering bus bars already then flexibility doesn't seem a big concern.  You can put them in parallel if you need something with even less resistance.

Yesh. We have that type cable too, often consumer grade is 16mm2, not sure of it's composition.

Do you or any of your friends have a furnace that's hot enough to melt copper?  The melting point is almost double that of aluminum, but not outside the realm of home foundry setup.  Scrounge whatever small pieces of copper you can (plumbing, electrical, whatever) and cast your own large block whatever size you need.

I'm trying to avoid printtin or castig at this point. Too much to swalow at this point - would set me back months instead of weeks :lol

Pekka

Offline philf

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Re: Microwave owen transformer spot welder?
« Reply #43 on: December 26, 2015, 12:54:25 PM »
Pekka,

I can't picture exactly what you're trying to do but why can't you connect the cable directly to one end of your 20mm copper electrode holder?

 :beer:

Phil.
Phil Fern
Location: Marple, Cheshire

Offline sparky961

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Re: Microwave owen transformer spot welder?
« Reply #44 on: December 26, 2015, 01:11:49 PM »
I'm little apprehensive when I push components beyond their intended use.

Isn't that what this forum is all about?  :dremel:

If you're the only one that will be using it and you've designed in enough safety that you're comfortable with it then I say it's well-built for the application.  Maybe there's an understood but undocumented limit on the duty cycle, or certain parts of the system that aren't quite to electrical code, but you are aware of them so it isn't a problem (as long as you keep it secure from other people's use).  We have all done some risky things with the potential for burning down a house or two, but most people with enough of a brain to succeed with these projects has enough sense to have things in place to prevent catastrophic failure.

If you're building this for someone else, it's a different story entirely.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #45 on: December 26, 2015, 02:25:05 PM »
Pekka,

I can't picture exactly what you're trying to do but why can't you connect the cable directly to one end of your 20mm copper electrode holder?

 :beer:

Phil.

That was my original plan, but then I need to mill a lug where the connector fits. This prevents me from using both ends of the bar 90 and 45 degree angles.

But it would work and is plan "B".

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #46 on: December 28, 2015, 04:53:33 AM »
Made almost full recovery...just before starting a new workweek.

I ordered some electronics stuff. I think thyristors will be fine....just about...ordered some spares and then one size bigger, takes more current, but gate current is higher too. have to check if the opto will trigger it. it looks like it does. Ages when I measured voltage/current with scopes.

Now the happy situation is that electrical components will come in a week or two and in meantime I can start to play with the mechanical part, which I think will be more straightforward!

Oh, and I got a piece of copper tube ID 20 mm and outside 22 mm, tried and it is a nice sliding fit. About 66m2 of cross section area if I need to go that way.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #47 on: January 04, 2016, 03:38:10 PM »
Got electrical board ready and tested on open secondary. Seems to work.

Has been too cold to work on mechanics.

A little progress.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #48 on: January 05, 2016, 01:19:55 PM »
And the electrical parts looks pretty much like this.

Just wonder how to measure thysristors on the circuit. Have to take oscilloscope out of the shelf and power it up.

* Osciloscope does not syncronize...No trigger function works....old philips 10MHz unit.

Any ideas for a new scope. I don't need it that often, but when I do, I really need it.

Pekka
« Last Edit: January 05, 2016, 03:29:18 PM by PekkaNF »

Offline PK

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Re: Microwave owen transformer spot welder?
« Reply #49 on: January 05, 2016, 05:16:12 PM »
Really silly good bench DSO's are quite cheap if you avoid the premium brands. Check out the Rigol range.
If you are doing mostly power electronics, then an isolated scope is just the ducks nuts (as we say in my country). We recently bought one of these: http://siglent.com/ENs/pdxx.aspx?id=93&T=2&tid=2
As a scope, well it's OK, low res screen and a slow UI. But I can poke probes into a live panel with a reasonable chance of survival, which I quite enjoy.

Nb, the non isolated variants are dirt cheap, but then you have a non isolated, slightly crappy scope! You're better off with a bench scope.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #50 on: January 06, 2016, 08:02:49 AM »
Thank you very much. I heard good stuff on Sigilent stuff, but one person warned me stay clear of http://www.siglent.eu/ site. He had trouble with that and does not show on sigilent page either.

Those handheld seems "perfect" but price is least doble on what I am prepared to spend at this point.

Some have recommended USB scopes like this:
http://www.ebay.com/itm/Hantek-6022BE-PC-Based-USB-Digital-Storage-Oscilloscope-20MHz-Bandwidth-48MSa-s-/331245851756?hash=item4d1fca946c:g:kaAAAOSwGiRTrT9N

But they will need a laptop, not sure if measurement is isolated from the laptop and where they are grounded or nulled.

Pretty ideal would be two channell benctop, simple triggering and with 1:10 attennuated probes I should be able to measure all threepahse stuff. It just looks like just might get that about 200, but really should shell out least 100 more to actually get the spec and usability.

I tried long time ago some of the first handheld scopes and they were damn too difficult to use and so limited that you actually had to know the wafeform and fiddle trough all menus and then you had to figure from few dot's on the screen that yup, subber is duff.....

Is there simple and easy to use benchtop type on very low end price range, or am I better off with USB cacadoodles and when I throw one trough window out of frustration I'll just swallow and prepare to spend 300 on something that is nearly enough.

Pekka

Offline PK

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Re: Microwave owen transformer spot welder?
« Reply #51 on: January 06, 2016, 08:34:48 AM »
We have a couple of PC based test tools. The purist in me says they are an elegant and cost effective solution. I mean why pay for a screen on every single instrument when you can just use a laptop? In practice I find myself preferring the stand alone gear..  Go figure!

So these are very good value for money http://www.emona.com.au/products/electronic-test-measure/oscilloscopes/ds1054z.html#.Vo0XjxV95hE, big screen 12 million points capture buffer (trust me, this is an important spec) and peanut cost.

They get even better when you unlock the 100MHz bandwidth with a simple hack http://hackaday.com/2014/11/12/how-to-get-50-more-zed-from-your-rigol-ds1054z

PK

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #52 on: January 07, 2016, 02:23:09 PM »
After lengthy negotiations with her royal highness I have legitimate fund for a new toy....but nowhee close to anything like 500 or any other that type of figure.

Rigol DS1052E starts to look like possible canditate, but where to get it in Europe?

Is it allways same or are there different versions floating?

Found these:
http://www.batronix.com/shop/oscilloscopes/Rigol-DS1052E.html
http://www.rigol.eu/products/digital-oscilloscopes/ds1000e/ds1052e/
http://www.rigol-uk.co.uk/Rigol-DS1052E-Digital-Oscilloscope-p/ds1052e.htm#.Vo6sGVl8dzk

Anything else I should know before.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #53 on: January 09, 2016, 06:11:30 PM »
Got one old UK-made 10MHz scope for free and nearly fried it today....

Got some measurements done. Have to dig up and connect my isolation transformer somewhere.

Have to get some probes and acessories.

Any good tutorial on AC power circuitry measurement. Figured I'm a bit rusty. Too long time from studies.

Pekka

Offline PK

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Re: Microwave owen transformer spot welder?
« Reply #54 on: January 09, 2016, 06:50:14 PM »
Like I said, hand held, isolated scopes are nice things in some applications.

All you really need to keep burned into your consciousness is that the little croc clip on the scope probe is connected to the earth and neutral wires in the plug.
If you can get your head around that then everything else becomes obvious.

The normal procedure is to plug the DUT (in your case your spot welder) into an isolation transformer. This lets it float with respect to ground and means that you have to touch two points on it to die instead of one.
Catch is, an isolation transformer that can handle the power your welder should draw are big and expensive. (maybe you could get two more MOT's and wire them back to back??)

So what you would probably do is plug the scope into an isolation transformer and float it WRT ground.  NB, this is QUITE A LOT MORE DANGEROUS because the case of the scope including  the front panel (do the knobs on the front have metal grub screws in them that your fingers may touch when you adjust the settings?) will sit at whatever voltage you connect the earth clip to....

Having said that, there's no reason not to do this, just plan ahead and write a short note bequeathing all your tools to me in the event of your death.

I have a bit of a process I like to follow when I work on high voltage stuff I'm not confident with.  I take a digital multimeter set to AC volts and hold one lead. Then I poke the other lead onto whatever bit of metal I'm thinking about touching. If I see more than 20VAC on the meter then I know I've just avoided electrocution. It's not a fool proof process, but I'm still here..

Oh, and RCD's are a MUST HAVE for this kind of work..


Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #55 on: January 10, 2016, 03:33:04 AM »
To think that for years and years I carried a Textronix 465 in the car as a standard computer servicing tool that had the mains earth lead disconnected and poking out of the plug so that it was obvious to all.

But Health and Safety hadn't been invented then, nor had RCDs so it was OK  :lol:

But on the other hand Common Sense hadn't been banned then, so that probably saved us  :ddb:
Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #56 on: January 10, 2016, 04:30:07 AM »
Yesh...that was all normal when I was a student and lab tehnicias hovering among us to prevent us from sme of the most dangerous stuff.

My problem here was a senior moment....I'm aware of the problem and in order to avoid it I had all figured and checked out, but then I put the plug wrong way in.... I actually have two poplarized Shucko plugs, but no power strip that is polarized.

We used flot sopes, but the scope had long plastic extensions for the knobs...for the reason mentioned before. We were wondering why the front panel was metal and plastic knobs had metal parts....maybe it's just cruelty to apprendices?

I had a look on current probes and isolated probes....good thing that I was sitting down. I must have sunk deeper in the couch. Least it felt that way.

Is there any economical floating probe/isolation amplifiers available for a) mains measuremet b) instrument level signals 24vdc, +/- 10V?

Or am I better of cobbling on a plastic enclosure double insulated system, that has it's own isolated PSU, then DIY voltage divider/differential amplifier and a EL-cheapo digital scope with very limited bandwidth but cheap price tag? Sort of bangood scope mentioned here?

Pekka

Offline PK

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Re: Microwave owen transformer spot welder?
« Reply #57 on: January 10, 2016, 05:09:47 AM »
Re all of the above, if you slow down and think it through then the risk is zero. The cautionary language is for the young'uns reading this who aren't going to take that approach.

On the topic of isolation..
We have a few DIY isolation transformer boxes here at work that are nothing more than two mains to 24 transformers wired back to back. We're still alive.

It sounds a bit excessive, but the cheapest option for you might be to get two more oven transformers and wire them together. This will give you an isolation transformer of some significant capacity...

I'm not sure I understand the requirement to isolate both the scope supply and the signal of interest?

Re options:
A battery powered handheld scope isn't the same thing as an isolated scope (look for cat II or cat III specs). Sadly the manufacturers of these devices understand this and charge commensurately.

All handheld scopes are complete crap compared to the same dollars in a bench scope, mostly because they have tiny, low res screens, also mostly because they have tiny capture buffers and finally mostly because they have slow processors which makes the menus slow to pop up and hard to use.

So my vote is for the bench scope and isolation....



Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #58 on: January 10, 2016, 05:36:51 AM »
There are some excellent bargains on eBay for analogue Tektronix oscilloscopes. 200 buys you a professional instrument in good order complete with probes - just because everyone wants more recent digital 'scopes it doesn't mean the analogue ones no longer did what the always did !

My 465 may not get used every day (or even every month!) but I certainly wouldn't part with it.

Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #59 on: January 11, 2016, 02:45:42 PM »
OK. ordered one hal conraption that might get me somewhere on current measurements, this type, but different shop:
http://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B00BLD6FB8

It's on the mail...I have palyed with hal clamps and transducers before...not having utmost trust on that one, but it IS isolated!

More questions:

1) Anyone found source for reliable shunt resistors (kelvin type)? No point of buying bad one measuremet, this one will be used for accurate measuremets and verify other measuremets.

2) Found few reasonable circuits for isolated differential probe, one way too much overspeck, but not too expensive BUT circuitboard would be a problem.

Here board and expense is no problem, but I have no idea of performance/speck.
http://www.chip45.com/products/detail.php?pid=isoprobe-1-kit
**UPDATE:
Looks like AM1200 isolation amplifier has Small Signal Bandwidth 100 kHz:
http://www.ti.com/product/amc1200
maybe 50% of it is final total system bandwidth??? Looks like a one of these cheap oscilloscope kits (with isolated power supply) would offer all that (except reference to another channel):
http://madmodder.net/index.php/topic,11145.0.html
**

Could not find circuit diagram or spesification. I would be very fine pretty much buying or soldering, but small surface mounted componenets or making PCB...

baby steps

Pekka
« Last Edit: January 12, 2016, 05:46:27 AM by PekkaNF »

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #60 on: January 31, 2016, 03:48:05 PM »
OK. ordered one hal conraption that might get me somewhere on current measurements, this type, but different shop:
http://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B00BLD6FB8

It's on the mail...I have palyed with hal clamps and transducers before...not having utmost trust on that one, but it IS isolated!...

Got it some time ago and it works! Pretty close on sine wave and it does shows if there are any triaks on the line.

I'm been reading and shifting some info on "floating" measuement and it still is as it used to be before: Needs very carefull concideration. Next measurement is going to be scope grounded, but DUT floating. Basically I'm grounding the DUT fairly close to return path anyway, therefore I should be able to to measure it without blowing anything up and measurement should be safe too. Now I can put my 100:1 probe on good use.

I actually might still try to build isolated differential amplifier, but there are some steps I'm not too confident with, like SMD and making circuit boards.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #61 on: February 02, 2016, 06:28:47 AM »
Put those probes into some use.

Probes were 1:100 passive probe and HAL current clamp.

My friend has a problem: He has a ceramic oven he plans to use for hardening and tempering. The thing is someone "rigged" it for sale: Heater resistors are 110V + big transformer 110/230VAC, broken temperature sensor and controller that does not belong to it.

Cunning plan is to use main contactor that feeds the tranny and then put SSR between tranny and resistor. Good thing that a little hysteris will not kill the main contactor, bad thing is that SSR needs twice the current rating on secondary.

But I need to test the concept. I had 15A zero crossing SSR that is too small for the job, but just fine for a quick and dirty test: isolation transformer, secondary on float. SSR between secondary and 200W load resistor. Secondary nulled where comfortable for voltage scope ref (ground) and current clamp allows current measurement at will.

1. even with zero crossing, there are 32v "spikes" over the SSR, nothing to worry.
2. current and voltage wave form is nice into resistive load
3. zero crossing switching ON!

Right