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Tubes in broken spotwelder & other questions

That's not a simple question. The first order approximation is that CURRENT is what creates the magnetic field that saturates the transformer. If you put a scope current transformer on the primary, load the secondary with the resistance and inductance of your welding setup, crank up the voltage until you see a sharp rise in the slope of the current pulse. That's the too-much point. What happens when you add more caps is dependent on the transformer characteristics. Energy is linear in caps but quadratic in volts.

25 years ago, I was tasked with fixing an OEM forward converter that would randomly self-destruct. I built a fixture to synchronize the load transient with the switching frequency. I could watch the primary current head for the sky on the scope as the load transient crossed the switching point. Took it to the vendor site and proceeded to blow up power supplies until they conceded that they had a board layout problem to fix.

After the weld, the field will be sitting somewhere on the B-H curve of the core. The next weld might be very dependent on where you left it last time.

This is a page from my Unitek CD spot welder. Shows how they reset the core.

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I experimented with a microwave oven transformer battery tab welder. I was hitting it with a timed pulse. Repeatability was horrible. When I synchronized the pulse with the line and gave it an integral number of full cycles, the starting point on the B-H curve was consistent and the welds got much more repeatable.

There was considerable discussion on exactly when you should terminate the pulse, but mine was constrained to somewhere near zero current by the triac.

Reply to
mike
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Thanks, that all makes sense. I'd like a bit more capacity if I can get it.

I'll have a look and see if it has a core reset current too.

Clifford Heath.

Reply to
Clifford Heath

Be careful, remember there is a secondary current and its magnetic field will largely cancel that of the primary, so looking at the primary current is a red herring unless the secondary is open-circuit.

The rate of change of flux in the core will be proportional to the primary voltage. What you need to look at is actually the integral of primary voltage with respect to time, as this will give you the change in the flux in the core. The longer the pulse lasts, the less voltage it will take to cause saturation. (For similar reasons, 60Hz mains transformers will saturate at a lower voltage if used on 50Hz mains.) You could get more energy into the weld if you increse the voltage of the primary pulse and decrease the duration, because the dissipation in the weld is proportional to the integral of v sqared with respect to time, whereas the change in the flux in the core is proportional to the integral of v (not squared) with respect to time. Also, make sure that the core starts out with maximum flux in the opposite direction. This might be achieved with a reset pulse as others have pointed out, provided the core material is one that will retain the magnetisation. If not, you could perhaps feed a reverse current through the primary using a low voltage power supply, to build up reversed flux just before the main welding pulse. That might make the switching a bit more complicated.

Reply to
Chris Jones

I can't use 100 caps. I did find photoflash caps but the leads are kinda thin. I'm still waiting to see if Just Radio thinks their caps will do. Eric

Reply to
etpm

So photoflash rating is probably not necessary? Thanks, Eric

Reply to
etpm

Greetings Mike, The machine I am working with is a Unitek model 1-048-03. Is this the same as yours? If not do you know if it is close enough to use for trouble shooting and operating the machine I am trying to get working? If it would be useful is there some way you could get a copy to me? Maybe scan and email? I don't mind paying you for your trouble. I wouldn't even ask but so far I have not been able to find a manual of any type for the model my son has. Thanks, Eric

Reply to
etpm

It's a unitek 125. All I have is a very poor schematic and three pages of part of the cal procedure.

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If you have a way to archive them permanently, please do so. They won't stay on my page for long.

This is my DIY battery tab welding fixture made out of an arbor press.

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I emailed Unitek years ago. At that time, they were very helpful.

Reply to
mike

I cannot see properly from the photos - but is there a connection to the last (bottom) regulator cathode? I would guess it might be to chassis so "no output" is correct.

If all three glow then the voltage across each should be fine.

Reply to
Geo

OK!! EVERYBODY!!

Step back a minute and have a look at what is being discussed here:

a) This is a TUBE-based spot welder designed probably more than 60 years ag o. b) The bean counters (a scourge even then) would NEVER have specified photo

-flash capacitors when just a bit more of conventional capacitance would ad dress 'slow chemistry' at a fraction of the cost. c) A healthy gap on the transformer would eliminate sateuration issues in t his application - 'at no additional cost' and without complications, and en tirely permanently. d) This is a piece of industrial equipment designed to be used by productio n worker who very likely have neither the time nor the inclination to do an ything other than follow directions, set the various knobs and switches the n GO for hours at a time. e) And, as with any decent tool from any decent manufacturer, it is designe d to be serviced in a simple and straightforward manner by techs who need d o no more than follow directions from a standard troubleshooting schedule. f) And, finally on this list, replacement parts, especially generics (capac itors, tubes) will be entirely conventional - no silliness about "matched p airs" for instance, or boutique caps. If one has a small machine shop in Bu cksnort, Tennessee (

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) one does not have the time to search down something exotic. One is going to get on the phone to Graybar and order whatever it says on the can, and Gra ybar will have it in stock.
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And, back in the day G raybar stocked industrial tubes as well.

Meaning that there is NOTHING esoteric about this device, and it will not r equire ANY special 'stuff' to make it go. The caps in this device are toas t. If even one of them "rattles" then all of them, being of similar age, li ving in similar environments and doing similar work, are also done. Not rep lacing all of them is just plain stupid. Full Stop.

Purchase physically rugged caps that either are, or add up to, 200uF & 450 VDC per each, at least. Make sure that the soldering points and connections can handle anticipated voltages and currents. Replace all the tubes, even if they are not necessarily done, as now you will be starting fresh, nor is the investment all that much. If I have 2D21s, I would send the whole sheb ang to Oregon/Washington State for US$30 including shipping and think I was making too much. Otherwise, AES will do the same for perhaps half-again as much.

Sheesh, guys and gals - it is almost as if this were rocket science. It ain 't nohow.

Peter Wieck Melrose Park, PA

Reply to
pfjw

There is a connection. It does not go to the chassis. I think the tube is bad. All tubes are gonna be replaced anyway. Eric

Reply to
etpm

That's it, I'm convinced. I'm gonna order the caps from JustRadio. They are the correct rating for voltage and capacitance, different connections-not screws, but big tabs instead. Easily soldered to the bus bars. I have been thinking about those big bus bars and am wondering if the size is either for mechanical reasons or lower resistance reasons. I can't see the original caps dumping enough current to need such robust bars. Especially considering the relay contacts connected to the cap bank and the much lighter wires running from the bus bars and relay to the xmfr. Lemme know if you have all the tubes and I'll send a check. Thanks, Eric

Reply to
etpm

On Wednesday, November 16, 2016 at 12:06:15 PM UTC-5, snipped-for-privacy@whidbey.com wro te:

Please note the interpolations:

Both. Mechanical as this machine moves, vibrates and is subject to various stresses thereby. And, consider that the shop I worked in a _long_ time ago used their welder two 10-hour shifts in a row, about 2 days per week. That is a lot of welds.

Electrical as the enemy of these machines is heat. Heat increases resistanc e which can throw off settings - and with 0.003 inconel pimple washers the difference between the weld not taking and a burn-through isn't much, and o n aircraft and/or nuclear rated parts that is unacceptable.

I can't see the original caps dumping enough

You will have to wait into the weekend for me to get an edgewise to check m y stock. Our youngest cat (3 years old, 18 pound Maine Coon mix) has just d iscovered that he can use the dog door. So, my primary task is to cat-proof the dog yard so he may go outside, but not any further. We may be suburban , but we have foxes, raccoons, other cats and cars to contend with.

As to sending a check, that is not how it works. If I have the tubes, I wil l send them to you - and then *if* they work out, you may send the check.

Peter Wieck Melrose p

Reply to
pfjw

Keep your old tubes until you can test them and be sure they are bad. These old tubes are not getting any more common! 2D21s were always a bit fussy and were replaced by 2050 tubes not long after they came out...even new out of the box there were failures. Seeburg jukeboxes used 2D21s for their early tormat design and quickly changed the design to 2050s part way through the second year of production due to read-out and write-in issues. I have schematics for 2D21 testers that I can dig up (probably find similar schematics easily enough online) and post of my tech ftp pages if there is a demand/request. The 2D21 is pretty easy to test, if you have access to a good tube tester it will usually show them on the Seldom Used auxiliary tube list. The 2D21s are go/no-go kinda things.

OA2s are also pretty basic tubes. They use a conductive gas to regulate to 150VDC. If the tube is not broken or gassy then it should be just fine. Check the Getter flash in the tube - it should not be showing any white powder, that is a tube that has lost its seal and oxygen has entered...

John :-#)#

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Reply to
John Robertson

2D21s are/were used commonly in dental X-ray and Fluoroscope machines, and when, also back in the day, I was working for a GC doing some serious rebui lding at HUP in Philadelphia, one of the docs needed to resurrect such a ma chine for historical purposes. I found him the tubes he needed locally, inc luding two 2D21s. This was "Before Internet", so not an instantaneous proce ss.

I also keep a very good tester (Hickok 539B), so no tube would leave this h ouse untested.

Yes, of course, keep any undamaged old tube.

Peter Wieck Melrose Park, PA

Reply to
pfjw

You're responding to Chris' answer to *my* question about how I can make *my* welder do more than it was designed to. I'm thankful to him for that, and I don't think he needs to "step back a minute".

Reply to
Clifford Heath

No, I made a generic suggestion that we not over-analyze what is, in actual ity, a very simple issue. A discussion about cap-reforming has no place in this particular discussion, nor do photo-flash caps except as a perhaps int eresting sidebar. A "you might try this if practical" type thing. And at th at level, I agree, one might try it.

This discussion, for the OP in any case, is about restoring a piece of indu strial equipment back to reliable and optimal function. Emphatically Not ro cket science.

Now, here is the issue with industrial tools with the goal of making it 'do more than it was designed to do'. Well designed tools have a level of resi lience already built in. Going beyond those parameters puts the tool, opera tor and surroundings at-risk either a little bit, or perhaps quite a bit de pending on the tool. It is, in every case, under every condition, an exceed ingly bad idea. If you choose to put yourself and your property at-risk, th at is your privilege - and may you never be in line for a Darwin Award.

I have worked in an industrial production environment with very fast, very powerful, very hot machines, materials and moving parts in close proximity. I would NOT want to think that some lashed-up tool operating outside its d esign parameters had my life or health dependent upon its smooth operation.

Peter Wieck Melrose Park, PA

Reply to
pfjw

meh. That is quite a generalisation. Sometimes upgrades and modifications make things safer, especially when starting with older equipment that, in its original condition, would not meet modern safety standards. Of course one has to apply sensible engineering, and not overstress parts, and consider any safety consequences of parts failing, but that does not necessarily preclude improving performance in some cases, as the original designers of the equipment did not have the components available to them that we do now.

Reply to
Chris Jones

Sure. But, look at what you just stated. Sensible engineering. Not willy-ni lly speculation by individuals with no or very limited basic knowledge of t he design parameters of the tool/machine involved.

"more than they were designed to do" is not sensible engineering.

Better bearings, better capacitors, better lubricants, more effective switc hes, better snubbers (rubber parts), better insulation, better electrodes, better shielding - all of the above are perfectly valid (and sensible) impr ovements for about anything. One does not have to use 30w non-detergent oil in a vintage automobile, or propylene glycol antifreeze today.

But, at the same time, running a stock Model T on nitro-methane is, perhaps , inadvisable.

Peter Wieck Melrose Park, PA

Reply to
pfjw

I totally agree. I rebuilt a nearly 40 YO gas dryer:

I upgraded the drum lighting to LED. I upgraded the kind of thrust bearing s. I added two thrust bearings. I bought a new old stock bearing assembly for the fan and upgraded the grease. I painted and replaced the new nylon hinges on the filter door. Nylon and heat don't like each other. I painte d the rusty side that was next to the washer. I replaced the 40 YO drum bel t. I replaced the blower belt. I upgraded/replaced, made from scratch a d uct gasket. The thrust bearings were $24.00 not including postage.

I changed a set screw to brass tipped so the pulley would slip if the beari ng housing froze. Now a cool upgrade would be a belt slip detector.

All of these are minor upgrades, but they make it better.

I have a few more planned:

1) Make a new lint filter 2) Make it easier to do preventative maintenance by adding Threadserts inst ead of sheet metal screws.

The upgrades were costly. The grease was about $30.00. The material to mak e the filter was about $70.00, but I'll use that also to make the lint filt er. The threadsert kit was about $80.00 USD.

I will try to measure and determine the type of wire in the ignitor and may be eventually make a replacement. I have two brand new ones.

Reply to
Ron D.

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