Any suggestions for a home made Resistance Soldering Unit?

I'm posting from an iPad, Frances

You may be onto something ...thanks for the thought.

MichaelG.

I just got logged out making the same point! I'm on linux and it looks as if there's something special about hyphens in a URL.

I tried overwriting the unicode substitution with an ordinary hyphen and the forum won't recognise the string as a URL at all.

Anyway, I've had no luck finding a Zinc Carbon battery in my recycling box, nor did Tesco's have any yesterday. Starting to worry they've gone the way of the firesteel, typewriter and floppy disk!

Dave

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I think you will find that they are still around, Dave

... It's just that 'Carbon' is such a dirty word these days, that they try to avoid mentioning it.

**LINK**

http://www.poundland.co.uk/leisure-and-entertainment/batteries

The 'Zinc' ones are almost certainly 'Zinc Carbon'

MichaelG.

Was it ever decided whether these devices, commercial or otherwise, do/can strike an arc?

It's rather a critical consideration if you have a pacemaker.

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Given the broad range of "these devices, commercial or otherwise" ... I'm sure there must be some that do/can strike an arc.

My own 'research' on pacemakers, however, suggests that the main risk comes from strong magnetic fields rather than EMI ... Modern pacemakers are apparently well hardened against interference, but most have a simple reed relay built-in, for switching to a special [low functionality] mode.

MichaelG.

My concern comes direct from the manufacturer (Medtronic). When I finally got them to directly discuss, with an end user, the problems, if any, of having a small machine shop (after the Doctors admitted that they didn't know). They did allow that small (up to a few HP) motors should be OK but that arc welding was a definite no-no. And the problem was the arc which I understood (or perhaps assumed) at the time was due to wide band RF (spark transmitter).

This was about 9 years ago with my original implant (which is actually an ICD rather than a pacemaker per-se) and it was swapped for a new and updated model when the battery ran out about a year ago. I doubt that much has changed in that respect though.

They did admit that (very) strong magnetic fields could also be a problem but didn't, as far as I recall, suggest that was the primary problem with arc-welding. It was my impression too that there was a fail-safe reed switch in the device but Medtronic denied that .... possibly this works for a simple pacemaker but perhaps not fail "safe" for an ICD so that the best safe method is avoidance.

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Rather tired, tonight ... but I will try to send you a brief P.M. tomorrow

[ I suspect we are a minority group here ]

The concern about Arc welders seems entirely reasonable ... but IF we're talking Resistance Soldering [which I think we were] then the level of arcing is PROBABLY trivial.

Your closing comment is spot on, of course !!

MichaelG.

For general awareness:

Two entries from the Glossary in Tom Kenny's excellent book:

The Nuts and Bolts of Cardiac Pacing

magnet mode ... A specially defined type of pacemaker behavior that occurs whenever a magnet is applied over the implanted pulse generator (causing the reed switch to close). Magnet mode varies by device, but generally disables most advanced features and may involve fixed-rate, asynchronous pacing. Also known as magnet behavior.

reed switch ... A small reed-like metal component within the pulse generator which can close to create an electrical circuit that causes the pacemaker to revert to magnet mode.

MichaelG.

Apologies for the delay reporting back on low voltage arcs - I had trouble finding a zinc-carbon battery.

However:

This is the set-up with a 6V accumulator with a Carpet Knife blade as the negative electrode.  The positive electrode is a the soft artists pencil that didn't work - it's resistance is too high.

This is the Mk2 electrode made from the anode of an 'AA' sized Zinc Chloride Battery.  I broke it taking the battery apart.

Not a good photograph but trust me you can easily strike an arc at 6V.  The resistance of the electrode is about 3 ohms, so this is about 2A.  The choc block terminal soon got hot enough to melt the polystyrene insulation, and the crocodile clip wires got warm.   Trying to keep the arc going with one hand while taking photographs with the other is tricky.  Also camera had trouble capturing the characteristic bright white point of light from the arc - most of the colour in this photo is red-hot carbon.

The arc is only 12W and most of the power is heat and light.  Even though it's not in the same power league as a welder, I wouldn't risk it if I had a pacemaker.

The arc does severe damage to the knife blade.

Dave

Edited By SillyOldDuffer on 13/06/2018 16:49:20

Very nice demonstration, thanks Dave

I would, however, just mention that although it is clearly possible to strike and maintain an arc ... that is not the way that conventional Resistance Soldering [the original subject of this thread] is done.

MichaelG.

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https://m.youtube.com/watch?v=piwVhrZTWA8

https://m.youtube.com/watch?v=2Mcl7DOX3WE

Edited By Michael Gilligan on 13/06/2018 17:22:56

Yes indeed. I wouldn't want to scare anyone off. I deliberately created the conditions necessary to strike an arc. Pushing the electrode firmly against the work and applying power with a foot-switch would reduce the risk massively. But a careless operator could cause an arc by accident, and the arc would be much more exciting with 200 Amps than my 2A!

My original point was that an AC Resistance Solder Unit is safer because AC is intrinsically much less likely to arc than DC. That led to discussion about the difference between sparks and arcs, and whether or not starting an arc needs lots of volts. It doesn't.

Fortunately AC Resistance Solder Units are easier to make than DC provided you can find or rewind a suitable transformer. (Lot's of good advice in the thread about that.) Pacemakers apart (get expert advice!), anyone who wants to build one can crack-on.

Dave