You can make a powerful magnet with it. I did that, covered the entire thing in epoxy and use it as a mag chuck for the drill press. Works great.

the secondary is the top winding – it can be lethal with a very high voltage – easy to cut through the winding without disturbing the primary (the lower winding ) the aux secondary is just a couple of turns of wire between the primary and secondary windings used to feed the low voltage cathode heater of the magnetron; once the secondary removed quite easy to insert a new secondary of a couple of turns of very thick wire  (insulated) which will produce 100A or so but at low voltage – this makes your spot welder.

Dave clearly hasn’t priced a commercial spot welder recently! Even a weedy one that struggles to join two pieces of car bodywork is several hundred quid. Used ones aren’t cheap, and potentially have all the mentioned safety issues of mains transformers.

In my youth I found an ex-crt television transformer. Connecting and disconnecting a 1.5V battery across the primary it would produce a spark about 20mm long tracking across the windings. Can’t remember what I was doing this for so don’t ask. Found this out by accident and never got a jolt from it as I didn’t try to do anything further with it after this observation.

Martin C

Several years ago, using an ex micro wave transformer I made a spot welder. I  removed the HT winding and for the new secondary I used a piece of insulated MIMS (Pyro) cable outer, NOT the inner, one complete turn was enough. It was a large size Pyro as it took some bending. For control I made foot operated power ON switch. Some time later after I’d used it a bit on very thin sheet steel sort of can size, space was required so out it went.

An interesting thing to do, much spoken about  but waste of time really and for those not into or understanding the dangers of Electricity leave it alone. John

PS. ALWAYS SHORT OUT ANY CAPACITOR TERMINALS (DISCHARGE THEM USING AN OLD SCREW DRIVER) WHEN ON A BENCH, before touching them. Just reinforcing, as some one has already mentioned this.

It could be the building block of a CDI (Capacitive Discharge Ignition system!). These are quite commonly used on motorcycles (Japanese origins) and especially two strokes (less common these days). They were also used on race engines and still are today. The DFV and derivative Cosworths used a Lucas CDI very effectively in the 1980’s. The difference between an Inductive ignition system (sometimes referred to as a Hall Effect ignition) and a CDI is the HE ignition gives a moderate Voltage peak output over a longer time (typically 40Kv for a duration of 300 microsecs) whereas a CDI will deliver a much higher voltage over a shorter time span (again, typically 120Kv over 50 microsecs). This was described to me by the ignition ‘guru’ at Lucas as ‘sheet lightening’ versus ‘forked lightening’.

I was once setting the rev limiter on a DFV engined F3000 car at 8,900rpm (to avoid the mandatory FIA 9,000 rpm ‘Monk’ limiter which deprived the driver for sparks for some 2 seconds). The setting was done using a hand held signal generator connected to the spark box dialled in at 8,900, and holding the coil’s king lead whilst looking for a suitable place to see the spark when near grounded by a 5mm gap, with my spare hand on the roll hoop, I saw the mechanic leaning into the cockpit to switch on the ignition – I got as far as NNNNoo! before I received the full force of the near 600Hz shocks. This threw me backwards in the garage and as a result, after the feeling came back into my left arm, it miraculously cured my arthritis in my wrist – not a very pleasent cure though.

The line of weld is hardly a problem. 5 minutes with a triangular file or 5 seconds with an angle grinder will fix that problem. I have done this when rewinding several transformers which have the line of weld.

Not much good for a decent Tesla coil. I work on a friends machine which uses a pig transformer. 240 volts AC into the secondary and 11,000 volts out of the primary. This goes to a rotary spark gap. Now that is a decent Tesla.

Before H&E fans complain. I am qualified to work on high voltages and have a lifetime’s experience in the business. The Tesla power supply is puny compared to some of the work I have been involved with.

Andrew.

It’s not, you can see the flat primary in the photo. And while a VDG produce high voltages it cannot produce the continuous currents needed for those arcs. It’s true that most VDGs use a spherical top load while TCs use torroidals, but both styles will work on either machine.

On 19 February 2024 at 07:25 Robert Atkinson 2 Said:

A mag chuck may be difficult with a microwave oven transformer. This is bcause they have a weld run across the laminations making it very difficult to re-arrange them as all E facing the same way to make exposed poles.

 

Coming from complete ignorance, why can’t you just saw/machine the top away to leave an E shape?

Hi Nigel Graham 2, well the one that I have worked OK when it was in the microwave oven that it came out of, and it doesn’t seem to effect the one in the Video that JohnF linked too.

Regards Nick.

On 28 February 2024 at 21:28 Nigel Graham 2 Said:

Don’t those welds defeat the object of the laminations? They are that so currents cannot circulate around the core.

No. If you consider each outer leg individually there would be no path for the Eddy currents to flow unless they were welded on the inside edge as well.

Russell