25kV AC

You could use something like the 2D21 thyratron for the second stage, probably! they can take 1300 PIV, switch half an amp and are very fast.

From the archives, 1952:

Gas thyratrons at bottom.

Convert low voltage AC to high voltage DC first via solid state, and then second stage HV DC to AC with tubes

Well, 20-year-old auto coils did 40kV peak, so there's at least SOME commercial units that can do the deed.

Not sure how the cores would stand up to continuous AC, I'd guess the iron is lossy.

whit3rd wrote in news:22395bd0-b492-48aa-8713- snipped-for-privacy@googlegroups.com:

They did no such thing s they are NOT "transformers" in the sense we know of them.

They rely 100% on the field collpase of a DC energization of the COIL that is curtailed by (the opening of) a switch. That sudden field collapse is why the voltage is so high. Running AC into the primary of a car coil does NOT provide the same 25kV that the coil makes when a set of points open on a big DC Standing field and it slams back in at a high slew rate.

That is the entire principal on which a points operated DC fired car coil ignition works. It even makes kV potentials on the primary when it happens. That's why it needs a damping 'condenser'.

I'd recommend using a small oil-immersed 60 Hz dental X-ray transformer powered from an autotransformer. The frequency should be in the right ballpark, you can easily tweak the output voltage, and the power level should be in the ballpark. Larger X-ray transformers are also available on the surplus market if you need higher power.

Why, then, does the primary side show a few hundred volts when it fires? One magnetic element, two windings: a transformer.

The '40 kV' is what a high-energy ignition is advertised for, though of course, it only actually gets to whatever the 0.050" spark gap will take.

whit3rd wrote in news: snipped-for-privacy@googlegroups.com:

A collapsing DC field will induce a high voltage even without a secondary.

So the promary side gets a huge voltage induced on it. THAT high voltage couples to the secondary on regular xfmr ratio, and gets stepped up and the collapsing field also helps that side produce a higher voltage. So the closed points energize *and hold* a primary that makes a nice strong field. Then, the points get opened and that field collapses. That collapsing field has a near instantaneous slew rate, and therefore *theoretically* the voltage can be infinite. But in real world use, there are factors that limit the in slam (FLOABT) inducement, so we know it is much less. But hey 25 to 50kV ain't bad (now they got solid state circuits firing the coil(s). The key is into what type of load. It can do an arc across a spark plug gap in a pressurized gas/particulate environment.

Not much capacitive loading on a plug wire.

You can get an accurate ratio by simply pumping it with a low voltage AC of a few volts. The secondary should show up, and you can do simple math for the ratio and be fairly accurate. If you can look up the specs on the coil itself, you can obtain an exact set of numbers.

whit3rd wrote in news: snipped-for-privacy@googlegroups.com:

You mean what it can drive into it.

It can do it. They say 40kV, that hot sucker fires those modern platinum tipped plugs *real good*. They do not use points though.

But even the old ones were pretty hot (25 - 35kV). I wasn't saying that it was not a transformer. I was just saying that the application a coil has compared to an actual transformer differs a bit. Though I did not frame it that way. I am more instructive in person. Especially if there is a pool table around and maybe a couple beers.

I used to build CD ignitions for motorcycles. I dumped a charged cap into the primary of the coil with an SCR, a closing switch. That's the opposite of field collapse.

Well, son, ya gots it ron / konfutzzled. The configuration is as follows: it is a transformer, with low-Z / relatively low number of turns primary and a high-z / large number of turns secondary; common ground. When the points close, the battery is connected to the primary and current increases until the points open and the (NOT "damping") condenser across the points /or, usually/ from ground to primary high end then resonates,as in a standard flyback system. The dV/dT and primary parameters like inductance and amount of current produces a 600V pulse (about). The rest is winding ratio to give one the thousands of volts.

Before those new-fangled spark cols there were magnetos,son.

But the interwinding capacitance in the secondary soaks up the energy.

The primary and the secondary of an ignition coil are tightly coupled, so both sides see the same voltage (scaled by the turns ratio, obviously).

You shouldn't talk about them as if they weren't tightly coupled.

It tries to, but the changing flux induces voltage across the secondary, and that voltage charges up the secondary's interwinding capacitance, drawing current through secondary in a way that slows down the collapse of the flux.

Until you figure in the internal capacitances.

But quite a bit between the turns on the secondary.

You do need to characterise any coil by measuring its self-resonant frequency, amongst other features.

Not true. An ignition coil is a 100:1 step-up transformer, as anybody who has built an electronic ignition around one will testify.

Electronic ignitions build up anything from 250V to 400V across a capacitor, and use a thyristor to apply that to the input side of the coil which generates anything from 25kV to 40kV across the output side of the coil.

There's enough inter-winding capacitance that the coil rings for a few cycles.

The original mechanical circuit breaker (points) interrupted a current to get the secondary to ring up to the same 25kV to 40kV

It doesn't make kV potentials across the primary - the points would have arced over if it had.

snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:

The caps on a points system are not big enough to do that work. They merely dampen the back emf, keeping the points from transferring metal from one to the other. While the points are closed and the coil energized, the cap (condenser)is not even in the circuit.

You induced a voltage in the secondary because you introduced a high slew rate current dump into the primary with your SCR switch.

The pulses induced in the secondary that way are a lot 'softer'.

Coil makes less noise too.

So with the field in place, standing there on the coil, and an open switch, the field collapses as fast as it possibly can. A single short pulse is induced. The coil makes a nice tick sound in its core laminations when it does that.

Points are high maintainence.

Bill Sloman wrote in news: snipped-for-privacy@googlegroups.com:

Sure does. Points DO arc. That is why they have the condenser, because if they did not metal transfer would occur and ruin the points in short order. That ONLY happens when an arc is present.

So the points are closed and the coil fully energized for the entire "dwell time", and when they open the bettery is OUT of the circuit and the field collapses and the slew rate it slams down at induces a high voltage in the secondary. 16 thousand times every minute for a good average (v8).

Take your 100:1 ratio. 14 V in makes 140 V out. NOT enough.

So the collapsing flux field is the mechanism by which the secondary snaps up to a high voltage and the plug gap fires on the secondary side and the point gap fires on the primary. The primary side gets the condenser because it keeps the points from eating each other up.

That is what the coil gets. Regular system voltage. So I said 14V as a good number.

This arrangement could help, both insulation and capacitance:

Best regards, Piotr

Where do you find them with enough insulation resistance that the secondaries don't arc over at 25KV?

Are you using a comma instead of a period? 15,756KC reads as 15.756MHz in the United States which would be an interesting sweep design. ;-)

US TVs used 15734Hz for NTSC color, and 15750Hz for NTSC Monochrome. (System M)

Smooth, rounder solder joints are the rule for HV, instead of the typical method of just enough solder for a good connection. Some HV second anode wire was made to handle up to 40KV

Ah, dental X-ray transformer, awesome, thanks Bert! Do you think I'll be stuck with using transformer oil? Maybe with degreasing and vacuum degassing thrown in?