25kV AC

DecadentLinuxUserNumeroUno@decadence.org wrote:
> whit3rd <whit3rd@gmail.com> wrote in news:22395bd0-b492-48aa-8713-
> e26daf08651d@googlegroups.com:
> 
>>
>> Well, 20-year-old auto coils did 40kV peak, so there's
>> at least SOME commercial units that can do the deed.
>>
> 
>    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'.
> 
   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.

On Tuesday, October 1, 2019 at 2:42:13 PM UTC+10, DecadentLinux...@decadence.org wrote:
> whit3rd <whit3rd@gmail.com> wrote in
> news:ce456904-c15f-4773-92c0-db0d1ef5926f@googlegroups.com: 
> 
> > Why, then, does the primary side show a few hundred volts when it
> > fires? One magnetic element, two windings: a transformer. 
> 
>   A collapsing DC field will induce a high voltage even without a 
> secondary.

But the interwinding capacitance in the secondary soaks up the energy.
 
>   So the primary 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. 

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.

> So the closed points energize *and hold* a primary 
> that makes a nice strong field.  Then, the points get opened and that 
> field collapses. 

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.

> That collapsing field has a near instantaneous slew 
> rate, and therefore *theoretically* the voltage can be infinite.

Until you figure in the internal capacitances.

> 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.

But quite a bit between the turns on the secondary.
 
>   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.

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

-- 
Bill Sloman, Sydney

On Tuesday, October 1, 2019 at 12:55:02 PM UTC+10, DecadentLinux...@decadence.org wrote:
> whit3rd <whit3rd@gmail.com> wrote in news:22395bd0-b492-48aa-8713-
> e26daf08651d@googlegroups.com:
> 
> > 
> > Well, 20-year-old auto coils did 40kV peak, so there's
> > at least SOME commercial units that can do the deed.  
> > 
> 
>   They did no such thing s they are NOT "transformers" in the sense 
> we know of them. 
> 
>   They rely 100% on the field collapse 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.

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

>   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'.

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

-- 
Bill Sloman, Sydney

jlarkin@highlandsniptechnology.com wrote in
news:9gm5pedtvnbk4ik6ugrath0baolk3cm08s@4ax.com: 

> On Tue, 1 Oct 2019 02:54:55 +0000 (UTC),
> DecadentLinuxUserNumeroUno@decadence.org wrote:
> 
>>whit3rd <whit3rd@gmail.com> wrote in news:22395bd0-b492-48aa-8713-
>>e26daf08651d@googlegroups.com:
>>
>>> 
>>> Well, 20-year-old auto coils did 40kV peak, so there's
>>> at least SOME commercial units that can do the deed.  
>>> 
>>
>>  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 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.
> 
  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.

Robert Baer <robertbaer@localnet.com> wrote in
news:KZAkF.9594$O_.6196@fx39.iad: 

> DecadentLinuxUserNumeroUno@decadence.org wrote:
>> whit3rd <whit3rd@gmail.com> wrote in
>> news:22395bd0-b492-48aa-8713- e26daf08651d@googlegroups.com:
>> 
>>>
>>> Well, 20-year-old auto coils did 40kV peak, so there's
>>> at least SOME commercial units that can do the deed.
>>>
>> 
>>    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'. 
>> 
>    Well, son, ya gots it ron / konfutzzled.

  You have already fucked up with this stupid shit.

>    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.

   Yeah...  I know what an ignition coil is, chump. (or is it pops?)

>    When the points close, the battery is connected to the primary
>    and 
> current increases until the points open

  Yeah...  That is exactly what I said.  Current reaches max very 
fast though, so your "increases until opened" crap is well.... crap.

  THEN the points open.

> and the (NOT "damping") 
> condenser across the points

  Never said it did.  It does not even get in the circuit until and 
only WHILE the points are OPEN.  Otherwise it is shorted across the 
closed points.  D'oh!    You are getting senile, pops.

> /or, usually/ from ground to primary
> high end then resonates,as in a standard flyback system.

  A flyback is a TV anode transformer.  An old points based 
automobile ignition coil and circuit is a different animal than a TV 
flyback.  Still a transformer, still a primary and secondary.  No 
diode string in a car coil though.

  And the 'condenser' is only there for the points, like I said.

>    The dV/dT and primary parameters like inductance and amount of 
> current produces a 600V pulse (about).

  Whatever it is, it is.  Could be as much as a kilovolt.  Without 
the condenser, it would register even more when the points open.

  Not about the current though, it is about the speed at which the 
standing DC field collapses.  So energization VOLTAGE is all that 
matters.

>    The rest is winding ratio to give one the thousands of volts.

  Yep.  We know how a transformer steps voltage, Clyde.

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

  Before you thought you were funny, I actually considered you to 
have a modicum of intelligence, fuckhead.

  I had magnetos when I was a kid too, jackass...  err...  pops.

  Ya Goddamned hillbilly wannabe fucktard.

Bill Sloman <bill.sloman@ieee.org> wrote in
news:744aac08-c0ed-405b-8c79-f46f52ecee58@googlegroups.com: 

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

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.

Tauno Voipio wrote:

> The tens of kilovolts need careful attention to electric
> field strength. The wires and terminals need to pretty
> bulky to keep the field strength under control.

This arrangement could help, both insulation and capacitance:

https://tower-pro.com/listings/austin-insulators-inc/austin-ring-transformer/

	Best regards, Piotr

On Monday, September 30, 2019 at 5:38:09 AM UTC-4, Piotr Wyderski wrote:
> Winfield Hill wrote:
> 
> >   We need a 25kV rms AC signal.  OK, that's 70kV p-p.
> 
> ~100 small 230V/12V transformers with primaries connected
> in series should do the job. This is 10x10 grid of them,
> doable and reasonably compact.
> 
> 	Best regards, Piotr


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

On Monday, September 30, 2019 at 10:23:17 AM UTC-4, John Robertson wrote:
> On 2019/09/30 7:05 a.m., Winfield Hill wrote:
> > Tim Williams wrote...
> >>
> >> Two CRT flybacks + pair 6BK4C + HV optos to drive them
> >> (since Vgk ~ 100V).  :^)
> > 
> >   Flyback plus HV diode, one each for pos and neg
> >   pulsing, into a 35kV cap, make a 25kV square wave?
> >   But we also do need some time at zero volts.
> > 
> > 
> 
> B&W TVs used ~15KV flybacks running around 15,756KC and were AC output 
> until the HV diode which was external in many cases.


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)


 
> Is the frequency a problem? If not then as suggested use a colour TV 
> flyback and cut open the shell to remove the HV diodes and that will 
> probably work. Flybacks are in the uA range, and I assume you aren't 
> looking for any current here.
> 
> A single flyback would then suffice. Still available from sources such as:
> 
> https://www.goldmine-elec-products.com/
> 
> Possibly
> 
> http://www.surplussales.com
> 
> I have a small pile of colour TV flybacks from both projectors and TVs - 
> any one of which will likely work.
> 
> John :-#)#

On Monday, September 30, 2019 at 11:33:36 AM UTC-4, Tauno Voipio wrote:
> On 30.9.19 18:17, Winfield Hill wrote:
> > Tauno Voipio wrote...
> >>
> >> The tens of kilovolts need careful attention to electric
> >> field strength. The wires and terminals need to pretty
> >> bulky to keep the field strength under control.
> > 
> >   Yes indeed.  We use a nice 4.8mm dia wire, AWM 3239,
> >   with a 40kV rating, CSA TV-40.  Judd Flexrad HV.
> 
> 
> Please be careful with radii of wire ends and terminations,
> so that your kilovolts won't sizzle into thin air as corona.


  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