On 9/30/19 8:19 PM, Winfield Hill wrote:> bloggs.fredbloggs.fred@gmail.com wrote... >> >> On September 30, 2019, Winfield Hill wrote: >>> >>> We need a 25kV rms AC signal. OK, that's 70kV p-p. >> >> What exactly is your output waveform? It sounds like >> a 70kVpp of 5-10ms pulses at 60-400Hz rep rate. > > The industry standard is 50Hz sine wave, often 24kV rms. > >what about the way the 25kV AC electrified railroad traction motors return power to the grid, low voltage AC to ~1-2k DC by PWM boost-type converter, DC to 3 phase AC "modified sine" with thyristors, then boost to 25k with 3 phase transformer. But in miniature...
25kV AC
Started by ●September 30, 2019
Reply by ●September 30, 20192019-09-30
Reply by ●September 30, 20192019-09-30
On 9/30/19 9:35 PM, bitrex wrote:> On 9/30/19 8:19 PM, Winfield Hill wrote: >> bloggs.fredbloggs.fred@gmail.com wrote... >>> >>> On September 30, 2019, Winfield Hill wrote: >>>> >>>> We need a 25kV rms AC signal. OK, that's 70kV p-p. >>> >>> What exactly is your output waveform? It sounds like >>> a 70kVpp of 5-10ms pulses at 60-400Hz rep rate. >> >> The industry standard is 50Hz sine wave, often 24kV rms. >> >> > > what about the way the 25kV AC electrified railroad traction motors > return power to the grid, low voltage AC to ~1-2k DC by PWM boost-type > converter, DC to 3 phase AC "modified sine" with thyristors, then boost > to 25k with 3 phase transformer. > > But in miniature...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.
Reply by ●September 30, 20192019-09-30
On 9/30/19 10:57 AM, jlarkin@highlandsniptechnology.com wrote:> On Mon, 30 Sep 2019 07:53:18 -0500, "Tim Williams" > <tiwill@seventransistorlabs.com> wrote: > >> Two CRT flybacks + pair 6BK4C + HV optos to drive them (since Vgk ~ 100V). >> :^) >> >> One flyback needs to be heavily isolated, suggest LEDs + PV for expedient >> isolation; otherwise, a custom resonant transformer will do. >> >> Tim > > Tubes are not a bad idea at all here. A fiberoptic fed cascode would > be fun. > > Win, can you use differential drive into your gadget? Maybe a > full-bridge with the uppers just constant-current, so the lower grids > are near ground. > > Watch out for x-rays. > > >From the archives, 1952: <https://imgur.com/a/ahNRzcH> 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
Reply by ●September 30, 20192019-09-30
On Monday, September 30, 2019 at 1:45:49 AM UTC-7, Winfield Hill wrote:> We need a 25kV rms AC signal. OK, that's 70kV p-p.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.
Reply by ●September 30, 20192019-09-30
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'.
Reply by ●October 1, 20192019-10-01
Winfield Hill wrote:> Steve Wilson wrote... >> >> On Monday, September 30, 2019 at 8:19:53 PM UTC-4, Winfield Hill wrote: >> >>> The industry standard is 50Hz sine wave, often 24kV rms. >> >> 50Hz in a 60Hz country? Then they have to generate it. >> How do they do that? Learn how, then you can do the same. > > The papers I've come across are all in the EU. But 60Hz > is really an equivalent. I suppose the issue is how long > the "zero-crossing" time is, when the voltage has dropped > below an effective value. Somehow the electrospinning > thread doesn't break, and when the voltage returns, a new > thread starts. Soon there are many simultaneous threads. > >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.
Reply by ●October 1, 20192019-10-01
On Monday, September 30, 2019 at 7:55:02 PM UTC-7, 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.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.
Reply by ●October 1, 20192019-10-01
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. 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.
Reply by ●October 1, 20192019-10-01
whit3rd <whit3rd@gmail.com> wrote in news:ce456904-c15f-4773-92c0-db0d1ef5926f@googlegroups.com:> 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. >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.
Reply by ●October 1, 20192019-10-01
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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
