Discharge a huge voltage
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From: Tim Wescott on 4 Mar 2010 14:10 lerameur wrote: > On 4 mar, 12:35, WangoTango <Asgar...(a)mindspring.com> wrote: >> In article <OdOdnTwYH-NUeRLWnZ2dnUVZ_vqdn...(a)web-ster.com>, >> t...(a)seemywebsite.now says... >> >> >> >>> lerameur wrote: >>>> On Mar 3, 9:20 pm, Hammy <s...(a)spam.com> wrote: >>>>> On Thu, 04 Mar 2010 03:03:26 +0100, Sjouke Burry >>>>> <burrynulnulf...(a)ppllaanneett.nnll> wrote: >>>>>> lerameur wrote: >>>>>>> hello, >>>>>>> I have a very simple circuit here, I am charging a 900uF capacitor to >>>>>>> 600v. (900v max capacity) >>>>>>> I want to discharge this at 0.01seconds interval. I have 30 ohm >>>>>>> resistance, without so from my calculation I should have 20 amp max. >>>>>>> All this element are in series with each other, I want to add a >>>>>>> transistor (or mosfet) to make and break the intervals I need. >>>>>>> DO I need to get a 600v and a 20 amp rated transistor ? >>>>>>> Thanks >>>>>> Always apply a safety factor, I would use 800 and 30. >>>>>> Whether the 30 amp is needed depends on your duty cycle, >>>>>> if the dutycycle is low, 20 and even 10 might be enough. >>>>>> Just check the allowed peak current. >>>>> If he is saying >>>>>> " (900v max capacity)" >>>>> Shouldnt he be useing a 1kV-1.2kV fet or IGBT with maybe a drain >>>>> clamp? >>>> The capacitor can take up to 900v, but I am only charging it to 600v.. >>>> I thought maybe if I can get some transistors in parallel to drain >>>> the current, but using transistor rated below 600v. But I do not think >>>> it will work. >>> Certainly not in parallel -- a parallel connection sees the full voltage >>> across each device. >>> In theory you could connect transistors in series, with appropriate gate >>> or base drivers. But it'd be a lot cheaper to just get a 900V transistor. >> What about a big assed 'puck' style SCR / thyristor? >> I don't know about how fast you can trigger the things, but don't they >> use them for big motor control apps? >> I know you can get them with hold off voltages in the 1000V+ range and >> dump hundreds of amps through them. Might get a bit hot, but what about >> the heat from the cap ESR???- Masquer le texte des messages pr�c�dents - >> >> - Afficher le texte des messages pr�c�dents - > > I do not want to discharge all the gap, > Ok Bob mentionned the time delay, I may have to reduce the resistance, > (increase the current) BUt I need a spark in the circuit. > So capacitor, resistance, spark gap and transistor. > Ok so I need several kV, lets say 3000v , but now lets say I use a 10 > ohm resistance, that gives use a wapping 300 amp. > Is there such a transistor rated at 3kV and 300 amp? > > That was my original idea, but when I saw outstanding figures I > decided to decrease the voltage and start low. Maybe if you share _all_ of what you _really_ want to do? There are IGBT modules (if not individual transistors) that do over 3kV, and if you can't find one that does 300A, you can probably gang them together if you can figure out the current sharing. 600V would make a spark gap difficult to control, although I suppose you could make it happen. Just how you trigger the spark has a huge cost/precision tradeoff; knowing how tightly you need to control the spark makes a big difference to how you may want to drive it. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
From: Ecnerwal on 4 Mar 2010 14:27 In article <K-OdneKLsMMhmQ3WnZ2dnUVZ_tCdnZ2d(a)web-ster.com>, Tim Wescott <tim(a)seemywebsite.now> wrote: > Turn-off becomes an issue. I know that there are ways to turn off an > SCR on a DC supply, but it's some wacky thing involving an auxiliary > inductor that snaps the current off briefly so the SCR can turn off -- > it all looks pretty smoky to me. It's definitely getting into the realm of tubes (mostly thyratrons) ruling, though at high amperage the tubes are available, but do tend to cost a few thousand dollars. At the lower amperage ranges, if you stick to those tubes that are still commonly available they can cost a lot less than silicon to do the same job. On the third hand, the application becomes highly suspect as I can think of a number of nefarious uses this might be aiming towards I wouldn't care to help with. Not quite as blatant as the person a few months ago that was evidently looking for help in designing a roadside bomb, but a spark gap creates an infernal amount of RF noise... -- Cats, coffee, chocolate...vices to live by
From: lerameur on 4 Mar 2010 15:20 On 4 mar, 14:27, Ecnerwal <MyNameForw...(a)ReplaceWithMyVices.Com.invalid> wrote: > In article <K-OdneKLsMMhmQ3WnZ2dnUVZ_tCdn...(a)web-ster.com>, > Tim Wescott <t...(a)seemywebsite.now> wrote: > > > Turn-off becomes an issue. I know that there are ways to turn off an > > SCR on a DC supply, but it's some wacky thing involving an auxiliary > > inductor that snaps the current off briefly so the SCR can turn off -- > > it all looks pretty smoky to me. > > It's definitely getting into the realm of tubes (mostly thyratrons) > ruling, though at high amperage the tubes are available, but do tend to > cost a few thousand dollars. At the lower amperage ranges, if you stick > to those tubes that are still commonly available they can cost a lot > less than silicon to do the same job. > > On the third hand, the application becomes highly suspect as I can think > of a number of nefarious uses this might be aiming towards I wouldn't > care to help with. Not quite as blatant as the person a few months ago > that was evidently looking for help in designing a roadside bomb, but a > spark gap creates an infernal amount of RF noise... > > -- > Cats, coffee, chocolate...vices to live by I am looking to make a unidirectional spark. I also thought of using like the old days a rotary spark gap, but with a 3600 rpm motor, even with 10 contacts around I get 3600rpm/60 =600rps with 10 contacts = 6000hz. I guess 6000hz is good enough. Also with a higher voltage, could I increase the resistance.? JP
From: sparky on 4 Mar 2010 18:25 On Mar 4, 3:20 pm, lerameur <leram...(a)yahoo.com> wrote: > On 4 mar, 14:27, Ecnerwal > > > > > > <MyNameForw...(a)ReplaceWithMyVices.Com.invalid> wrote: > > In article <K-OdneKLsMMhmQ3WnZ2dnUVZ_tCdn...(a)web-ster.com>, > > Tim Wescott <t...(a)seemywebsite.now> wrote: > > > > Turn-off becomes an issue. I know that there are ways to turn off an > > > SCR on a DC supply, but it's some wacky thing involving an auxiliary > > > inductor that snaps the current off briefly so the SCR can turn off -- > > > it all looks pretty smoky to me. > > > It's definitely getting into the realm of tubes (mostly thyratrons) > > ruling, though at high amperage the tubes are available, but do tend to > > cost a few thousand dollars. At the lower amperage ranges, if you stick > > to those tubes that are still commonly available they can cost a lot > > less than silicon to do the same job. > > > On the third hand, the application becomes highly suspect as I can think > > of a number of nefarious uses this might be aiming towards I wouldn't > > care to help with. Not quite as blatant as the person a few months ago > > that was evidently looking for help in designing a roadside bomb, but a > > spark gap creates an infernal amount of RF noise... > > > -- > > Cats, coffee, chocolate...vices to live by > > I am looking to make a unidirectional spark. I also thought of using > like the old days a rotary spark gap, but with a 3600 rpm motor, even > with 10 contacts around I get 3600rpm/60 =600rps with 10 contacts = > 6000hz. I guess 6000hz is good enough. > Also with a higher voltage, could I increase the resistance.? > > JP- Hide quoted text - > > - Show quoted text - You could go higher. 600 volts is certainly not a HUGE voltage.
From: lerameur on 4 Mar 2010 20:15
On Mar 4, 6:25 pm, sparky <sparky...(a)yahoo.com> wrote: > On Mar 4, 3:20 pm, lerameur <leram...(a)yahoo.com> wrote: > > > > > On 4 mar, 14:27, Ecnerwal > > > <MyNameForw...(a)ReplaceWithMyVices.Com.invalid> wrote: > > > In article <K-OdneKLsMMhmQ3WnZ2dnUVZ_tCdn...(a)web-ster.com>, > > > Tim Wescott <t...(a)seemywebsite.now> wrote: > > > > > Turn-off becomes an issue. I know that there are ways to turn off an > > > > SCR on a DC supply, but it's some wacky thing involving an auxiliary > > > > inductor that snaps the current off briefly so the SCR can turn off -- > > > > it all looks pretty smoky to me. > > > > It's definitely getting into the realm of tubes (mostly thyratrons) > > > ruling, though at high amperage the tubes are available, but do tend to > > > cost a few thousand dollars. At the lower amperage ranges, if you stick > > > to those tubes that are still commonly available they can cost a lot > > > less than silicon to do the same job. > > > > On the third hand, the application becomes highly suspect as I can think > > > of a number of nefarious uses this might be aiming towards I wouldn't > > > care to help with. Not quite as blatant as the person a few months ago > > > that was evidently looking for help in designing a roadside bomb, but a > > > spark gap creates an infernal amount of RF noise... > > > > -- > > > Cats, coffee, chocolate...vices to live by > > > I am looking to make a unidirectional spark. I also thought of using > > like the old days a rotary spark gap, but with a 3600 rpm motor, even > > with 10 contacts around I get 3600rpm/60 =600rps with 10 contacts = > > 6000hz. I guess 6000hz is good enough. > > Also with a higher voltage, could I increase the resistance.? > > > JP- Hide quoted text - > > > - Show quoted text - > > You could go higher. > > 600 volts is certainly not a HUGE voltage. Ok here is the circuit I am trying to replicate. Some of you will say it is not possible, it is not concrete, but hey I am just trying it out. Like I said , I just want to make a simple circuit with a capacitor discharging through a spark gap for now, nothing else. http://www.energeticforum.com/renewable-energy/3235-gray-tube-replication-2..html&usg=__iSdcL6jpOkRkqf7S8vhO8UyJzew=&h=711&w=831&sz=132&hl=en&start=6&sig2=-iiXL_uogSvS1uj0DcYeXw&um=1&itbs=1&tbnid=ZeLwLSgYlT4p6M:&tbnh=123&tbnw=144&prev=/images%3Fq%3Dgrey%2Btube%2Bbedini%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26sa%3DN%26rls%3Dorg.mozilla:en-US:official%26tbs%3Disch:1&ei=bDGQS7j0N8_I_gbih4nVDA Also, in the schematic shown, there is a diode that seems to be on backwards, but some dud on the web site says it is not.. I still think it is on backward, can somebody has an explanation for that. The circuit is doable, the effect well not so much I think thanks JP. |