Post by thread:[EE]:Capacitor Charge

Here's an interesting challenge. How can you charge a 450V 160uf Electolytic capacitor from a 12V 1A source, quickly as possible to a pre-defind charge upto 300V. Once charged I want to disconnect the charge circuit and connect another circuit that will quickly discharge the capacitor. A bit like manually connecting the capcitor to a charge circuit that is connected to a DC meter, when it reaches 300V manually connecting it to a discharge circuit. Charge circuit connected via a relays so once charged I can fully disconnect it from the charger. Also just to make it a bit more complex, I want to test that the capacitor has reached it's charge and get the result into a micro controller. Think of an automated machine that tests low power high voltage ignition coils . Known variables Charge must reach 300V or higher Once 300V is present on the capacitor it must be verified and then injected into the discharge without any effects from the charge circuit being possibe. While the capacitor is being charged it must not be connected to the disscharge circuit. Supply cannot be over 12V 1A Charge speed is important. Andy Faulkner ===== Andy Faulkner spam_OUTandyf97TakeThisOuTyahoo.com Pyrosync International http://www.pyrosync.co.uk Tel +44 778 896 6087.....................UK Dial 0778 896 6087 Fax +44 870 132 3275.....................UK Dial 0870 132 3275 http://www.event-supplies.co.uk http://www.spectacular-fireworks.co.uk __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! Mail - only $35 a year! http://personal.mail.yahoo.com/ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

Andy, its not hard to do. I've pulled apart a low cost "personal protection" device, the ones that zap the attacker with a high voltage. It was very simple, 2x C cell batteries for high A low V supply. A simple one-transistor inverter (self excited) and simple low-turns transformer with a single rect diode. That charged a 2kv polyprop cap to a few hundred volts, and very quickly, about 1/20th of a second. Then there was a simple sparkgap, so when the cap volts got high enough it jumped the gap and this energy dump was fed straight into a low turns primary of a simple autotransformer. The secondary of the autotransformer was about 120kV, at about 20 "zaps" per second. This is similar to a tesla setup. Interesting that the crude mass-produced thing just keep charging the first cap, the inverter was not disconnected at all for the secondary discharge/sparking. One transistor, one diode, and a couple of discretes. And no PIC chips in sight! -Roman Andy Faulkner wrote: {Quote hidden}> > Here's an interesting challenge. > > How can you charge a 450V 160uf Electolytic capacitor > from a 12V 1A source, quickly as possible to a > pre-defind charge upto 300V. > > Once charged I want to disconnect the charge circuit > and connect another circuit that will quickly > discharge the capacitor. > > A bit like manually connecting the capcitor to a > charge circuit that is connected to a DC meter, when > it reaches 300V manually connecting it to a discharge > circuit. > > Charge circuit connected via a relays so once charged > I can fully disconnect it from the charger. > > Also just to make it a bit more complex, I want to > test that the capacitor has reached it's charge and > get the result into a micro controller. > > Think of an automated machine that tests low power > high voltage ignition coils . > > Known variables > > Charge must reach 300V or higher > > Once 300V is present on the capacitor it must be > verified and then injected into the discharge without > any effects from the charge circuit being possibe. > > While the capacitor is being charged it must not be > connected to the disscharge circuit. > > Supply cannot be over 12V 1A > > Charge speed is important. > > Andy Faulkner > > ===== > > Andy Faulkner .....andyf97KILLspam.....yahoo.com > Pyrosync International http://www.pyrosync.co.uk > > Tel +44 778 896 6087.....................UK Dial 0778 896 6087 > > Fax +44 870 132 3275.....................UK Dial 0870 132 3275 > http://www.event-supplies.co.uk http://www.spectacular-fireworks.co.uk > > __________________________________________________ > Do You Yahoo!? > Get personalized email addresses from Yahoo! Mail - only $35 > a year! http://personal.mail.yahoo.com/ > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

At 08:26 AM 2/19/01 -0800, you wrote: >Here's an interesting challenge. > >How can you charge a 450V 160uf Electolytic capacitor >from a 12V 1A source, quickly as possible to a >pre-defind charge upto 300V. You need an inverter, obviously. At 1A/12VDC, you get 12J/s energy. The energy in the capacitor at full charge is 0.5*CV^2 = 7.2 J. It's thus possible to charge the capacitor in 0.6 second if the inverter had zero losses. So, maybe 1 second in practice. See a book on switchmode power supply design for details (eg. Pressman). >Once charged I want to disconnect the charge circuit >and connect another circuit that will quickly >discharge the capacitor. You can use something like MOSFETs or IGBTs. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" @spam@speffKILLspaminterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

{Quote hidden}> -----Original Message----- > From: Andy Faulkner [SMTP:RemoveMEandyf97TakeThisOuTYAHOO.COM] > Sent: Monday, February 19, 2001 4:26 PM > To: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU > Subject: Re: [EE]:Capacitor Charge > > Here's an interesting challenge. > > How can you charge a 450V 160uf Electolytic capacitor > from a 12V 1A source, quickly as possible to a > pre-defind charge upto 300V. > > Once charged I want to disconnect the charge circuit > and connect another circuit that will quickly > discharge the capacitor. > > A bit like manually connecting the capcitor to a > charge circuit that is connected to a DC meter, when > it reaches 300V manually connecting it to a discharge > circuit. > > Charge circuit connected via a relays so once charged > I can fully disconnect it from the charger. > > Also just to make it a bit more complex, I want to > test that the capacitor has reached it's charge and > get the result into a micro controller. > > Think of an automated machine that tests low power > high voltage ignition coils . > > Known variables > > Charge must reach 300V or higher > > Once 300V is present on the capacitor it must be > verified and then injected into the discharge without > any effects from the charge circuit being possibe. > > While the capacitor is being charged it must not be > connected to the disscharge circuit. > > Supply cannot be over 12V 1A > > Charge speed is important. > > Andy Faulkner > > The charging speed is limited by your specified power source. 300volts and 160uF give a total charge of 0.048 Coulombs For the sake of argument say the PSU can provide an maximum current of 12/300 = 0.04 Amps. t=0.048/0.04=1.2 seconds. In practice the PSU would probably be able to supply higher currents when the cap has a lower voltage accross it but this gives some kind of idea. The traditional manner in which this is done for igntion coils, is to charge the capacitor via the discharge load (i.e. the coil), and a SCR is connected directly across the charging supply. Firing the SCR discharges the cap into the load, but also shorts the output of the supply which has to be designed for this kind of operation. You also have the disadvantage of having the load in series which will increase charge time. Discharge 300v load ------UUUUU----- | | | | -- --- /\ SCR --- Cap | | | | ___|____________| 0v I'm no expert on switching converters, but all the Capactive Discharge igntions I have seen use a ringing choke type converter. Detecting when the voltage on the cap has reached 300volts should be trivial, a high impedance potentiometer, dropping the voltage to a level suitable for intput into a comparator and a suitable reference should do the trick. As long the the total impedance of the potentiometer is large enough, impact on charge time should be negligible. Mike -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email TakeThisOuTlistservEraseMEspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

Andy, If you charge at a constant current, the voltage will rise linearly as a function of time. So use your 1A source, and charge until the terminal voltage gets to your cutoff point. To get the cutoff, you could through trial and error measure the terminal voltage of the cap as it is charging, and see how long it takes to get there. Do this several times to get a good feel for the time interval, and then just charge that long before switching. Regards, Jim On Mon, 19 February 2001, Andy Faulkner wrote: {Quote hidden}> > Here's an interesting challenge. > > How can you charge a 450V 160uf Electolytic capacitor > from a 12V 1A source, quickly as possible to a > pre-defind charge upto 300V. > > Once charged I want to disconnect the charge circuit > and connect another circuit that will quickly > discharge the capacitor. > > A bit like manually connecting the capcitor to a > charge circuit that is connected to a DC meter, when > it reaches 300V manually connecting it to a discharge > circuit. > > Charge circuit connected via a relays so once charged > I can fully disconnect it from the charger. > > Also just to make it a bit more complex, I want to > test that the capacitor has reached it's charge and > get the result into a micro controller. > > Think of an automated machine that tests low power > high voltage ignition coils . > > Known variables > > Charge must reach 300V or higher > > Once 300V is present on the capacitor it must be > verified and then injected into the discharge without > any effects from the charge circuit being possibe. > > While the capacitor is being charged it must not be > connected to the disscharge circuit. > > Supply cannot be over 12V 1A > > Charge speed is important. > > Andy Faulkner > > > > > > ===== > > Andy Faulkner RemoveMEandyf97TakeThisOuTyahoo.com > Pyrosync International http://www.pyrosync.co.uk > > Tel +44 778 896 6087.....................UK Dial 0778 896 6087 > > Fax +44 870 132 3275.....................UK Dial 0870 132 3275 > http://www.event-supplies.co.uk http://www.spectacular-fireworks.co.uk > > > __________________________________________________ > Do You Yahoo!? > Get personalized email addresses from Yahoo! Mail - only $35 > a year! http://personal.mail.yahoo.com/ > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservEraseME.....mitvma.mit.edu with SET PICList DIGEST in the body EraseMEjimjpes.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservEraseMEEraseMEmitvma.mit.edu with SET PICList DIGEST in the body

At 10:07 AM 2/19/01 -0800, James Paul wrote: > Andy, > > If you charge at a constant current, the voltage will rise linearly > as a function of time. So use your 1A source, and charge until the > terminal voltage gets to your cutoff point. To get the cutoff, you > could through trial and error measure the terminal voltage of the > cap as it is charging, and see how long it takes to get there. > Do this several times to get a good feel for the time interval, and > then just charge that long before switching. I did this in a different scale for a thermal printer. A current-limited boost SMPS charged 1000uF of output caps as fast as it could, to 32V, from whatever it could get on the input. The PS then signals the micro when it's ok to print the next dot-line. That requires as much as 19A from the caps. This let me run the printer WAY down on line voltage, and still get good printing. Final operating range was 70-140VAC into the wall-wart, using a 20W transformer. Even at very low line, the current limiting kept me from overheating the transformer. -- Dave's Engineering Page: http://www.dvanhorn.org Where's dave? http://www.findu.com/cgi-bin/find.cgi?kc6ete-9 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservspam_OUTKILLspammitvma.mit.edu with SET PICList DIGEST in the body

Andy; The most traditional way of meeting your goal is with a flyback converter. It can be self oscillating or driven, but it is almost immaterial, since feedback does not exist in a traditional sense. You will want to pursue the discontinuous mode. The continuous mode lends itself to feedback in a much easier manner, and you have no such feedback. You just reach 300VDC and stop. A comparator will sufice. The goal is to design the flyback with the ratio that you need at a reasonable duty cycle. The duty cycle can be chosen for a target value, and then let the current sense in the current mode controller cut it off on every cycle. This will charge up 'packets' of energy in the transformer, which are then transfered to the secondary. If you have guestimated a duty cycle, you can then select a winding ratio to meet this goal. Say you choose the ratio for a max possible voltage of 400VDC. The unit will than have the capacity to meet 300VDC while production tolerances wander all over the place. Be careful that you do not try to apply the equations for continuous mode, they are all different. I suggest you buy the Pressman book on switching supplies if you are going to go any further. It is like opening a treasure chest of stuff you cannot find anywhere else (or at least in one place). A forward converter might do the job too. Refer to Pressman, again. Also, refer to automotive CDI ignition and xenon flash power supply designs, they are both very similar. If this is a one of, you could steal the gust of a flash! Rub your rabbit foot, this one could be a pretty big job (because of the small details). Chris~ Andy Faulkner wrote: > Here's an interesting challenge. > > How can you charge a 450V 160uf Electolytic capacitor > from a 12V 1A source, quickly as possible to a > pre-defind charge upto 300V. > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body