Please help me understand this circuit - Page 1
Forum section: electronics / general

author: wirehead_freenode
author_rank: Contributor
timestamp: August 15, 2020, 04:57:58 pm
content: Hello,I am trying to understand how this circuit delays the discharge of the middle capacitor bank across the inductor. Has to do with the potentiometer settings.What's more, I tried building the circuit and it only lit up the lamps and turned off, and didn't pulse, regardless of what the potentiometer was set at. Probably faulty wiring or something.Any assistance will be appreciated!

author: Ian.M
author_rank: Super Contributor
timestamp: August 15, 2020, 05:35:20 pm
content: Up to the photoflash cap bank, its a voltage doubling charge pump, with the 120W bulb as a current limiter. From 120V RMS in, it will give non-isolated 340V DC on the positive terminal of the cap bank. However the component ratings are all wrong - the cap bank needs a >350V working voltage rating, the 130uF cap needs a 200V rating, and both diodes should be 1N5404 to have enough margin on their voltage rating.to the right of the cap bank its a mess. In theory it should pulse if the cap bank voltage rises fast enough and the selected 1Meg variable resistor isn't set too low and the SCR is sensitive enough. However if it ever fails to pulse it never recovers as the 10uF cap just charges up to the cap bank voltage then there's no volts across the neon to trigger it, so YMMV!

author: wirehead_freenode
author_rank: Contributor
timestamp: August 15, 2020, 06:04:01 pm
content: Thank you very much.I was this close to using an Arduino-based relay to control the pulsing. Would have raised costs substantially. But you provided a lot of info. Can work with that.

author: wirehead_freenode
author_rank: Contributor
timestamp: August 15, 2020, 06:36:00 pm
content: What happens without the neon bulb?Edit: Also, the reason this circuit wasn't working is that I am using a different SCR that has a 50 mA gate trigger. The circuit was designed for a 40 mA gate trigger SCR. How can I make up that difference?

author: Renate
author_rank: Super Contributor
timestamp: August 15, 2020, 10:46:12 pm
content: Ah, this circuit looks like it came from an earlier era when life was cheap.If you analyze it, what it is is a lightbulb in series with a PC power supply."Oh, yeah, if we short the power supply output then the power supply input will present a dead short and the light bulb will go on.Nah, you don't want to do this.First, the current through the SCR could get large.You're using a bunch of big capacitors for no reason.Your timing control is not only referenced to the AC line, it has voltaged doubled DC on it.Oh, and you don't have any bleeders across some big honking capacitors.Also, I think they have the R's and the 10µF switched.Use a triac and an optoisolator running off a 555 or a microcontroller.

author: Zero999
author_rank: Super Contributor
timestamp: August 16, 2020, 05:05:43 pm
content: Quote from: wirehead_freenode on August 15, 2020, 06:36:00 pmThe neon lamp is a spark gap. When a certain voltage is reached, it starts conducting, until the current through it drops below a certain level and it stops conducting. I don't think the reason why it isn't working has anything to do with the SCR.This circuit isn't suitable for the beginner. It can easily kill you. Those capacitors hold their charge for a considerable time, after the power has been disconnected. This is the typical case of: if you have to ask such questions, about such a potentially dangerous circuit, then don't build it, as you clearly don't have the experience to do so safely.What are you trying to do? If it's a strobe, then how about using some high power LEDs? They run at much safer voltages and can be over driven to produce very short, bright flashes.

author: Ian.M
author_rank: Super Contributor
timestamp: August 16, 2020, 05:49:48 pm
content: I'm unsure of its purpose myself. *MAYBE* its to produce a high pulsed magnetic field in the 2.5mH coil, or depending on the coil self-capacitance it could be a LF radio jammer. Even if the neon trigger circuit worked reliably, its still ill thought out as the resonant reversal will kill the Photoflash caps fairly quickly!

author: JackJones
author_rank: Regular Contributor
timestamp: August 16, 2020, 06:06:23 pm
content: It's a magnetic pulser for some extremely dubious purposes. A quick search brought up this:http://www.newmediaexplorer.org/chris/2009/02/19/build_a_low_cost_simple_magnetic_pulser.htmQuoteQuoteThis is the kind of device where if you need to ask for instructions, you should not be touching it. Even if you do know you should not be touching it. This is a deadly accident just waiting to happen.

author: langwadt
author_rank: Super Contributor
timestamp: August 16, 2020, 06:15:17 pm
content: Quote from: JackJones on August 16, 2020, 06:06:23 pmQuackery , now with high voltage to help cull the herd

author: dbctronic
author_rank: Regular Contributor
timestamp: August 16, 2020, 07:00:29 pm
content: It's a pre-zotzer for comet pills, quartz crystals, pyramid razor blade sharpeners, and the like. Applied just before using them. It gives them--you know--a zotz.Subdodgy technology--a new forum section!

author: Renate
author_rank: Super Contributor
timestamp: August 16, 2020, 08:07:41 pm
content: You have to be careful, if you get the phase wrong it will erase your mind.

author: wirehead_freenode
author_rank: Contributor
timestamp: August 17, 2020, 01:44:48 am
content: Ah, I should have said off the bat. It's a Pulsed Electrical Magnetic Field (PEMF) therapy machine. It's a legitimate form of treatment, the FDA has given that technology the OK to be used for treating brain cancer even.I'll be careful not to erase my brain with it. lol.My halfway working version of the machine stuck on rapid pulse mode was somewhat useful for my chronic headache, I just want the pulses to get in deeper with a longer charge.I bought an SCR with good voltage specs that has a 40 mA gate trigger that should work with the circuit. Also the designer said it needs a 1M resistor from the gate to ground.I've been careful to discharge the caps with a high watt 10k resistor before working on it.Thank you all for your help and your concern.A study on PEMF treating cancer, if interested:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5119968/"Mice exposed for 60 and 180 min daily showed a 30% and 70% tumor reduction, respectively, at week 4, if compared to baseline." Pretty promising stuff.I know using a rando PEMF circuit to treat a chronic headache is a bit off the beaten path but I was really pressed for solutions. Neurologist didn't do anything for it.I'm not saying I have brain cancer, but it does facilitate deep tissue healing.

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2020, 08:10:44 am
content: Quote from: JackJones on August 16, 2020, 06:06:23 pmSome of the other material on that site is total BS.Quotehttp://www.newmediaexplorer.org/chris/2007/08/22/cell_phones_ear_eye_damage_high_blood_pressure_more.htmQuote from: wirehead_freenode on August 17, 2020, 01:44:48 amThat study was on mice.Transcranial magnetic stimulation is a legitimate medical treatment, but it has no approval for cancer. It's not without its risks and is performed by clinicians, using a medically approved device, not something slapped together in someone's garage. See a different neurologist, rather than playing with something, which could kill you. If you want to get into electronics, there are much safer things to play with.

author: Renate
author_rank: Super Contributor
timestamp: August 17, 2020, 11:17:56 am
content: Well, I missed the whole point of this circuit and I don't want to particularly encourage you, but...Step one: Put a bleeder resistor across the big capacitor bank.You are asking to get killed here, there is a lot of energy stored.A 150k 1 Watt resistor will eat 770 mW.Even then it will takefive minutesto discharge it to 15 V.5*130µF*150kohm*ln(340V/15V)A lower resistance (and higher wattage) resistor would be even better.Be careful and discharge the capacitors first!I still say that the 10µF and the pots are all backwards.

author: Gyro
author_rank: Super Contributor
timestamp: August 17, 2020, 11:43:21 am
content: Speaking as somebody who actuallyhasbrain cancer, this thread relating to 'Dr Beck's' alternative cancer therapies and "Professional" quack treatment machines (http://drbeck.net/) deserves, at least, to go into the Dodgy Technology section - it being the closest thing we have to a trash can!It's also a very dangerous circuit for a newbie to be failing to understand, let alone playing with. It certainly doesn't belong in the Beginners section.

author: Circlotron
author_rank: Super Contributor
timestamp: August 22, 2020, 12:00:14 pm
content: Quote from: Ian.M on August 16, 2020, 05:49:48 pmWhen the capacitor voltage gets to zero (and the inductor current is at max) as the inductor tries to charge the caps in the reverse direction the two voltage doubler diodes will begin to conduct and prevent the caps from being damaged. Approximately the same topology as a capacitor discharge ignition.

author: Ultrapurple
author_rank: Super Contributor
timestamp: August 25, 2020, 10:51:12 am
content: I agree with the 'if you need to ask, don't proceed' comments. I'm all in favour of learning, but not at such wanton risk to life and limb.If you build this circuit as shown and use it regularly then you're unlikely to suffer from your medical ailments for long. But that won't be because they're cured.Looking at the instructions construction photos found by JackJones gives me nightmares. Just a layer of insulation tape between mains hot and the light bulbs that rattle around the aluminium case? Lethal, maybe not today but certainly in a few weeks when the tape has come unstuck (very likely because the bulbs will get hot, particularly in an unventilated case). For the sake of my sanity I'm not going to analyse the circuit any further...