newbie question about transformer - Page 1
Forum section: electronics / beginners

author: Jed841
author_rank: Newbie
timestamp: December 24, 2010, 01:35:51 am
content: ok i want to build this circuithttp://kipkay.com/wp-content/uploads/2010/12/snip-burn-galley_Page_088.jpgBUT my transformer has an extra middle leg...... what is that for!? also when i hook 9v up to it, i get no voltage out the other side.......

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 24, 2010, 01:55:12 am
content: 9v what? dc or ac?

author: williefleete
author_rank: Regular Contributor
timestamp: December 24, 2010, 01:58:35 am
content: its most probably a center tapping, if you have a multimeter test that pin to any of the others using the ohms range if it doesnt measure then its probably just for support when its on a PCB and open circuit

author: osmosis321
author_rank: Regular Contributor
timestamp: December 24, 2010, 05:58:00 am
content: Transformers need AC to work, a battery won't do the trick. It's the dv/dt, or the change in voltage, that transfers the power. That's why DC won't work, it's a steady voltage.The middle wire is called the center tap. A center-tapped transformer is capable of push-pull operation and is commonly used in audio amplifiers.

author: Jed841
author_rank: Newbie
timestamp: December 24, 2010, 06:53:56 am
content: ahhh i was using dc.... THNX!!!

author: jimmc
author_rank: Frequent Contributor
timestamp: December 24, 2010, 02:54:08 pm
content: NOOOO!!!9vDCis the correct supply, with an AC supply the electrolytic capacitor will blow up!The circuit works by charging the capacitor to 9v and then discharging it through the transformer when the button is pressed.This produces the required dV/dt (or more correctly dI/dt) and gives a short high-voltage spike across the secondary of the transformer.Jim

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 24, 2010, 05:23:44 pm
content: Quote from: Jed841 on December 24, 2010, 01:35:51 amQuote from: jimmc on December 24, 2010, 02:54:08 pmhook to "it" what? the transformer alone? or the complete circuit? whats the cap V rating? will be much fun to see an explosion!merry christmas!

author: Time
author_rank: Frequent Contributor
timestamp: December 24, 2010, 07:38:16 pm
content: This is pulse transformer basically. Sounds like you answered your own question. Charge the Cap to 9V and than dump the charge into the transformer getting a higher voltage pulse on the other side. The relay is your switch. Kind of rudimentary but it works. To get the highest voltage possible youll want to take the ouput across the outside legs of the 2ndary. It might be a fun learning experience, if you have a scope, to probe between the different legs and see what comes out.

author: Fraser
author_rank: Super Contributor
timestamp: December 24, 2010, 07:56:47 pm
content: I think the poster needed to explain what the circuit actually is.....Looking at the provided link, this appears to be a joke that you play on friends (?) A container with a metal lid has the unit built inside. The circuit is triggered by movement using a tilt switch. I suspect that this joke relies upon someone picking the container up and the movement causes the charge/discharge cycle across the transformer and shocks the person using the high voltage winding.The deployment of such a device would require the use of a container with a conductive body and a separeate conductive lid insulated from the rest of the container. To work, the 'victim' would have to be touching both the container and it's lid.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 24, 2010, 09:27:49 pm
content: Quote from: Aurora on December 24, 2010, 07:56:47 pmand i suggest the poster will be the victim, for testing purpose.

author: Zero999
author_rank: Super Contributor
timestamp: December 25, 2010, 09:06:05 am
content: The capacitor will charge in the reverse direction even if DC power is used. The transformer is inductive and when the capacitor is connected to it, the capacitor will discharge but the current will keep flowing causing the voltage across the capacitor to go negative before discharging again, the osculation will exponentially decay. This is a classic LC tank circuit.