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Everything Else » Tips for working at higher voltages

December 08, 2010
by exussum
exussum's Avatar

Hi,

Im currently working on a Camera with a flash. trying to make my Nerdkit control both the picture and the flash. Currently the nerdkit can turn on the camera and take a picture, And I figured out how to charge the flash. Since then ive not really been able to touch it, As soon as I do I get a (pretty big) shock, The camera is still working (the screen and stuff was broke when I bought the camera).

I just need to sort of insulate myself while still keeping a working flash.

Any ideas ?

December 08, 2010
by exussum
exussum's Avatar

"Many compact cameras charge the flash capacitor immediately after power-up, and some even just by inserting the batteries. Merely inserting the battery into the camera can prime the capacitor to become dangerous or at least unpleasant for up to several days. The energy involved is also fairly significant; a 330 microfarad capacitor charged to 300 volts (common ballpark values found in cameras) stores almost 15 joules of energy."

From wikipedia.

The one in this camera is 310mF

December 08, 2010
by exussum
exussum's Avatar

http://www.youtube.com/watch?v=R8_dAgaBBdI&feature=player_embedded

Was looking to do something like that without a DSLR camera

December 11, 2010
by n3ueaEMTP
n3ueaEMTP's Avatar

Exussum, your mention of the 15 Joules got me thinking. I work as a paramedic and am specifically interested in the cardiology aspect of my job. That being said, I take special interest in our heart monitors. Every time the technician comes to do the preventative maintenance on our monitor/defibrillators, the first thing he does is shorts the capacitor (unknown uf & volts but up to 360 joules) with a resistor for safety. Is it possible to short the capacitor in the camera with a resistor so you don't get shocked?

The following is in all caps intentionally.

PLEASE USE EXTREME CAUTION WHEN WORKING WITH THIS ENERGY. I HAVE SEE 15 JOULES KILL PEOPLE!!!

Hope this helps

Chris B.

December 12, 2010
by exussum
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What value of Resistor would allow the camera to still function and be safe ?

Or just use the resister when i have to touch the camera ?

December 13, 2010
by hevans
(NerdKits Staff)

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Hi exussum,

n3ueaEMTP's advice is right, especially his warning. The amounts of energy you are talking about are well within the range that can cause damage.

That said, a capacitor is an energy storage element. When you get down the physics of it, it stores it energy by having more charge on one side than the other, and therefore a voltage across it. The fastest (not at all recommended) way of discharging a capacitor is to just short the leads (sometimes done by touching both leads with a screwdriver). This presents a zero resistance path for the stored charge to flow through, and the charge will very quickly flow to equalize the charge on both ends of the capacitor. A lot of charge moving very quickly is a very high current, so you are probably going to get sparks and possibly damage your components.

A more sane way of discharging large capacitors is to use a resistor to limit the flow of charge, which gives you a smaller current. The resistance value you use, combined with the capacitance of the capacitor set-up an RC time constant that dictates how long it will take the capacitor to discharge. A very large resistor will give you a large current but it it might take a while to discharge. A small resistor will discharge quickly, but it might not be able to handle the high current and become either very hot or actually pop. The safest suggestion is to use a large resistor, about 10K should be fine, and hold it there for a good 15 seconds (assuming it is a 300 microfarad cap) to discharge your cap. Make sure you are not physically holding the resistor, use insulated pliers.

Again I cannot overemphasize how careful you should be when working with these voltages.

December 13, 2010
by mongo
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Rapid discharge of a capacitor, especially the larger electrolytics, can cause damage to them. I have had capacitors explode through rapid discharge. It was the braking method on older motor control systems. Every now and then, I would have to clean out a panel that got filled with foil and paper from one. Not always a pleasant job.

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