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Unread postAuthor: jackssmirkingrevenge » Sat Dec 06, 2008 7:25 pm

Thank you for the JSR double entendre compendium hehe
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Unread postAuthor: Ragnarok » Sat Dec 06, 2008 8:09 pm

jackssmirkingrevenge wrote:Thank you for the JSR double entendre compendium hehe


I think I missed a couple.

Seriously dude, with your efficiency and grammar Nazi-ing, your *facepalmheaddeskcombo*, the repeated innuendo and double entendre (so bad that the Flaming Pink Elephant was formed), inventing some extra double meaning, your foot aversions, internet memes and tendency for cannons that hang open and fart loudly - I'd say you're a teensy bit predictable.

In fact the only time you're not predictable is when someone accuses you of being predictable, and that in it's own way is predictable.

No doubt someone will now dissect me to show I'm hypocritical, so I'd like to start by saying I'm a hypocritical nerd with unnatural obsessions with wolves, safety, launchers, spelling and grammar, an unnatural hardiness, a tendency to use the word "Myriad", generally Bowdlerised (Except for the words "Bugger" and "bollocks"), a very typecast writing style, the habit of taking jokes and running off with them, a wannabe moderator, riding on the success of one particular cannon, a general eejit, occasionally mildly inspired, and probably too willing to see the best in people.

That's most of of it I think... no wait... and far too thorough when it's not important, forgot that one.
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Unread postAuthor: Insomniac » Sat Dec 06, 2008 11:19 pm

Ragnarok wrote:
jimmy101 wrote:Off hand, I would WAG a photocap as losing perhaps one volt per second when fully charged to 300V.

They can hold a charge for a good while longer than that. Can't tell you exactly how long, but they certainly don't lose charge that quickly.


I put a multimeter across a photoflash cap, and the volts did tick off quite quickly... although I know they can still have enough charge to spark days after they were charged. Perhaps the rate drops off when they get to a lower V, or perhaps the loss of voltage was mainly from the multimeter.
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Unread postAuthor: Ragnarok » Sat Dec 06, 2008 11:30 pm

Insomniac wrote:perhaps the loss of voltage was mainly from the multimeter.

Yeah. Most multimeters have a resistance of about 1 megaohm across the wires in voltage mode, so you can't sit there with the multimeter constantly attached. You need to charge it, measure it once very quickly, then disconnect the multimeter and come back in a couple of minutes and measure it again, which generates much less voltage drop.

Perhaps the rate drops off when they get to a lower V

Also true. The rate of discharge of a capacitor is directly proportional to the voltage in it. It will discharge twice as fast at 300V than 150V.

This also technically means a capacitor can never truly fully discharge, because as it's voltage goes to zero, so does it's rate of discharge.

However, for practical purposes, we're talking mere millionths of volts.
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Unread postAuthor: Insomniac » Sun Dec 07, 2008 3:21 am

Ragnarok wrote:Most multimeters have a resistance of about 1 megaohm


Let me guess... You measured the resistance of your multimeter, with another multimeter. :D
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Unread postAuthor: TurboSuper » Sun Dec 07, 2008 9:23 am

It's also usually written on it somewhere.
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Unread postAuthor: Ragnarok » Sun Dec 07, 2008 10:02 am

TurboSuper wrote:It's also usually written on it somewhere.

Bing, one point.

It's also a very common value for voltmeters to have as a resistance.
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Unread postAuthor: starman » Sun Dec 07, 2008 12:50 pm

Voltmeters typically have a ohms/volt rating. So the input resistance will depend on the present voltage range setting.

So as an example, a typicial cheap analog meter may have a rating of 10,000 ohms/volt (or less). Therefore it's input resistance is going to be 500,000 ohms when it's set to the 50 VDC range and 100,000 ohms when its set at the 10 VDC range. Typically, the better the meter, the higher the ohms/volt rating is.

Digital meters almost always have a multiMEGohm range ohms/volt rating.
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Unread postAuthor: jimmy101 » Sun Dec 07, 2008 8:50 pm

Wow, lots of folks know their meters! Analog meters have varying resitances depending on the voltage range. Usually it is printed on the dial face. Digital meters are much higher resistance and 10 Megaohm is common.

The rate at which a capacitor will disharge through a resistor is easy to calculate. About 63% of the cap's voltage will bleed off through the resistor in (resistance in ohms)(capacitance in farads) seconds. When the voltage cross a cap is measured with a meter the meter acts as the resistor.

A typical photo cap is 120 microfarad, figure 1 Megaohm resistance in the meter;
Time for cap's voltage to drop by ~63% = (120x10<sup>-6</sup> Farad)(1x10<sup>6</sup> Ohm) = 120 seconds

If the cap starts at 300V it will drop to 111 volts (a 63% drop from 300V) in 120 seconds. The initial voltage drop will be about 1.6 volts/second.

If the cap's leads are not connected to anything then the voltage will drop much more slowly. Perhaps a volt every few tens of seconds.
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Unread postAuthor: iknowmy3tables » Mon Dec 08, 2008 3:19 pm

jimmy101 wrote:Not sure why you (in the OP) have the charging circuit at the muzzle (if I correctly understand the drawing). A high voltage high capacitance cap takes a while to fully charge. Photoflash boards take several seconds to charge their cap.

its connected to a top and bottom rail note the color, so it will be connected until the capacitor exits the barrel
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 09, 2008 1:38 am

Ragnarok wrote:No doubt someone will now dissect me to show I'm hypocritical


See I knew you'd say that ;p
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Unread postAuthor: Ragnarok » Tue Dec 09, 2008 1:48 am

jackssmirkingrevenge wrote:See I knew you'd say that ;p

And I knew you'd pick me up on saying it... :tongue5:

And if I didn't say it, there were a great many people that I knew would say it instead. :roll:
You can't ever win in this game, you just keep going until someone flames you.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 09, 2008 2:38 am

Thing is, when you don't live up to the image you've built up for yourself, folks tend to get a little disappointed and fear something might be amiss, it's a curse I tell you :roll: :D
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