Build Your Own Arcade Controls Forum
Main => Everything Else => Topic started by: Nefesis on August 11, 2004, 12:04:31 am
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hi. i know what what i'm using (a pentium4 pc) has 5 volts, and am trying to find out how many amps that is. do i have to know the resistance (?) in order to find this out? or is there a formula for converting them. a 15-20 min search on google didn't come up with anything on just volts to amps.
thanks in advance,
Nefesis
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According to Ohm's law V=I*R but what are you wanting to know? Do you want to know how many amps your power supply is rated for on the +5V? If so you will need to check the specs on that specific power supply.
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He he you can't just convert volts to amps, I suggest you invest in a multi-meter. If you are at all serious about building your own arcade controls they are very useful.
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Quick lesson in electronics -
the 5V you have is potential energy. It will depend completely on resistance as to how much amperage you recieve. Lets say for a moment that you hooked your +5V line directly to ground. You have probably a 200W to 400W power suppy. P = V * I or P = V^2 / R. Since you have close to zero resistance, you basically can get the max 400W out of the power supply, therefore frying the CRAP out of everything. figure your max current is going to be I = P/V or 20 amps, enough to kill you, in the right conditions.
Application will help us answer your question better
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as stated above, you need to know two things to find the third. in your case you need to know the voltage and the resistance. in theory. but so many things change their resistance when in use for instance. yeah get a multimeter with at least a ten amp scale. i bought a digital one for twenty bucks (aus) the other day.
also you need to know that voltage times amperage = watts since there is a limit on your power supply.
oh and 5v @ 20 amps cant possibly hurt you and in fact its hard to imagine your bodies resistance being low enough to allow 20 amps @ 5v to go through your body...
edit: i should say that 5V @ 20 amps couldnt flow through your body because of its high resistance...
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The big thing to remember is, you can't convert directly between Volts and Amps like you can with Farenheight and Celcius, they measure two different things. Think of it as water running through a garden hose:
Voltage (E) = How high the water pressure is (Loose analogy)
Amps (I) = How much water is flowing
Ohms (R) = How much crud is in the hose restricting water flow, or a crimp in the hose.
The REAL definition of a Volt is the amount of "pressure" it takes to push one Amp of current through one Ohm of resistance. Obviously in electronics you can acheive situations that couldn't happen (1 drop of water at 2,000 PSI) with a standard garden hose, but it gets the point across.
As stated multiple times in the thread, you can use Ohm's Law (I = V/R) to find amps if you have the voltage and resistance values.
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Danny - That is only partially true - Your skin has a very high resistance (some where in the mega ohms) when it is dry and calloused. Wet skin resistance drops to around 500 Ohms, and passed the skin barrier, the resistance drops to around 10 Ohms, arm to arm. Hence, it takes very little voltage to kill someone under the skin.
The greatest thing is reading about the experiments where they fried monkies to figure that shtuff out.
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still, even if he accidentally inserted two wires under his skin the flesh resistance would have to be 0.25 ohms to get 20 amps. hehe, just to show how silly i used to be when i was a fourth year apprentice i used to freak out the first year guys by holding both ends of a 110v test light!! we have 240v here so it was through a transformer. was a nice buzz but not harmful (well short term anyway. it might explain why im such an under-acheiver...)
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still, even if he accidentally inserted two wires under his skin the flesh resistance would have to be 0.25 ohms to get 20 amps. hehe, just to show how silly i used to be when i was a fourth year apprentice i used to freak out the first year guys by holding both ends of a 110v test light!! we have 240v here so it was through a transformer. was a nice buzz but not harmful (well short term anyway. it might explain why im such an under-acheiver...)
Yes, but it only takes 100mA to kill yourself, and at 10 Ohms you only need 1V to generate that. There's an entry in the Darwin awards where a guy was using a cheap multimeter to measure his resistance thumb to thumb , but he pressed down on the leads so hard he broke the skin and the resulting current was enough to stop his heart and kill him.
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well geez, i guess id better not test 1.5v batteries by putting it on my tongue then ;)