Here comes another stupid questions... but better safe than sorry.
I was planing on using regular AC wire to connect lights and switches and if there is an easier way of figuring out what type of wire would be OK, please do tell. The AC wire I'm going to use will power 2-light switches (you guessed it regular ac wall switch) to two separate light bulbs, the proximity is no more then about 8-9ft (3M). The wire is rated for 120V-15 amp. (USA standard) The light bulbs will be less then 25W @ 12V or less then 40W @ 120V.
The reason I would like to use AC is if for whatever reason I need to plug into the grid, all I have to do is replace the light bulbs and I'll be in good shape.
Normally I would not even ask a question like this except for the fact (don't laugh now) that from my early teenage years I remember someone trying to educate me about 110/220/12 volt differences... needless to say I should have been paying more attention then. Well an something about higher voltage needing thinner wire then lower voltage... and that being the reason for think battery cables in cars or something of that nature, anyways could someone please refresh my memory?
Just thick wire. For 25 watt bulb the current is low enough to not worry about it. The more current the more voltage you loose. I/R=E (current/resistance=voltage) 0.5 ohm wire resistance with 2 amps through it will loose 1 volt and waste 2 watts of power. As at 12v current is higher to get the same power thin wire will loose alot of voltage and dissipate alot of power if drawing heavy current.
Here's a page on my basic electrical knowledge, ohms law was taught to me in secondary school, and I remember the teacher telling me at the time - this is the most important thing you need to know - He was right...
Just a little corection. You state What value resistor do I need for a 3.6v white led running at 20mA
3.6v divided by 0.020A = 180 ohm
3.6v is the forward voltage drop of the LED. It is the voltage needed to make the majority charge carriers move from one side of the junction to the other. What is important is the voltage you have.
EG 12v battery, need 20ma current flow, LED is dropping 3.6v. 12-3.6=8.4 8.4/0.02=420 ohm resistor. It is the voltage you are left with after subtracting the VF (forward voltage) of the LED that determine the resistor used to limit the IF max (forward current maximum) of the LED.
Is AC wire safe for DC applications?
Posted - 01/09/2007 : 23:30:16
