DIY Soldering Iron From a Pencil!

vb_master · Post by **vb_master** » Sun Mar 12, 2006 3:33 pm

Hey guys I just did something weird. I was messing around with a 20 volt power supply and a pencil, and I found out that if you get the graphite out of the pencil, and connect the negative lead to it, and connect the positive lead to solder, it will melt the solder! Weird stuff here, like a ColdHeat clone or something! It instantly heats up to melt stuff (and it stays relatively hot!) Discuss. I can post a video or something maybe...

sniper_spike · Post by **sniper_spike** » Sun Mar 12, 2006 3:58 pm

Your basically shorting out the power supply (uh oh!), and using the heat created by that to melt the solder. You could do it with out the pencil even, you just need to touch both leads on the solder.

vb_master · Post by **vb_master** » Sun Mar 12, 2006 4:12 pm

sniper_spike wrote:Your basically shorting out the power supply (uh oh!)

So I guess I should stop doing it?

NES_fanatic · Post by **NES_fanatic** » Sun Mar 12, 2006 4:17 pm

You shouldn't do it a lot, or for a long amount of time.

timmeh87 · Post by **timmeh87** » Sun Mar 12, 2006 5:26 pm

well it depends what the resistance of the graphite is. i mean lightbulbs "short out the power supply" too.

if the resistance is 20 ohms or greater (creating a current of 1A or less), then you should be perfectly fine.

Harshboy · Post by **Harshboy** » Sun Mar 12, 2006 5:34 pm

Graphite has resistance!?

Post by **Skyone** » Sun Mar 12, 2006 5:37 pm

Supposivley, yes it does...?

jeep · Post by **jeep** » Sun Mar 12, 2006 5:45 pm

Harshboy wrote:Graphite has resistance!?

Even you have a resistance ! Everything as a resistance....

My pen graphite have a resistance of 3k ohm... so,

V=RI
V/R=I
20V/3000 ohms = 0.007 A = 7mA

sniper_spike · Post by **sniper_spike** » Sun Mar 12, 2006 5:48 pm

If it didn't create any sparks when you shorted the PSU, it probably has a pretty high resistence... So according to timmeh, it should be fine.

But double check with a multimeter.

Metroid fan · Post by **Metroid fan** » Sun Mar 12, 2006 5:49 pm

I found a new resistor then.... My finger!

Harshboy · Post by **Harshboy** » Sun Mar 12, 2006 6:02 pm

jeep wrote:
Harshboy wrote:Graphite has resistance!?
Even you have a resistance ! Everything as a resistance....

My pen graphite have a resistance of 3k ohm... so,

V=RI
V/R=I
20V/3000 ohms = 0.007 A = 7mA

Me no likey your formula! Me say it's:

V=C*R
C=V/R
R=V/C

I just doesnt seem right

blackbox_dev · Post by **blackbox_dev** » Sun Mar 12, 2006 8:04 pm

my construction teacher made DIY wood burners the same way.

vb_master · Post by **vb_master** » Sun Mar 12, 2006 8:26 pm

If I turn the voltage down (I have an adjustible power supply), I don't have multimeter batteries, so I need to check that out.

timmeh87 · Post by **timmeh87** » Sun Mar 12, 2006 9:04 pm

harshboy... you just said the exact same thing but with C instead of I.

carbon has a resistivity several orders of magnitude higer than normal metals... it was in my materials book. i forget exactly how much.

also, everything has resistance except superconductors.

also, if you want to have some fun with power calculations, heres 3 formulas for you:

P = IV
P = V^2 / R
P = I^2R

thats power in watts.

so 20^2 / 3000 = .13 watts. not much. im guessing vbmaster is using a smaller (and therefore less resistance) piece of graphite. still, theres a lot less thermal mass (which makes things take longer to heat up) and surface area (which makes things cool down faster) than a normal soldering iron.