Another maths question

[tombear]

Several years back I made a hot wire foam cutter. I recently dug it out and am now wondering what power supply I originally used. The site I got the instructions is no more but I remember it was run off a phone charger. Of these there is a obscene number in the house.

The question is what output am I looking for to cut foam at a reasonable rate?

The screw on thingies that hold the wire are 5.25 inches apart and the reel of wire I bought to use on it is the 0.25mm nickel chrome bare stuff here

http://www.wires.co.uk/acatalog/nc_bare.html

i randomly tried a charger with a piece of wire and it quickly glowed red then white then went twang....

And if anyone can suggest a model of charger that has the right output that's likely to be at a carboot I'd be profoundly grateful!

atb

Tom

 

[Gary Elson]

I maybe able to move you along a little
Just need some info
What was the voltage of the charger ?
How long was the piece of wire you twanged was it 5.25 inches ?
Gaz

 

[Gary Elson]

Sorry what thickness of wire have you got?

 

[tombear]

The wire was indeed 5.25 inches long but the old silver paper sticker thing on the charger ( its pretty ancient and after the burning wire up thing went in the bin ) is unreadable/worn off, hence me trying it. Input was normal uk mains.

Says 0.25 mm on the roll.

Cheers!

Tom

 

[Gary Elson]

Hi Tombear
I'm no expert but using 22ohms per metre your piece of wire is about 3ohms
Again using V= I R you want to be pulling about 1.5 amps ( checked a couple of how to type websites)
Therefore
3 ohms X 1.5 amps = 4.5 volts
This is the output of your charger
Please note if your wire doesn't get hot enough you can increase the voltage CAREFULLY
If it still goes twang then I never told you anything Right !!!!!!!
Hope this helps
Gaz

 

[unit392]

If I were in your place, I wouldn't experiment with chargers, no matter how much calculations were made. In my opinion, the best thing to do is to take your device to an electric shop and ask the guys there. I had a similar problem some years ago and they were able to help me pretty quickly.

As to calculating output using wire resistance, use an electronic multimeter to measure the resistance of the very piece of wire in question. But then again, electric shops usually have special devices like variable output chargers with which they can test your device with little risk.

 

[rik_uk3]

They are a tenner on ebay including delivery.