Homemade Pyrography Tool

[Will_s87]

Hello, I was hoping to make a wood burning tool for my girlfriends birthday, shes had a soldering iron type but it takes along time to heat up and loses its heat quickly when burning. I started having a look around and decided I might be able to make my own...

Something like this seems to be the order of the day...
The wire tip at the end of the torch is ~ 1.5" of 26awg nichrome wire. at 2.5 ohms/foot I make that to be about 0.31 Ohms. The colour is cherry red indicating about 900'c...

I found a table on wiki;
http://en.wikipedia.org/wiki/Nichrome
Current (A) vs. temperature characteristics, straight wire.
This states that to get a piece of 26awg nichrome to 900'c it requires ~ 6.5A.

So I need a DC power supply capable of 6.5A through a load of 0.31ohms. so Vout would be 6.5x0.31 = 2V, however it might be nice to have some head room in the circuit so I can use a larger tip. 23awg would probably be ample so;
23awg @ 1.3 ohms/foot. 0.16ohms per 1.5" (length of wire tip)
23awg @900'C needs 9A. 9A x 0.16 = 1.4V.

My plan was to use a 12v dc power supply to drive a DC to DC converter.

DC - DC converter something like this I thought would be suitable.
http://docs-europe.electrocomponents...6b80af7cf3.pdf

The info of the datsheet that interested me was;
Iout= 10A
Vout is adjustable from 1.2V to 5.5V
short circuit protection is auto reset @ 20A.

So I figured if I hooked up a pot to adjust the output voltage this would adjust the output current and hence control the temperature of the wire tip.

Can anyone tell me if this will work. I have concerns that I the DC converter wont work as I expect it...

thanks, Will.

 

[rtbcomp]

I'd give it a go.

 

[J.B. Welding]

Make sure the pot is rated at that amount of current your talking about and it should be ok, just make sure to over-rate everything to allow for duty cycle issues. You could use a smaller pot and control voltage operating a power MOSFET for a bit more complication.....

 

[rtbcomp]

Make sure the pot is rated at that amount of current your talking about and it should be ok, just make sure to over-rate everything to allow for duty cycle issues. You could use a smaller pot and control voltage operating a power MOSFET for a bit more complication.....

I think the pot controls the inverter circuit, not the current directly.

 

[J.B. Welding]

I'de use an old buzz box for such a project, wound right down and balance the wire length to suit. That's just because I have an old buzz box handy though. It worked great to power my polystyrene cutter and this looks similar. Probably a bit overkill for said application.

 

[Will_s87]

Hey guys, thanks for the input,

JB Weld - the fact that you mention power mosfets leads me to believe you have a better understanding of this circuit than me. Would you expect the circuit to operate as I expect? I know its a pain would you mind glancing through the datasheet?

RTBcomp - you are correct there is a seperate control connection for the pot which trims Vout

Thanks for looking guys, much appreciated

 

[rtbcomp]

I'de use an old buzz box for such a project, wound right down and balance the wire length to suit. That's just because I have an old buzz box handy though. It worked great to power my polystyrene cutter and this looks similar. Probably a bit overkill for said application.

You'd need to add a rectifier, and possibly a smoothing cap.

 

[J.B. Welding]

Ok I had a quick look at the data sheet, and I guess it should be ok, is that an expensive item? If you have the power source already then you need 'something' to vary the current, but other options would be a variable core transformer or MOSFET circuit. There are often lots of ways in electronics, you just have to run with one. Good luck with the 'wood burner project'!

You'd need to add a rectifier, and possibly a smoothing cap.

Easy arc 150 produced a constant red/orange heat in a ring of stainless, running AC. Heat is a crude use for electricity I don't see a need for super precise regulation, but generally the less complicated the better for home made items. <I'm not an electronics pro its just a hobby>

 

[rtbcomp]

............

Easy arc 150 produced a constant red/orange heat in a ring of stainless, running AC. Heat is a crude use for electricity I don't see a need for super precise regulation, but generally the less complicated the better for home made items. <I'm not an electronics pro its just a hobby>

I was assuming you were going to use the buzz-box as the supply to the DC converter - if you're using it stand alone then the AC output will be fine.

 

[Will_s87]

Ok I had a quick look at the data sheet, and I guess it should be ok, is that an expensive item? If you have the power source already then you need 'something' to vary the current, but other options would be a variable core transformer or MOSFET circuit. There are often lots of ways in electronics, you just have to run with one. Good luck with the 'wood burner project'!

Hi JB - Thanks for having a look,
a) £20 for the item on the data sheet.
b) I already have a 12v DC SMPS - I'm not sure what you mean by something to vary the current. I was going to adjust the trim voltage using a pot, 10k or so, this should adjust the output voltage from 1.2-5.5V according the the ds. this should give me enough range to get the tip to glow...

I think I may have missed the point you were making though...

Thanks, Will.

 

[johnrev]

I made a woodburner for my wife a couple of weeks ago. Used an old spare PC power supply and a very simple PWM mosfet circuit (six components and a pot built on a tiny piece of vero) which adjusts output of the 5 volt line. Piece of hollow wood for the 'pen' and a few pieces of nichrome wire for the burning tips. Works a treat.

First try was using a 12volt transformer and light dimmer switch but this had very poor control and either no heat or melted wire. Using the PC supply and PWM gives good temperature control.

All info came from web searches and nichrome wire from fleabay.

 

[AndyStobbs]

Why not go in for a potential divider and keep it simple?

 

[Will_s87]

Hi Andy - in what capacity would I use a voltage divider? Wouldn't this mean a lot of loss unless its running at 100% load?
Johnrev - Have you got any pictures, or a diagram you used. I've just started looking at mosfets and basic electronics. Jeeeez haha! A whole new world of unknowns!

Do you re call the part number of the mosfets you used.

Using a PWM output seems logical know but I can see this dragging the project out somewhat..

 

[johnrev]

Pretty basic knocked together thing at the moment but proves concept and if 'the guv' enjoys it I'll make a more presentable machine for her. Don't know about your place but here "ooh I'd like to try that" often stops at the 'try' stage!!!

Already had the PS from an old PC and several of the components plus veroboard were in the 'store' from when I was sorting out the wirefeed for my old SIP mig.

Can't remember URL where I found the circuit for the PWM but I remember there were two out there both very similar and both very simple. Only parts still not fitted are a resistor or two to 'load' the unused PS output/s as this apparently gives a more stable supply from a PC power unit.

 

[johnrev]

Sorry didn't answer re mosfet. Have put box together again now but it was just a power mosfet something like the IRF 540 which are common and cheap (especially online). IC is a 555 and other parts just common resistors, caps and diode. Found one of the circuits-

 

[tgv1978]

Sorry because i'm not good at English. As I see, this circuits and yours is not the same ???

 

[MattF]

Don't know about your place but here "ooh I'd like to try that" often stops at the 'try' stage!!!

I know that one all too well.

 

[johnakay]

why are those types so expensive.
I bought a wood burning pen(basically a soldering iron)
it was a 60w but it stopped working so had a looky but all now only 30w.
has the law changed on these now?
anyway I bought a 100w soldering so hopefully that should do the trick.
oh and sorry if I've hijack this thread.