Pyrography - Update - Homemade unit

[SVB]

Folks,

A question for the more electrically minded.

I believe most pyro. stations contain a transformer and a AC-DC converter together with a means of regulating the output power to control heat at the tip.

I would like to know why the AC-DC converter is required. I know AC has a high peak rather than effective rms output but surly enough power could be transmitted at low (eg 12V) voltage to make an effective device without the need for conversion?

Am I missing something?

With thanks,

Simon

 

[Racers]

Hi,

Its easer to control a DC voltage than a AC one, so they can be made cheaper.

Pete

 

[SVB]

That is an interesting comment Pete.

Are there any other issues at play here as a 400W lighting dimmer essentially controls AC and has an rrp of approx £7 so at component level cannot be too much of an issue surely?

BRgds
S

 

[Racers]

Hi,

You will find that its probably got just one chip in the lightning controller, because they make millions of them it is viable spend millions on designing a custom chip. Pyro stations aren't made in the same numbers so its not worth it.

Pete

 

[CHJ]

That is an interesting comment Pete.

Are there any other issues at play here as a 400W lighting dimmer essentially controls AC and has an rrp of approx £7 so at component level cannot be too much of an issue surely?

BRgds
S

Yes there are a lot of other issues, for starters the a light dimmer controls a low current hi voltage by chopping off some of the power curve, if you put this on the input to a transformer the power efficiency of the transformer would plummet.

The pyro tip requires a relatively high current controlled within small percentages if it's to be really accommodating, whether older technology variable DC voltage/current control via a power transistor/thyristor or a more modern switched mode power supply (like in your PC) the costs escalate considerably.

You can of course just have a large lab type variable resistor in the pen feed line (or a bulb/s) but this will of course just deflect the heat elsewhere and be less efficient.

 

[SVB]

Hi Chas - thanks for the thoughts.

So, are you saying this will not work or will be inefficient. The former is bad news, the latter I can live with.

I was thinking of a circ 150W low voltage lighting power supply (on of the designed to be dimmable types) See Here controlled via a dimmer switch to make the unit.

(After all, pyro tools are effectively a filament lamp anyway - just 1 coil and dimmed down!!!!)

Simon

 

[CHJ]

In all honesty I don't know, I've never tried doing such, only experience I've had is having to take out the dimmer on a couple of systems because of the poor noise factor of the dimmer involved when in use.

For Safety you would need to ensure that the output lines are totally isolated from the mains supply, only a view of the internal construction/circuit could guarantee this.
They are listed as Low Voltage Electronic transformer, that covers a multitude of circuit possibilities.

 

[SVB]

An update.

I have got the bits together and set it all up.

For now, I just have a bit of pyro (NiCr) wire, approx 24 swg I think, shaped into a narrow loop.

Loads of power - dimmer set to around 20 - 25%

The only problem here is that the tip goes floppy at this power for the intense burning I want. At lower power seems ok although the thin wire loses heat and therefore can only be used slowly.

Next step is to make a proper pen handle, box in / mount the electircs and get some decent pyro tips which have a bit more mass.

Early steps look promising though for a spend of less than £20!

BRgds
Simon

 

[adidat]

thats great have thought about making one of these, i have made a foam hot wire cutter, which was very simple.

adidat

 

[Jonzjob]

You will need nickle wire for you pen. It can take the temperatur without the 'brewers droop'. My kit is a Janik set and runs on 2 volts and will produce enough current to make that nickle wire glow quite hot.

I turned my own pen because I didn't like the one supplied, but it just got too hot after a while in use, so I decided that in the quest of confort I bought a Peter Childs pen and that was more than you are considering for the whole project.

Personaly I wouldn't consider even trying to make my own power pack when there are such good ones on the market that you know will last for as long and longer than you will be able to use them?

Life is too short to fart about like that me-thinks!!

 

[adidat]

very nice goblets indeed!!

 

[Pvt_Ryan]

That setup just looks dangerous.. Could you not just buy and use a cheap soldering Iron?

 

[Jonzjob]

Thank you Adidat, but it's 2 sides of the same goblet. It holds almost a pint. Just about enough wine for a meal!! 8) 8)

Not a really good way to go PR. You can do pyro with the soldering iron types, but if you get into it then you need the temp control that a hot wire unit gives. The iron bits take time to heay and cool. OK for the simple things, but if you do get hooked then you are into buying a second time.

As for using a cheap soldering iron. Not really an option. You won't have the necessary control of either the tip or the heat... Your hand is at the wrong end of the tool.

 

[SVB]

Jonzjob - this is using Nickle wire from a pyrography supplier - I think it is just a bit fine at around 1mm in diameter. I know I can buy a ready made unit, but for using pyrography as a texturing tool I need a higher power unit that comes in at £130 plus rather than the £20 for this unit (which leaves another £110 for other toys!). I agree with your comments to PR re the modified soldering iron versions as being not really very good. (Nice goblet by the way).

PR - I don't believe this unit will be dangerous. The set up in the photo here is just to prove the principle, I will be mounting it with a back-box for the dimmer etc and making a nice pen etc before it is in 'production' trim! In some ways it may be safer as because it is 12v for a given heat output it will have less than 20% the current flowing and I am sure I read somewhere it is the amps not volts that kill.

Either way, provided I survive, watch this space for further developments!

BRgds
Simon.

 

[Jonzjob]

Simon, you are correct in thinking that it's the amps that kill, but they must have the volts to drive them. That's why you can get a belt off the ingition on a car at 12,000 volts and have nowt more than a nasty shock, not many amps.

All you need to kill is about 30 milli amps.

2 volts will not make any impression because the resistance of your body will make sure that there will only be micro amps flowing through you, but put it through a small length of nickle wire and it gets very hot!

The wire that I use is a lot finer than 1mm, 20 thou in real money. About 1/2 mm I think, so it takes a lot less current to heat it and you can do finer work with it too.

As far as £110, here is the modern version of mine http://www.craft-supplies.co.uk/cgi-bin ... cgi/J40116 . A lot less than £110.

Or even this one http://www.peterchild.co.uk/pyroinfo/pyinfo.htm

I would be willing to bet that by the time you have made your box you could have earned more than enough to make up the difference by getting one of these?

 

[SVB]

Another update.

'Production' version now complete:

Detail of the pen:

Any my first attempt at outlining an airbrushed design: (not great - very jerky - a combination of having used some scrap ply with very corse grain + lack of skill at this game!)

John - I am interested to hear how fine your wire is - I think I will probably need to practice with a lighter touch!

So - Job done in as far as I want to go at the moment. Cost about £20 all in (including a pen blank and ceramic block). Time, about 15 mins (took longer taking phots / uploading to do the write ups on here!).

All in all I am please with this. Time will tell how successful I can make it as a tool to add to my work.

BRgds
Simon

 

[jimi43]

Hi Simon

This is an actual pyrography pen tip...

This is a Janik one...it may help you design yours....you are probably best to wind the nickel wire around a former...try copper.

Jim

 

[Jonzjob]

Jim, I assume that your pen is one of the solid tip ones? If so it is a completely different type to the one that Simon is working towards. Simons' is literally a small loop of wire and the tip formed in the wire is the part that's used to do the pyro work..

There are some 14 solid points, each at £4.95, instead of about 2" of fine wire that I use.

 

[jimi43]

Yes...it is a solid tip one...you get different bits..the chisel...(this one) and the fine point are the best for fine work.

Jim

 

[chipchaser]

Nice job Simon. How many volts and amps are you using at maximum useful setting?

Following your earlier post on this subject in March I fell over one of these plug through dimmers reduced to £4 in Lidl

I tried it with a ratty old 12V 4A battery charger found in the corner of the garage and a Peter Child pen from my wife’s kit. The dimmer is set at about 50% and the pen is not touching the steel rule!

It worked reasonably well but I had little confidence in the life of the assembly due to the poor quality of the transformer. It is rather old (c1975?), loosely wound and buzzed quite a lot at some settings. Also, I took note of the restriction to 20-50Watts on this particular dimmer when used with 12V lamps fed from an iron core transformer, i.e. my old battery charger. At the typical useful setting the power was off for half the time and when turned on had a rapid voltage rise as seen in this photo.

It did prove the principle but, as my modified PC switch mode power supply works ok, I didn’t pursue this any further.

The good quality lighting transformer and dimmer is a very good find and your project is definitely quicker and less expensive to make than my modified PC psu even taking into account that I had an old PC as donor. It must be more efficient too as the PC psu has 4 different voltage outputs 3 of which are unused and a cooling fan.

I can recommend Peter Child as supplier of the resistance wire in small rolls, quick and helpful. It would be interesting to see a comparative test of the solid tip like the Janik against the bent wire type, anyone used both?

There is a useful short summary of the risks from AC and DC at this site:
http://www.pat-testing.info/electric-shock.htm
Graham