psu power help...

[QUIKSILVER]

ok, im in my workshop as i type this, i have my rails and pullys ready for my automatic gravity foam cutter for wings...

one issue is the power..

currently i am using a garden transformer that says:

pri: 240vac 50hz 70va
sec: 12vac max 60va

no problem working with my 30inch bow

i really need to be able to controll the output to the bow.

i have 2 old computers say upstairs doing nothing im thinking of taking out the power supply and using this.

i have a house hold 240v dimmer switch sat here also, how do i get some wire temp resolution for this?

i know the dimmer will have around 5 steps only but can this be done?

someone help me please :D

[BushmanLA]

Hey quick, old computer power supplies are great if you need a steady DC voltage source that can supply a decent current of a few amps or so.

For your foam cutter I would imagine you would want a current source that you can adjust so a PSU from a computer wouldn't do the trick by itself. Unless one of the voltages off the PSU just so happens to be exactly right for the amount of current you need to keep the wire hot.

Here is my PSU supply that I can't live without.
http://www.pasqualy.com/PowerSupply/


Do you have any idea of what the power requirements are for your cutting wire?

[QUIKSILVER]

very smart!

no ill check the ohms.

one of the reasons is i want to cut eps beaded foam all the way upto epp my bow is around 48 inch

i did have a dimmer switch on a transformer that gave me some diffrences but the transformer buzzed like hell so i binned it

[BushmanLA]

A simple solution might be a resistor in series with the cutting wire, you just need it to be the right resistance to limit the current at a known voltage like 5V or so coming from the PSU, also the resistor will have to be able to dissipate the right amount of power.

If you have a radioshack nearby, try picking up a power transistor or FET that can handle the current you need, wire it up with a simple voltage/current divider with a potentiometer.

I can draw up a schematic if you need me to.

[BushmanLA]

Here, my pinouts on the FET or BJT are sure to be wrong so just check the device package and it should correct it. Just match the Emitter/Base/Collector to my drawing etc.

The resistor in the BJT is just to stop you from nuking it by turning the pot all the way in one direction and essentially connecting it straight to +5V. It is not needed for the FET because they don't draw any current at the gate. (Its magical!)

[QUIKSILVER]

meh.........

no radio shack near me...

i have stacks of resisters ill have to search the internet to find out what the bands are

a quick drawing would ber perfect im not 100% electronic you see :)

thank you

[BushmanLA]

Hrm... So you probably have some little 1/2 or 1/4 watt resistors, its going to take a bunch of them in parallel with each other and then that bundle in series with the wire.

I guess what we need to know is what kind of current do you need to keep the wire at the right temp, and what is the resistance of the wire at this temp.

What kind of wire is this anyway?

[QUIKSILVER]

the kind of wire you find in a hairdryer :eek:

humm shall i just start from scratch again? :(

[BushmanLA]

Hrmmm.

Really you should find a power FET or BJT someplace and a simple volume knob type potentiometer.

But you can do it with a big bundle of resistors, you will just have to experiment.
This should make things clear.

[QUIKSILVER]

lol thank you very much! i love the melting goop picture! let me go find these resistors 1 sec and read off what they say!

[BushmanLA]

lol thank you very much! i love the melting goop picture! let me go find these resistors 1 sec and read off what they say!


Start with a 100k resistor, and keep adding 100k's into the bundle like I drew. 100k's are brown black yellow.

Every time you add another resistor to the bundle the total resistance will go down, but the total current that the bundle can handle without blowing up will go up.

Hopefully you meet someplace in a happy middle point :)

[QUIKSILVER]

picture quality is rubbish i know quick snaps!

also if you need anything from here help yourself

[BushmanLA]

picture quality is rubbish i know quick snaps!

also if you need anything from here help yourself


Oh man.

You remember that time you lost your EasyStar, Broke your transmitter, and scratched yourself up all in a matter of seconds?

That's how this is going to end. :D

[QUIKSILVER]

damn it i knew that would bite me back in the ass again :D

shall i just connect a brushed speed controller to the cutting wire?

i cant kill myself that way? :p

[BushmanLA]

damn it i knew that would bite me back in the ass again :D

shall i just connect a brushed speed controller to the cutting wire?

i cant kill myself that way? :p

whoa, thats a great idea. It might not have the low speed (low current) ability that you need but try it out and see. Probably the worst you can do is kill the speed controller.

[QUIKSILVER]

cant i just put a few light bulbs in the link to act like resistors?

can you see my non electronical knowledge here lol

[BushmanLA]

cant i just put a few light bulbs in the link to act like resistors?

can you see my non electronical knowledge here lol


Yeah, a lightbulb in series would help too. A 12V lightbulb I mean, if you put a 120V bulb it will be too high a resistance for the wire to ever get warm.

[dmccormick001]

Man, I can't wait to see how this is going to end! Better than anything on TV tonight! :D

[QUIKSILVER]

:p ha, i wont even show or tell you how i have now done this, lets just say in involves some old christmass tree lights, some black tape, a speed controller and half of a wooden broom handle to turn it on and off :p

[dmccormick001]

Sounds like vintage DIY!

[rich smith]

Start with a 100k resistor, and keep adding 100k's into the bundle like I drew. 100k's are brown black yellow.
Every time you add another resistor to the bundle the total resistance will go down, but the total current that the bundle can handle without blowing up will go up.

Pretty obvious Bushman is not good with electrical stuff. You'd need thousands of those 100k resistors to warm up the wire. :eek: Like Dave says, better than TV.

Quick and dirty solution is use a PC supply with alligator clip on excess length of the wire to adjust current.

[BushmanLA]

Pretty obvious Bushman is not good with electrical stuff. You'd need thousands of those 100k resistors to warm up the wire. :eek: Like Dave says, better than TV.

Quick and dirty solution is use a PC supply with alligator clip on excess length of the wire to adjust current.


Well now that I think about it, I'm off by an order of magnitude or two. (or three)

I guess I'll just never ever offer anyone advice again.

[rich smith]

Well now that I think about it, I'm off by an order of magnitude or two. (or three)

I guess I'll just never ever offer anyone advice again.

I have a strange feeling your desire to help people will eventually overcome our little "lovers tiff". :)