Power source for heating a .025 wire

[Broken Arrow]

I'm trying to make a thin piece of wire (guitar string) get red hot to use as a cutting tool. My power source is a 12V 2amp battery charger which overheated the wire in about 2 seconds. Should I use heavier gauge wire or a 6V charger or do you have any other ideas. I already have the 12V and was really hoping to use that.
Thanks

 

[davenn]

what are you wanting to cut ?

for polystyrene, and a lot of plastics, it wouldn't need to be red hot as in glowing red

Dave

 

[Broken Arrow]

davenn,
Thanks for getting back...what I'm doing is making a burner for cutting feathers used on arrows. I've built the jig from plans on the net, but narrowing down a power source has been hard. Anything from model train transformers to car battery chargers. I've tried it with my 12V battery charger and it cooked the wire in about 1 sec. Any help is appreciated.

 

[(*steve*)]

You need to balance the resistance of the wire with the capabilities of the power source in such a way that the wire gets red hot (without melting) and the power supply is not overloaded.

In your case, a resistance under 6 ohms will overload the power supply.

I would suspect that any length of guitar string short enough to glow red hot under these circumstances is likely to have a resistance well under 6 ohms.

The cure is to use either a finer wire, or a lower voltage, higher current power source.

You may need to regulate the voltage (or preferably the current) output to prevent the wire melting whilst allowing it to remain red hot while cutting.

 

[Broken Arrow]

Thanks again...as I have clue about volts, amps., ohms, resistance....I'm guessing I need to reduce the voltage of the charger to 6V and experiment with the wire gauge. I tested an .025 guitar wire, .031 welding wire and some really thick multi-purpose wire with the 12V charger with the following results:

.025 - 1-2 secs before burning up
.031 - 5-7 secs before burning up
mult - 5-7 secs before tripping the charger to shut off

If you can let me know if I'm on the right track I'd appreciate it and thanks for taking the time to deal with an electronically challenged do-it-your selfer.

 

[(*steve*)]

1) measure the resistance of the wire

2) tell us what it is (and how long the piece of wire was that you measured)

3) tell us the specs of your various power supplies

 

[duke37]

I supplied my doctor with the necessary parts to cut poystyrene glider wings. The data I generated has gone but various wires were used including suture wire. You will need stainless or resistance wire to take the heat., I do not know what a guitar string is but nylon will not do !!

The wire will expand when heated so will need to be held in with spring tension. We used the technique used by Robin Hood in this area to start with and then made a bow saw frame to get extra clearance.

The solution I arrived at was a transformer (battery charger will do) and fed it with a series bulb and a light dimmer to control the heat. Light dimmers can give an asymmetric output which can put the transformer into saturation, the bulb provides a nicer load for the dimmer and limits the current in this case. A variable auto transformer (Variac or Regavolt) will also do but is expensive.

 

[Broken Arrow]

Steve,
I don't know how to measure the resistance of the wire, but I've tried an .025 steel guitar string and .031 welding wire. The length is about 7 -8". The power source is a 12V car battery charger set at 2 amps.
Thanks,
Jeff

 

[duke37]

With low resistances, the four contact method is the way to go because it eliminates contact resistance troubles which may be bigger than the resistance to be measured.

Set up a current through the wire with the battery charger and then measure the voltage across say 6" of the hot wire. R = V/I

Note that the resistance will go up as the temperature goes up.

 

[sirch]

Look for Ni-Chrome wire on ebay, a metre is quite cheap. I made a polystyrene cutter years ago with it and it worked fine off a 6v supply.

 

[Broken Arrow]

Thanks for all the help...the commercial version of the feather burner is Young Feather Burner and printed on the unit is 115-120 VOLT / 50-60 CYCLE AC ONLY. This is basically what I'm trying to duplicate on the cheap.