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Hot wire troubleshooting

Hot wire duck

New Member
Hi, I have just built a basic hot wire with a momentary on off switch using 28 gauge steel wire but it isn't heating up. I do not own a multimeter so I cannot tell if the adapter isn't working. The power adapter outputs AC at 12 volts 1.5 amps with a 20cm wire. Please help
 

gophert

Well-Known Member
Most Helpful Member
Hi, I have just built a basic hot wire with a momentary on off switch using 28 gauge steel wire but it isn't heating up. I do not own a multimeter so I cannot tell if the adapter isn't working. The power adapter outputs AC at 12 volts 1.5 amps with a 20cm wire. Please help
The resistance of a 20cm piece of steel wire 1 to 2 ohms. At 12 volts, the power supply is expected to dump 6 to 12 amps through the wire. Just over 1.5amps, your modern power supply will fault over into a safe mode - no power. That is why it is not heating - no power.
 
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Pommie

Well-Known Member
Most Helpful Member
Your wire will have a resistance of ~0.5Ω. Assuming your supply will limit the current to 1.5A then the the heat produced will be ~1W. You need a better wire of a bigger supply. Nichrome is the best wire to use.

Mike.
 

gophert

Well-Known Member
Most Helpful Member
Your wire will have a resistance of ~0.5Ω. Assuming your supply will limit the current to 1.5A then the the heat produced will be ~1W. You need a better wire of a bigger supply. Nichrome is the best wire to use.

Mike.
Since the OP said the wire is not getting warm, I think the power supply is shutting down to safe mode - since it cannot possibly output 24 A by your resistance assumption.
 

be80be

Well-Known Member
Hook it to a car battery it soon melt the wire it's not going to just get hot if you had a supply big enough. It would melt very fast.
Id go for some Nichrome wire. as said

And yes i see the OP using a 1.5 amp supply from a old netgrear or something hard to tell my crystal ball needs cleaning
it's kind of foggy. But they shut down fast with a short.
 
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Hot wire duck

New Member
I have invested in some 32 SWG nichrome that is the same length. I have tried with a 12v 1.5 amp DC adapter and it is warm. I tried with a 19.5v 3.34amp ac adapter and it melted the wire. How do I decrease the power?
Thanks
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Way back when I was at school, I was asked by the woodwork teacher (Mr. Woodward - appropriate name :D) to make a hotwire cutter for the art department. I was always given the strange jobs to do!.

We simply used a multi-tapped transformer, these were common place back then, and we simply connected each tap to a 4mm socket, and to adjust the power you simply selected the taps which provided the correct level of heat for the specific length of cutter wire you were using.

For a more modern approach, I would suggest a constant current PWM design, with a simply knob adjustment to set the current.

As usual, a PIC would be an excellent choice, or an Arduino for that matter - it's a very simple programming project.
 

gophert

Well-Known Member
Most Helpful Member
I have invested in some 32 SWG nichrome that is the same length. I have tried with a 12v 1.5 amp DC adapter and it is warm. I tried with a 19.5v 3.34amp ac adapter and it melted the wire. How do I decrease the power?
Thanks
Forget all the conversation about PIC and constant current BS for now

Just move the connector on your 12v setup to shorten the length of resistance wire by one inch, measure temp, then another inch and so on until you have the temp you want. Then report back. Just remember, resistance is a function of wire length if you only have one wire thickness in stock.

Also, keep the 19v power supply in a box for now - unless we have trouble with your wire on a 12v setup getting to short for good performance.
 

dr pepper

Well-Known Member
Most Helpful Member
I borrowed a commercial one of these, but it didnt seem hot enough, maybe the wire was too heavy gauge.
Temporarily I used a croc clip to croc clip lead to short out a 2" or so section of the wire, it worked nicely, even though it probably overloaded the transformer.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I borrowed a commercial one of these, but it didnt seem hot enough, maybe the wire was too heavy gauge.
Temporarily I used a croc clip to croc clip lead to short out a 2" or so section of the wire, it worked nicely, even though it probably overloaded the transformer.
Probably not, if it wasn't hot enough there was obviously something wrong, and it's not the kind of device you're design with barely capable transformer.

Nice trick with the croc clip lead though! :D - and you could slide it up and down to vary the power.
 

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