Hot wire cutter disaster

Thread Starter

Alexcapacitor

Joined Nov 11, 2021
4
Hey gang, first time here.

I’m trying to make a hot wire cutter with enough sauce to cut through wax. This should be a simple + - to nichrome wire short circuit but nothing seems to work.
Attached is my power supply and I’m using a voltage adjuster (up to 32v and 30guage nichrome wire.

no matter what I do it just won’t work.

Any help?
 

Attachments

Last edited:

Thread Starter

Alexcapacitor

Joined Nov 11, 2021
4
Hey bob.
Ok the wire doesn’t heat at all. And when the voltage adjuster is attached it just shuts down when the wire is screwed in.
the pos and neg terminals show a perfect read on my multimeter pre wire attached.
 

sagor

Joined Mar 10, 2019
538
You show a 12V 2.0A power supply. That is 24W total power. I suspect it does not supply enough current. If you are boosting the voltage up to 32V, somehow (you don't explain that part), you would be lucky to get about 0.75A out of the 32V supply if using a buck/boost converter. Also, what is the 32V converter rated at? The term "voltage adjuster" is very vague.
Again, I suspect there just is not enough power being supplied to the nichrome wire. The 12V supply may even drop voltage/shut down with a heavy load.
 

Jon Chandler

Joined Jun 12, 2008
58
30 gauge nichrome has a resistance of about 6 ohms per foot. With your 12v 2 amp power supply, if the length of your wire is a foot, you'll be right at the rating of the power supply. Anything shorter is definitely an overload.

But....the surge current when connecting the wire will be even greater. A switching power supply's response to a gross overload is to decrease or even shut off the output voltage. You need a power supply with several times more output capacity.
 

AlbertHall

Joined Jun 4, 2014
11,704
It looks like the wire is about 50mm long and so would have a resistance of about 0.8Ω and this would draw about 15A so your supply will shut down.
I don't think that wire will stand up to 15A even if the supply could cope.
We nned to understand how much current the wire needs to get to the right temperature for cutting.
 

Alec_t

Joined Sep 17, 2013
12,477
If you have an old ATX supply, the 5V output on that might be better. It should be able to handle 5cm of 30 gauge nichrome.

Edit: If the only insulation between the wire and its metal holder is pvc insulation tape (which is what it looks like in your pic), the hot wire will soon melt that and result in a short circuit that would shut down or damage any power supply!
 

LowQCab

Joined Nov 6, 2012
1,619
What You need is a Microwave-Oven-Transformer with a 10-gauge, re-wound Secondary,
with around ~30-Turns through the Core,
followed by an Adjustable-Current-Regulator Circuit.

This can be adjusted for any sized Wire, or temperature requirements,
and will automatically have a "Soft-Start" which will extend the life expectancy of your Wire.
.
.
.
 

Tonyr1084

Joined Sep 24, 2015
6,624
Welcome to AAC. I noticed nobody caught on to you being new here. So welcome.

When I was cutting styrofoam insulation I used a long length of welding wire, solid core, and I don't recall exactly what material it was. One problem I encountered was when the wire heated up it slacked significantly. I had to make a spring loaded arm to keep the tension on my wire. I was cutting 4 x 8 sheets, so mine was significantly longer than yours is. For a power supply I used a welder, 24V with serious power for heating a long wire. It worked sweet.

Just my opinion here, but You don't need a DC source, you just need sufficient wattage. Rewiring a Microwave Oven Transformer (MOT) is likely your best bet.
What You need is a Microwave-Oven-Transformer with a 10-gauge, re-wound Secondary,
with around ~30-Turns through the Core,
followed by an Adjustable-Current-Regulator Circuit.
I have so many of those darn things I stopped collecting them. I still have the welder too. But using a SMPS (Switch Mode Power Supply) isn't likely the best approach. Those things have built in protection against short circuits and overloads. You just might never get there that way. Not saying you won't, just I suspect it will be hard to find the right combo. Me? I'd go with a low voltage transformer capable of enough watts so as to not overheat the transformer. That, however, may be harder to come by in the form of scrap materials. That's why rewiring a MOT is probably your best bet. In fact, I have a MOT sitting on the floor right behind me. Nice one at that. Has a squirrel cage cooling fan to keep it cool. Don't know what I'm going to do with it though. I collect junk. Maybe one day I'll open a small shop and call it "Another Man's Treasure".
 
Last edited:

djsfantasi

Joined Apr 11, 2010
8,078
30g Nichrome wire is about 0.54 ohms per inch. Knowing that, you can use Ohms Law to calculate the current required for a given length of wire.

If you know the temperature required, you can use it this calculator to determine the power and current required.
 

shortbus

Joined Sep 30, 2009
9,065
Why do people continue to think/use DC power supplies for this hot wire cutters? The companies that make hot wire cutters use AC, a transformer to drop the voltage and isolate. A quick Google shows what I'm saying.
 

MisterBill2

Joined Jan 23, 2018
10,580
Why do people continue to think/use DC power supplies for this hot wire cutters? The companies that make hot wire cutters use AC, a transformer to drop the voltage and isolate. A quick Google shows what I'm saying.
I was going to suggest the same thing. Us a transformer and run the hot wire on AC Get a 24 volt ten amp supply and that might be enough current. BUT be careful to verify that the transformer secondary is isolated because there are also non-isolated transformers available. They will work BUT there will be a shock hazard.
 

Ford Prefect

Joined Jun 14, 2010
207
Quite a few years ago when I built my hot wire foam cutter I used one of these dimmer switches below. I used a 12vDC power supply rated about 5 amps.
It controlled the heat on about ½ metre of 0.3mm nichrome or kanthal resistance wire and adjusted the heat depending on the thickness of the foam. I found it was possible to regulate the wire temperature from slightly warm to red hot. I admit that it worked very well.
Check out this link:
Hot wire cutter

IMG_20211114_131731.jpg
 
Last edited:
Top