# hotwire question

if i have a hotwire and I have it connected to a 12v 6a battery charger and I connect a SECOND 12v 6a battery charger, does that increase the charge on the line? does it cause nuclear fusion? will I die?!

OH GOD YOU’RE GOING TO RIP A HOLE IN THE FABRIC OF SPACE/TIME AND KILL US ALL!!!

Whew, glad we got that out of the way.

Now, I’m guessing what you’re really asking is will you double your power?

Going to take a little bit of writing so please hang on…

They sell these things called variacs, you know?

This bloke reckons it works (scroll down to the fifth post), but he’s a SUP’er (enough said): http://www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/Hotwire/

Since the same potential (12V) is across the same resistance, the total current drawn through the hotwire would remain unchanged. The net outcome would be that the power per transformer would halve - your wire won’t get any hotter. You really need to up the voltage instead, which will increase the current proportionally for the same resistance. If you want to stay on the cheap, just get a 24V transformer instead and control the voltage with a dimmer on the input side. But you should also look at the resistance of your wire and maybe move to a slightly smaller gauge too.

I don’t know enough snark from real questions but given this is a recurring topic that I’ve not found a detailed answer based on the math, (if there is, please forgive the repeat) here goes.

Too, alcohol was involved in the write-up so you’re responsible for checking after this to make sure it’s correct.

Hot wires work anywhere from just hot enough to part foam all the way to glowing with the white heat of Mob amputational justice*.

A variac will make it easier to adjust your temperature but what you really need is a good idea of how much power you’ll use so you can size your power source appropriately otherwise you’ll buy a power source then possibly get pissed off because you may set up a safety risk, spend to much or not enough.

What you’re trying to do is dissipate power over the length of your wire.

Simplified ballpark calculations for calculating the power of electrical devices are as follows:

Power (watts) is equal to I (current in amps) multiplied by E (volts) or P=IE and yes, I like 3.145…
Voltage dissipated over the wire may be calculated by E (volts) which equals I (current in amps) multiplied by R (resistance in ohms) or E=IR.

Before you can solve for power you need to determine how much current is passing through your wire.  To do this you’ll really need a simple Volt/Ohm meter but moron that later.

Nichrome wire will usually have a Ohm/length spec associated when you order it but don’t bank on it.  Instead, use an ohm meter to measure the resistance of the length of your hot wire without any connection.
For instance, the 0.032" nichrome wire I scored off of Amazon is ~ 1 Ohm/ft.
Next, check the specs on your power supply.
You said you have a DC 12V supply good for 6 amps.  If I was using your supply with my length of wire it would go like this:

Divide 12V by R (3 Ohms) and you get a draw of 4 amps.  This is under the spec’d 6 amp rating which is good however it may not be hot enough for what you’re trying to cut so…

Remember, P=IE.  12 volts multiplied by 4 amps = 48 watts.  Think of the heat that comes off of a 40 watt bulb though granted, it’s giving off much of it’s power in light but you get the idea.

If you’re stuck with the wire, you’ll have to shorten your wire to pull more current and/or raise the voltage.
You asked if you could double up chargers?  Well if you attach leads from another charger beside the first one, you’ll still wind up with a 48 watt hot wire cutter because it’s still only 12 volts so no, that won’t work.
However, if you can safely - and that is the key - put the output from one charger to the next you should now have 24 volts.  Sounds great right?
Well if - and that’s a big IF - you can do this without frying the chargers because of the way they may be internally wired coupled with the potential for shorting the supplies - then:

24 volts divided by 3 ohms is 8 amps.

Rut Row!  You just blew your chargers which are spec’d at 6 amps.

Okay so now you need a different power supply so let’s look at the variac Mike mentioned.
How do you know which one to get?

My 130 volt (AC), 3 amp variable transformer supply was about \$60 US.

Wait, 3 amps?  I just blew two chargers by pulling 8 amps.

Well, remember power.

AC calculations should include a power factor but unless you’re close to the limit ignore this for now.

How much power will the variable AC 130 volt, 3 amp (input fused) supply provide?

P=IE so 130 multiplied by 3 is 390 watts (approximately due to the power factor but again, if you have the head room, don’t worry about it).

Now let’s assume you want to use 24 volts (which by the way makes the wire I’m using a nice glowing red) from this transformer.
The setup we’re using at 24 volts draws 8 amps so 24 volts multiplied by 8 amps is 192 watts.  This is well under the 390 watts the transformer is capable of delivering so that works.

However at this point you should really have a meter to check the real numbers because cheap transformers like mine have meters that are up to 5 volts off and a couple of volts is enough to make a big difference so get a meter and check the resistance of your wire and volts supplied.

• My hotwire cutter will burn wood parts, fingers, small animals, wives/children, the house, bookies who short the take…

well, damn.

I use a variac and some 150# stainless steel fishing leader on my hotwires…

you variac users are just lazy and/or unadventuristical…possibly both.

set the controls for the heart of the sun!!!

I happen to have some lower gauge wire…I’ll give that a whirl first.

I didn't make it all the way through the details on the hotwire build. I'm more interested in building boards. The directions sounded good though!

Some of us don't have the attention span to make it through a long well thought out step by step. Just give me a few pictures and I will figure out the rest through trial and error.

Ask and you shall (sometimes) receive - the ghetto table saw hot wire attachment for profiling, angle fairing and slabbing.

If as Barbie says “Math is Hard!” for you - really sweetheart, lose the metro sexual and find yourself a G. I. Joe with Kung Fu Grip who knows how to handle a real doll like you - then here are a few pics;

Before we get started, a quick note on safety - hokey I know but none-the-less, literally vital.

Good idea to use GFI protected outlets, fuse down the power supply
to a bare minimum, dial limiters to prevent accidentally running the
voltage up to maximum, cover all non working components with
non-conductive material to prevent shorts, etc. ad nauseum.

This stuff can keel you.

That’s it.

If you don’t know how you should probably study the possible scenarios before finding out the hard way (and ending up on “10,000 Ways To Die” though the episode about the woman and vegetables, well, err, never mind) because I prolly aint yo’ daddy (to my knowledge) and can’t and won’t take responsibility for your stupidity, accidents and/or injuries when I’ve got headaches from trying to get a handle on my own.

Unless you’re a real (three fingered, one eyed, half eared, limping, patchouli reeking) surfcraft building waterman in which case, yeah, well, whatever.

What works in our Private Non-Profit Art Studio® may not be appropriate in a factory.

Oh, and like Francis?  Goat head, sue me.  I keel you.
I keed, I keed.
Sorta.

The itemized list

• Adjustable base from a leftover dish network antenna

• Variable transformer (the red thing with the dial)

• 0.032" Nichrome wire

• Volt/Ohm meter

• A few wire ties

• A couple of springs

• Scrap computer power plug

• Crimp on leads (terminal and alligator)

• Mounting nuts, bolts, screws, washers

• Electrical tape

First up, the wire.  As mentioned above, many types of wire may be used but Nickel Chromium wire has a good resistance profile and is tough.  This roll is ~ 80’ for ~ 14\$ US.

The brackets from satellite dish receivers are pretty heavy duty, fully adjustable and usually free.
Pull apart the supports and reassemble them to whatever configuration best works for you.
The supply should probably be as close to the cutter without getting in the way to keep leads short.
Note the spring.  This is attached to non conductive wire ties at the base.  Terminal leads attach to the spring and the hot wire terminal is attached on the other side.  The spring dissipates any heat that may transfer from the hot wire to the mount point.

The variable transformer is the red thingy with the dial, (crappy) meter, switch, input fuse holder and outlet.

Looking down the length of the extensible boom shows both terminal ends.

An additional note on the springs - they’re set to about 10 lbs of tension with approximately 1/2" of travel.  As hot wires heat up they expand which causes sagging and poor cuts.  Don’t be surprised if over the life of your rig you have to continually readjust the mount due to changes in the wire caused by continual expansion/contraction cycles.

NEXT LEVEL

also, i received a bunch of really bitchin' inconnel wire from our friend M.Ward (he says it works better than the Nichrome stuff)... i can mail you some if you want

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Ask and you shall (sometimes) receive - the ghetto table saw hot wire attachment for profiling, angle fairing and slabbing.

If as Barbie says "Math is Hard!" for you - really sweetheart, lose the metro sexual and find yourself a G. I. Joe with Kung Fu Grip who knows how to handle a real doll like you - then here are a few pics;

Before we get started, a quick note on safety - hokey I know but none-the-less, literally vital.

Good idea to use GFI protected outlets, fuse down the power supply to a bare minimum, dial limiters to prevent accidentally running the voltage up to maximum, cover all non working components with non-conductive material to prevent shorts, etc. ad nauseum.

This stuff can keel you.

That's it.

If you don't know how you should probably study the possible scenarios before finding out the hard way (and ending up on "10,000 Ways To Die" though the episode about the woman and vegetables, well, err, never mind) because I prolly aint yo' daddy (to my knowledge) and can't and won't take responsibility for your stupidity, accidents and/or injuries when I've got headaches from trying to get a handle on my own.

Unless you're a real (three fingered, one eyed, half eared, limping, patchouli reeking) surfcraft building waterman in which case, yeah, well, whatever.

What works in our Private Non-Profit Art Studio® may not be appropriate in a factory.

Oh, and like Francis?  Goat head, sue me.  I keel you.
I keed, I keed.
Sorta.

The itemized list

- Adjustable base from a leftover dish network antenna

- Variable transformer (the red thing with the dial)

- 0.032" Nichrome wire

- Volt/Ohm meter

- A few wire ties

- A couple of springs

- Scrap computer power plug

- Crimp on leads (terminal and alligator)

- Mounting nuts, bolts, screws, washers

- Electrical tape

First up, the wire.  As mentioned above, many types of wire may be used but Nickel Chromium wire has a good resistance profile and is tough.  This roll is ~ 80' for ~ 14\$ US.

The brackets from satellite dish receivers are pretty heavy duty, fully adjustable and usually free.
Pull apart the supports and reassemble them to whatever configuration best works for you.
The supply should probably be as close to the cutter without getting in the way to keep leads short.
Note the spring.  This is attached to non conductive wire ties at the base.  Terminal leads attach to the spring and the hot wire terminal is attached on the other side.  The spring dissipates any heat that may transfer from the hot wire to the mount point.

The variable transformer is the red thingy with the dial, (crappy) meter, switch, input fuse holder and outlet.

Looking down the length of the extensible boom shows both terminal ends.

An additional note on the springs - they're set to about 10 lbs of tension with approximately 1/2" of travel.  As hot wires heat up they expand which causes sagging and poor cuts.  Don't be surprised if over the life of your rig you have to continually readjust the mount due to changes in the wire caused by continual expansion/contraction cycles.

[/quote]

Pictures are worth 1000 words. Thanks for the details Brian.

You’re welcome, anytime.