Is it possible to regulate a 12 volt battery output in a short circuit type situ

You need a rheostat to control the voltage by increasing the Ohm's.

Maybe some resistors might do the job or even a light globe in line to suck some of the power out the battery and preventing a dead short which ain;t good for the battery.

Cheers,

Hi GN,

I recommend some halogen bulbs wired in parallel to control the current.
Filament bulbs are almost ideal current sources, meaning the current stays pretty constant with varying voltage across your mig wire.
Problem is that the mig wire resistance has positive temperature coefficient which means that it tends to get hotter and hotter because the voltage across it increases while the current through it stays constant.
But you may actually get used to this by increasing the cutting speed to cool the wire more.
I think you can get 100W, 50W and 20W units.
If you make them all switched you can make the current adjustable.

cheers, Peter

Hello GN,
The 8 - 10 amps you indicate is a long way from a short circuit. A good battery will supply hundreds of amps to start your vehicle. In your need a bit of resistance in the circuit to reduce the current to the 10 amps you say you require. Normally in hot wire foam cutters this is done by using nichrome wire which has the resistance built in and also having an adjustable voltage regulator to fine tune the heating. To get your 10 amps you need 1.2 ohms of resistance. A very rude and crude way to get the required resistance would be to connect the mig wire to the battery via a long length of fencing wire. You need to experiment with the length. Use a battery clip to connect and adjust the length. I stress this is a rude and crude method just to do a quick bit of cutting and be careful that you don't short the battery. Don't breath the fumes produced by the cutter as they are toxic.
Cheers,
Al-one

Hi,

You could also use some heating element from a toaster or similar and adjust the length with the help of an alligator clip till you get a suitable current.

Cheers, Graham.

I doubt that the mig wire will have enough resistance to generate the heat required to melt styrofoam in a controlled fashion.

need resistance wire. Something like this
http://jaycar.com.au/productView.asp?ID=WW4040&keywords=resistance+wire&form=KEYWORD

About 2 amps through this cuts styrofoam nicely.

Hi GN,
I use a hot wire cutter to cut foam wing cores for model aircraft. I use my old 48 voltTransarc welder as a heat source and I use thin ni chrome wire in the cutting bow.
To control the temp I use a very simple resistor.
You need a small panel of wood say 250mm x 100mm although this is not critical.
Drive rows of nails into the wood at 25 mm intervals and wind your thin fencing wire around each nail in turn and along to the next. The wire from the cutting bow needs to be ordinary 2 core flex to which you have fitted two small alligator clips. Put one end on the first nail and the second on the last. It probably will be too cold to cut.
Move the clip back along from nail to nail until the heat cuts clean without dragging or burning too wide a channel.
Used this method for 30 years.
merry xmas
Guy