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# What is the current on my foam cutter? Should I be worried? Answered

I built the 5 min. foam factory, but instead of a model train transformer (\$45 for the cheapest one they had) I used a regular 12 volt transformer and a rectifier bridge (I had to borrow it from my infinite LED tunnel :'( ) Now when I went to buy a variable resistor/potentiometer for the thing my local electronics shop guy said that the 12 volt transformer put out too much current for the ones he had. Now this has me worried. How much current is currently going through this thing? Should I be worried?

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## 12 Replies

pure punjabi (author)2012-04-06

i have same problem like this .when i connect the wires to the wire the diodes heat up.and then blows

gmoon (author)2009-03-21

Should you be worried about the current?

Short answer : No, assuming you treat it with respect.

Long answer : Foam cutters use a "hot wire" with relatively low resistance. A cutting wire might be 10 ohms, for instance.

Do the math to find the wattage: W =V2 / R, or ~28 watts = 16.9 * 16.9 / 10 (your voltage is higher than 12V-- rectified RMS AC voltage is V * 1.414: 12 * 1.414 is approx 16.9V.) This is just an example, of course--we don't know the resistance of the wire.

Since most POTs are rated for 1/2 watt or less, the shop guy was correct: it's the POT that's in danger, not you.

Since the wire resistance is so low, you'd need a rheostat between 10 and 50 ohms, rated for 50 watts.

Sandisk1duo (author)2009-03-17

it would FRY the potentiometer

12v cannot harm you unless you purposely licked the contacts

frollard (author)2009-03-18

12V CAN KILL YOU. it needs the volts to get thru your skin. The amps, only thousandths of which are needed to stop your heart. Always treat electricity with care.

Sandisk1duo (author)2009-03-18

there needs to be at least 50v for you to feel it go thru your skin when it's dry

frollard (author)2009-03-18

2 words. Car Battery.

Sandisk1duo (author)2009-03-18

car battery < 50v

frollard (author)2009-03-18

depends on placement of the voltage. I don't have my multimeter here, but take a jolt to the chest, with even moderate clammy-ness and you will see serious cardiac problems.

Sandisk1duo (author)2009-03-18

i know for a fact the car batteries are at maximum 14.7V i know that your skin's resistance is so high, that you need 50v+ for you to barely feel it you can get your hands wet and touch both terminals of the battery, it won't do a thing... now, if you had BBQ skewers inserted into your chest, and 12v passed thru, you can stop your heart

frollard (author)2009-03-19

I digress.

frollard (author)2009-03-17

Ohms law says Current (I) = Volage (V) divided by Resistance (R)

You need an ohmmeter, or an estimation based on the gauge of your cutter wire, and its length - I'd use a multimeter to be sure.

You are running it at 12 volts, divided by the resistance. Huge resistance = less amps. Small resistance = huge amps.

Why do you rectify the ac going into the wire? It would do just as well to leave it off. (the heating element in most heaters/ovens etc is AC.)

NachoMahma (author)2009-03-18

. To pick a nit, resistive heating elements don't care if they get AC or DC. When AC is measured using RMS, the average power of 12VAC is the same as 12VDC.
. But your point is still valid - no need to rectify.