[thedoc]

Guy asked the Naked Scientists:
   
I have a neon sign transformer from a broken beer sign.  I have seen on you tube, a person electolyzes potassium chloride to potassium chlorate. Can I make an electrolysis device with this transformer and what parameters need to be adhered to if I make my own chlorates?

What do you think?

[Geezer]

What do you plan to do with the potassium chlorate?

[Bored chemist]

The voltage needed for an electrolytic cell is a few volts at most.
Using a neon sign transformer would be even less efficient than using the mains directly, and also more dangerous.

[CliffordK]

So, you could wire it as a step-down transformer, rather than a step-up transformer?

[Bored chemist]

It depends- they are not all straightforward transformers.

[evan_au]

Transformers convert one AC voltage to a different AC voltage.

You need a transformer which converts from mains voltage (usually 110V AC or 240V AC) down to about 3-5V AC. (The neon sign transformer will convert mains voltage to 10,000 volts or more). In either case, these are potentially lethal voltages, so make sure you get an experienced person to help with the wiring, and insulate it well.

Electrolysis requires a DC voltage of a few volts. AC doesn't work, because any electrolysis is undone when the voltage reverses, which it does 100 or 120 times per second (depending on the country).

AC can be converted to DC with diodes - a bridge rectifier is a good way to do it. You will lose about 1.5 volts in the bridge rectifier: http://en.wikipedia.org/wiki/Bridge_rectifier#Basic_operation

You don't need a smoothing capacitor for electrolysis.

It's a good idea to put a 6V light globe in series with the electrolytic cell, so if the plates touch, the light globe lights up, and protects the transformer (but it's getting hard to find light globes these days...)

[Geezer]

It's current rather than voltage that produces electrolysis. The voltage is determined by the particular chemical reaction involved, so you need enough DC voltage for that particular reaction, and a means to control the current. If you don't control, or somehow limit, the current, the reaction can consume an enormous amount of energy with potentially very unpleasant consequences.

Also, you could easily overload the transformer. If you do, it will get very hot and give off a lot of very undesirable chemicals, and it might start a fire.

Current could be controlled by an electronic device. A DC power supply with an adjustable current limit or a constant current output would work, or it could be controlled with an old-fangled rheostat in series with the electrode circuit. You'd definitely want to include an ammeter in the circuit to monitor the current.