Step 1: Watch the Video
Step 2: Variac Vs Scariac
In a tight situation, it's good to be aware of options, and that's why I was happy to learn about the idea of the water resistor.
The Scariac is a name I got from www.youtube.com/user/acronus in his video http://youtu.be/GLBZjAd4wKg and duplicated with permission. It's a fitting name since the system acts similar to a Variac. The idea is to use a water based medium as an electrolytic resistor. A bit of electrolyte is added to the solution to make it slightly conductive, and when two electrodes are placed in the solution, the allow more or less current to flow, depending on whether there are closer or further apart.
Step 3: "How I Did" Vs "How To"
Although I've taken thought to minimize risks in operation, I have to stress that I don't consider this device safe or fool proof. It has the potential to be lethal, and even though I show step-by-step how it was made, this is more of a "How I did" project rather than a "How to".
The system has a power lever to vary current output, and a loop of wire for connecting an ammeter.
The outlet on the board is where the devices plug in, and the switch acts as a kill switch to turn the device completely on or off at will.
There is no grounding wire connected, and always possibility of failure in any part of the system, so extreme caution and respect is needed when operating. The device doesn't have any internal fuse/circuit breaker/current limiting device so there is also risk of fire if the system shorted out and your home circuit protection system failed. This fire could potentially happen inside the walls of your home.
Step 4: Electrolyte As Variable Resistor
2 gallons of tap water (Distilled water will also work great, but is more expensive)
1/4 teaspoons of 100% Lye (NaOH)
Even though the amount of lye is very low, it makes the water conductive very quickly.
I found my lye in a drain cleaner from the hardware store. 100% lye infact!
Any salts could probably be used as an electrolyte, but using something like table salt (NaCl) seemed to introduce the possibility of generating Chlorine gas, and that's why I went with the NaOH instead.
Step 5: Additional Considerations
The system is also open (ventilated) so any gas generation escapes quickly. In my experience, this doesn't give Hydrogen and Oxygen gases enough time to build up to a dangerous level, and I wasn't able to achieve any gas explosions, even at ultra high power settings, despite trying.. However, it is good to be aware of the risks, and operate in a well ventilated area as a precaution.
Well, there you have it! That's how I sacrificed safety to build a variable power controller on a very small budget.
If you haven't see the video yet, it's not too late. Watch it here!
If you like this project perhaps you'll like some of my others. Check them out at www.thekingofrandom.com