Introduction: The Scariac (Poor Mans Variable Power Controller)

About: Random Weekend Projects

Mixing water with electricity is risky, and can be lethal.  However, in this project we're using it to make one of the cheapest kinds of power controller.  The Scariac.

Step 1: Watch the Video

WARNING: This project is extremely dangerous and should only be attempted by those highly skilled in working with electricity.  High voltages and high currents passing through the water provide an open hazard of electricution, and may cause death.  This design does not include any electrical ground.  This system is not recommended as a safe device.  It's purpose, rather, is to regulate electrical current in a simple and low cost way.  Toxic gases may be released from the solution during operation.  This project should not be attempted without adult supervision and adequate training.  Misuse, or careless use, of tools or projects may result in serious injury.  Use of this video content is at your own risk.

Step 2: Variac Vs Scariac

I needed a way to adjust the power running to my homemade stick welding system, as seen in the video below;

Even with enough power to the welder, the main problem was finding a system that could vary electrical current without costing an arm and a leg.

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 in his video 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"

In its simplest form, this device is just a glorified version of 2 wires in a bucket of water.

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

I used a water based medium for the variable resistance.  

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

During operation, the electrolysis does produce some gas, however it seems to be minimal when supplying with AC power.  DC would be a much greater concern.

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