Lightbulb Current Limiter

 

Should something go awry while you're working on some gear it's a good idea to have the gear plugged into a current limiting device. The reasons are two fold. First, an inrush of current can seriously damage your power transformer, amongst other things, which is the most expensive part found on most guitar and other audio amplifiers.  Second, current is a requirement for you to be electrocuted so an unexpected inrush of it greatly increases the danger for you. Best to use the lightbulb as a fuse and have the inrush blow it which breaks the circuit saves you... hopefully. 

 

An inexpensive way to build a current limiting device is to build a lightbulb current limiter.  We chose to illustrate the base model of lightbulb limiter in the diagram below because we didn't want to confuse the idea with unnecessary bells and whistles. Ours is an always on model.  Plug it into the wall and whatever you are testing into it. That's it.

 

It's not necessary for the bulb to actually blow for you to see the warning sign. If it glows brightly or even just significantly it's a warning sign that something is probably not right on the circuit you're testing. You should shut the test down and re-evaluate your options. 

 

        Lightbulb Current Limiter

 

The info graphic above illustrates how to build a light bulb current limiter. It's simple...

 

  1. Get a ceramic lightbulb socket base, a normal home wall socket and a box for it from a home store like Lowes or Rona. 

  2. Get a cord like the one shown in the graphic and strip away enough insulation to route the white, green and black wires.

    1. Tip: Route the cord, insulation and all, into the receptacle box and use the clamp that comes with the box to secure it. The only wire then needing to leave the receptacle box is the black one. Route it to the lightbulb socket starting from within the receptacle box. 

  3. The white and green wires get wired to the receptacle as shown in the graphic.

  4. The black wire goes to the lightbulb socket base and should connect to the base's black wire (or the hot lead)

  5. The base's other wire, regardless of colour (probably white), is wired to the receptacle's Hot/Black pole as shown in the graphic.

  6. Secure the lightbulb base and the receptacle box to the board and use wire clamps() to secure any wires not in the receptacle.

 

And that's it, you have one lightbulb current limiter ready for use.  Parts cost is roughly $35 CAD. 

 

Lastly, we decided against making a video to show the construction because Uncle Doug has one on his YouTube channel.. If you don't know Uncle Doug yet you should click the link and check him out now.  Very cool dude.   He's a great resource for early learners in the hobby. His videos are informative and easy to follow along with.  He's not affiliated with the DellBill ecosystem but we love him just the same. 

 

Note:

Some of you might wonder why we're connecting the socket base's white wire to the receptacle's hot/black lead?  Wiring it this way is called wiring it 'in series'. The bulb is placed first in the series so an inrush of current has to go through it first. If we were to attach the white wire to the Neutral terminal of the receptacle then the bulb would have been placed in parallel. This means that even if an inrush were to blow the bulb that would not stop the current from reaching the gear you're testing and then causing damage to it. If you see or hear the phrase "put the bulb in series with the load", that's what this is all about.  The load is whatever gear you plug into the limiter.