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Homemade Power Box
If you have read Gerald Musy previous article about Light Bulb (click the below link)
I’m sure you have noticed a power box was used to plug in the load (light bulb) and gain access to voltage and current test points. What is exactly inside the power box and how it was made? I have emailed him and he kindly shared out his experiences on how to built the power box. Let us check out his article below:
Time to time we need to measure voltage and current from mains connected equipment (240V here in Malaysia). I built the above box to make this operation as easy and as safe as possible. We know that mains electricity is dangerous and stripping wires can be hazardous. This power box proved to be so useful that it won a permanent position on my workbench…
The load to be measured plugs into the mains socket. The red and black jacks (in parallel but also controlled by the switch) provide an easy connection for a voltmeter. On the right hand side a jumper made of the two green banana jacks and a wire loop is connected in series. Here is a picture of the wiring inside:
I added a 1A fuse and an extra pilot lamp. The extra lamp is to indicate presence of a voltage because I found the lamp built into the mains socket too dim…
The serial jumper with a wire loop allows measuring the current using a clamp meter:
Alternatively we can use an ampere meter. In such case the jumper needs to be removed. Be careful to disconnect the power box before doing this as the green banana jacks are not controlled by the switch:
We can also connect a light bulb instead of the jumper for the famous “light bulb trick”, just plug the power supply to be tested into the mains socket:
Please note the following:
1) I drilled a hole into the back of the mains socket to connect the red banana socket after the switch. So there is no voltage when the switch is off.
2) However, the green banana jacks will be life, even when the switch is off. I had no choice because the switch is built in the mains socket and soldered directly to the life contact. A safer alternative would be to use a separate switch. I might do this one day… For time being I am careful to unplug the box before connecting an ampere meter.
In any case, be careful.
This article was contributed by Gerald Musy from Penang, Malaysia.
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