Homemade Battery Discharger
Hello friends from around the world and welcome to my latest offering. In this post I will be showing you how I built my own variable battery discharger. I won't be giving any circuit diagrams as it is quite a complicated build and could be very dangerous for the untrained operator. Discharging batteries is a dangerous operation even for the fully trained person. During discharger batteries can explode causing injuries, damage and fire. I always recommend using a Li-Po fire proof discharge bag, which are inexpensive and widely available.
The reason for building the discharger was because the discharge times on my Imax B6AC are far too long. The reason for this is the Wattage of the resistors in the Imax are very small, hence the lower discharge rate and time increase. So I decided on 100 Watt alloy clad resistors. Ideally, I would have liked 200 watt resistors but the cost of them was too high. However, when these resistors are used in parallel I will have 300 Watts across the whole circuit. After many, many of calculations, I decided on an 8 ohm resistor as it was a value that suited batteries up to 6S (22.2 Volts). However I found the maximum battery size I could discharge safely was only 3S (11.1 Volts). This was done to heat build up, due to where the discharger is situated. The wiring design and specification is capable of discharging up to 8S, so it is safe to use without the worry of it catching fire. Having said that, I would not leave a discharging battery unattended for any length of time.
It was quite the challenge to build something like this from scratch as I had no ideas of what it was going to look like. So I set out what I wanted from it and from there I knew what I needed. My first concern in any electric build is removing any heat from the case. In this case, there will be a lot of heat build up because the resistors are transforming the electric current into heat, which in turn discharges the battery. I needed a heat sink, so I did some experiments.
I also needed a temperature measuring device on top of a voltmeter, ammeter and watt meter so I built an all in one device that you can see above. It is a very handy little instrument indeed. I can now free up my multi meter to employ elsewhere.
I have populated the front panel with components to check the fit. The above displays are for demonstration purposes only and will change. I have also installed the control potentiometers for the variable DC power supply. Time to remove all of the components and get the front panel painted.
Cheap and cheerful, yet super bright. It is 12 volt and sucks around 1.8Ah. This illumination will be a blessing when cutting and shaping polycarbonate rc car body shells. It looks ugly and cheap but has in fact it's own circuit protection through a simple circuit. The protection circuit employs:- 2 LED's, 1 resistor, a momentary switch and a 12 Volt, 10 Amp relay (which will be another future post).
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