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Circuits designed by David Johnson, P.E.
Last Updated on: Wednesday, October 18, 2017 05:04 AM

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More  details for in DC Magazine

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Vertically Lifting Security Gate Power Source
Designed by David Johnson

A few years ago, I designed a control circuit for a client’s nifty security gate which lifted vertically, instead of the usual horizontal motion.  The act of moving the gate vertically and folding up was ideal for mountain homes, where narrow roads and heavy snow depths were common. 

Instead of using a battery to store the needed energy, so I opted for a supercapacitor bank. I sized the capacitor bank so it could operate the gate motor four times, without help from the solar panel.  The solar panel would be able to quickly charge up the capacitor between gate activations during sun lit days but much more slowly during cloudy days.  Once fully charged, the unit performed flawlessly.  The high quality capacitor bank should last for at least 10 years.


The circuit that I came up with is shown below.  It uses 5 identical circuits.  Each one is wired in parallel with it assigned 650F super capacitor.  A LM385 provides a 1.2v voltage reference.  A resistor divider measures the voltage across the capacitor and feeds the voltage to a low power, low voltage op Amp. The output of the op Amp drives an n-channel FET.  I designed the circuit for a maximum charge current of 600ma.  This would allow the use of a 10 watt solar panel, if needed, in the future.  Each of the five circuits forms a shunt type voltage regulator, limiting the voltage across each capacitor to about 2.6v. 

Click on Drawing Below to view PDF version of Schematic

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