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Circuits designed by David Johnson, P.E.
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Energy Harvesting Using a Current
Transformer -- January 17, 2010 |
| Energy harvesting is all the
rage these days. With some modern electronics, information from low power sensors
can be sent to a distant data collection point using a low power RF transmitter. To
power these remote sensors, various energy sources can be tapped into. Machine
vibration, temperature differences, ambient light and stray RF have all been used as low
power energy sources. Sometimes, the sensors are located near AC power cables.
Rather than making a direct connection to those cables, an AC current transformer, such as
the one shown below, can be used to capture a bit of power. |
| The CR3110-3000 current
transformer is one example of a useful energy-harvesting device. It is a fairly
small device and can easily be snapped onto a thick cable. Its center hole measures
about 0.4 inches. It has a high turns ratio, so even with a low AC current, the
device can produce a useful voltage. The circuit shown below is an example of converting
the AC from these devices into DC. |
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Magnetics Inc CR3110-3000 Current
Transformer |
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| The circuit is a classic
voltage-doubler, using two efficient schottky diodes. With 1 amp of AC current
flowing through a single wire in the center of the transformer, a voltage of 3v DC with an
86uA load can be produced. The circuit tracks a square law function so with 2 amps
of current through the center wire, 360uA of DC current can be generated. With 4
amps nearly 800uA of DC current can be collected. To increase the power collected
you can also wrap more than one turn through the center hole. Although the part is
small there is room enough for 3 turns around a heavy 10 gage insulated wire as the
photograph shows. |
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