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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.
Magnetics Inc CR3110-3000 Current
Transformer
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.
Click on Drawing Below to view PDF version of Schematic
