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12V 20-120W Solar Panel Simulator

How do you test or develop a solar charge controller such as the unit described in SILICON CHIP last month? You could use a solar panel but then you are at the whim of the weather and time of day. Also you would need several panels of different sizes to test it properly. This device solves all those problems.

by John Clarke

Main Features

• Simulates 12V solar panels, 20W to 120W

• Can be run from a 24V battery or supply

• Adjustable open circuit voltage (Voc)

• Adjustable voltage drop with current

• Adjustable current limit threshold

• Adjustable current limit slope sets short circuit current

• Additional over-current protection

This Solar Panel Simulator allows charge controllers to be tested without a solar panel. A simulator is handy because a solar cell panel will not always provide power and will certainly not deliver its full power output at all times.

It is only around noon on a sunny day that the solar panel will deliver its rated power. In other conditions (eg, cloudy days), the panel delivers less than full power, while at night it will not deliver any power at all and may even draw power from the battery (unless precautions are taken).

So when the Sun is not shining, an alternative source of power is necessary if you wish to test a charge controller such as the SILICON CHIP unit described last month. This is where this Solar Panel Simulator comes in handy. It can not only deliver power when required but can also deliver full power for as long as is necessary, regardless of the amount of sunlight.

Click for larger image
Fig.1: the current/voltage curve for a typical 120W solar panel. VR1 in the simulator is used to set the open circuit voltage while VR2, VR3 and VR4 adjust the other parameters as shown.
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Fig.2: the current/voltage curve for a typical 40W solar panel. The simulator can also be adjusted to match this curve (or the curve for any other panel rated from 20-120W using trimpots VR1-VR4.

Typical system

Solar panels are becoming increasingly popular for charging batteries and supplying power to equipment where mains power is not available. A typical system comprises the solar panel, a solar charge controller and a battery. The charge controller ensures that the battery is correctly charged and is a necessary part of the system. Without it, the battery may be overcharged by the panel, resulting in shortened battery life.

Basically, this device can be set up to simulate a 12V solar panel rated anywhere from 20-120W. It can be used to ensure that the charge controller’s MPPT (maximum power point tracking) circuit is operating correctly and features adjustable open-circuit output voltage, adjustable voltage drop with current slope, an adjustable current limit threshold and an adjustable current limit slope to set the short-circuit current.

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