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Step 12Populate the PCB
Solder the components on according to the image. The left eight-leaded component in the image is the MCP6002 op amp, and the right eight-leaded component is the FDS6898A MOSFET. The resistors are, from left to right, 100k, 16.2k. 100k, 5k. The left diode is the Schottky and the right diode is the standard or zener diode.
There are a couple ways to solder surface mount components. One good option is to melt a blob of wire solder onto each solder pad, then with tweezers hold the component in place and with the iron wick the solder up to meet the component. A very fine tip and a temperature controlled soldering iron make this go a lot more smoothly. A better option is to use a syringe of solder paste to place paste on each pad, then heat the entire board with an air pencil or heat gun.
The circuit operates as a comparator circuit with hysteresis. If the output of the comparator is high, that turns on the FET, which turns on the AnyVolt Micro, which charges the cell phone from the storage battery.
If the output of the comparator is low, that turns the FET off, which turns off the regulator and stops the cell phone charging. This allows the solar cell to recharge the storage battery.
If the output of the comparator is high (cell charging ON) the comparator is looking for a battery voltage of 2.3V. It will stay on until the battery voltage falls below 2.3v, then turn off the cell phone charging. At this point, it starts looking for a voltage of 2.7v. When the solar cells have charged the battery to 2.7v, the charger turns on, and the cycle repeats. In normal operation with a phone connected, the battery voltage is always rising to 2.7, then falling to 2.3, then rising again. how long this takes depends on the amount of sunlight, but a 30 minute cycle seems typical.
The 3.9 ohm resistor limits the charge current, to prevent overloading the regulator or the phone.
There are a couple ways to solder surface mount components. One good option is to melt a blob of wire solder onto each solder pad, then with tweezers hold the component in place and with the iron wick the solder up to meet the component. A very fine tip and a temperature controlled soldering iron make this go a lot more smoothly. A better option is to use a syringe of solder paste to place paste on each pad, then heat the entire board with an air pencil or heat gun.
The circuit operates as a comparator circuit with hysteresis. If the output of the comparator is high, that turns on the FET, which turns on the AnyVolt Micro, which charges the cell phone from the storage battery.
If the output of the comparator is low, that turns the FET off, which turns off the regulator and stops the cell phone charging. This allows the solar cell to recharge the storage battery.
If the output of the comparator is high (cell charging ON) the comparator is looking for a battery voltage of 2.3V. It will stay on until the battery voltage falls below 2.3v, then turn off the cell phone charging. At this point, it starts looking for a voltage of 2.7v. When the solar cells have charged the battery to 2.7v, the charger turns on, and the cycle repeats. In normal operation with a phone connected, the battery voltage is always rising to 2.7, then falling to 2.3, then rising again. how long this takes depends on the amount of sunlight, but a 30 minute cycle seems typical.
The 3.9 ohm resistor limits the charge current, to prevent overloading the regulator or the phone.
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Nov 17, 2007. 9:35 AMunitedelectric
says:
Wow. Cool project indeed. Is there any logic to adding a diode to protect from the battery draining through the solar cells in low light situations (ie battery voltage higher than panel voltage)?
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Jul 18, 2008. 9:18 AMShmemilyWoodey
says:
yes yes yes. without the diode the current will run back into the panels. You are correct.
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Aug 3, 2008. 6:33 PMjoe57005
says:
Leaving the diode out could also damage the solar cells, not just drain the batteries.
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