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Step 5Building the Circuit, Part 2: The Load
Flipping the switch "down" will enable the devices you've attached to work. Here, we don't want do draw off the batteries unless the total voltage across them is higher than around 2.7V (0.9 x 3).
Here, I've wired up a normal blocking diode (the 1N4001 which I originally ordered with the solar cells) in series with an LED for a charge status indicator light. Since the voltage drop across the diode is 0.7 V, the total voltage drop should be around 2.4-2.7V. When the supply voltage drops below that level, it doesn't give enough potential to drive the LED, turning it off. So when the light goes out, I know its time to stop using the various devices I've got hooked up and start recharging.
Once again, dirty, but it works.
Resistors
When using LEDs, make sure to include a resistor in with them, so they don't burn out. Even when they're in parallel, a resistor should go with each LED. Basically, since resistors resist the current flow going though the part of the circuit they're in, the higher a particular resistor's value, the less current will flow. Remember V=IR.
In the case of the charging circuit, we want as much current to flow through to the batteries as possible, without damaging the LED. 100 Ohms will work.
With the Load side of the circuit though, we would theoretically want a higher-value resistor, in the interest of keeping waste current flow down to a minimum. Here however, I want to make sure the voltage drop across the LED stays around the 2V area, and giving a stronger current would make it more obvious when the voltage finally drops off below the minimum threshold we want. So I've thrown in a 100 Ohm resistor here too.
Here, I've wired up a normal blocking diode (the 1N4001 which I originally ordered with the solar cells) in series with an LED for a charge status indicator light. Since the voltage drop across the diode is 0.7 V, the total voltage drop should be around 2.4-2.7V. When the supply voltage drops below that level, it doesn't give enough potential to drive the LED, turning it off. So when the light goes out, I know its time to stop using the various devices I've got hooked up and start recharging.
Once again, dirty, but it works.
Resistors
When using LEDs, make sure to include a resistor in with them, so they don't burn out. Even when they're in parallel, a resistor should go with each LED. Basically, since resistors resist the current flow going though the part of the circuit they're in, the higher a particular resistor's value, the less current will flow. Remember V=IR.
In the case of the charging circuit, we want as much current to flow through to the batteries as possible, without damaging the LED. 100 Ohms will work.
With the Load side of the circuit though, we would theoretically want a higher-value resistor, in the interest of keeping waste current flow down to a minimum. Here however, I want to make sure the voltage drop across the LED stays around the 2V area, and giving a stronger current would make it more obvious when the voltage finally drops off below the minimum threshold we want. So I've thrown in a 100 Ohm resistor here too.
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