After lot of reading I finally made the solar engine. It is
the same solar engine found almost everywhere . I was amazed that
something actually worked and this did a lot to my confidence. Before free
forming I bread boarded the circuit. I used two 4700µF Capacitors for the 9400µF.Unfortunately
capacitors available in Chennai with high farad rating also have high
voltage rating which increases the size to an extent that the capacitors
become really heavy and cannot be used for BEAM. I didn't incorporate it
into a robot because somehow the pager motor didn't seem to be
healthy enough to take load. Just a little touch while the motor rotates
and the shaft doesn't move. Didn't know whether the robot will move if I
use a pager motor. For those in Chennai -I found spoilt pagers in Moore
Market for as low as Rs.20 after hard bargaining. Try to get pagers that
don't work. U don't need a working pager anyway. U can get for cheap those
with spoilt LCD displays. Take out the motors from that and have fun. I
spoilt 3 motors trying to take the weight out of its shaft. Tried all
things but couldn't help. The last time it was almost out, but I ran out
of patience and pulled out the whole shaft. Best of luck to you guys and
gals. Have a good shaft pull out time. You can find a lot of solar engines
based on the 1381 J voltage regulator in the net. But I haven't been able
to make one as I haven't found this component anywhere in Chennai. I even
ripped open a working Panasonic cordless phone, but as it always happens I
didn't find the 1381 J. The red FLED I have used I found it in Apex
Electronics, Ritchie street, Chennai. About the solar cells I took them
from solar calculators. I ripped about 5 calculators I found in Moore
market (next to central station), took out the solar cells glued them
together and connected them in parallel. The Sanyo solar cell in one of
the calculators was really good. It generated a good voltage and current
in bright light. While testing the solar engine always do so in bright
sunlight. Tube light won't be enough. Be careful while removing the solar
cell from the calculator frame. Don't pull out the connecting wires
stuck to the solar cells. I did that in one of the cells thinking I could
put it back, but I couldn't. Its almost impossible to stick it back. We
get conducting ink in Ritchie street. Didn't try it out though.
This is the free formed engine I used for Moby
How it Works?
First of all you should know these facts
1. In a NPN transistor current flows from emitter to
collector. For this N(emitter) should be negative, P(base) should be
positive and N(collector) should be negative.
2. In a PNP transistor current flows from collector to
emitter. For this P(emitter) should be positive, N(base) should be
negative and P(collector) should be positive.
3. Certain components like Flashing LED's , LED's etc. let
current flow through them only at a particular voltage across their
terminals. Let us call these components trigger elements.
The need to use a capacitor in the solar engine arises out
of the fact that the solar cell doesn't generate enough current or charges
at an instant to overcome the resistance of the motor and run it
efficiently. So sufficient charges are stored in the capacitor and are
then discharged to the motor whenever required.
As you can see the capacitor is charged by a solar cell and
continues charging till the maximum voltage of the capacitor or the solar
cell (whichever is minimum) is reached, if no connections are made to the
Let us assume that the motors used in the solar cells work
most efficiently when supplied with 3 volts. So the solar cell must be
capable of generating minimum 3 volts and the capacitor must also be able
to store charges up to more than 3 volts.
If the motor is directly connected across the capacitor the
stored charges are immediately discharged to the motor and hence the
capacitor has no significance. Hence we need a circuit that will
automatically discharge the energy in the capacitor to the
motor when the charge in capacitor has reached the required level to
run the motor efficiently.This is accomplished using the transistors, FLED
and the resistor.
Charges build up in the capacitor starting from 0 volts. The
base and the emitter of the PNP are positive (emitter +ve directly through
the positive terminal of the cap and base through the resistor and
the motor). Since both base and emitter are +ve the PNP transistor doesn't
work (current doesn't flow from collector to emitter).
The PNP doesn't work until the voltage across the cap equals
trigger voltage of the FLED or LED or diode. At this voltage the current
flows through the trigger element. Since current flows through the trigger
element ,not to the base of the PNP, the base of the PNP becomes negative.
Hence the PNP conducts and current flows from the collector to emitter
Similarly the NPN doesn't conduct as the emitter(N) is
negative( through the -ve of the cap) and also the base is negative. For
the NPN to work current must flow from emitter to collector. For this the
base must be positive. Such a situation arises only at the trigger voltage
of the diode when the PNP conducts and thereby makes the base of the NPN
positive. At this point current from the capacitor flows through the NPN
to the motor and causes it to rotate.
Even if the voltage across the cap falls to less than the
trigger voltage and the base of the PNP becomes positive, the motor
continues to rotate.The rotation continues until the motor resistance
becomes high enough to prevent further discharge of the capacitor. Now the
voltage in the capacitor again rises until it reaches the trigger voltage
of the trigger element and the above cycle repeats.
Upon notice, the starting of the motor is controlled by the
trigger voltage of the trigger element and the stopping of the motor is
determined by the resistance of the motor( 2 independent factors). Hence
the solar engine acts like a silicon controlled rectifier (SCR).
Solar Engine Types
Type 1 - The motor turns when the voltage in the circuit reaches
a preset level.
Type 2 - The motor turns at a preset interval of time.
Type 3 - The motor is "charge curve differentiated." It's sort
of a combination of type-1 and type-2. When capacitor slows down it's
charging rate, it triggers the circuit.
Most solar engines are type-1, because it is the easiest to get good
efficiency using it. Type-2 solar engines are fairly efficient, and are
useful in single neuron solar engines for creating phototropic behavior.
Type-3 solar engines would be the most efficient, but they haven't been
Instead of using trigger elements like FLED , LED or diodes
there are solar engines that use IC's like 1381 voltage triggers that are
much more efficient than the FLED's , LED and diodes. Solar engines can be
configured to trigger at particular time instants rather than voltage
values using neurons. Such solar engines find use in circuits that
activate a load at night , charging throughout the day.
Below are the schematics of most of the types of solar
engines I have come across. The following schematics are the beautiful
work of their creators and I don't take credit for any.
Diode triggered Solar Engine
This is the original circuit designed by Mark Tilden,
and is the basis for all of the other solar engines created. The
Zener diode can be replaced with diodes in series , a flashing
LED, or even a resistor.
1381 Solar Engine
This very efficient Solar engine is more complex than
the normal version, but is much more efficient. This circuit was
designed by Andrew Miller.
|Time triggered Solar Engine
The twist on this circuit is that instead of being voltage
triggered, it's time triggered. Adjust the values of resistors R2
and R3, or the values of C2 and C3 to suit your needs. Increase the
values of the resistors as a general rule, but to get really long
time values you are going to have to increase the values of the
Micropower Solar Engine
If the circuit has a power source which will provide
2.5Vdc at 10uA this circuit should drive a pager motor. It turns on
at 2.3 to 2.5Vdc and switches off at 1.2 to 1.5Vdc.
This circuit was made by Ken Huntington.
PM1 Solar Engine
This is an SE that can drive a bicore. Good for solar walkers,
heads and more. For C1 Ian recommends somewhere in the 4000uF range
for a head and in the Farad range for a walker. If you would like to
be able to control when your robot moves just put a switch across
the source and drain of the 7000. Just make sure you turn the switch
off when it runs out of juice or else it won't charge.
D1 Solar Engine
This is a neat circuit that comes alive when it gets
dark. You can adjust the sensitivity using the 150K variable
resister. The outputs can be connected to a LED bicore or whatever
This SE made by Wilf Righter uses a 1381E voltage detector with a
red LED in series to raise the trigger level to 4.0V. A 10uF cap
between the 1381 power and ground pins together with the 1M resistor
on the output pin causes the SE to reset after about 1 second. A
single NPN transistor used used as a inverter to match the
requirement for a low current active low enable. For this
application the 1381tr SE works just like the Miller Engine
and draws less than a uA of current during charging.
1. new 1381 SE with timed reset
revolve (turn) left/right
4. new ultra low power delay Nu
new delay Nu memory
CHLOROPLAST Solar Engine
- The solar panel will slowly charge up the storage capacitor C1
towards 6.8V. U1 will assert a ground ( believing the
voltage is too low ) which keeps U2 ( a high gain darlington NPN
transistor ) open and the motor OFF.
- When 6.8V is reached, U1 will open. The base of U2
will then be pulled high ( through R1 ) and U2 will turn on,
allowing the solar energy in the capacitor to discharge through
the motor. The motor spins.
- The motor will continue spinning and discharge the capacitor
until the solar voltage falls to 5.5V.
- At 5.5V, U1 will assert a ground at its output (Out),
believing that the voltage is too low, and it must apply a
RESET. This ground turns off U2 and the motor stops spinning
and the system is ready for another cycle!
Miller Solar Engine
A much more efficient solarengine compared to the 1381 SE , using