impulse power scavenger

Have fabricated a circuit that takes a low power solar cell (3 volts ((Max)) at 4.2 mA full sun , 4.2uA interior room l)0ight) and dumps charge into starage cap. When voltage is high enough and on a varaible period, and implse sign triggers the dc c conversion of the stroed enrgy into a reguated outpt to pulse charge batteries.

The driving force behiund this design was to extend the life time of a battery operated, and wirless sensor pod... "indefinately". The sensor pod consumes and average current of 42 uA... with a typical drain of 20 uA and wirless poweed time slots of 10 mA... using alakaline batteires this would last 3-4 years. a very reasonable perodand an improvent over exisitng devcies ( these are primarily a PIR motion detector, temp humidity and a wi fi tx tx ability. akey to the design was lowering the current and voltage that a PIR based motion sensor uses as this function cannot be switched of to save power!

Adding the solar power scavenger should replace the energy used through out the day, during a typical 6 hours of abmient room light. The period varies with light influx and state of cahrge on the storage capacitor. This circuit is created with the latest dc dc converters, and ultra-low power discrete components. this design can be modualrized or added to another design in about 2 sqaure inches of space for pcb, a solar panel (or other power source)and smal hole to enable ambient light sensing for feedback inot timing control....

Does anybody else have requirments like this for thier battery operated products?

Best regards,

Marc Popek

Reply to
LVMarc
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Is this any advantage over directly charging the batteries?

John

Reply to
John Larkin

Yes in this case of indirect sunlight, the rate and load point that the solar cell ( or fuel cell)) outputs is not directly suited to the battery voltage and its charging characteristis. For exmaple, if you have a relatively over sized soalr cell, you can produce 13 to 14 volts open circuit at .5 1 amp with ease. This can be dietly jammed inot a car battery and provide some sort of trcikle charge during the mid day.

Wha if you get indirect light or an under sized cell? you then need to integrate and store the enrgy, then occasionally dump iota reasonably effcient dc d converter and pulse charge the battery. ONe challenge is to consume vey litel enrgy in the ciontrol and switching priocess as this panel is 1.4 inch by 4 inch so the inputis limited in full sun and way down in inside room lighting. That the tricky part as well, adapting the range of outputs and times for integrating and dumping enrgy around.

Data shows a peak power charged into a set of two alkaline AA batteries, as a load:

56 J per hour @ 3 volts output @ 42 mJ per pulse. Peak

and

1 J per hour in @ 3 volts output @ 38 mJ per pulse .. Min in a shadowed room interior.

So, far the test load ( two aa alkalines) have charged from thier original half used starting state. The next lelve is to slowly discharge is set o control aa batteries and then discharge another set and add the solar savenegr and see if the added circuitry and panel extnes the lifetime significantly..

Marc

Reply to
LVMarc

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