Nope, not the battery ....

A project log for Hack-a-Bear

My wifes solar lawn bear has died and it is my assignment to find the cause of death and re-animate it if possible

Dr. CockroachDr. Cockroach 07/06/2018 at 10:202 Comments

OK now, I have found out a few things.

First, the battery does take a good charge after connecting it to my variable power supply and a series resistor to charge at about 25ma overnight C/20 more or less.

Second, When I place the battery back into the circuit and switch on there is constant voltage on the led wires but no light, very strange. The led is not lighting at all and even putting full light onto the solar cell, the circuit does not cut off the voltage to the led as it should.

Assumption number one ( yeah, I know not to use that word )....

Led is bad for what ever reason...

Number two, If the led worked then It would be constantly drawing current and the battery would never charge...

Not sure what type of white led is being used here but the output voltage is only at the 1.2 - 1.4 volt level

The circuit board only has a resistor and single special 4 leg semiconductor package and the print is so small that I can not read it and no magnifier around :-)

Time to think about rolling my own transistor circuit and perhaps a Joule thief to boost the voltage up so I can use a different led...


Dr. Cockroach wrote 07/06/2018 at 18:06 point

Thanks, I have already decided on wiring up something along those lines, I was not even thinking that what I saw as a resistor might be an inductor :-)

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roelh wrote 07/06/2018 at 14:24 point

Hi Dr. Cockroach,

The output of the single cell is only approx. 1.2 Volts, this is not enough for the white LED, that will probably need 3.5 to 4 volts.

The thing on your board is probably not a resistor but an inductor. Together with the 4-pin semiconductor (IC probably) it is a step-up regulator (boost regulator), that makes the higher voltage that is needed for the LED.  It is possible that this semiconductor is defective.

I suggest you search the web for a circuit that lights a LED from a single 1 or 1.5 volt cell, and use that circuit as replacement. Then probably have to add a circuit that switches the circuit OFF when there is still sunlight.

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