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Zener Diode to regulate solar voltage Answered

I'm new to electronics, and I'm having trouble with varying voltage.

I'm running a 6V solar panel through a charge controller, and out to a lithium battery (3.7V) and a load (3.7V), in this case a GPS data logger. My issue is the varying voltage to the GPS.

The GPS works perfectly off the battery (constantly diminishing voltage), but when the solar panel kicks in the voltage increases, the GPS thinks it is being charged, and switches off. The GPS will work on any voltage above 2.75V

I was wondering if I put a 3V zener diode in series between the charge controller and the GPS, would this keep the voltage at a constant 3V even if the solar panel is producing the 5V needed to charge the lithium battery? 

I hope this makes sense



In theory it would probably work, dependant upon the current consumption of the GPS logging device and as long as the input voltage stays above 5.75 volts. It should really be wired as a regulator across the power input with a series resistor to give a fixed voltage out but they are not very economical on current.

Since you're only looking to power the unit, a voltage regulator would be a far better solution and they don't cost much either, although a couple of other components are necessary too.

Thanks for getting back to me. I've included a circuit diagram (to the best of my abilities) of my setup. It turns out the GPS is fine with whatever voltage I feed in, but the Accelerometer needs a constant voltage to keep running.

The accelerometer will work on any voltage between 2.75V and 4.25V, but it needs a constant or diminishing voltage continue recording. If the voltage increases while it is running, it thinks it is being charged and switches off.

What I want to do is include something in the circuit where I've placed the question mark that will only allow 3V to pass to the accelerometer, even if the circuit is producing 4-5V. However, whatever I include must not effect the voltage to the battery. The battery needs at least 4V to charge, but can accept the 3-5V produced without issue.



I'm not really sure what your modules are and I would have thought the accelerometer module would already be regulated to be honest.

A simple 3v regulator should do the trick though. The sketch below shows where to place it in your circuit and includes a sample schematic taken directly from the datasheet for a MCP1702 type regulator. The datasheet is available at http://ww1.microchip.com/downloads/en/DeviceDoc/22008E.pdf

This regulator is ideal for battery powered devices so I'm assuming it would work although I have never used one. It's also available as a through hole device so would be easy enough to solder into a small circuit with the capacitors.

It will also supply up to 250mA which I assume your accelerometer will not exceed.

Charger Schematic Regulator.jpg