I took this panel off of a charger unit. The unit had a USB port for charging devices such as phones and small electronics, had a lipo battery stuck to the back of it and the solar panel which I show here.
As you can see the panel reads 6V (and 3V at the bottom). I took off the usb connector and just soldered 2 pins to the +/- terminals of the USB which I have been measuring in direct sunlight but it never goes above 5V. It seems that is not the panel's output because it was actually the usb connector which was probably regulated to 5V for charging electronics. So Im wondering if anyone can help me take the measurements of what the solar panel's actual potential is.
The panel is probably capable of much more than that , they have a wide voltage range,one of the reasons a shunt regulator is used, provided there is enough voltage its the current you need.
As Boardburner2 said, you'll have to disconnect everything from the panel to get a true reading, I have a "9V, 1.5W" panel that puts out 11.6V open circuit in full July sun and best power @ 8.2V, 177mA, 1.45W.
That is not a shunt regulator.
Shunt regulators dump the excess power into a heatsink.
I only see an inductor.
Educated guess: buck/boost converter.
Leo..
Show us the front of the panel. You'll get about 0.45 to 0.55V per cell, in bright sunlight under load
if its any type of silicon PV array.
Typically you would expect 18 cells for charging 6V lead acid (6.6V), anything less and it
won't be efficient in overcast conditions when the cell voltage drops a bit.
If you want to characterize the panel properly you need to disconnect the panel from the circuit
board and measure both the open-circuit voltage and short-circuit current in full sunlight.
The normal photovoltaic cell is not a voltage source but effectively a current source (which depends on the light level) in parallel with a diode that is forward biased by that current (Ignoring series and shunt resistances). So if measured with a high impedance meter a panel will read about 0.7 V per cell. Maximum power will be extracted when the load reduces that voltage to about 0.6 V.
Not quite, usually 0.55V open circuit, 0.45 or so is typical of max power point. Have you measured any
yourself?
For instance from wikipedia:
You are confusing a normal silicon diode run at several amps per square mm or similar current densities
with the 500uA or so per square mm of solar induced current.
Yes thanks Mark your figures do seem to be more accurate being governed by the diode equation. My point remains that the solar cell should be considered as a current source in parallel with a diode and not a voltage source.
From the picture i would suggest the panels are all in parallel and that panel is specifically designed for charging a lipo cell rather than anything else.
3W is probably achievable in california desert, but not much else IME.
I would expect that call to take 2 full days to charge a 4000 MAh cell in those conditions.
Most small Solar chargers designed to charge phones etc have a Solar panel directly connected to a single cell battery, usually a LIPO or NIMH.
The battery output feeds a 5V regulated boost converter which provides the USB power to charge whatevers plugged in .
The Solar panel is non critical in terms of power output, as long as it can charge whatever type of battery is in the charger.
OK but what I'm wondering is whether the panel is capable of more? In other words, the boost converter is needed to take the 3.7v from the battery to exactly 5v for the electronic device to be chsrged, which is the output I'm getting at what used to be the USB terminal.
But the panel should be capable of the 6v it's rated at. So as boardburner said, I would have to tap the panel directly at the panel terminals.
I was just wondering if I could tap the 6v somewhere else in that circuitry on the pcb.
