Hi!
I recently put together a simple solar phone charger using two 500mA 5v solar panels, each with a 1N4001 blocking diode, wired in parallel.
It seems to work fine charging my kindle, but my iPhone won't accept it.
On the multimeter, it outputs a max of about 4.7 volts. When measuring the iPhone wall charger, I got a solid 5.1 volts.
Is this why the iPhone won't accept my charger? It should be outputing 1 amp, 5 watts.
If so, how do I bring the voltage up to an acceptable level?
Thanks!
What is the voltage before the blocking diodes. Maybe that is dropping more voltage than needed.
If you really think you need them, may try germanium for a lower voltage drop. In many systems they are not even needed tho. I think that the blocking diodes is useful if you are feeding into a battery, and it gets dark (night), to prevent the batteries from sending a reverse voltage back into the solar panels.
Are your results from using the solar panels in full sunlight?
It may not be safe to hook your expensive equipment directly to solar panels that have no regulation. You may consider, putting your two panels in series, to give you ~10 volts, then use a regulator to send 5V to your devices.
The iPhone requires certain voltages on the USB data lines in order to accept the charger as valid. See iCharging | Minty Boost | Adafruit Learning System
I agree with jack, you should use a regulator. Since naked solar panels do not work well with a regulator, usually they are used to charge batteries, with a regulator on the battery output.
CantSayIHave:
Hi!I recently put together a simple solar phone charger using two 500mA 5v solar panels, each with a 1N4001 blocking diode, wired in
Thanks!
Solar panels will give a very large Range of terminal voltage open circuit, some form of regulation is needed.
If you are charging directly into iphone etc they expect 5 V.
A nominal solar panel 5 v charger dependings on no of cells , 5 V could be anything from about 6 to 24 volts , depending on make, if cheap tends to be lower, need to lok at the sellers detailed specifications.
5 V could be anything from about 6 to 24 volts , depending on make
The OP said his was 4.7 volts. That's a bit low, but we don't know if that was the max, in full sunlight or not.
The 4.7 volts is definitely the max, tested in full sunlight.
I'm aware I can wire them in series and then use a 5v regulator to bring it back down, but wouldn't this keep the current at 500mA?
I know the lightning charger is 5v at 1 amp, so that's what I'm shooting for. If I wore them in series, I would have to get another pair of panels in series to get the full 1amp, and that would be inconvenient.
I also know I could use Schottky diodes to reduce voltage drop, but I'm not even sure if that would do the trick.
Should I just upgrade to 9v panels and use a regulator?
On the other hand, like jack was talking about, are blocking diodes necessary in this circuit? After testing iOS devices, none seem to allow power to be taken out of them, so is there really any risk to the panels?
If I could eliminate both diodes, the voltage would probably jump up to 6v.
If I could eliminate both diodes, the voltage would probably jump up to 6v.
I am not sure that 6 Volts will be safe. You still should use a voltage regulator.
If you are up to switching solar panels, maybe the more standard 12Volt may be an option, and then use a regulator.
Why not add a boost regulator to get up to 5V?
more here
Iphones need 5V regulated.
Getting a regulated output from Solar panels is very hard unless the Solar panels themselves charge a battery, and then the battery provides the 5V regulated output to charge the Iphone via some kind of switching regulator.
The rating of Solar Panels is at STC conditions , ie 1000 W/sq Metre solar intensity and cell temp of 25C.
As the Suns intensity varies over the day, the Solar Panels power output varies over the day so something has to compensate for the power differance that the Iphone requires to charge it , and what the Solar Panels are producing.
Getting a regulated output from Solar panels is very hard unless the Solar panels themselves charge a battery, and then the battery provides the 5V regulated output to charge the Iphone via some kind of switching regulator
I think a regulated output is actually an over limit protection. It is hard to regulate a voltage that is under the target voltage. So, no pre battery is needed (I think). If the cloud comes over, then the charge stops temporaly.
Hi,
The 4.7 volts is definitely the max, tested in full sunlight.
Under what conditions, what is the max open circuit voltage?
You can regard a PV as a current source, not a voltage source.
Tom....... 
CantSayIHave:
I'm aware I can wire them in series and then use a 5v regulator to bring it back down, but wouldn't this keep the current at 500mA?
That's a YES, if it's a lineair regulator.
And a NO, if it's a switch mode regulator.
A switchmode (buck) regulator lowers the voltage, and increases the current.
Much like a transformer does for AC.
Tiny ones, e.g. the Pololu 5volt/500mA stepdown, does that with upto ~90% efficiency.
Leo..
4.7 v is the fully charged voltage of a lipo cell , this photocell has not enough voltage to fully charge a battery i think .
Rather than waste time and money, connect in series and use a 5 v zener as a shunt to protect against overvoltage.
As said panels are a current scource so no power is wasted until battery is charged.
Edit
As an aside my iphone charges quite happily from a 2 amp charger.
TomGeorge:
Under what conditions, what is the max open circuit voltage?
You can regard a PV as a current source, not a voltage source.
Bears repeating.
As you draw more current from it the voltage will drop. You can measure it at 4.7V in bright sunlight with no load attached, but as soon as you attach any load that voltage will drop. Try attaching a small automotive (12V) light bulb and see what the voltage reads.
Boardburner2:
4.7 v is the fully charged voltage of a lipo cell
4.2V is the fully charged voltage for a LiPo. 4.7V is the exploding or on fire voltage.
BTW have you measured whats on pin 5 of the connector.
Its part of the connector standard and iv noticed some android leads do not play nice with apple.
Charger themselves are interchangable.
Chagrin:
Bears repeating.As you draw more current from it the voltage will drop. You can measure it at 4.7V in bright sunlight with no load attached, but as soon as you attach any load that voltage will drop. Try attaching a small automotive (12V) light bulb and see what the voltage reads.
4.2V is the fully charged voltage for a LiPo. 4.7V is the exploding or on fire voltage.
Apologies yes, i was making allowance for a series diode and was not clear.
But he said it works with a kindle, 5 pin connector.
I assume he uses a lighning adapter.
Another possible problem even if pin 5 is configured correctly is, under load can the solar cell supply sufficient volts to power the authentication chip in the adapter.
Hi,
See post #11.
How did you measure the PV output.
Thanks ..Tom........
using two 500mA 5v solar panels,
Solar panel ratings are not to be relied on. You must test them with a VOM to find out what voltage and current is really being provided while driving your load, and the sun where you want it.
I suspect the 500ma rating is with maximum sun, and into a short circuit (less than .5 volts).
I suspect the 5V is with no load and a nominal voltage (meaning it could go up higher around 6 or 7v).
I suspect the panels output current at 5V would be lots less than 500ma (maybe 90ma).
Was there a rating in watts ?
If you want to provide 1000ma (1 amp) at 5 volts into your load, that would require 5X1= 5 watts. Add another 3 watts for good measure (sun not exact, efficiency of regulators etc.), then you need 8 watts. I suspect your solar panels will not provide 8 watts (I could be wrong ).
The ratings for the panels are 5v, 500mA, and 2.5W.
This is where I got my panels from. As you can see in customer reviews, most people are fairly happy with it.
You can also see it outputs much higher than 90mA when running at 5v. For these reasons, I'm fairly confident I can get this to work.
If I wire them in series and use a switching regulator, is there any way I can boost my current from ~500mA to ~1A?