# Solar powered Arduino charging issue

I'm not a pro with these, but I have several solar panels. None that small. They are a pretty much a constant current device.

Have you checked the input voltage to the 1555 from the solar panel just charging and under load?

What are the ratings on the solar panel? These might help: Maximum Power (Pmax) Voltage at Pmax (Vmp) Current at Pmax (Imp) Short-circuit current (Isc) Open-circuit voltage (Voc)

You might find this to be a good read about charging via solar. The solar charger she sells works great. John

Sounds like the regulator is not functioning as you expect. The info you gave me helps.

The solar panels are constant current. If the panel produces 17ma at 5v, then it should produce about 18ma short circuit, and about that current at every voltage in between.

But as you can calculate, the power it produces depends on the output voltage of the panel. At 5v output, that would be 85mw. At 1 volt output, that would be 17mw.

Since the panel output voltage is increasing when you add a load, I would think the challenge is in the battery charger, not the panel.

@bHogan: Good article on MPPT.

agreed, that is a good article and thanks for posting it!

I am not using a regulator since the GPS and Arduino work well at the li-po voltage. I did more testing and have some observations though. When I put a fully charged battery on the charger I read 5.5V on the solar input line. When the battery requires charging it appears to draws on the solar as hard as it can and brings the voltage down to 4.2V on the input side. As the battery gets close to being charged it ramps down the charge and the solar voltage works its way from 4.2V up to the 5.5V when the battery is charged and it stops. When I connect a discharged battery and put it under load (even small loads) I see the solar input voltage go up from 4.2 to 4.6-4.9V which suggests that the charger is not sensing that the battery needs to be charged. It seems to think that the battery is mostly charged and it is starting to taper off the charge. It is not clear to me why a load on the battery would impact the voltage the charger see's but somehow it seems to.

I am not using a regulator

The battery charger is a regulator of a sort. I should have use battery charger instead.

In that case it may be some type of low voltage or overheat problem. The datasheet does mention on overheat, it will taper off the charge rate current. On low voltage (3.5v) it will shut off until the input goes above 3.9v.

How does that charger do if you power it with a 5v-6v wall wart?

Edit: My apology. I was interrupted by work.

If the voltage from the solar panel drops below its Vmp (voltage at maximum power), then you are probably using more power than the solar panel is capable of producing. But I can’t see the “big picture” from here.

I just gave a 6V wall wart a try. The input voltage was steady at 6.24V with or without a load on the battery and the charge rate was about 80Mah with and without a load on the battery. So by all accounts the charger worked properly with a wall wart.

fbriggs4: I just gave a 6V wall wart a try. The input voltage was steady at 6.24V with or without a load on the battery and the charge rate was about 80Mah with and without a load on the battery. So by all accounts the charger worked properly with a wall wart.

Then in the now almost famous words of Tim Taylor, "MORE POWER!"

Solution: Bigger solar panel.

unfortunately in my case size and weight are critical so more power is not an option. Even 1 gram more would be problematic so I think I need to find an alternative charger.

May I suggest a lower current, switching-type charger. You might take a look at that other charger posted above by bHogan.