Mysterious problem with external solar battery charger!

Hi guys,

I obtained a solar battery charger (like this one: http://www.walmart.com/ip/5000mAh-Portable-Shockproof-Waterproof-Solar-Charger-Battery-Panal-Double-USB-Power-Bank-for-Cell-Phone-MP3-Green/41475368 but not exactly this one, seems to be a Chinese imitation). I already charged up my phone with it, seems to be working fine. I want to use it as an external power supply to my Arduino Uno R3. I have built a project with it, wrote the code, tested it on my laptop, works flawlessly. The problem is not in the code or circuit.

The problems occurs when I connect my Arduino project to the battery (it has two 5V 1A outputs) It works for (as I've measured) 14~15 seconds, then the Arduino stops working (the LEDs are turned off) and the LEDs the battery has are also being turned off. It has a button next to them, when I press it, everything works for 15 seconds and then stops again.

Strangely, when I connect my Arduino to the laptop, it works fine and flawlessly. Connect it to the battery again - stops after 15 seconds. Every time.

I wonder what's the reason and how can I fix it? Is it because too much current is drawn? Why exactly 15 seconds?

Another thing, when I have both my phone and Arduino connected to the battery, everything works fine. Remove the phone, and it stops.

I would be very glad if anyone helps, it's a complete mystery to me.

How are you connecting the Arduino to the battery charger ?

I use my standard USB cable, which I use to connect the Arduino to my laptop too. The battery outputs standard 5V.

Did you take a look at the product reviews on the Walmart web page? Those small solar cells cannot possibly charge a 5000 mAh battery in a reasonable amount of time.

So, you have a cheap(er?) clone of a pretty much nonfunctional product. Don't waste any more time with it.

The usb phone chargers will turn themselves off if not enough current is being drawn from them. Running the Arudino is not above that threshold and the battery turns itself off.

Thank you guys.

My charger is not bought from Walmart, I just gave an example with this one.

I really didn't know that there is a minimum limit for the current drawn from such batteries, if it's really so, I'd better stop trying to get a USB charger to power my Arduino and search for a better solution.

Is there actually a possible way to use a mobile phone USB charger to power it? I'd be glad if I receive an answer.

Anyways, thank you very much!

Low load turn off is a "feature" or many battery chargers. Some of them have an "always on" setting.

There are several threads I have found which document using a pulsed load to keep the battery pack running. http://www.dorkbotpdx.org/blog/paul/battery_pack_load

The proposed solution has been to pulse intermittent high current through an external resistive load to trick the charger into thinking it should stay on. Most postings indicate that one to five percent duty cycle of switching 5v over 22 ohms does the job.

I tried to implement this solution with an npn transistor switched on/off from a digital output pin, low side switching 5v across a 22 ohm resistor. I confirmed that constant current across the 22 ohm is enough to keep the charger turned on. My pulse circuit is working but I can not achieve lower than a 50% duty cycle to keep the charger turned on. I have tried longer and shorter pulses, higher currents, and other variations of the duty cycle with no success in getting to the 5% or less that others have achieved.

The pulsed solution did not work with a charger I had, and it's success is dependent upon the charger you have. Mine was too stupid, or too smart, to be fooled.

search for a better solution.

One solution is to power the Arduino directly from a low voltage battery. The ATMega328p will run on voltages as low as 1.8 V, with reduced clock speed.

See this informative article on low power operation.

The reason those chargers turn off with low load is that the boost converter in them is optimised efficiency wise for their full rated output power, and boost converters lose efficiency as their output power drops. If the charger didnt turn off, it would slowly drain its own battery.

Thank you very much guys! I appreciate it.