I had one of these batteries lying around and decided it would be fun to try charging it with my tiny DIY solar array.

The wall power adapter that came with the battery says it outputs 14V, 850mA.
My solar panels are giving about 14V, 650mA.

When I made the connection through the barrel jack, the charging indicators lit up and I thought, "wow, that was too easy...". Upon metering, though, I found it was only taking 50mA (probably just to power the LED indicators.)

I assume I'm triggering some kind of protection circuitry. With the help of a boost converter, I've managed to get the voltage within 0.01V of target, but the battery still says "no thanks." I'm sure I could take it apart and bypass the roadblock if I wanted to, but I don't need to charge the thing that bad. This was just an experiment.

My question is more just for general knowledge/curiosity: What obstacle have I likely come up against here? I suppose I could purchase a linear voltage regulator to get the volts closer to "perfect," but maybe the lower current would still be a problem anyway?

Thanks.

 

Your Panels are probably not able to maintain ~14-Volts.

Measure the Voltage-Output of the original Wall-Wort-Charger,
while it's charging a mostly dead Battery-Pack.
This is the Voltage your Panels must produce.

Just because the Wall-Wort says "14V" doesn't mean that it can't produce more Voltage than that.
"14V" is a "nominal-Voltage", and it may not be Regulated at all,
meaning that it might produce ~18-Volts with no Load,
then sag down to ~14V under full rated Load.
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Fascinating, I hadn't thought to check the adapter's actual output...

Even more fascinating: It came in at 13.91 Volts consistently. Also, dances between 600-700mA.

EDIT: That's the voltage charging the battery when its at approximately 30%. I drain it lower and re-meter like you said.

 

You may also need a "Bulk-Storage-Capacitor", like around 1000uf, on the Output of your Panels
because the Current and Voltages that You are measuring are "Average" or "RMS" values.
The actual "Peak" Current that is required by the Charger may be 3 or 4 times higher when it "switches" states.
The Large-Capacitor can "smooth-out" those Current-Spike requirements.
The Charger is very likely a regulated SMPS ( Switch-Mode-Power-Supply ),
and not a Linear-Regulator which would draw a steady Current.
What You see on a Meter, and what You would see on an Oscilloscope-Display, are very different.
The Meter is not "fast-enough" to show what's really going on.

Solar-Panels do not perform the same way as a "Linear-Power-Supply" would,
they are a rather weird mix of a Current-Source and a Voltage-Source, at the same time.
They're generally kinda "mushy", instead of "hard-line".
You can make them "appear" to perform like a Voltage-Source,
but you'd probably be disappointed by the results.
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Amazing... This is exactly the kind of education I was hoping for. Thanks for breaking that down for me!

 

Your solar panel might produce 14V with no current or produce 650mA with no voltage (shorted).

 

Capacitor did it! Mostly...

I didn't have any 1,000uF caps (they're in the mail now), so I put together ten 100s. Plugged in, and the battery started taking 350mA! (Up from 50).

As it charges, though, it's taking less. I estimate it's up to 35% capacity, and is now only taking about 160mA. At least it's charging instead of just making indicator lights blink. Big win.

EDIT: Actually, I believe the increased current is due to the fact that I started with a "more dead" battery. I removed the capacitors from the circuit and the current stayed the same.