Solar charge Li-Ion battery pack

[Kiwi_Ed]

Hello all,

First off: let me apologise for my ignorance, this is all new to me..

Recently I bought a set of a 10W solar panel with a 12V 6800MaH battery pack on Ebay advertised as being 'all you need' for a simple solar set up.

The battery pack is protected with an over charge controller and over discharge protection.

The pack charged nicely with the charger it came with, but did very little charging while connected to the solar panel.
I contacted the supplier who kindly is sending me a new solar panel under the assumption that this is the fault. Even though I was measuring voltages up to 17V coming from the panel. I haven't received the new panel yet, so I cannot tell you if the first panel is different or not.

Personally I though that a solar charge controller would be better as this would level out the charging voltage to the battery. So I went ahead and bought a PWM charge controller. However when I opened the package and read the manual I saw that the charger was described as not being suitable for Li-Ion batteries. Which got me wondering...

After doing a bit of reading online I found a lot of pages that said that you cannot float charge a Li-Ion battery, some tell of dire consequences like exploding batteries and toxic fumes.. Obviously we want to avoid this! We want to use this solar panel battery pack set up during a camping/road trip and will be mostly charging the battery during driving. The last thing we want of course is the battery catching fire or exploding while driving or even worse while the car is parked up somewhere while we are on a long hike only to come back to a torched down car

So: to make a long story a bit longer: What is your take on this?
As far as I can see Li-Ion batteries only explode when overcharged, so would the over-charge controller in the battery pack prevent this from happening?
Also what would be better charging the batteries directly from the solar panel or through the charge controller?
And finally, as I am getting a second 10W solar panel: would it be harmful to connect these panels in parallel and connect this to the charge controller or the battery?

Thanks a lot!
Edwin

 

[audioguru]

When a lithium charger IC detects a full charge then it shuts off. A full charge occurs when the voltage is as high as the charger allows which is 4.20V per cell and the charging current has dropped to about 1/40th the mAh capacity of the battery. The protection circuit in a battery or controller is not a charger circuit.

 

[Kiwi_Ed]

Thank you for your reply, audioguru.

If I understand your reply correctly you think that the overcharge protection will not stop a charge going into the battery when the battery is full, while a normal charger circuit would.

 

[audioguru]

I think the over charge protection does not detect a full charge. Then it will allow a continuous trickle charge that is bad for a Lithium battery.
A proper Lithium battery charger circuit also "balance charges" multiple cells when they are in series to prevent the weakest cell from overcharge. It will also detect that a battery has been discharged too low and attempt a very low current charge to prevent an explosion or fire.