LiPo Low Voltage discharge cut-off events
I have built a Solar Minty Boost charger for my iPhone 4. It consists of
a) 6 V 3.4 W Solar Panel
b) USB / DC / Solar Lithium Ion/Polymer charger - v1.0
c) 3.7 V 2700 mAh LIthium Polymer Battery and
d) MintyBoost Kit - v3.0.
Also included in the circuit is a three way switch and the 2 x AA battery holder that comes with the Minty Boost (so I can alternate between batteries if needed). I can also charge with a 5V 2000mA switching power supply.
All parts discussed are from Adafruit except the three way switch.
I have been experiencing a recurring problem after charging the 2700 mAh LiPo battery to full charge (“green light” on, measured 4.20 V) with either the solar panel or the charger: the iPhone 4 will only partially charge - say from 13% to 46%, at which time the iPhone 4 will indicate it is no longer connected to a charger. When this happens, the LiPo battery shows an extremely low no-load voltage - such as .685V or .740V. For all intents and purposes, the battery looks to have discharged below its shut off voltage of 3.0 V.
If the LiPo battery is charged with the solar panel or the charger for a period as brief as 10 seconds (then disconnected) - the battery will show a no load voltage such as 3.61 V(!) and can then be used to continue charging the iPhone 4 to 100%. Sometimes the charging cycle will stop several times during the process, but can be always be “restarted” as indicated.
Thinking this problem might involve the battery, I ordered a new 3.7 V 2700 mAh battery and fully charged it with the charger. The battery showed a no-load voltage of 4.20V. The iPhone 4 was initially showing a charge of 14%. I left it connected over night. In the morning the iPhone showed a charge of 49% and the LiPo battery showed a no-load voltage of .64V. I connected the charger for 10 seconds (then disconnected it.) The LiPo battery showed a no-load voltage of 3.82 V. I reconnected the iPhone 4 and was able to charge the iPhone 4 to 100%, at which time the LiPo showed a no-load voltage of 3.10V.
Can you suggest what might be causing this or offer any suggestions on how to troubleshoot this further.
Love your stuff. Thanks for your help.