We are trying to charge a 3.7V LiPo 150mAh battery with a 30W 12V Solar Panel.
The circuit we're using is a simple derivative the of the MPPT Solar Charger for Sparkfun's Sunny Buddy:
Our circuit is almost the same, except for on our prototype board, we use different resistances for \$R_3\$, \$R_6\$, and \$R_2\$. This is done to set the float voltage to 4.1 V as described in the datasheet for the LT-3652 2A Solar-Powered Battery Charger.
When powering the circuit with a DC supply, everything works OK. When supplied with at least 6.5 V, the circuit "turns on" and supplies a small but significant charge current to the battery at around 60-100 mA (to measure this, we cut the trace at JP5). With the solar panel disconnected, we measured ~15 V with a voltmeter.
However, when the solar panel is connected to the circuit, the voltage is a consistent 4.485V and current is drawn from the battery since the charger is "off" (circuit will only "turn on" with >=6.5 V power supply). Even when we connect another 6V @ 9W solar panel, we still measure 4.485V. We have tried using the two separately and in series, all of which maintain the 4.485V.
We considered exposing the solar panel to more light. However, since we measured the same voltage from different panels, we think the circuit itself is the problem.
How do we "turn on" this circuit with the solar panel(s) connected (how do I approach this / what do I try next)?
Note: I've read the datasheet & know a good amount about the LT-3652's capabilities.