Advice on a Solar Charger

[David_Khalatyan]

Hi there,

I'm trying to design a solar charger that will trickle charge a rechargeable 9V battery that will then charge my mobile device as needed. I've got two PV cells, both 1.5V at 240mA. To prevent damaging the device's battery, I'm planning to connect the 9V battery to the circuit from an emergency charger that runs off of 4 AA batteries (2 batteries in series that are parallel to the other 2 in series as far as I can tell). Also, to prevent the 9V from discharging into the PV cells I'm planning on adding a diode. Does this seem like a reasonable/accomplish-able plan? If so, can anyone give me diode recommendations as I'm new to the electronics world and don't understand a lot of the specifications.

Thanks,
David

 

[ajayghosh]

@ David_Khalatyan - You will have to solder a BAT43 or IN4100 blocking diode to the positive terminal on the solar panel to avoid reverse current, hope it helps.

 

[D.A.(Tony)Stewart]

1. How do you plan to convert the 3V to 9V efficiently?
2. Is 3V the MPT operating voltage (max power transfer) or the open circuit voltage and short circuit current at max solar input power?
3. I assume you phone uses 9V input down to 6V? Is that a Lithium rechargeable 9V cell?
4. I think a 1N4100 (not IN4100) is a 7.5V zener and the 1N4001 is a 1V@1A silicon diode or 0.85V@250mA is too lossy.
5. and the BAT43 is 1V @200mA and is undersized.

You want a 3A Schottky diode so the voltage drop @250mA is low like 200mV and rated for -10 to -30V
e.g. PMEG3030EP
VF forward voltage
IF = 0.5 A - 235 270 mV (typ max)
IF = 1 A - 260 290 mV
IF = 3 A - 315 360 mV

Got a block diagram?