6v solar battery charger (boost)

Hi all,

This post is the continuation of the a similar post.

So i am trying to charge a 6V battery from solar panel (12 V/5 Watt).

I am using the classic transistor 2SC1061 to control the charging. To turn off this at full charge i have included a IC NE 555 control(IC LM7809 to create exact reference voltage for trigger and threshold too).

Here comes the problem,The sun. let me explain,most of the time the charging doesn't happen because there is no enough voltage( or power) to drive the circuit. The charger behaves mysteriously when low light happens an Vref of 555 decreases and thus it turns the ckt off.

So i have an idea, a boost circuit. that is a constant voltage(12 V,varying current).

I have tried a joule thief with a zener (12 V ) shunt at output,only problem is the result at high light is depressing ( 500 mA input and gives only 20 mA to the battery !!!).

So what do you guys suggest, I just want a circuit which does its best at all times.

Next month rain starts here, so its going to be lot cloudy here.

Pls help.

If your charging a 6 volt batt, you should have a solar charger that works at 5-6 volts.

I would suggest a 12 watt, 5 volt portable solar charger like the sCharger-12. You would get a better charge rate than what you currently have.

sCharger-12 also claims you can charge even in cloudy weather as well.

You will need complex circuitry to automate all the jobs to be done here.

A) On a sunny day you only need a controller to halt charging when the battery reaches full.
If the PV panel can put out greater than 9 or 10V, you do not need a booster.

B) On a cloudy day you need the boost circuit to maximize charge rate.
The battery may not reach full, so you don't always need the controller.

And, whatever components you install, they need to have low effective impedance, especially on a cloudy day.

I have tried a joule thief with a zener (12 V ) shunt at output,only problem is the result at high light is depressing ( 500 mA input and gives only 20 mA to the battery !!!).

Click to expand...

A boost converter (such as a joule thief) only helps you when the supply V is insufficient to charge the battery.



The diode is needed, to prevent the battery from discharging when the transistor turns on.

The resistor at top depicts the fact that the PV panel is only able to put out a few tens of mA, on a cloudy day. That current gets chopped into pulses. The battery gets only a few tens of mA. (I'm guessing.)