Solar charger / Led lighting

[vwchico]

I'm looking for a simple few component and efficient circuit diagram of a solar charger to charge 3 1.2v NiMh batteries during the day and at night it must switch to light up 3 White LED's.

I got an idea of using a LDR 1 transistor, diode and resistor, but I don't think it will be efficent because at night I will be losing some power to the resistor ?

And does anyone know what will happen to a 4v lead acid battery if I charge it with a 12v solar panel ? Will it burst from overcharge ?

 

[Nigel Goodwin]

And does anyone know what will happen to a 4v lead acid battery if I charge it with a 12v solar panel ? Will it burst from overcharge ?

You're not likely to get enough power from a solar panel to damage anything!, unless it's a seriously LARGE panel, and you live in a very bright country. The usual size of hobbiest solar panels only provide small amounts of power.

But the project seems rather pointless?, they are already freely available, at very low cost, as garden lights - if you want to make you own 'better' one, I suggest you buy one, take it to pieces, and examine it's circuit.

 

[vwchico]

Yip I realise u can buy them, but I wanna make a better one.

My 12v solar panel can produce about 500ma

 

[Nigel Goodwin]

Yip I realise u can buy them, but I wanna make a better one.

My 12v solar panel can produce about 500ma

Have you measured it?, or is that the given spec?.

 

[vwchico]

I have measured it, it normally measures about 19volts at full sunlight without load, then add a load and with about 500mah load it will drop down to 12volts.

 

[Nigel Goodwin]

I have measured it, it normally measures about 19volts at full sunlight without load, then add a load and with about 500mah load it will drop down to 12volts.

OK, try feeding it to your 4V lead acid battery, and measure the current you get?.

 

[Oznog]

3 NiMH=3.6v which may not be enough to light while LEDs when you add the required ballast resistor.

That type of panel will destroy a 4V lead acid battery. They can't take overcharge; it's gotta have a voltage regulator on it. Actually a 500mA charging current is worse for a NiMH pack. The charge can't be controlled by voltage regulation, the simplest thing to do is limit the charging current so if it gets sun while already fully charged the extra current is not that high. But then it's slow to charge, this is an unavoidable problem unless a considerable amount of complexity is added to the charger.