Solar 12-15vdc to 7.4vdc

[Kiev88CM]

I have a Sunsei SE-150 slor charger and would like to use it to charge my 7.4 vdc 1500 ma Lion handtalkie battery . The Solar panel specs are 2.25-Watt (150mA, 15-Volt)..... what's the most inexpensive way to make this work?

 

[kc8adu]

build a buck converter that can stand 24v on its input and outputs 8.4v.
li-ion must be voltage limited at 4.2v/cell.
your panel without load may approach 24v

 

[ExitThirteen]

Very easy, actually. Simply use a LM7808 voltage regulator IC. They're really cheap, can be had easily, and it requires all of 3 parts.

The LM7808 is a +8V 1 Amp regulator IC in a TO-220 case.

Pin 1 is the input voltage
Pin 2 is ground
Pin 3 is the output voltage (+8V)

Tie the (+) output of the solar panel to Pin 1 of the IC, and also put a .01 uf disc capactior to ground at Pin 1.

Pin 2 of the IC you would just ground.

Put a 22uf 16V electrolytic capacitor on Pins 2 and 3 of the IC, negative lead of cap goes to pin 2, positive lead to Pin 3.

Install a small heatsink on the IC as needed if it runs warm.

Hook up the (+) side of the battery you want to charge to Pin 3, and ground the (-) side of the battery. You're ready to go.

This should provide a good stable +8V source to charge your battery, up to 1 amp of current available.

Good luck!

~Cheers~

 

[kc8adu]

i suspect the o.p is trying to charge directly.he must get 8.4v to achieve full charge.the pack should have internal protection so going a bit high probably wont hurt.my suggestion errs to the side of caution.
the buck converter also makes the most of the low and variable panel output.
while the 7808 will work it will never bring a li-ion to full charge.
some experimenting with diodes in the ground pin may make it come close.