Solar charging a small battery

[peter nap]

I have a 5 watt solar panel and want to charge a 6 volt lantern battery for a game camera, I haven't looked at the amperage on the battery yet but it's pretty light. Is the 5 watt panel OK to direct charge or should I put a current limiting resistor in line?

Thanks

[AbyssUnderground]

You will need a charge controller if the battery is small. A current limiting resistor will only charge it slower and waste power. It also doesn't stop overcharging. You might as well have only a 1w panel if you use a current limiting resistor.

Also are you sure the solar panel is 6v and not 12v?

[wdyasq]

"I have a 5 watt solar panel and want to charge a 6 volt lantern battery"

Need to know type of battery before one can advise. Need to know voltage of panel also.

Ron

[peter nap]

OK...the battery is:

Volts 6

Amp-Hour 5

I may be mistaken but every panel I have produces up to 23 volts. The battery should not overcharge unless it receives too much wattage regardless of the wattage. The idea of the current limiting resistor is to trickle charge it and hopefully eliminate the need for a charge controller.

Yes a 1 watt panel would be the same as a 5 watt with the current limiter but I have several 5 watt panels that I used before I started buying 15 watt units. I do not have a 1 watt panel and would need to buy one.

Am I mistaken on this?

[peter nap]

<<<<<<unless it receives too much wattage regardless of the wattage>>>>>>

Sorry, that should have been:

<<<<<<<unless it receives too much wattage regardless of the voltage>>>>>>>>

[AbyssUnderground]

23v open circuit means you have a 12v panel. You can charge a 6v battery with this but you WILL overcharge it unless you have a charge controller rated for 6v and allows an open circuit panel of 23v. A current limiting resistor will still overcharge it but it will also make it charge more slowly from when it is flat. I find it really pointless having a 5w panel and then limiting it to 1w with a resistor just because you don't have a charge controller.

A better idea might be to get a second identical battery and put it in series to make 12v and then charge it with the panel. You will harvest a lot more power that way and have twice the battery as well.

[alancorey]

What about using something like an LM317 chip (under $1) as a charge controller?  You'd need a pot to adjust the voltage, a heat sink of some sort, maybe a couple of small capacitors on the input and output.  Sort of like you'd use a PB137ACV, but they don't make one for 6 volts so you have to roll your own.  A switching regulator would be more efficient, but more complicated to build.

  Alan

[peter nap]

That may work Alan, thanks!

I may also just buy a little 6 volt panel. They are just $25.00 or so. I just having panels that I'm not using.

I could use one of those silly charge controllers that came with some of the HF kits and charge a small gel cell 12 volt battery and use the 6 volt output on the Controller. I have both controllers and batteries gathering dust. That's getting bulky though and this is for a game camera.

[wdyasq]

What is the battery chemistry? ..... If these folks can advise without knowing what the actual charging voltage should be they are more clairvoyant than I.

Ron

[ghurd]

I wouldn't want to risk the camera connecting it to the HF stuff.

I've had good luck with voltage regulators for SLA and nicd/nimh.

May want to check the reverse current at night.

Might want to charge the battery up all the way every so often, if it's in the woods where solar won't keep up.

G-

[alancorey]

Just curious: is this game as in sports or wild game?  Hard for me to imagine what a game camera is, except maybe something triggered by a light beam at a watering hole or feeder.  I had a webcam in a bird/squirrel feeder once.

BTW the Harbor Freight 45 watt kit is on sale for $199 again: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90599

  Alan

[ghurd]

I thought it was wild game.  Pics of 8-point deer, etc.  

Not sure now you mention it, but solar at a night time football game is... 8-point-less?

Google 'game camera', lots of hits. If it shows a deer, bear, etc, thats what I was thinking about.

G-

[Dzisko]

That will help.

R2 depends of load, something about 3-5 Ohms.

Zener's voltage is 6.5 V, R1 - 5...10 kOhms

Transistor - almost any NPN BJT allowing current 1 and more Ampers and voltage 30 and more Volts, heatsink is requered.

All parts can be extracted from almost everything.

[Dzisko]