Solar Charging

[new2u]

Here is what I have. I have a battery bank of AA batteries wired in series (8)of them that produce about 5 volts for my application. I want to be able to charge the battery bank using one of my extra solar panels.

The PV is 12 volts 1 amp

The AA's are 2650mah (1.2 volts)

I am sure that I can use the 12 volt panel to charge this bank however I am worried that I the voltage might be way too high for the battery bank.

Is there an easy solution to clamp down the voltage of the panel to say 6 volts or so?

I only need over 5 volts. My application uses 5 volts and 1 amp to run.

Please help me figure this one out. I know its not very often we have more then we need and have to find a way to lower our output but here is one of them.

Thanks,

Larry

[ghurd]

Hey Larry,

Would you be against using 10 AAs?

Then you could use a PB137ACV (with a very Big heat sink) to regulate the voltage to 1.37V max per cell.

Could use a 78XX voltage regulator to get the output to the voltage you need. (7805 is 5V, 7806 is 6V, etc)

Seems like an awful lot of panel for AAs!

G-

[madlabs]

8* 1.2 = 9.6V. I assume you are using a Vreg of some kind to step it down? What about making a 12V battery pack that you can tap at 6V? That way with a low drop out regulator you will be dissapating very little wasted wattage in the vreg. You could use a small latching or regular relay to switch between the banks.

[new2u]

Yes, I could do 10 of them.

I think I mis-typed this though here is actually what it is.

2 packs of 4 AA's wired in series = 4.8 volts per pack (1.2 volts per cell)

The 2 packs are then wired in parellel to maintain the same voltage of 4.8 volts but the amps have increased.

I was just wanting to use the only one solar panel I have that is not good for anything else I have rather then having to buy another panel.

I could just buy another panel just for this project though as I am trying to keep the cost as well as the parts to bare min.

Maybe there is a perfect size panel for this project?

Not sure.

Thanks,

Larry

[ghurd]

That (4 x 2) would be a more efficient use of the panel.

I would want some way to limit the voltage.

Maybe an adjustable voltage regulator in TO-3, but dang, Newark gets $68.86 plus $20 handling fee and they ship from UK!

ebay, $6.

Need a couple resistors, capacitors, and maybe a diode.  Plus a big heat sink.

Must be a better way that is still cheap and simple.

G-

[Bruce S]

Larry;

 You could connect 10 rechargables in series, let the panel charge them as is, and tap the set at the 6th battery for the 5V you need. The 2600+mA should hold the charge well enough down to not worry too much about overcharging.

You said it rated at 12V 1A, is it possible to put it out in the sun and get a true charging level going into say a small 12V battery?

Of course if the higher current is needed for longer running time, then even then the batteries connect series/parellel should be able to hold the panel down to the voltage since the current recharge will be so much more. That's 5200+mAh.

IF they are NiMh, I assume due to the high current rating, try the later; let them get to charging and do the touch test to see if they are getting hot; if they feel hot or overly warm then got the route of putting a 78xx in place to hold charging level down.

Keep Smiling;

Bruce S