Instructables

Would a solar panel with more amps/lower voltage charge 4AA batteries faster or slower than more volts/fewer amps?

I'm trying to make a solar powered battery charger for my 4AA rechargeables, and I'm stumped on what kind of solar panel I should use. I have two solar panels: one 0.5V 800ma, the other 2V 200ma. Which solar cell would be better for what I'm going to be using them for? And I'm wondering what the specs of those solar garden lights are, and if the solar panel for the garden lights is strong enough to charge the batteries.

appolo5 years ago
Hi, your 4AA rechargeable batteries will have to be parallel connected. That's all four + ends connected together and all four - ends connected together. These cells are 1.25volts so your 2v 200Ma solar cell can be used to charge them. Each cell will share the available 200Ma = 50Ma each. Depending on each cells current discharge capabilities, will denote how long the charging time. I presume all cells are matched characteristics. Note your solar cell will provide the stated current during good sunlight _so dull days means lower output current. Should you wish to charge one or two cells only you would probably need to limit the maximum charge current as they could overheat ! The preferred methods for charging both Nicad and Nimh batteries can be very involved. If you have a basic knowledge of electronics and can build simple circuits there are several sites you can down load charger projects.
Garden lights generally use a single 600Mah nicad cell with a white LED operating from 10Ma_20Ma depending on the circuit design. The solar panels from these lights could charge your cells but would take sometime to charge four at a time. I've tried to keep my answer as simple as possible for you without delving into the technicalities of which you can search the nett.
Hope this information will help you achieve good results. Regards
=D (author)  appolo5 years ago
So charging the 4AAs in a regular battery pack (positive ends connected to negative ends) wouldn't work? What would happen if I didn't put the batteries in parallel? And thanks, that really helped me.
rocktot1 year ago
http://www.reuk.co.uk/Basic-4-AA-Solar-Battery-Charger-Plans.htm
appolo5 years ago
By connecting the cells as you suggest, positive to negative you will require at least 6 volts. Each cell in series adds up to 4.8 volts (1.2 volts each). Each cell in parallel however = 1.2 volts each. The same current flows through a series string, while a parallel combination the available current is shared. A couple of points worth mentioning_ Nicad cells have a charecteristic known as "memory effect" if they are continually topped up and will not always deliver their full capacity. Under these condition they require a full discharge and then charge up. The other point to be aware of if you are experimenting, don't over current charge them. Nicad batteries have a strange charging curve and at some point towards a fully charged state a chemical change alters the internal impedance which results in extreme overheating if the charge current is to high! so beware.
lemonie5 years ago
You'd be best with the 2V panel I think. My plug-in battery charger says it does 4 AAs at 2.8V 220mA 0.5V is too low, you would need to step up the voltage, which can be done, but the 2V panel should work as is I think. L