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# Solar power & battery? Answered

Hi everyone,

I would like like to power a circuit that requires 6v from a battery charged by a solar cell.

Could someone recommend a battery & cell specs?

Would like the circuit to run at night for at least 3 hours.

Battery needs to be quite small. I've picked Powerfilm solar cells, just need to know what voltage & amperage to use for a small 6v rechargeable battery.

Thanks!

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Too much information in your reply to Rick most of it is not important.

If you want to run a 200 ma circuit for 3 hr you need a 600 mah (millamp hours) plus a little for good measure so 6 volts 800 mah minimum.

A wireless phone or cell phone battery should do you.

Now for solar charging.

Most solar chargers for day charging night use are based on a 10 hour full sun day so if you are charging a 6 volt 800 mah battery in 10 hours you need 80 to 100 ma for 10 hours. Some batteries need more the needs should be on the side of the batteries with the voltage and mah.

If you want to charge in a shorter time like 5 hours 160 to 200 ma but don’t go higher than that.

Joe

That's great, thanks, makes perfect sense.

So the voltage of the solar cell is irrelivent? You haven't nessisarly got to match the voltage of the battery then. So a 6v cell for a 6v battery?

Here is something you can try.

Get a solar garden light, (I play with a lot of them).

Check the voltage on the solar cell connected to a circuit in bright sun light.

You will get something like 5 volts.

Add a battery being charged to the circuit. (In this case 2 AA)

And the voltage drops to just above the battery voltage with out a voltage regulator.

Joe

It all depends on what you load is - What is the wattage or amperage of the load?

How small is "quite small!

Your solar cell will need to supply at least 2 volts over the battery voltage. Charge time will be dependent on the soalar cell current.

I'm using a 555 MSOP size I.C & this is it's specs..

• Mounting Type Surface Mount
• Package Type MSOP-8
• Dimensions 3 x 3 x 0.86mm
• Height 0.86mm
• Length 3mm
• Width 3mm
• Maximum High Level Output Current -200mA
• Maximum Low Level Output Current 200mA
• Maximum Operating Supply Voltage 16 V
• Maximum Operating Temperature +70 °C
• Minimum Operating Supply Voltage 4.5 V
• Minimum Operating Temperature 0 °C

I've found the circuit works perfectly with an assortment of coin batteries, like x2 2025s which are also a perfect size.

I've added a picture of my circuit if it helps...