Hi guys,I currently have a marble machine powered by 2 x AA batteries.I want to do away with the AA batteries and want to connect a solar panel which would work using indoor light…can any help.Something off the shelf,assembled and ready to go would be ideal…HELP!!…Joe,Sydney…
Hi Joe,
Welcome to the forum, that’s a great question and I think we should have some options which may work, though they may be a bit DIY/some-assembly-required which is pretty standard around here 
By the way, I’ve removed your email address from the end of your message since this forum is open and visible to the entire internet which means you can end up with a lot of spam emails if a bot gets a hold of your email and adds it to a list.
First of all not all AA batteries are created equal, typical alkaline AA battery has a voltage output of around 1.5 volts and a current output up to a few amperes depending on the load, but they are often rated for 1800-2600mAh.
On the other hand, a typical Nickel-Metal Hydride (NiMH) AA battery has a lower voltage output, usually around 1.2 volts but can have a higher mAh rating, typically around 1800 to 3000mAh. This means that while each NiMH battery delivers less voltage, they typically can deliver that voltage over a longer period of time before needing to be recharged or replaced.
In your setup it’s probably safe to assume the product was designed for alkaline batteries so a pair of them wired in series will be providing around 3V to your project.
For a typical alkaline AA battery, the voltage starts at around 1.5 volts when completely full. As the battery life gets consumed, the voltage drops gradually. Toward the end of the battery’s life, the voltage might drop to a level around 0.9-1.0 volts. So your battery pack is running from 3V at full charge to 2ish Volts when the batteries are due for replacement.
Solar panels without built in voltage regulators will typically have much higher voltage ranges. Take this solar panel for example.
This one with no load connected can reach up to 8.2 V on the terminal, and outputs around 5.5V with a more typical load. If you apply a heavy load to the panel the voltage will continue to drop until it is a dead short circuit between the terminals and maximum current flow.
This means the most power you get out of a panel is a sort of happy medium between the open circuit voltage and the short circuit current.
A smaller panel like this may be more suitable.
With a load it should hold around 3V output, but we’ll need to know a bit more about how the marble machine works to know if one panels worth of current supply is sufficient, otherwise you may have to add a few in parallel to get enough current supply to drive the machine.
Please let us know what the battery pack from the marble machine connects into. Does it directly drive a motor and if so, how large is the motor? Some photos of your setup will help a lot in figuring out what kind of panel will be needed to keep it running.
Hi Trent,thanks for your reply.The battery pack(which holds 2xAA batteries),connects directly to the gear motor.The gear motor is a GM9;143:1;3V operation;no load RPM ~40;no load current ~50mA; stall current ~ 400mA;stall torque ~44oz-in…hope all this helps …Thanks,Joe
is a very loose term. Let’s work the figures - from your description of the motor, it may take 100mA @ 3V = 300mW (as a ball park starting point). Best insolation is about 1000W/Sq M in full sun, conversion efficiency around 20% so solar cell area required is 0.3/(1000*0.2) sq m = 15 sq cm. That is the absolute minimum in perfect conditions. Indoor artificial light condition can vary between 1/100th daylight to 1/1000th daylight so the panel would need to be between 1500 sq cm and 1.5sq m. Those are big to very big panels.
So if you are prepared to convert part of a wall into a solar panel, this is probably a no go. Much cheaper to have a plug pack. If battery power is required, then LiPo delivers just above 3V and is rechargeable. And they have better capacity than AA cells.
