Replacing 3 A3s

Please suffer a newbie question? I'm playing with accent lights. I have a disassembled doohickie that uses 3 A3 button cells to power some surface-mounted LEDs. I'd like to replace those with a rechargeable Li-On battery.

The numbers for the A3 button cells are Voltage: 1.5v Capacity: 28mAh. Could I use something in the AAA mileu to replace that without blowing these tiny SMD LEDs?

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Originally Posted by DragonStar

Please suffer a newbie question? I'm playing with accent lights. I have a disassembled doohickie that uses 3 A3 button cells to power some surface-mounted LEDs. I'd like to replace those with a rechargeable Li-On battery.

The numbers for the A3 button cells are Voltage: 1.5v Capacity: 28mAh. Could I use something in the AAA mileu to replace that without blowing these tiny SMD LEDs?

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You could easily replace the button cells with any other 1.5v cell. Voltage is voltage.

If you're firmly set on Li-Ion cells, you'll need to get creative with your resistors to limit the current from the 3.7v effective from the cell to something manageable by the little SMD LEDs.

If it were me, I'd go with AAA alkalines or AAA NiMH cells (1.2V) and be done with it.

Thanks for the reply, it's really helpful. I don't understand electricity and this is a cheap way to experiment. :) Are three 1.5v A3s are 4.5v when stacked together? If so, would I need three 1.2 NiMH AAAs to match the voltage as closely as possible?

I'm hoping to get away with one AAA or AA sized battery to replace the 3 A3's (hopefully to get longer run time as well).

To follow up, this is what I read about batteries:

There are two ways that cells may be combined to make batteries: series connections and parallel connections. When cells are connected in series, their voltages add but their ampere-hour capacity does not. Series batteries should be composed of cells with equal capacities. When cells are connected in parallel, the total voltage remains the same, but cell capacities add.

So I thought that three 1.5v A3s would be 4.5v when strung together, and that one 3.7v LiON might approximate that at 3.7V.

Quote:

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Originally Posted by DragonStar

Thanks for the reply, it's really helpful. I don't understand electricity and this is a cheap way to experiment. :) Are three 1.5v A3s are 4.5v when stacked together? If so, would I need three 1.2 NiMH AAAs to match the voltage as closely as possible?

I'm hoping to get away with one AAA or AA sized battery to replace the 3 A3's (hopefully to get longer run time as well).

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Yes, if the button cells are stacked, they are in series and you're adding their voltages. 3 x 1.5 V = 4.5 volts.

Regardless of what solution you use, your runtimes wil be much, much longer. Your current button cells have a capacity of 28mAh...pathetic. A decent AAA alkaline or NiMH has a capacity of 700-900mAh. That's a big, big improvement for runtimes.

Thanks, I set it up against a 3.7 lithium cell and it didn't fry. Whew!