Lithium battery that can fit in a .65" tube?

[Triode]

I made a light up hula hoop for my wife, it's filled with AAA size NIMH batteries for 12V. She uses it a lot and they've started to die. It's always been a bit heavy so I'm thinking of going to Li-po or Li-ion, but I don't know of any that can fit in a tube that small (0.65"). A 11.1V or a set equaling that should work. I guess I could string together tiny ones but I don't really understand these batteries well enough to modify them and still charge them. Does anyone know of a battery that would fit, or small ones that could be made into one that fits and still be charged?

 

[MrAl]

Hi,

10440 is AAA size Li-ion. 350mAh.

 

[alec_t]

Be aware that charging lithium batteries can be DANGEROUS (there's a very real risk of fire or explosion) if you don't follow the correct procedure.

 

[audioguru]

Did you use NINE AAA Ni-MH cells to get 11.1V?
Then with Lithium you need only three cells.

A lithium battery must have a circuit to disconnect the load when the battery voltage gets to 3.2V per cell (9.6V for your 11.1V battery) or the battery will be ruined. The charger must be a "balanced" type so that one or more cells are not over-charged.
Hobby stores sell many Li-Po batteries and chargers for them.

 

[Triode]

Thanks, I hadn't been able to find that size of Li-po, I didn't know to search for 10440. If I put "10440 with tabs" in to google I find exactly what I need.

I do realize the charging is a bit complicated, so I got a charger meant for 2 and 3 cell packs. I would wire them like this right?


Besides attaching the leads in that way (im just going to buy a standard charging connector) is there anything else I need to do? Other components or steps I'm missing?

 

[audioguru]

You show 4 cells with an average total of 14.8V and the battery will be 16.8V when fully charged. Will the light bulbs or LEDs burn out?

You need a circuit that will disconnect the load when the voltage gets low enough to damage the battery.

 

[Triode]

Oh, I just grabbed that off an image search to show how I understand the batteries should connect to the charger. I'm planning to use 3 cells. I don't think the LEDs would burn out from over voltage, but my charger won't do 4 cells anyway.

 

[audioguru]

We do not know how you are limiting the current in your LEDs. If it is a simple resistor for each string of LEDs then when the voltage increases the current also increases which might burn out the LEDs.

 

[Triode]

Yep, just resistors. 220 ohm ones. They are pre mounted on a 3M brand strip which did not supply their maximum ratings, it just says 12V, I could probably find out the type of the tri-color surface mount LEDs they used and look it up if I do some research.

 

[audioguru]

We do not know how many LEDs are in series and in series with a 220 ohm resistor.
Maybe they are four 2.0V red ones in series with a 220 ohm resistor then their current is 12V - (4 x 2V)/220= 18.2mA.
Maybe they are two 3.7V blue ones then their current is 20.9mA.