Recommendations for smallest rechargeable 12v battery available?

[Deeg]

I'm working on a wearable project using EL panels with a 12v inverter like this one at Ada Fruit. I'd like to use a rechargeable battery to cut down on waste. I've done some research but the options are almost overwhelming and the smallest ones seem to be on sites that require bulk purchases. Does anybody have suggestions? Weight is probably more important than volume. I'm comfortable doing some soldering so the connector does't matter much.

 

[Visitor]

Start by explaining your current draw and how long you want whatever to run.

 

[audioguru]

I cannot think of anything that uses a small rechargeable 12V battery. Then it is rare and is custom-made for you.

Kid's toy drones use a small 3.7V rechargeable battery sold in hobby stores. They also sell chargers for them.
Use a Chinese voltage booster module for a 12V output.
The size of the battery determines how long a charge will last when powering your EL panel.

 

[Deeg]

The Ada Fruit panel draws 210 mA but I will be cutting it down so it'll draw less, maybe around 140 mA but that's a guess. If it could stay at full brightness for 5 hours that would be enough; longer would be better but at that point weight is more of a factor.

 

[Deeg]

Use a Chinese voltage booster module for a 12V output.
The size of the battery determines how long a charge will last when powering your EL panel.

That's an interesting idea. I have some rechargeable LI 9v batteries that I could pair with a booster like this one on eBay. Thanks!

 

[audioguru]

5 hours at 140mA= 700mAh. A 9V Ni-MH battery is 175mAh and if a booster gets an output of 12V then the 140mA is also increased to 12/9= 1.33 times more plus 20% inefficiency= 410mA. The 9V battery charge will last 175/410= 0.43 of an hour= 26 minutes but maybe the last 10 minutes will cause dimming.

 

[Pommie]

You'll need 12V*140mA = 1700mWH - Something like this will probably suffice - should give approx 4 hours - they also have a 2Ah version. You'll need a boost circuit to get the 12V. Note the Sparkfun warning " Please use caution when using this battery in wearable projects. When using conductive thread, a short in the thread can create sparks and heat. We recommend using coin cell batteries for beginners. "

Mike.

 

[Deeg]

The 9v batteries I have are li-ion 600 mAh so presumably they'd last closer to an hour but that's not as long as I'd like. The inefficiency is higher than I thought. <sigh> This is never as easy as I'd like it to be. I guess this is why you guys get the big bucks. I'll look into Pommie's suggestion.

Thanks all!

 

[audioguru]

140mA at 12V is 410mA at 9V. Then the 600mAh little battery charge will last for 600/410= 1.46 hours, just about one and a half hours.
The 3.7V Chinese battery from SparkFun has built-in protection against over current. But the maximum allowed current is a big secret. Why??

 

[Pommie]

140mA at 12V is 410mA at 9V.

Where did you go to school? 140mA at 12V is 1.7Wh . At 9V that's less than 200mA, stop trying to make out that everything is Chinese rubbish, even the stuff sold by a reputable US company.

Mike.

 

[audioguru]

My battery current calculation was wrong because the rechargeable battery is 3.7V but I calculated for a 9V battery.
If the EL panel draws 140mA at 12V but a 3.7V battery is used and has a voltage booster, then the input current to the booster is 12/3.7=3.24 times more at 454mA. The efficiency of the booster is only 80% so the 3.7V battery must produce 454 /80%= 568mA. The battery current will increase as the battery voltage runs down. A charge in the 2000mAh battery will last 2000/568= 3.5 hours if the battery specs are truthful.

All my Li-PO batteries have a "C" max current rating and are sold by a reputable US company, but the Chinese battery from SparkFun does not have a max current rating (missing in the translation?).