How to use 5v USB adapter in place of 3 AA batteries

Robotics and electronics discussion Electronics
1

I have a number of small Christmas decorations that are normally powered by 3 “AA” batteries. I also have a bunch of 5v USB power supplies just sitting around (various mA). So what I would like to do is power the decorations with a USB power supply. My research said that a AA battery was 1.2-1.5V @ 2000-3000mA. But given the most powerful 5v USB supply I have is only 1200mA, I’m kind of thinking this won’t work (assuming I drop the 5v to 4.5v) ? Might go on, but would be very sloooooow ?

If I’m right and it won’t work, does anyone have any other suggestions ? I have a bunch of these decorations and my rechargeable batteries wind up dead after about 3 days of use.

Thanks
Newbie Jack

2

The power supplies should work fine, unless the 5V could be a problem. 3xAA batteries in series provide between about 3.6V and 4.6V, depending on type.

Don’t confuse battery capacity in mAh (milliAmpere hours) with current (mA).

A typical rechargeable NiMH AA cell has 1200-2000 mAh capacity. If your lights drain the battery completely in 3 days (72 hours), that suggests the average current draw to be at most 2000 mAh/ 72 h = 28 mA.

3

Hello, Jack.

I agree with Jim’s assessment. If you are still confused about the difference between battery capacity and current, I recommend reading this “Understanding battery capacity” blog post.

- Patrick