How To Figure Size Of USB Power Source

My recent post about my review sleeping bag liner heater received sone feedback from a good friend. Post link below

http://macaloney.blogspot.com/2022/03/sleeping-bag-heating-pad-game-changer.html?m=1

She has a vehicle lithium jump starter that has a USB port that she used with the identical sleeping bag heater and wanted to know how long should she expect the 18000 mili amp hour to last with the sleeping bag heater.

My tests of the sleeping bag heater showed that on high (red) it used 1.42 amps

In order to calculate total amp hour needs, the first thing you need to do is convert the battery (18000) mili amp hour battery to amps so you can compare both battery and how much you are using.  Ie. Changing milliamperes to amps

18000 milliamperes /  hour battery is 18 amp hour.

My friend said that her battery was 87% full when she started using the battery to run the sleeping bag heater one night 

That means you would need to multiply 87% by 18 amps and you get just a bit more than 15.6 amp hours of battery life to start the night with.

Although you will use less on the medium (blue) or low (green) settings we will focus on worse case of 1.42 amps per hour.

To get the hours you can get from heating with her battery you take 15.6 amp hours available and divide by 1.42 amps per hour used to heat the sleeping bag heater.  The answer is you get just over 11 hours of sleeping bag heater time.

Above is the battery in my pictures that I tested with.

In my experiment I used a 10200 mili amp hour battery.  With it fully charged what do I get for how long it will last heating the sleeping bag heater?

It gives me just over 7 hours.  Although I have used this USB power source, when I’m in my camper I plug it into my camper house battery and I have no overnight time limit.

Regardless of your battery size this is how you figure out how to determine the size battery you may need for the sleeping bag heater or any other constant draw device.  Of course the temperatures you are sleeping in and how old your battery is will have an effect on how long a battery will last.

Here is the USB device I use to measure the current draw.

Mine is a USB-A as I plunge standard USB cables into it.  You can plug two USB cables in at one time.  

Lastly, if you have devices that do not run for a full hours round to next highest tenth of an amp. 

Brent

macaloney@hotmail.com