Interesting...you learn something new every day.
I have a 10 amp-hour battery bank for USB stuff (cellphone, etc.) lying around, and it occurred to me "hey, it's free 5 volts, why the heck not use it?". Quick and easy for a quick, flat, 5V....and 10 AH is nothing to sneeze at.
So I tried it (modified a USB cable to just use the power wires) and it works great. Until it suddenly shut off. I was powering some stuff, and suddenly it shuts off all by itself. WTF??
So apparently those battery banks have internal circuitry to shut the thing down when it thinks nothing is connected. Go no, right?
So the other day I just happened to finish some software to access my Labjack USB data acquisition device, and it grabs data and plots it. So I figured I'd try to get to the bottom of this. So I hook up the battery to the Labjack, turn on the recorder, and it gives me the attached plot. With no load on the bank it shuts off about 35 seconds after you turn it on.
So I then applied a 20 ohm resistive load (250mA) and it stayed on forever. So I tried a 47 ohm resistor (106 mA) and it stayed on forever. So I applied a 100 ohm load (50 mA) and it shut off in 35 seconds.
So apparently these things shut off if there's less than 100-150 mA of output current. So what people do is put together a circuit to apply a burst of load every 10 or 15 seconds to keep the thing awake. Of course you could just tie a resistor, but that's just a waste of amp hours.
I'm curious, anyone know of a cheapo device I can get to do this load cycling? I saw a TI paper on this phenomenon, and they have some recommended circuits, but I'm too lazy
Thanks.