I need a light USB-load

Hi, I have modified our bread machine to run from a Nano and a couple of SSRs and powered internally from a 12vdc buck. I have a USB cable poking out so I can update as needed.

It is all good but overnight there are some power glitches (joys of country living) and the program sometimes gets scrambled.

I have been plugging in a power-brick to the USB and that seems to maintain the program, but overnight in "waiting" mode, the current draw drops below 200mA required to keep the brick alive.

I tried a small USB book reading lamp plugged in as well but it draws too much current and flattens the brick before morning.

What can I use (off the shelf item) for a 250mA or so load? The USB dummy-loads I have found so far have all been around 1-A and higher mark.

Ohms law to the rescue:-

5V / 0.25A = 20 ohm resistor

At a power rating of above 5 * 0.25 = 1.25W

Maybe you can make the program to recover from brief power loss (saving important data to some nonvolatile memory). Or use the battery power only for the (brief?) periods of power loss - probably a pack of rechargeable AAs?

Had that problem and solved it by blinking the dummy load (33 Ohm 1W resistor) on for 50mS every 15 Seconds, power bank remains on until depleted.

Thanks to all, I will probably go with the batteries.

It would be my luck that an outage would happen while the load was blinking off. :)

I am already saving stuff in EEPROM for a restart or continue. But as mentioned, the Nano is not restarting during the brief power hiccup or brownout (around 60vac) is just making the Nano go crazy. If power goes off for a full ten or more seconds, it is all good I can recover with the EEPROM system already in place. It's just these momentary things that doesn't shut down the Nano.

What I'm saying is you may not have to have the dummy load on and wasting power [u]all the time[/u], I found that by turning on the dummy load for a short time periodically would keep the power bank from shutting down. In my case I found a minimum current of 120mA would keep the power bank on, then I tried interrupting that current and found the power bank didn't shut off until 25 seconds later, then I tried applying 150 mA pulses of shorter and shorter lengths at 15 second intervals, I quit at 50mS. Maybe a shorter pulse would work? Anyway, that cut the power waste in the dummy load to 0.33%.

756E6C: that cut the power waste in the dummy load to 0.33%.

Ahhh, OK, that makes some sense. I didn't think it through. :)