Emergency power show-down

Being an amateur radio operator and a nerd in general, I make sure I have emergency power available. This is in the form of gel cells, several UPS units and of course the obligatory inverter for road trips. I have a solar panel that can put a reasonable charge back into my gel cells with one bright day's worth of sunshine. I don't feel like I need a generator. If the power goes out for a week or two over a wide area, most of my gadgets will be marginally useless, and I'm pretty comfortable living without electricity, as I go backpacking and camping frequently.

I do use my netbook for certain digital modes with amateur radio, and I could see it coming in handy for emergency operations. Considering the electronics I might choose to use sparingly in a power outage, I did some experimentation over the weekend.

My netbook requires 19VDC, and It seemed silly to me to turn DC into AC, and step it all the way up to 120 volts, just to step it back down, rectify and filter it for devices that fundamentally operate on DC to begin with. The same goes for desktop PCs that take 120VAC and turn it into +-12VDC, 5VDC and 3.3VDC. The rest of my "ham shack" runs fine on car batteries. Why not my computers?

In all of the following photos, you'll see amperes on the display, but I'll reference watts. The battery pack was sitting at 13.2 volts for all of these tests.

To baseline this thing, I went with the obvious choice of plugging into one of my UPSes. I have a feeling this is how most folks would choose to operate their computer in a power outage if it were an option.

The UPS consumes a paltry 5 watts without a load. This is looking pretty good.


Plugging the power brick in bumps consumption up less than a watt for a total of about 5.7 Watts.


With the laptop booted up and running on the UPS, battery consumption tops out at around 20 watts. I noticed numbers higher than 1.5 amperes momentarily. One of our cats also has some obsession with laying on warm electronics such as power bricks.





Next, I tried my 450 Watt inverter. Without a load, it uses about 6.6 watts. Not terribly surprising. It has two noisy fans and a display to power as well.


Plugging the power brick in without any load bumped consumption up to 7.1 watts. This is similar to what happened with the UPS, but still less efficient.


Attaching the netbook spiked the load to about 43 watts total. Ouch!




Finally, I tried operating my laptop on a DC-to-DC power supply. This was vastly more efficient than relying on an inverter, and considerably better than my UPS as well. The DC-DC converter consumed 11 watts from my battery pack.



The clear winner is obviously the DC-to-DC converter. If the laptop were the only thing in use, I could expect about four times the run time from the DC converter compared to using my inverter.

The DC converter I used was originally for a Macintosh G3 PowerBook, and was set for 24 VDC. My netbook requires 19VDC, and I was fortunate enough to find a set of potentiometers on my old DC-DC supply to allow me to adjust the voltage, and then I hacked a plug onto it that works for my netbook.

Most laptops require somewhere between 15-24 VDC, and are sensitive to dirty power. Good DC-DC converters are capable of dealing with 10-30+ volts of input and provide stable, clean power on the output suitable for sensitive electronics. They're easy to find, if a little pricey compared to traditional transformer bricks. They are often sold as "Laptop Car Chargers"

Similarly, a company called PicoPSU makes a tiny solid-state DC-to-DC power supply that plugs directly into a computer motherboard's ATX connector and provides power cables for a few hard drives or other peripherals as needed. They're not designed to run powerful desktops or servers, but work fine for lower-power workstations or "book PCs." You'll have to find a way to power a monitor, though. Hint: many LCD displays can be powered by a DC-DC converter, too.