HAL 9000 Meets Kill A Watt(TM)

“I’m sorry, Dave…”

Motorized chair charger getting Kill A Watt analysis

OK. It’s really not HAL 9000, although you’ve got to admit, it looks a bit like one of HAL’s ubiquitous camera eyes.

Actually, it’s a charger used to re-charge the two 12V batteries that power the mobility chair in the background. In my Kill A Watt™ EZ measuring madness, I decided to see how much power the charger uses. It’s a good example of an appliance that can generate a significant phantom/vampire load, if left on all the time.

What I found was that, to bring the batteries up to a full charge after being very close to completely run down, required the charger to run for about 9 hours. The Kill A Watt™ EZ recorded a total power consumption of 0.91 kWh, at a total cost of $0.18.

Then, I reset the Kill A Watt™ EZ and left the charger to run overnight, even though it was idle now and no longer charging the batteries. After 11 hours, the Kill A Watt™ EZ reported that the idle charger still consumed .11 kWh of power, at a cost of $0.02.  It might not seem like much, but the cost estimation function of the Kill A Watt™ EZ shows that this comes to about $1.46 a month, and $17.78 a year. That’s more than it costs to run my cable modem continuously for a year. But unlike the modem, all that estimated idle time is serving no purpose whatsoever.

Of course, in reality, the charger wouldn’t be idle all the time; a certain percentage of its time would be spent trickle charging the chair. But still, the morale of this story is that there’s no sense in leaving the charger on continuously, as long as the chair’s batteries have  a sufficent amount of charge on them.

“I’m sorry, Dave. I’m afraid opening the pod bay doors would waste too much energy…” :)

About John Poole

My interests include historic homes, architectural preservation and restoration, improving the energy performance of old houses, and traditional timber frames.
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6 Responses to HAL 9000 Meets Kill A Watt(TM)

  1. Joe Lopes says:

    I have been a kill-a-watt fan for some time. I tried out several chargers on it and also on a Watts-up data logger. Some curious results… A camera battery for a Canon digital SLR ran at 5 watts at first, then declined down to zero in 2 hours to charge fully (no vampires here), totaling 5 wh (watthours, or 0.005 kWh). No waste.
    Cell phone (2011 Motorola Droid 2) used 6 watts for 90 minutes (total 9 wh), also dropping to zero (no vampires). But, a AA battery charger used 1.8 watts and did not drop off once the batteries were charged (vampire!). So, it pays to check – newer chargers may have lesser vampire qualities.

    • John Poole says:

      Thanks for the comments, Joe. Yes, it’s interesting how you start off just using the Kill A Watt to assess cost, then discover something about the behaviors of the various devices being tested. I noticed you mentioned a WattsUp data recorder. Have you used WattsUp? Do you have a preference for one over the other? WattsUp seems great if you’re intested in detailed profiles of specific devices over time, but Kill A Watt seems much simpler for doing quick checks, etc. (Just my impression, anyway; haven’t tried WattsUp yet)

      • Joe Lopes says:

        John, While I’ve used kill-a-watt for many years, I only started using a Watts-up Pro for a few months. Your assessment is correct. Kill-a-watt is great for quick spot checks for demand and cumulative energy. Watts-Up Pro is great for more detailed profiling. What I really like is that you can configure it to record any interval length from 1 second to an hour (or more), with the tradeoff being how many intervals, although since it records so many variables (including integrated totals, max and mins of watts, volts, amps, etc. by interval), you can stretch recording even up to a week for 1 minute data if you only record watts and max watts, which are most useful. In the “Pro” version, a USB interface and supplied software enables downloading to your PC. The software is a bit techie but I’m used to that, and gives you a table and a zoomable graph. I’ve been able to copy out the table data and write my own spreadsheet analysis app. I love it! You don’t lose data if you unplug it, you can get alot of data right off the display, though it’s like programming a thermostat, and then download the data to its software to view the detailed intervals. I would definitely recommend it for more detailed work.

  2. James says:

    I have a friend that uses one of these chairs to get around. She is extremely budget sensitive since she’s on social security disability. I’ll let her know your findings. ;)

    • John Poole says:

      Thanks, James. Hope it helps her out. My guess is that she might use her chair more frequently than we do. Our family member who requires this chair only uses it on occasion. Your friend, on the other hand, may need to keep the charger going a bit more if she uses her chair all the time. But I hope that I’ve helped her in some way.

      • James says:

        Ahh, yeah, she uses it every day. She’s a polio victim. Don’t feel sorry for her, though. She gets more done than most people I know who have full function of their legs, lol.