[aprssig] $60 WinBook TW700 Tablet - Power Drain Tests

Stephen H. Smith wa8lmf2 at aol.com
Mon Feb 9 11:15:48 CST 2015

I have now made power drain tests of the $60 Microcenter Winbook TW700 tablet.

I had the tablet running UIview + Precision Mapping + the UZ7HO Soundmodem 
"soft TNC", with the display set at full brightness.

On the provided 5V 2.1A wall charger, the KIll-A-Watt AC wattmeter indicated 
about 7.5 watts at initial power-up up including a slight inrush to the 
internal battery.   After a 15-minute wait for the battery to top off at full 
charge, the AC drain dropped, to about  6 watts.  Obviously this will be no 
pain at all to a Field Day generator setup...

For the DC power test, I used a generic two-USB-port 2.1 amp charger that plugs 
into a lighter jack (a.k.a. "12VDC power outlet" in newer cars) acquired for 
USD $10.95 at a Pilot truck stop.

[The large chain truck stops a.k.a. "travel centers" such as Pilot, Flying J 
and Love's are actually a very useful source for all manner of 12 VDC gadgets 
including inverters & chargers, power connectors, heavy-gauge red/black DC zip 
cord, 12 VDC fans, 12 VDC TV/DVD players, and even microwave ovens & 
mini-fridges that run on 12 VDC. Not to mention the wide assortment of coax 
jumpers, antenna mounts, SWR meters, external speakers, RF connectors and 
adapters, etc targeted at the trucker CB trade but also useful for hams. 
Driving a VW Jetta TDI diesel, I tend to stop at these places fairly regularly...]

With the display at full brightness, the "Watts Up" DC 
wattmeter/ammeter/voltmeter indicated 12.6 VDC from my shack battery plant with 
a drain of 4.9 watts (bouncing between 380mA and 400 mA).

With the display dimmed to "50%" in the Windows "Power Options" dialog, the 
drain dropped to about 3.7 watts (300 mA)

With the display dimmed to absolute minimum in "Power Options", the drain 
dropped to 2.7 watts (220 mA).

At this extremely reduced brightness the display is nearly unreadable (except 
perhaps after "lights out" on a campout) but all program processes are still 
running at full speed.   Since Windows Power Management allows the display to 
be dimmed to a low level normally, and then brighten up when keyboard, mouse or 
screen taps are sensed, this could still be a practical minimum-standby-power 
mode for an APRS digipeater, igate or messaging terminal.

With the display at minimum brightness, I am now going to pull the power 
connection and what the maximum run time on battery alone can be.  Reports later.


Stephen H. Smith    wa8lmf (at) aol.com
Skype:        WA8LMF
EchoLink:  Node #  14400  [Think bottom of the 2-meter band]
Home Page:          http://wa8lmf.net

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