Archive for November 24th, 2015
This sheaf of tests shows three of the four STK NP-BX1 batteries deliver about 4 W·h during a constant 500 mA discharge, with battery B trailing behind:
After the three most recent bike rides, I popped the partially discharged battery into the tester and used the same test current:
The longer curves come from the top chart (with different colors), the shorter ones from the partially discharged batteries. In an ideal world, the shorter curves should give the energy left in the battery after the ride, so subtracting that from the before-ride capacity gives the energy used during the ride.
The results for battery A may not be typical, as the camera turned off before I rolled into the garage. The camera may run with a battery voltage below the 2.8 V cutoff in those tests, so it can extract more energy than the tests. The slope of the curve toward the end suggests it won’t get much, but that will still bias the results.
In round numbers, the bike rides required:
- A: 3.8 – 0.1 = 3.7 W·h
- B: 3.6 – 1.4 = 2.2 W·h
- D: 4.2 – 1.0 = 3.2 W·h
I generally turn the camera off during the mid-ride pause (Protip: never wear a helmet camera into a Port-a-Loo), so at least two of the rides have discontinuous usage. I figured the total run time from the video file sizes at the rate of 22.75 min/4.0 GB, blithely ignoring issues like the battery recovering during the pauses, the effect of ambient temperature vs. camera heating on battery temperature, and so forth and so on.
In an ideal world, dividing the total energy by the run time (converted from minutes to hours and not venturing into pirate·ninja territory) should produce a nearly constant value equal to the camera’s power dissipation:
- A: 3.7 W·h / 1.25 h = 2.96 W
- B: 2.2 W·h / 1.0 h = 2.1 W
- D: 3.2 W·h / 1.4 h = 2.25
Ignoring the suspiciously high result for battery A, it looks like the HDR-AS30V really does dissipate a bit over 2 W while recording 1920×1080@60fps video. That’s with GPS, WiFi, and NFC turned off, of course.
Which turns out to be pretty close to the test conditions: 3.7 V x 500 mA = 1.85 W. I could goose the test current to 600 mA = 2.2 W/3.7 V for the next tests, but maybe long-term consistency is a virtue.