After a weird start to some testing involving connecting a new multimeter up incorrectly causing the data to be out by a factor of 10x we managed to get some decent run-time data. I’ll update this post as I get more figures in.
So with the ST-760 unit, running under Night-Vision mode without the use of the inbuilt IR illuminator. The average current draw was 204mA over a 7.95 hour burn-down of a Panasonic, protected cell rated at 3,200mAh. Now this button top battery is to long to fit in the ST-760, but the non-protected flat-top batteries are essentially the same cell without the extra button tacked on and the protection-circuit which helps protect the battery against over charge, over discharge, etc. Use of a good quality, intelligent charger negates the need for this feature and we presume the ST-760 contains a voltage regulator circuit as it has inbuilt charge capability and powers alternately off 5V USB leads, which should also mean that the unit switches off as the 18650 cell hits end of cycle drain voltages in the safe zone for the battery. We will confirm this as we tear down the unit and analyse it’s internals in the near future.
Back to the test results though. The windows laptop we used to log the data off the unit as we did the burn-down test decided to do windows updates overnight and rebooted itself cutting short the test. So the Night-Vision only mode test terminated abnormally at 7.95 hours. At 204mA draw, we would expect 14 odd hours of run time but at least >8 hours can be expected with a good quality and reasonable condition 18650 cell.
Secondly we ran burn-down tests on two 18650s using night mode again, but with the IR set to IR3 (brightest setting).
|Run Time (hours)||2.31||2.37|
|Current Pull (Amps)||1.287||1.294|
|Battery Rated Capacity (mAh)||3,200||3,200|
|Actual Usable Capacity (mAh)||2,978.51||3,066.34|
Note “Actual Usable Capacity” is based on the described scenario and whilst impacted by cell performance characteristics isn’t the only discriminating factor. It gives an indication of the expected performance in field use. It’s also useful to note that measuring current means that the meter used is in series with the battery. Power is necessarily lost through the meter and the cabling used to connect the unit and cell for test. Additionally the meter has an error rate of about 2.5%. However the test results are consistent with field tests and with the expectation of usable capacity from the cell’s datasheet.
Update October 20, 2018
Overnight we ran the standard night mode only, with nothing else turned on. It resulted in a 12.29 hour run with an average current draw of 280.73mA. That means we pulled 3,450.4mAh off the battery before it switched off. Burn down tests on batteries at a low current is much better than with high current in general and this certainly fits. More testing to come.
Update October 21, 2018
So based on a battery cell which yields 2,750mAh usable (we reduced by 10% to model shelf leakage, if any, and a battery that’s reduced in life somewhat).
|Mode||Current Draw (Amps)||Projected Run Time (Hours)|
|Recording in Night Mode||0.2813||9.78|
|WiFi turned on, not connected||0.3828||7.18|
|WiFi turned on, connected||0.4201||6.55|
|Infrared Illuminator On (1)||0.6094||4.51|
|Infrared Illuminator On (2)||1.1002||2.5|
|Infrared Illuminator On (3)||1.2905||2.13|