Power Consumption and Battery Endurance
Updated 25 March 2015
So far this application note is based on running a recorder to battery exhaustion here in the lab, then applying adjustment factors per the Tadiran datasheet for the TL-5930 battery for other conditions. So, the green field is the direct measurement and orange are derived numbers. You'll see more 'green' in future versions of this document. My next direct test will be at low temperature, single battery.
You will also note that endurance is not much dependent on the sample rate. The main power consumer in microMARS are the SD cards themselves, and these in turn are dominated by a base current that appears as soon as the cards are in data streaming mode; whether any data is actually being streamed or not.
Finally, power consumption in standby mode (such as in the off-phase of duty cycling,or before mission start) is negligible as you'll see in table 2 and the discussion on duty cycle. Thus, if you select a 10% duty cycle for example, you will pretty much get 10x the recording endurance… and so on.
|Battery Endurance in Recording Mode|
|BATTERIES||OPERATING TEMPERATURE (Cº)||ENDURANCE @ 25,000 Hz (days)||ENDURANCE @ 100,000 Hz (days)||ENDURANCE @ 250,000 Hz (days)|
For battery Tadiran TL-5930/F
Measured with SanDisk Extreme Pro SD cards.
Green fields are direct battery depletion measurements. Orange fields are derived from measurements, using adjustment factors for the stated conditions based on TL-5930/F data sheet information and direct recording current measurements for the stated sample rate. More direct measurement results will be provided in future versions of this document.
Specific measurement conditions for test case '1 battery, 20 deg C and 100,000Hz sample rate': Test 2/19/2015-3/3/2015. Recorder in lab, approx.20 deg C. 64GB SanDisk Extreme Pro cards in the first two slots and 32 GB cards in the remaining slots. Firmware V1.22. Battery Tadiran TL-5930/F, date code July 2014. Recorder equipped with 0.5F power demand smoothing capacitor.
|microMARS Power Consumption|
|CARD TYPE||OPERATING MODE||SAMPLE RATE (Hz)||microMARS AVERAGE CONSUMPTION IN RECORDING MODE (mA)|
|SanDisk Extreme Pro 32GB||Recording||25,000||49|
|SanDisk Extreme Pro 32GB||Recording||100,000||51|
|SanDisk Extreme Pro 32GB||Recording||250,000||54|
|SanDisk Extreme Pro 64GB||Recording||100,000||53|
Battery Endurance with Recorder Duty-Cycling
During the off-phase of duty cycling, the recorder consumes approx. 0.06mA to maintain the clock and general operations (see table 2, Standby mode). This is approximately 0.1% of the consumption in recording mode; a negligible amount for recording endurance computation in duty cycled mode. Therefore, recording endurance in duty cycling mode can be estimated base on the duty cycle alone. For example, 10% duty cycle will yield 10x the battery endurance stated in table 1 for continuous recording.
|For Single Battery Recorder|
|25kHz||12 days||2 each 32 GB cards|
|100kHz||12 days||2 each 128GB cards OR
8 each 32GB cards
|250kHz||11 days||2 each 256GB cards OR
8 each 64GB cards
|For Quad Battery Recorder|
|25kHz||63 days||2 each 256 GB cards OR
8 each 64GB cards
|100kHz||60 days||2 each 512 GB cards OR
8 each 128 GB cards
|250kHz||57 days||8 each 512 GB cards|
The table provides recommended SD card use for single and quad battery microMARS configurations operated at 25kHz, 100kHz or 250kHz sample rate. Using these SD cards, the memory endurance will meet or exceed the specified nominal battery endurance.
The actual memory consumption in GigaByte is computed as follows:
Memory Consumption (GigaByte) = Sample Rate (kHz) * Endurance (days) * 0.1728.
For example, the actual memory consumption for recording 12 days at 100kHz sample rate is 12*100*0.1728 = 207.36 GB. If using two cards, half of this much or 103.68GB is needed per card. The next bigger available card size of 128GB should be used. If using eight cards, 1/8th of 207.36GB or 25.92GB per card is needed. The next bigger available card size is 32 GB.
Where did the number 0.1728 come from? It's a multiplier for 'sample rate * days' to get memory consumption in GB. Specifically, if you record at 1 kHz, the memory consumption per day is 0.1728 GB or 172800000 bytes.
There are 60 * 60 * 24 = 86400 seconds in a day. And, each sample is two bytes. So, 86400 * 2 = 172800 bytes of data per day at a 1 Hz sampling. And, 1000 as much (or 0.1728 GB) if you are sampling at 1 kHz.
Note that microMARS is tested and specified for use with SanDisk Extreme PRO cards. Other cards, if slower, can produce more data losses. Or, power consumption or reliability may vary.
Note: These numbers are based on giga bytes (10^9 bytes), not GB (2^30 bytes). SD card actual memory tends to be less than the number on the label in GB. Thus, the giga byte assumption is conservative.
Maximum Available Mission Duration
Battery self-discharge is stated by Tadiran as 1% per year. Recorder standby mode battery discharge rate is about 3.5% per year. Tadiran stated battery shelf life is 10 years. Further, battery voltage response declines after long storage. The Tadiran datasheet predicts about 3.3V in first second with 60mA load after five years of storage, which is still acceptable for microMARS. After eight years it is shown at about 3.075V, which is marginal for microMARS operation. Therefore, we recommend that microMARS mission duration with any duty cycle not exceed five years. Please be aware that this recommendation is based on a review of the Tadiran TL-5930 datasheet only (ECN 1501879 Rev. C 11/08), is not guaranteed by Desert Star and has not been verified through endurance measurements.
Performance Policy for microMARS Devices
Please be aware that Desert Star Systems does not guarantee any performance parameters reported in this document or elsewhere. Instead, we run tests and report the results of these tests. Please be aware that our test results are specific to the conditions under which our tests were conducted. As your operating conditions may be different, the recorder performance in your deployments may also be different. For best results test thoroughly, verify your recorder’s performance, apply appropriate safety margins or performance de-rating and go through a ramp-up process.