The equipment used in the field is all powered off of 12VDC batteries. A very rough rule of thumb is that it takes about 10AH of capacity to run a typical reftek site for a single day. This assumes a battery that is in very good condition and fully charged. That rate goes down for smaller capacity batteries and up for larger capacity batteries (or arrays of batteries) because of voltage drops induced by the high current draw of disk spinup. The voltage drop will cause the disk spinup to fail or even for the DAS to reboot. Higher capacity batteries see less voltage drop, so usually fare better. A single 92AH deep cycle battery will run the site for ~1 week and a 31AH deep cycle battery will run a site for ~2.5 days. Two 92AH batteries in parallel should be good for close to 3 weeks.
It is preferable to have a way of recharging the batteries at the site. Solar Panels or AC chargers are typically used to do this. Which, if any, is determined by the site location and security concerns.
We have seen some DASs operate on as little as 10VDC, but typically they should have at least 11.5 volts. Below 11.5VDC (depending on battery capacity) disks may not be able to spin up. In a low voltage situation such as this, the battery voltage can end up "cratering" (dropping really fast). What happens is that if the DAS reboots, it will check its parameters and determine whether a disk is expected. If it is, it tries to spin the disk. When the disk spinup is attempted, the voltage drops and the DAS reboots, repeating this cycle forever. A charging system will most likely be unable to keep up with the draw as the frequent disk spinups cause the overall discharge rate to exceed the charging capacity. Even if the DAS eventually shuts all the way down, if an FBA (or other load) is hooked to the battery, the battery will continue to discharge.
Low voltage disconnects (LVDs) should be used whenever possible. The LVD disconnects the load (reftek, fba interface, etc...) from the battery if the voltage drops below a preset level (11.5VDC typically) and reconnects it when the voltage rises to a different preset level (typically 12.5 or 13VDC). The LVD serves several purposes:
The MorningStar SunSaver SS6L or SS10L are a preferred system since they use a non-shorting input which allows a charger or power supply to be used for charging as well as solar panels.
| PSC-12500-A Charger | 0.1A in fast charge mode, which equates to 12W (about a third as much as a 40W light bulb) |
| PSC-12500-A Charger | Fast rate charges at about 400ma and drops as need be |
| DAS | 240ma typical, fluctuates between 200-300ma during boot |
| DRS | 600ma once spun up, 1700ma during spinup (this will vary depending on drive model) |
| GPS | 130ma while attempting lock, 30ma at start of boot |
| FBA (using active interfaces) | 40ma quiescent, up to 50ma if being shaken vigorously |
As this table shows, the disk uses more power than any other device (while running). Having more RAM in the DAS makes a HUGE difference in the overall site power consumption as this will cause the disk to spin up less frequently.
The GPS systems are typically configured to come on once an hour for up to 20 minutes to attempt satellite time lock. If the clock does lock, the GPS will shutdown after locking for a couple minutes.
Large offsets in the FBA will cause increased power consumption.