We want to better understand the spotter’s power system architecture and be confident that it can support our mooring equipment energy requirements over many weeks/months.
The scenario we need to avoid is where we deplete more energy than the solar panels can replenish on a daily basis, causing long term battery drain.
Q1: Do you have a block diagram of the spotter’s internal power system? We want to understand the power path between solar, battery, and Bristlemouth loads.
Q2: Do you have guidance on how much energy (Wh) the spotter can supply over Bristlemouth under various solar conditions?
Q3: The spec lists 5x 2W solar panels. Is this the maximum power from the panel’s spec sheet, or is this the realistic power accounting for panel angle and only some panels facing the sun?
Here’s what I’ve learnt:
-no solar with a fully charged solar battery and a 2.5W load lasted 12 hours 30 minutes before power to dev kit was cut so I would assume about 30Wh available battery capacity
-the 10W solar rating is max power rating of the cells assuming perfect insolation. in mid latitude locations a good rule of thumb for average energy production is about 5Wh/W but that will vary by season (summer better, winter worse). So on a sunny day in early spring I would expect about maybe 30Wh from the solar somewhat arbitrarily adjusting for the mixed azimuth of the solar cells (i.e. some are facing the sun some are not).
So in summary my guess is that on average there’s about 30Wh of energy available daily. With that said there will be many days where there’s almost no solar energy (really cloudy winter day) and some days where there’s a lot more.
In case you missed the great session @sldiehl led at BristleCon, I’ve attached a PDF of the Dev Kit Super-user guide [here], which goes over some of the details of the Bristlemouth power system.
(We also have a ticket high in our documentation todo list to convert this presentation to a guide in the Bristlemouth docs - cc @estackpole / @zack_j).
Q1: We can’t share a detailed schematic of the Spotter power management system, but a general block diagram is:
The Charge Management System does the solar power point tracking and controls when to charge vs discharge the battery based on available solar power. There’s a more detailed description of Bristlemouth power systems in the Super-user guide.
Q2: This ends up being a pretty tricky question, and one that we put a lot of effort into internally. It depends heavily on latitude, season, and also specific location. We have in-progress simulation and modeling tools I hope to be able to share externally this year that predict exactly how a system of a particular configuration will behave, but some testing and monitoring are needed to dial this in. Until such tools are available, we can offer dedicated assistance for the specific challenges of your mission, and some general coarse guidance:
A Spotter with no Bristlemouth payloads will be year-round sustainable off of solar power to ~60º latitudes (give or take a few degrees based on seasonal weather of the specific location).
At latitudes > 40º, you’ll need to duty-cycle the BM bus using Bridge sampling configurations to keep average external load to 10s of mW.
Latitudes between 30º and 40º, you’ll be able to support an external average load in the neighborhood of 100mW to 300mW.
In the tropics, you’ll be able to support external average loads of 300mW to 1W.
++ Checkout the PWR.csv SD card log file (described in Spotter user docs [here]) to get a granular readout of your system’s power consumption when you test.
Note: - there are a number of under-the-hood configurations in the Spotter to reduce the system’s hotel power (default configuration results in 150mW consumed by Spotter), and to duty cycle and manage the BM bus. If you provide more details on what and where you want to deploy, we can help dial in some settings to maximize deployment goals.
Q3: This is the maximum power from the panel’s spec. Realistic peak solar power generation of Spotter at optimum sun angle is a little under 5W total, and will typically be 2-3W on a random given sunny day.
@peterive - Yep - spot on. There’s a 47Wh battery pack in the Spotter.
The system is configured to charge to 95% to maximize life.
The system will cut off the BM supply at ~15% to preserve telemetry and delay brownout.
At 2.5W load end-to-end efficiency from battery through BM to load should be 85% - 90%.
The Spotter + BM system will consume 250mW to 300mW in default configuration.
=> 30Wh available to a BM load with a full battery and no solar input is right on what we’d expect.
