Power
You can’t have a reliable station without a reliable power source. For this reason, it’s best to ensure more than an ample supply is available.
Power Sources
Receivers can be powered by either AC or DC. AC power supplied by mains should be used whenever possible as it is generally a more reliable and cheaper power supply than DC. DC supplies usually come in the form of Deep Cycle batteries and require regular charging via solar or another method to maintain power. Also keep in mind that since DC typically requires a solar panel and battery it is a more attractive target for thieves.
AC Supply
If using mains AC power from a typical wall outlet, ensure you use a good quality power adaptor that is rated for the mains power of that region (e.g.: North America is 120 Vrms @ 60 Hz; South America is highly variable, 115-230 Vrms @ 50 or 60 Hz). A good quality adaptor can tolerate this variation in mains voltage which makes them more versatile for projects across multiple countries. A poor quality adaptor will produce an unstable voltage which can damage a receiver or not produce enough power to keep it operational. You may also want to connect your station through a proper surge protector.
The type of adaptor required will depend on the type of receiver being used. For CTT SensorStations and Lotek SRX receivers, these power supplies are usually included with the receiver. SensorGnomes will also be shipped with an AC power supply when ordered through Compudata or RFS Scientific.
If you do not have a power adaptor for your SensorGnome receiver, you can use a standard USB power supply for your phone (“fast charger” or minimum of 2.5 Amps) with a USB cable. For CTT or Lotek receivers, contact your supplier to purchase an adaptor.
If mains power is unreliable and 24/7 coverage is needed, then you may wish wish to connect your station through a battery powered backup power supply.
DC Supply
Powering electronics directly from DC is more complicated since there is no single setup for all stations. Instead, the type and amount of power required will depend largely on region and available resources. In order for a station to be compatible with a DC power supply, it must have a method for converting the voltage of a battery - usually 12 volts - to something the receiver can handle, which ranges from 5 to 18 volts, depending on the model.
CTT SensorStations have built-in voltage converters, allowing them to accept a direct connection to the battery; however, in practice NEVER connect your receiver directly to the battery without a low-voltage cutoff to protect your battery.
SensorGnomes require a DC buck converter to lower the voltage down to 5 volts. This component is standard when purchasing from Compudata. Buck converters are only provided in SensorGnomes if requested by RFS Scientific.
Contact Lotek or see your receivers user manual for more information on SRX series receivers.
Battery
Type
Lead-acid batteries are based on very old technology, but still provide the cheapest, non-volatile power storage for electronics. Lithium-based batteries offer the highest energy density of any commercially available battery, yet they are far more expensive relative to the power they store. In addition, Lithium-based batteries are typically far more volatile, risking chemical spills and fire if they are charged/discharged too quickly, if their temperature is too high or if they are punctured. For these reasons we do not recommend Lithium-based batteries unless space and weight is very limited. Since lithium-based batteries are used so rarely in the Motus network, they will not be discussed further here.
Most people refer to 12-volt lead-acid batteries as “car batteries,” but in this instance you might get the wrong type if that’s what you ask for. This is because car batteries are not designed to be discharged over long periods of time and require constant top-ups, such as from a car’s alternator. In a Motus station, batteries must be able to go down to voltages as low as 10-11 volts each night without losing much capacity - this would ruin the typical car battery in no time!
This is why we use deep-cycle batteries which allow a deep discharge during each charging cycle. Most deep-cycle batteries that are readily available are marine grade (a.k.a.: “marine battery”) which are designed around offering high cranking amps to start up large boat motors, but this is not anything we need in a radio station. Nonetheless, in remote locations with nothing else available, a marine battery will do. While more expensive, specialize solar deep-cycle batteries are also available that are designed provide small amounts of power continuously and varying degress of recharging.
You may also notice there are flooded and sealed lead-acid (SLA) batteries that exist. This refers to whether the internal chemistry can offgas externally. Flooded lead-acid batteries are well known for producing highly flammable hydrogen gas and can be extremely hazardous if not stored in a well-ventilated area. We usually store batteries in a closed tupperware bin which increases the potential of this hazard which is why we recommend SLA batteries. Even so, batteries should be handled with care so as to not puncture the battery casing, potentially allowing the slow release of hydrogen gas over time.
We recommend the following batteries, depending on application:
| Application | Battery type | Capacity |
|---|---|---|
Summer only (12+ hrs of daylight) | Sealed lead-acid (SLA) | 50 Amp-hours |
Sealed lead-acid (SLA) | 75 Amp-hours | |
Lithium Iron Phosphate (LiFePo) | 100 Amp-hours |
All batteries should be rated for 12 Volts. You can also combine two or more batteries in parallel, however they must be the same capacity, brand, and model to reduce the risk of damaging cells.
Capacity
Battery capacity is recorded in Amp-hours (Ah) or Watt-hours (Wh) which is a measurement of current or wattage consumed multiplied by the amount of time current flows. This is helpful because we can easily calculate the amount of Amp-hours we expect our receiver to consume by reviewing the power consumption table or by measuring the current of a connected receiver using a voltmeter. Put simply, a SensorGnome which consumes 0.5 A of power at ~12 volts can theoretically run off a 50 Ah battery for 100 hours (50 Ah / 0.5 A = 100 h). Keep in mind that you won’t ever use the full capacity of a battery since it should not be discharged below 10.5 volts (see Undervoltage Protection). In addition, the capacity will slowly decrease over time with each discharge of the battery, so ensure you add an extra 10-15% of capacity to account for this drop over time. Batteries vary in performance at different temperatures as well and average a shorter lifespan in warmer climates.
When shopping for batteries, we recommend a 50 Ah battery for day lengths greater than 12 hours and a 75 Ah for day lengths under 12 hours.
Cold weather
For cold weather conditions, we recommend self-heating Lithium iron phosphate batteries, however there are some risks involved with deploying this type of battery. While the chemistry is stable and unlikely to combust like typical Lithium-ion batteries, they will be damaged if they are charged when below 0 C (32 F). Self-heated batteries are rated to temperatures as low as -20 C and have protective circuits to prevent them from damaging themselves. Batteries can be charged at even lower temperatures if they are stored in an insulated box. More information about storage and use of Lithium iron phosphate batteries can be found in the PDF below.
Undervoltage Protection
When using any type of battery to power a station, it is recommended to always use undervoltage protection so you do not ruin your battery. While your station may function without one, it greatly reduces battery life and will eventually result in the battery not holding any charge. If using a solar panel to charge the battery, you will require a charge controller with low voltage cutoff. Without a charge controller, you will need to buy a low voltage cutoff, also known as an undervoltage protection module.
We recommend Sunsaver charge controllers with low-voltage cut-off - minimum 10L (depends on size of solar panel), Specifically XXX, and any solar panel (minimum 90 watt).
Motus Pro Tip
Get more than you think is needed. Bigger panels = more power. Bigger batteries = longer-lasting power.
Solar Power
Type
Just like batteries, choosing the right solar panel for your setup can be a daunting task considering the number and types of panels available, but usually your local wholesale retailer of solar panels can help you with picking one out. There are a few different types of solar panels, but the two main ones we deal with are monocrystalline and polycrystalline. The main difference between the two is that monocrystalline cells are on average more expensive, but provide more efficiency and have greater heat tolerance; however, performance appears to vary considerably by manufacturer. Panel efficiency is not necessarily important considering the relatively small panels that we use to begin with. Heat tolerance may be an important consideration in more southern latitudes; we recommend speaking to local suppliers for their recommendation. We generally recommend polycrystalline solar panels to save on costs.
Wattage
The amount of power your panel needs to produce depends on the amount of sun exposure you expect on the shortest day of the year. In Canada, 80 Watt panels have been effective for ¾ of the year, but do not produce enough for continuous operation in the winter. For continuous winter operation, we have been recommending at least 150 Watts by industry experts. In the summer, 50 Watt panels have been sufficient.
Charge Controller
All solar panel setups require a charge controller. This is the device that mediates the power flow between the solar panel and the battery, keeping the panel from overcharging the battery, and ensuring electricity doesn’t flow into the panel at night when the panel voltage drops. We recommend getting a charge controller that also includes undervoltage protection, or ‘low-voltage cutoff’, to further protect the battery from getting overly drained by the receiver, or ‘load’. If your charge controller does not have undervoltage protection, a separate device should be used between the battery and load. See undervoltage protection for more details.
The charge controller most often used by Birds Canada is the MorningStar SunSaver SS-10L-12V. This can charge a 12-volt battery with up to 10 Amps of current and includes a low-voltage cutoff. These have proven robust and longer-lasting than cheaper models, but they can still fail so it’s always important to have spares around.
Power Outages
The main issue is that if the power happens to cut out when the receiver is writing to its storage, it could corrupt the storage and prevent the receiver from ever booting back up.
AC Power
Some sites have AC power available, but there may be problematic power outages. To get around this, you will need an uninterruptible power supply -- or UPS. They come in various shapes and sizes, based on the device being used and the amount of power you intend on drawing.
A generic UPS is commonly available at local electronics stores as they are often used to protect databases and servers. The ratings of UPS can be difficult to interpret, so its important to look at the spec sheet to identify how long it lasts while under load. Usually, it's reported as the number of minutes under full and half load which can be used to calculated the length of time the receiver will last based on the expected load of the receiver. Motus receivers use very little power (usually less than 5 Watts) so you can expect it to last much longer than what is typically advertised.
For example, a UPS on Amazon is rated for 510 Watts and it has a spec sheet that says it lasts for 6 minutes while under half load. That means the battery has a theoretical capacity of (255 Watts) * (0.1 hours) = 25.5 Watt-hours (Wh). That means you can expect a 5 Watt load to last 25.5 Wh / 5 W = 5.1 hours (in theory, probably less in reality).
If you can find the manufacturer specifications you should be able to get more accurate results by using the battery hardware specifications. For example, the CyberPower SX950U-FC has the battery size in the spefications listed as (12 Volts) * (7.2 Amp-hours) = 86.4 Watt-hours. That means a 5 Watt load would last 86.4 Wh / 5 W = 17.28 hours (probably less due to conversion losses).
The nice thing about getting a generic UPS is that nearly all of them also have surge protectors which is important when you have an unreliable AC power supply. However, it's a good idea to test any system if the battery capacity is an important factor in your purchasing decision.
Raspberry-pi based SensorGnomes can use a UPS HAT, but these systems have not been adequately tested so aren't recommended for regular deployments.
Solar Power
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