Power supply options for beacons

The best and recommended way to power beacons of indoor positioning system is to have a fixed external power supply.

For Super-Beacons we recommend regular AC to USB converters or chargers. For Industrial Super-Beacons – AC to +12V converters or chargers.

Our converters and chargers support ~110V and ~220V. External power supplies give a peace of mind and freedom to focus on other aspects of the system.

However, if the fixed power supply is not feasible, there are different battery options available. There are even more exotic options, like solar panels, that could be useful in some special applications as well.

Defining factors for the power supply options

Powering of modems is not a problem

First of all, notice that we don’t discuss powering of modems. Modems are nearly always active. They typically don’t sleep. In the majority of cases they are even computer connected. Thus, powering them is typically not an issue: either they are USB connected and powered via USB, for example, Modem v5.1; or the power is easily available via ~220V to +12V converter for the Super-Modem.

Mobile beacons vs. Stationary beacons

Stationary beacons (anchors) have fixed locations. At a first glance one may think that to provide the power to them is not a problem and the main focus shall be on the mobile beacons. Thus, there are claims of 1 year, 3 year, 5 year battery lifetime for tags in UWB or BLE systems…

But in the reality, it is opposite in the majority of cases:

  • To provide power to stationary beacons is simply costly: wires, work, permits, restrictions
  • The stationary beacons are placed high on the wall or ceilings and often one needs a special permit to access to the area in order to install the beacons or to wire the power supply or to change the depleted battery. Such works are often expensive or restricted, i.e. even more expensive
  • Basic ~110/220V wiring + converters may be the least expensive option. PoE can be costly and an overshoot, particularly, if you don’t need Ethernet. Try to find solutions that wouldn’t require costly data wiring to each stationary beacon. Wireless options for data connectivity is the best. Wireless + a basic fixed power supply
  • Batteries are not recommended for stationary beacons unless absolutely not avoidable, because with batteries there are always risks and limitations: (1) accidentally you forget some settings and the battery will run out of energy in days rather then weeks or months; (2) Sooner or later the battery must replaced (very bad) or re-charged – potential interruption and additional work; (3) you will have to sacrifice/compromise the performance in order to find a balance between the battery lifetime, battery costs and the update rate, range, etc.
  • Mobile beacons, on the other hand, are typically either powered by the electrical grid of a robot, drone, forklift, or simply charged often (daily, weekly), because unlike stationary beacons their easily accessible and people used to charge their devices: phones, cameras, players, lights, etc.

Therefore, it is important to very clearly understand that powering of mobile beacons (tags) is typically not a problem. But powering of stationary beacons could be due to the cost or limitations of wiring or size and costs of required batteries and associated battery replacement/utilization and recharging costs.

Beacons sleep most of the time

Like the majority of other modern electronic devices, Marvelmind beacons sleep most of the time. They wake for a very short time, do the job, and go to sleep immediately in order to save energy.

Beacons have a duty cycle with highly irregular power consumption: some milliseconds of relatively high current during the active phase are followed by tens or hundreds of milliseconds of nearly zero current during the sleep phase. The difference in current consumption between the modes is 1000:1 or even more.

Typical power consumption pattern:

  • Wake up into a low consumption mode. Wait for a trigger via radio from the modem
  • Receive a radio signal from the modem – “time reset”
  • Either emit or receive ultrasound – depending on the mode of operations
  • Process the data
  • Transmit the resulting data to the modem and to an external user connected to the beacons
  • Go to sleep until the beginning of the next cycle

As a conclusion:

  • It is not very correct to talk about “average power consumption”. It is possible to talk about “the average power consumption with a specified location update rate and other settings”
  • Battery lifetime most of all depends on the location update rate. The dependence nearly linear: for 1Hz the battery lifetime will be nearly 10 times longer than for 10Hz

Location update rate is the most important parameter for battery lifetime

As discussed above, the beacons sleep most of the time. Thus, it is possible to calculate a required energy for a single location update. By knowing that energy and by knowing the battery capacity, it is possible to calculate the number of location updates the battery can provide before it will depleted.

For example:

  • The battery has a capacity of 1Ah
  • The beacon consumes 1mAs (0.001mA*1/3600h)
  • The battery will be able to provide roughly: 1Ah/1mAs=3 600 000 location updates
  • You can consume them with 1Hz or with 8Hz update rate, for example
  • With 1Hz location update rate it will result in 3.6e6/(1*60*60*24)=41 days
  • With 8Hz location update rate it will result in 3.6e6/(8*60*60*24)=5.1 days

As it can be seen, the difference is drastic.

In reality, the difference is less dramatic, because there is a current in sleep mode as well, which is not zero after all. Thus, if the sleep time is long, the sleep current starts notably contributing to the total power consumption. For a 1-year battery lifetime, the sleep current consumption may prevail over the active current consumption.

Recommended power supply options

Stationary beacons

External fixed power supply is the best and most reliable choice.

AC to USB converter

  • Supports both 110V and 220V AC
  • It is a typical +5V USB converter. Other similar USB converters or even USB chargers giving 0.5A or more work just fine
  • Intended for the wide range of applications when the beacon/modem is stationary and AC power supply is easily available
  • Usually, the least expensive and the most recommended option
  • Supports: Super-Beacons, Beacons HW v4.9, Mini-TX, Mini-RX, Beacon-UWB, Watch, Helmet, Jacket, Cap, Modem v5.1, Modem HW v4.9 and their outdoor versions

AC to +12V converter

  • Supports both 110V and 220V AC
  • It is a special IP67 converter for Industrial beacons and Super-Modem
  • Intended for the wide range of applications when Industrial Beacons or Super-Modem are stationary and the AC power supply is easily available
  • Usually, the least expensive and the most recommended option
  • Supports all types Industrial Beacons: Super-Beacon, Industrial-RX, Industrial-TX. Supports Super-Modem

Mobile beacons

External DC-DC power converters is the best and most reliable choice for mobile beacons:

DC to USB or DC to +12V converter

  • Supports up to +48V DC input voltage
  • There are two variants for the converter: (1) with USB output and USB connector, (2) with +12V output and mating connector for Industrial beacons and Super-Modem
  • Intended for the wide range of applications when the beacons/modems are mobile, for example, installed on a robot, drone or forklift and the DC supply is available from the mobile vehicle
  • Usually, the least expensive and the most recommended option
  • Supports all types of beacons

In many cases, an external USB power supply is available and you can simply connect a micro-USB connector to the beacon and get both power and the data stream to and from, for example, Raspberry Pi or nVidia Jetson.

Similar can be done with Industrial beacon or modem, if external +12V (+6V…+15V) available from the onboard sources of the mobile vehicle/drone/robot.

Battery power supply

Internal battery

The majority of Marvelmind devices have internal LiPol battery. Typically, it is a 3.6V cell. For example:

  • Super-Beacons: 900-1000mAh & 3,6V
  • Mini-RX (Helmet, Jacket, Cap): 500-700mAh & 3.6V
  • Mini-TX: 500mAh & 3.6V

Some devices have additional external batteries, for example, Headlight: it has 2 larger-capacity external LiPol cells that extend the capacity of the internal battery by the factor of 3-5 – depending on the chosen external cells.

Other devices, like robots, have massive internal batteries – up to 96Wh for Boxie and expandable; and 740Wh and expandable for Robot v100. Those batteries supply the motors, electronics and the beacons on board of the robots.

Industrial beacons don't have internal batteries

Industrial beacons intentionally don’t have internal batteries:

  • The beacons are designed to work in an extended temperature range of -40C..+60C (provided by design. Not tested nor guaranteed). But regular LiPol batteries can’t take a charge with temperatures below 0C – they may be irreparably destroyed. Moreover, the charge inside the batteries drop by a factor of 2-3 at least, when the temperature drops to -20C..-40C, thus making them low capacity
  • LiPol batteries are good, but they are one of the least reliable element of the system and even the best batteries are prone to bulging and other bad surprises. It is particularly undesirable for industrial beacons

External battery options

USB power banks

USB power banks are the simplest and the most straightforward way to expand the battery lifetime of Super-Beacons or other USB powered beacons. Notice the following though:

  • The majority of the USB power banks are too “smart” and they cut off power supply when the beacon is fully charged and doesn’t require energy. In order to restart it, one needs to connect and disconnect the power bank or press the ON button, which is impossible if the beacon is high off the ground, for example. See more in the video
  • Power banks are often misleading. They often state, for example, 10,000mAh capacity highly visible, but it could be the capacity of the internal 3.6V LiPol battery – not the resulting +5V battery. Thus, the total energy capacity is not 10*5=50Wh, but 10*3.6=36Wh. Be aware
  • Many power banks simply lie about their capacity. It can be written 15,000mAh, whereas the real capacity is just 5,000mAh
  • Resulting battery lifetime increase would be close to Battery capacity/internal battery capacity using Measure and Extrapolate method. Thus, if you have a fully charged 10,000mAh power bank, you can expect 10x increase in the beacon working time – from 3 days to 1 month – with 8Hz and default settings for Super-Beacons. With power saving features enabled and update rate of 0.5Hz, the same power bank could last for a year. But that would already depend on the self-discharging of the power bank. They often have much shorter self-discharging time

Battery-12V-5Ah-Outdoor

External Battery-12V-5Ah-Outdoor is the simplest battery supply option for Industrial beacons. With default settings and 8Hz update rate it provides about 2 weeks of autonomy (depending on the mode and size of a submap). With different settings and with slower update rate, it can last for a year, if needed.

External Battery-12V-5Ah-Outdoor can be charged with Charger-12V-1A. You can use another other charger for 12.6V LiPol batteries, but our charger is already equipped with the mating IP67 connector for easy use.

Customized high-capacity LiPol batteries

For those he really need batteries, we are offering customized external LiPol batteries. Then can be literally any capacity, voltage and and size. You need a 1 year battery lifetime – not a problem! 5years? – not a problem either.

Options:

  • LiPol cell 3.6V & 43Ah – up to 1-2 years for Super-Beacons
  • Similar options for smaller or larger capacity or different shape or implementation – on request

Battery lifetime

Mathematical calculations

Though possible, it is rather difficult to calculate mathematically an expected battery lifetime because:

  • Many moving variables
  • High uncertainty of real power consumption, because it consists of pulses with not exactly known current and not exactly known time
  • Too high risk of not taking into account some factors that may eventually prevail: battery leakage current, undocumented surge currents, effect of different temperatures on the current consumption and real battery capacity, etc.

Besides, pure mathematical calculations live too much room for uncertainty and a design to measure in practice in order to prove the validity of the results

Pure power consumption measurements

It is possible to measure the current consumption of each element of a cycle and integrate. It is possible, but difficult still not very reliable, because:

  • It is simply rather difficult to measure 1000mA and 0.1uA during the same cycle. Each pulse can be as short as a millisecond or even less in some case
  • High uncertainty due different temperatures and multiple modes of operations
  • Measurement devices may alter the real power consumption

Measure and extrapolate

The best option in practice is to measure the real battery lifetime and extrapolate it keeping in mind underlying physics:

  • It is possible to estimate in a point with given settings. Other settings and another mode of operation will require different calculations
  • For example, if with internal battery of 1Ah the beacon worked 3 days (72h), it could be pretty confidently confirmed that with 10Ah battery it will work 30 days
  • If the beacon worked 3 days with 8Hz, the expected battery lifetime with 1Hz will be slightly less than 24 days. (Note, that it is a subject to power saving features. In some cases for more stability or for more accuracy the power saving features can disabled, thus the reduction from 8Hz to 1Hz update rate may bring only very little difference)

Other factors affecting on power consumption and battery lifetime

There are many affecting factors on the battery lifetime. The most affecting – the location update rate – already covered earlier. What else:

  • The size of the submap. The larger the distance, the longer the system has to listen to the ultrasound and the more it has to process the data. Thus, the current consumption per cycle is longer. In some case – large submaps of 30m and the highest possible update rate – the beacons doesn’t sleep at all
  • Radio profile. The higher the baud rate (38kbps vs. 500kbps), the longer radio shall be on and the more energy it will consume during this time. It is better for the working range and for the interference resistance to have 38kbps radio profile. But it is better for the battery to have 500kbps radio profile
  • The mode of operation. Ultrasound transmitting beacons have very short (1ms), but very powerful peaks. But then they sleep very long in terms of the cycle. The ultrasound receiving beacons do not have high-power consumption peaks. But they have to listen to the ultrasound and process it digitally for significantly longer time (100ms) than the ultrasound transmitting beacons. Thus, the resulting total power consumption during the cycle can be even larger
  • Temperature. Beacons can work with down to -20C, but remember NOT to charge them before they have temperature above 0C. Negative temperatures reduce the battery capacity by the factor of 2..3 or even more in some case

If anything is unclear, contact us via info@marvelmind.com