Chapter 4. Operation
4.1 Hibernation mode
In normal use, the PPM's charge-control and monitoring circuitry consumes a small amount of power. During shipping or storage, this would deplete the battery and, potentially, shorten its life. To prevent this, the PPM has a hibernation mode (also known as "sleep mode")..Almost no power is consumed during hibernation and no power is provided to the output connector.
This section discusses :
waking the PPM from hibernation mode, which must be done before use; and
putting the PPM back into hibernation, which is strongly recommended before shipping or storage, in order to prolong the battery life.
4.1.1 Waking the PPM from hibernation
The PPM will wake from hibernation when it senses a DC voltage on its charge input. The voltage must be between +1 V and +30 V and must be of the correct polarity (although the unit itself is protected from reverse-polarity connections).
To wake the PPM, any suitable voltage source can be used, including a multimeter set to "continuity test mode" or "diode test" mode. Note the polarity required.
Once woken, the Power Module’s internal charge control and monitoring circuitry will start consuming a small amount of power. At this point, the battery voltage will become available at the Power output connector, provided sufficient charge is available in the internal cells.
Note: Before shipping, the unit’s internal battery is factory-charged to approximately 50% of its capacity , providing an output of between 7.2 and 7.4 volts. This prolongs the battery life. See section 6.1 for more details.
For installations with solar panels, if the panels are exposed to light, simply connecting them will wake the PPM from hibernation.
Caution: Before connecting solar panels to the PPM, please read the notes and instructions in section 4.2.
4.1.2 Putting the PPM into hibernation mode
Note: Before putting the PPM into hibernation, arrange for the charge on the unit’s internal battery to be approximately 50% of its capacity , providing an output of between 7.2 and 7.4 volts. This prolongs the battery life. See section 6.1 for more details.
The PPM can be put into hibernation mode in two ways:
using the web interface of a connected Certimus; or
using an RS232 diagnostic cable and a PC with a terminal emulator.
These two methods are described in the following sections.
Note: The diagnostic cable is not normally supplied and must be ordered separately from the PPM.
4.1.3 Using the web interface
When the PPM is powering a Certimus, visit the web page of the Certimus and select the "Power" tab.
Note: The "Power" tab of the Certimus' web interface is only present when the Certimus has been booted with a PM connected.
Left-click on the 
button. This enqueues the shutdown: The PPM will continue to function until the charge input voltage drops below 1 Volt. At this point, communication with the PPM will be lost and the data displayed for it will freeze. The power output will be turned off so, if the Certimus doesn’t have power available from PoE on the Ethernet cable, it will power down at this point.
4.1.4 Using a diagnostic cable (not supplied)
The PPM has an RS232 serial console which is available via pins on the Charge Input connector. To access it, a diagnostic cable can be constructed. This cable should connect the RS232 pins on the Charge Input connector (see section 6.2.1) to the appropriate pins of the serial port of a PC or laptop running terminal emulation software such as PuTTY or Minicom. Configure the emulator for a line-speed of 115,200 Baud.
Once connected, enter the command
bat ship 1
If the diagnostic cable is designed to also provide power, the PPM will continue to function until the charge input voltage drops below 1 Volt.
4.2 Working with solar panels
4.2.1 Connections and polarities
Warning: Never connect or disconnect either end of the charge cable while the solar panel is illuminated. When making or breaking DC circuits, an electrical arc may form which can tarnish or damage contact materials, resulting in increased resistance. This can then cause a risk of over-heating, leading to connector damage and, potentially, fire.
The industry standard connector for Solar Panels is the MC4, a single-pole, IP67 weather-proof (when assembled correctly with appropriate cables) connector which is available in two mating forms.
Note: While MC4 connectors can be mated by hand, a special tool is required to disconnect them.
Note: If the chosen Solar Panel has different connector polarities or types, an alternative connection method must be chosen. Take care to maintain the IP67 environmental protection of the connections.
Caution: It is important not to confuse the genders of the two connectors. The female-looking body, shown on the left below, actually contains a pin contact and is officially known as the male connector. Similarly, the male-looking body on the right contains the matching socket contact and this is, officially, the female connector. The illustration below shows the contacts above their corresponding connector bodies: male on the left and female on the right.
One connector of each type is required for each connection so it is important to distrust any polarity markings ( '+' or '-' symbols, red or black bands etc) and check the relevant specifications before connecting.
In standard use, the positive output from the solar panel is terminated with a female connector (see the caution above regarding connector gender) and the negative return is terminated with a male connector.
Note: It may be useful to remember that the “nose” of the female connectors points in the direction of flow of conventional current.
4.2.2 Installation considerations
When planning the installation site, consideration should be give to possible electrical storms, wind conditions, local temperature variations and incident light.
These are each discussed in the following sections.
4.2.2.1 Electrical storms
An exposed installation in a region affected by electrical storms requires some form of lightning protection.
Warning: Lightning strikes can cause lethal voltages, very high currents and risk of fire. If in any doubt, seek professional advice when installing in affected regions.
Caution: No electrical equipment can withstand a direct hit from a lightning strike. Even strikes some distance from the installation can cause serious damage in two ways: induced currents in electrical connections and voltage differences between ground points caused by high currents flowing through the earth. In general, only partial protection can be provided.
One method of partial protection consists of a lightning rod: a conductive target mounted on a mast. The target is connected via a high-ampacity cable to a ground point. In the event of a lightning strike, extremely high currents can flow to ground, causing significant horizontal voltage gradients. For this reason, the grounding point for the lightning rod should be as far as practical from the grounding point for the seismic installation and the installation should have only one ground point.
A lightning rod provides a cone of protection with a radius equal to its height.
4.2.2.2 Wind considerations
Solar panels exposed to winds cause vortices and eddies downwind of the panel. These can couple to the ground, creating earth movements which can be detected by seismometers. For this reason, the solar panel(s) should be installed a suitable distance away from the instrument's emplacement.
4.2.2.3 Temperature considerations
The PPM must be protected from extreme temperatures during operation. If the ambient temperature falls below 0° C or rises above 45° C, charging of the lithium-ion cells inside the PPM will be adversely affected.
If the chosen installation site may get too cold, thermal insulation around the PPM may maintain its temperature by trapping its own operational heat energy. If the site may get too hot, burial of the PPM may be required to protect the PPM from direct sunlight.
For more information, please refer to section 6.1.2.
4.2.2.4 Incident light
To maximise the chance of harvesting energy, the panel should be aligned so that the surface is perpendicular to the incident sunlight. As the sun traverses across the sky during the day, however, the instantaneous optimum alignment will change. A compromise alignment needs to be chosen to maximise the total energy captured across the deployment duration. There are many on-line ‘Solar Panel orientation calculators’ available which can provide information regarding the best orientation of the panel, given the location and season.
When deploying in winter, note that the amount of foliage on surrounding plants and trees can increase dramatically in the spring and summer. Take care not to choose a location which could end up being in shadow.
4.2.3 Principle of operation
4.2.3.1 Charge curves
Solar panels provide energy at different rates during daylight periods, depending on the intensity and angle of the incident light, and not at all during darkness. The total energy provided by the solar panels, summed over a day, must be higher than that required by the Certimus and any ancillary equipment, also summed over a day. If the length of a day is likely to vary over the lifetime of the deployment, this must also be taken into consideration. For this reason, the nominal power - expressed in Watts - of the required solar panel(s) will be considerably higher than the average power draw of the connected equipment.
In the graph below, the incoming power from the solar panel(s) is shown as the red curve and the outgoing power for the instrumentation and ancillaries is shown by the green curve. Total energy is the integral of power with respect to time so it is represented by the areas under the curves. The area under the red curve must be more than the area under the green curve for the installation to be feasible. If this is not the case, a larger, more powereful panel must be used or additional panels installed.
The PPM's battery will be charging whenever the red curve is above the green curve (unless it is already fully-charged) and discharging whenever it is below it.
We can overlay a third curve showing the percentage charge of the battery. This is proportional to the amount of energy stored and is shown by the blue curve below:
It can be seen that, in this example, the second day has not provided enough energy to fully charge the battery but the third day has provided more than enough to compensate.
The PPM is designed for use with "12 volt" solar panels. Note that this is a nominal voltage and the actual output of the panel will vary between zero and around 18 volts.
Caution: The voltage input to the PPM must never exceed 32 volts.
The PPM is designed to work with a wide range of 12 volt solar panels. Modern, mono-crystalline photovoltaic panels are recommended for their high efficiency. Flexible “roll up”, semi-flexible and foldable versions are available, which can significantly simplify installations with poor accessibility.
4.2.3.2 Maximum Power Point Tracking
Nominal 12 volts panels typically output around 18 V when operating in strong light. This voltage will drop under load because solar panels have an inherently high source resistance. This makes them sensitive to the amount of current drawn from them. For any given light condition, if too much current is drawn, the output voltage will drop to a low level and, because energy varies with the square of the voltage, the amount of energy harvested will decrease dramatically.
For this reason,the PPM has an integrated MPPT (Maximum Power Point Tracking) charge controller and will automatically track the panel’s optimum operating point to ensure that it harvests energy at the maximum achievable level of power, regardless of changing light conditions. It does this by adjusting its own input impedance, which determines the current drawn from the panel. The PPM can attain a maximum instantaneous charge input power of approximately 80 Watts. The input current is limited to 8 A.
4.3 Stand-alone working
4.3.1 Operation
The PPM can be used to provide power to a Certimus without using solar panels. In this mode, the PPM will continue to provide power until its battery voltage reaches 6 V, at which point it will automatically shut itself off in order to protect the cells from damage.
Note: If the PPM is operated until it has shut itself down due to low battery voltage, it must then be recharged to at least 6.4 V before the output power is turned on again.
The initial charge on the battery limits the duration of the deployment so it is important to fully charge the PPM prior to installation. This maximises the "up-time" of the system. Monitor the supplied current when charging the PPM: this will fall to zero and charging will automatically stop when the battery voltage reaches approximately 8.4 V.
Provided that the PPM has sufficient charge and has been woken up (see section 4.1.1), it is only necessary to connect the PPM’s Power Out to the Certimus’ Power Input (using the supplied cable). The PPM will then immediately output power to the Certimus without requiring further action.
4.3.2 Charging
The PPM can be charged using an DC power supply capable of providing a voltage between approximately 10 and 32 volts. The PPM is fitted with over-voltage protections so, if the input voltage exceeds 36 V, charging will be disabled in order to protect the cells.
Note: Because of the MPPT function (see section 4.2.3.2), if the input voltage is suddenly reduced, the input current may drop to zero for a short period while the MPPT controller adjusts the input impedance to suit.
Caution: If the PPM has been left totally discharged for a very long time, it will need to be reconditioned in order to avoid damaging the cells. The reconditioning process involves structured charging with a very low initial current. Please seek advice in this situation.