Power

For any sensor system you have (DIY or commercial) you will need a way to power it. This page will go though a few different options and designs of power systems to suit any of your sensor designs.

For any type of sensor system (DIY or commercial), you will need to provide some sort of power source for long term deployments. How you choose to power them depends largely on your needs, and on what infrastructure you have access to, in the locations you are working. In general there are 3 main types of power you can provide: Batteries, Solar, and Shore/Generator. Each one has its pros and cons, but ultimately all 3 options will provide the power you need to utilize the DIY systems presented in this site, as well as many other off-the-shelf sensors.

If you are planning on using one of these options to power the DIY systems shown on this site, I strongly recommend you run your power source through some sort of external voltage regulator (like this one) and supply 5 - 6v directly to the Vin/VCC and ground pins of the Arduino board (or 3.3v if using the 3.3v Pro Mini). This is a more efficient and stable way to provide power to these systems. Refer to the Sensors page if you want more information on how to power sensors via the Arduino.

Batteries

Batteries are one of the most common options used to power environmental sensors. They provide the most flexibility in where you can deploy a sensor system, and they can be scaled up or down to provide more or less power depending on your deployment needs (i.e. how long you need the sensors to last). In general it is a good idea to try and use rechargeable batteries, as these will allow for repeat deployments without the need to dispose of batteries every time. Amazon and Digikey are two useful online retailors that provide a wide range of battery options. Keep in mind, though, the size of your sensor housing / case. Whatever batteries you decide to use will need to be able to fit inside of your waterproof case (unless you make an external battery housing). So make sure you get measurements of available space inside of your case before you buy any batteries.

One import concept you need to be aware of with batteries is how wiring them in parallel and series affects the total voltage / amperage output by the batteries.

When wiring batteries in parallel, you connect all of the negative terminals together (and then connect that to ground on your system) and then separately, you would then connect all the positive terminals together (and connect that to Vin/ Vcc). When you do this, the overall voltage output by the batteries wired together stays the same, but the overall capacity (amp hours) adds together. For example, if you wired two batteries together in parallel, each of which is a 6v 10Ah battery, you would get a total voltage output of 6v, but a capacity of 20 Ah. This is a great way to wire batteries if you need your system to run for a longer time.

When wiring batteries in series, you connect the positive and negative ends of the batteries together in a chain. At the end of your chain you would have a positive connection coming off of one battery (connecting to Vin/Vcc), and a negative connection coming off of a separate battery (connecting to ground on your system). When batteries are wired like this, their capacity stays the same, but the voltage adds together. If two batteries of 6v and 10 Ah, are wired in series, their overall voltage output would be 12v but still have a capacity of 10 Ah. This is a great way to wire batteries if you need a higher voltage for your system.

Depending on your needs, you can wire batteries together in parallel, or series, or both to achieve the desired voltage and capacity. BUT it is important that you use batteries that are all the same voltage and capacity. Mixing batteries of differing voltage / capacity when wiring them together, can lead to some discharge issues. Also it is important to use all batteries of the same chemistry - i.e. using all Lithium Ion batteries, or all NiMH batteries. Again mixing them can lead to issues. You can read this for a bit more information on wiring batteries in parallel vs series.

For recharging batteries, most chargers you buy will come with a voltage rating. This is the voltage of battery that that particular charger is capable of re-charging. So, if you wire some number of batteries together to achieve a 12 v output, you can re-charge that entire group of batteries at once using a 12 v charger. Just something to keep in mind if you are building out larger battery packs, or creating your own external battery system. Also, like what is discussed in the Waterproofing section of this site, you can fill your battery systems full of mineral oil if you are needing to deploy power in deeper water environments. This is in essence what a Deep Sea SeaBattery is. They are a series of smaller batteries wired together to achieve the desired capacity / output, then the entire unit is filled with oil and sealed.

Lastly you will want to have some estimate of how long your system will run on the batteries you use. Li-ion and NiMH batteries are great because they keep outputting the same voltage until they die, but this also means it can be difficult to know how much life is left in one of these batteries (because they have no fall off of voltage as they loose capacity). So for estimates of time it is best to do a simple calculation. First you will need to know the overall amps used by your sensor system. One way to do this is to hook up your system to a DC external power supply, set the supply the the same voltage as your battery, and let the amps be floating. Then run your sensor system and make note of the amp draw on the power supply. You may need to do a rough average of amp draw over the full sample cycle. Once you have an estimate of amps, you just need to find out what the capacity of your battery is. Most batteries come with some documentation that indicates capacity as Ah (amp hours). If you know this, then simply divide your battery capacity in Ah by total amp draw of the system. So Ah / A = hours of run time. Obviously this is a rough calculation, and there are more precise ways to do this, but this will at least give you a rough estimate. This link has a bit more detail on calculating run time from battery capacity.

Example Li-Ion battery

Example NiMH battery + charger

Credit: Minder. Examples of how two 6v 10Ah batteries are wired together in series and parallel.

Credit: Ecolithiumbattery - example of how batteries are wired in parallel

Credit: Ecolithiumbattery - example of how batteries are wired in series

Credit: Deep Sea Power and Light: example of commercially available sealed external battery system.

Solar Power

If you need these sensor systems to be deployed for a long period of time (months to years) in a more remote area, solar power is probably your best option. Assuming you are using a large enough solar array, with plenty of sun exposure, you can power these or other systems almost indefinitely from a solar power setup. Solar does require a lot more components, and it can be difficult to 'hike' in all that equipment to remote areas. But often that is the best option you have, especially if you are in an area that doesn't have access to a power grid of some sort.

Almost all solar setups (for sensor systems at least) will work the same. You will have some number of solar panels, all running to a solar charge unit. You will also have a large battery connected to that solar charge unit, as well as your sensor system. The solar charge unit is the key to working with solar. It controls the distribution of power: ensuring that your sensor gets power during the day, and that the backup battery is getting charged during the day (when the sun is out). Then it ensures your sensor gets power from the battery at night, or during cloudy / rainy days. In essence, the solar charge unit ensures your sensor (or whatever you have connected to it) continually gets the power it needs: day or night, rain or shine.

The size / number of solar panels you use is mostly dictated by 1. how much power you will be using, and 2. how much sun exposure they will get. You may need larger / more panels if you are deploying them in a more shaded (i.e. forest) or cloudy area. You will also need larger / more panels if you are using a sensor system that has larger power demands. Just make sure your solar charge unit is capable of handling however many panels you end up using (i.e. can handle the total voltage and wattage generated by all panels together).

With any solar setup, you will need to have a battery wired in as well. This battery will provide power to your sensor systems at night, or when the solar panels aren't getting enough sun. It is important to pick a battery that is large enough (i.e. high enough capacity) to supply your sensor system with power for multiple days (without the solar panels). This ensures that you will still be collecting data even if there is a multi-day rain storm or some other cloudy event that limits your solar panels effectiveness. Batteries like this or more traditional marine batteries are often used.

To build out a solar system: start with figuring out how you will mount your panels. You will need some way to keep the panels fixed in place (on the ground, from a pole / tree, etc.), and tilted at an angle (between 30 and 45 degrees from the ground). Also, depending on where you are working, you will want to orient your panels to face different directions to maximize your efficiency. For example, if working in the northern hemisphere, it is best to orient your panels in a southern facing direction. Refer to this site for more explanations for why and how this all works. Once your panels are fixed, run their output wires back to a waterproof enclosure of some sort (often called a solar junction box). This enclosure should contain your solar charge unit, and your battery. Connect the solar panel wires to the charge unit as described by the unit's manual. Wire the battery to the solar charger as well. Then connect the DIY sensor systems' power wires (Vin / Gnd) to an external voltage regulator (setting the output to 5 v) and then to the solar chargers output section (again refer to your units manual for more information). In the layout picture below, the DC OUTPUT would be where you'd connect your sensors' power.

Make sure any wires / circuit boards that are outside of the waterproof enclosure containing your battery and charge unit, are waterproof and protected. Using something like this outdoor wire is a good idea to keep them protected from the elements. It is also generally a good idea to try and bury your wires or weight them down (if they run through the water), especially if you are running wires more than a few feet to equipment. If burying wires, often people will enclose them in conduit pipe to help better protect them.

There are a lot of online resources for how to build out a solar system. For the purposes of powering a few sensors, the solar system can be pretty small and simple (one panel, one battery and a simple controller). But if you are curious about learning more about how to design and build an off-grid solar system you can read through a guide like this.

Example Solar Charge Controller

Example Solar Panel

Example Solar Junction Box

electicaltechnology solar wire up_edited

Example of Solar Charge Unit. Connections at the bottom (green circles) would be where you tie in the solar, battery and sensor connections.

Credit: electicaltechnology.org. Example of solar wiring setup. This diagram shows how to wire for 12 v, but you could do any voltage as long as your DC output is above 5 v.

Credit: Valarm - example of real world solar setup.

Shore / Generator Power

The last common power source for a sensor system is shore power. Shore power is a term used in boating to refer to the power coming form the mainland electrical grid. For the purposes of this discussion shore power is referring to any sort of electrical grid power; such as the power you get from the outlets in your house / lab, or the power you would get from a gas generator. While generators aren't technically grid power, they often still output the same type of power as other grid sources.

Shore power tends to be a very stable source, and can be seen as having nearly unlimited capacity, making it a great choice if you want to run a sensor system indefinitely. The main issue with shore power is that you need to be in an area close to a source, which is often not the reality. But if you happen to be deploying a sensor system somewhere where you have access to an electrical outlet or a generator, then this can be a great option. But a note on generators: they can be a great power source, as long as they are running well and have fuel in them. Obviously a generator that is dying (either from mechanical failure or lack of fuel) isn't of much use. Also some generators can have fluctuations in their power output as they run low on fuel. Often people will have a battery backup surge protector in-between their sensor and the generator. These can help protect your sensor from major swings in power.

Like all the other power sources, the power coming from an electrical outlet will need to be converted to a 5 v DC power source for your sensor system (or whatever voltage your sensors need). Depending on the country, the type of power coming out of the wall will be different. For the purposes of the example below, I am going to walk through how to do this for the United States.

Most standard wall outlets in the United State will output 120 v of AC power. For the DIY sensor system used on this site, we want to supply them with 5 v of DC power. The easiest way to do this conversion is to use a USB wall charger / adapter (like what you use to plug in your phone to recharge it). Something like this, will output 5v of DC power from the USB port once it is plugged into a standard wall outlet. From there all you need to do is run a USB power wire (basically a USB connection that goes to 2 wires) to your VCC / Ground pins of your Arduino (or to an external voltage regulator.

There are other types of AC to DC converters you can use if you need a different output voltage. Something like this unit will output 12 v of DC power once it is plugged into a standard US wall outlet. Then from there you could connect in a DC to DC converter and set your output voltage to whatever you need (as long as it is below 12 v).

Adapt this basic layout to fit your specific needs based on the type of power coming from your electrical grid / generator. As noted different countries (and different outlet types) will supply various voltages. In the USA the most common outlet types will supply 120 or 220 v. Power outlets in Germany are typically 230 v while China is 220 v. So just look up (or test with a volt meter) what the power source is in the location you are installing your system. As for generators: most portable gas generators (like the one pictured below) will output 120 v, though some larger industrial ones are capable of 220 v. They also will typically have a standard wall outlet available for plug in somewhere on the unit.

As you can see no matter where you are doing your work, or what type of system you need to power, there is a potential solution to fill your needs. What will work best, largely depends on what types of resources your have access to, and where you want to deploy your system. Hopefully these short summaries can help in your decision making, and can help guide you forward with building out an appropriate power system.

Example AC to DC converter

Example Gas Generator

Simple example of how to get power from a wall outlet to your sensors. The adapter will convert the 120 v AC power from the wall to 5v DC. Then the USB connection provides the necessary wiring for your sensor.

Typical example of a gasoline generator.