I want to power an Arduino project for several weeks on a remote location. At the location, data is gathered and sent over the internet. The project runs on 5V and draws 200mAh max. I need a power source that runs on its own, without cables.

To do so, I was looking into big batteries. My idea was to use a battery like this. It has a capacity of 50Ah and an output of 6V which I can downstep with a voltage regulator.

I have several questions:

  1. How safe is this battery? Can directly touching the contacts cause harm?
  2. Can my project draw 200mAh or will the battery push out more due to its high capacity?
  3. And if it's dangerous, how can I protect myself and my system?

Hope my information in this post is sufficient, thanks for any responses.

  • $\begingroup$ How is device connected to the internet? Ethernet. Wifi, cellular etc $\endgroup$ – Mahendra Gunawardena Jul 14 '16 at 11:08
  • $\begingroup$ I'm using a Particle Photon. $\endgroup$ – Len Jul 14 '16 at 11:09
  • $\begingroup$ Based on my research you are using wifi Particle Photon. Wifi is requires a lot of current for transmission. A part that I am using take about 350mA for transmission. So what I will do is limit the amount of transmission depending on the requirement. Example if you are collecting weather data then transmit every hour. This way you can use a smaller battery. $\endgroup$ – Mahendra Gunawardena Jul 14 '16 at 11:16
  • $\begingroup$ That's not really what I'm asking. The Photon has a typical usage of 76mA with some peaks to 150mA. I need a huge battery because it will be placed in a remote location. I cannot change the batteries and using the wallsocket for power isn't an option. $\endgroup$ – Len Jul 14 '16 at 11:17
  • $\begingroup$ What I am saying is that if you manage your power utilization, you will not need a huge battery, that is very expensive to transport to a remote location. $\endgroup$ – Mahendra Gunawardena Jul 14 '16 at 11:32
  1. How safe the battery is depends on the build quality. Make sure you get a good one (maybe more expensive...). Also the conditions in which the battery (and the Arduino) will operate matter: humidity temperature, ...
  2. Your project draws the current of 200mA. A battery never 'pushes'. (for that matter, NO source pushes power... Tension [Volt] STANDS, Current [Ampere] RUNS.) Consider this: the power grid is capable of delivering... thousands(???) of amperes. good thing it doesn't do that to every appliance in your house :p
  3. it's not dangerous, however...

which I can downstep with a voltage regulator.

be careful. 1V doesn't see much, but voltage regulator has to dissipate the excess power. this means: 1V x 200mA (the 200mA runs of course also through the regulator) means that 0,2W has to be dissipated by the regulator. Make sure it can get rid o this power. Also, this is power that is lost.

maybe it is better to get a 12V battery (which are also more compact) and get a descent DC/DC converter (+90% efficiency is easily available) which gives you a nice 5V output.

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  • $\begingroup$ Thanks for your response. About (1), assuming the battery is of good quality, does touching the contacts create any danger? I've read that 6V or 12V for that matter is not strong enough to create a circuit through a body as our bodies have a very high resistance. Is this correct? And in which case could it cause problems? About (2), so basically, even if I have a 100Ah, and my application only draws 1Ah, it essentially, in an ideal situation, allows my application to run 100 hours on that power source? About (3), yes. I am aware, I'm looking into all options, thanks for your advice. $\endgroup$ – Len Jul 14 '16 at 8:15
  • $\begingroup$ 1) you're not going to get shocked from 6V. However, higher voltages might give you a bit of a thrill ;-) (a 12V or 24V car battery (100Ah) might get you burned. Also, DC is worse for you body than AC. Be careful anyway! 2) correct (if you don't take the losses into account. Also, a battery cannot be drained completely. (have a look at discharging charts). Your 6V battery, connected to your regulator (which also need a dV of a couple of 100mV will drop the output when the battery level is going down (eg at a battery voltage of 5,5V). Then your Arduine will halt - no power! $\endgroup$ – Tim Denis Jul 14 '16 at 14:38
  • $\begingroup$ 3) if you use a DC/DC converter (input range of 9-36V?) on a 24V battery, you're able to get way more power from the battery: even when voltage is down to 22V or 20V, the DC/DC does the job (on a rechargeable battery this might be damaging the battery... Another thought: Why not use a solar panel, a bootscap and a DC/DC? $\endgroup$ – Tim Denis Jul 14 '16 at 14:44
  • $\begingroup$ I've looked into a solar panel, but the device is going to be placed inside. Furthermore, solar panels aren't really reliable in their voltage output. $\endgroup$ – Len Jul 14 '16 at 15:09
  • $\begingroup$ indeed, they are not, but that isn't a problem. Being indoor is indeed a problem... so no solar panels. $\endgroup$ – Tim Denis Jul 14 '16 at 15:44

These batteries are designed for quite high current applications so can provide quite a punch. It won't hurt you but if you short circuit it, it will get very hot very quickly. Short-circuits aside, it should be fine. I used to set fire to steel wool using one of these...

I would not waste time or money on the DC DC converter as the arduino will handle 6V very effectively. Also, if you look at the voltage curves on the datasheet, you will see that the voltage will rapidly decline to 5V anyway so a converter would just be draining power.

Have a look at http://gadgetmakersblog.com/arduino-power-consumption/ which discusses arduino power consumption.

As others have suggested try to transmit your information infrequently to save power. Unless you really need real-time data, you could consider storing the data on an SD card and retrieving it when the project is over. Of course someone might run off with it and the internet is so much more fun!

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