Powering 12 arduino's over 125 meters

Projects General Guidance
1

Hi all,

There's been a lot of talk on powering arduino's.
But I would like to explain my specific case and my proposed solution and see if anyone has some wise words, agree or disagree with my solution.

My case:
12 Arduino Pro Mini's 5V spread over a 120 meters, every 10 meter, there will be an Arduino.
Arduino's will run simple sketch with:

  • A small PIR sensor, monitoring constantly
  • a MAX488CPA+ for full duplex rs485 sending a few bytes (on masters request) every 100ms through FTP5e cabling (arduino's <-> master is 125 to 250meters apart)
    2 Arduino's will also have a Weather sensor shield and Weather Meters (Sparkfun).

Computer (master in rs485 chain) is at least 125 meters away from the first Arduino, running MAX/MSP and a whole lot more, but that's not important for now.

The installation will need to run approx 8hrs during daytime, for 12 days.

My solution and thoughts:
Powerconsumption will be quite low
MAX288 specs at 0.12mA
PIR (mini) specs at 0.40mA
Ardiuno aprox. 1mA? (can't actually find any thing on that)
We will leave the 2 Weather stations out of the equation for now.

So my idea is to power each arduino from a USB Power Bank (2200mA?) and take those powerbanks inside during the night to recharge, if needed.
I would rather stay away from using 220v at the location of each arduino.
I can potentially supply 220v AC power from a location 125 meters away from the first arduino (where the computer is, which is a 250meters away from last arduino)
It is all part of a metal structure, outdoors, in potentially foul weather and people will walk through it. (it's an interactive art installation)

I still need to develop/search for an enclosure for each arduino with PIR and a possible powerbank.
Will largely depend on power solution / size.

Does anybody have any thoughts on my proposed solution of using a powerbank that can be taken out from the 'water-tight' enclosure to re-charge at night? What would be my approx. power needed for at least 8hours. Will a 2200mA powerbank keep me running for quite a while?

I though about solar panels too, but since this is a temporary (12days) installation and costs are also to be considered, I don't think that is a sensible/affordable way to go...

Maybe someone has some ideas/comments on the above described installation...or is just interested in more info or anything. I will try and publish a full build story and share experiences when it is all done.

I thought I could at least share my ideas with the community and see if someone has any comments.

Regards,
JD

2

When you already need wired connection for the communication, you can add a DC power supply line to the cable. That's fine since the Pro Mini boards already include an voltage regulator. Then you can power on (reset!) and off the whole installation from one place, and you don't have to charge that many batteries in between. If possible,

I'd also power the master controller by DC, not by 220V AC; it may be easier to add an (sufficiently fat) accumulator there, to become independent of access/availability of local AC power, and of 220V power hazard issues.

I'd suggest rugged water proof boxes, cables and connectors, this may become the most expensive item on your list. Make sure that the boxes let enter radiation to your PIR sensor!

It may be easier (and cheaper) to seal the devices by epoxy, then you don't need expensive boxes and have no problem with IR reception. Since this technique will disallow later repairs, consider to hold spare devices for replacement of defective devices. You'll need spare devices anyhow, so that a single box failure will not break the communication chain.

3

Thank you for your reply.

I though about powering all arduino's with DC. But I'm worried about cable thickness and costs.
Having a hard time calculating what will be needed.
I could use the left over 4 wires from the FTP cable. Bundle 1 pair voor Vcc and a pair for GND.
Problem is that I'm not sure if the total length (250 meters from power source to the last arduino) will be too long and loss will be too big. (23 or 24AWG cable)
I would need to run a seperate thicker cable (18AWG) to overcome the problem of the voltage drop becoming too high.

This is where I lack sufficient electronic knowledge to calculate this reliably.

Here's what I roughly calculated:
Need approx. 20mA each (safe side)? Read somewhere that a Pro Mini uses approx 16mA.
That will count up to 240mA for all Arduino's.

That master station won't be a problem, that's were the computers, audio installation etc. will be.
220V there will be available and it's where I could hook up a 12V DC powersupply.

Or would it be better to run a 220V AC cable to the beginning of the installation (approx 125meters) and place a 12V DC powersupply there to run the remaining 125meters in the installation itself, supplying the arduino's each 10 meters.
(put the 12V DC powersupply in a suitable enclosure ofcourse)

Maybe that option is even more doable, come to think of it.

Sealing the Arduino's in epoxy will render them unusable after the installation has ended...feels like a waste. And as you have pointed out, any repairs or changes will be nearly impossible.
I'd rather have them enclosed in some PVC piping or something. With screw caps and rubber seals for the cables. Might need a whole other topic for that :wink:
Drilling and glueing the PIR in place won't be a problem.

4

Look up AWG wire resistance.

125 meters of 24 AWG has resistance 10.6 ohms (8.4 for 23 AWG), so if the full estimated 240 mA were carried from one end to the other, Ohm's law predicts a voltage drop of 2.5 volts (5.0 counting both directions). Since the current draw is distributed among closer points as well, you can apply 12 volts on one end of the cable and power the entire string.

Refine this calculation with better estimates of the current draw, and individual cable sections.

Edit: meters instead of feet

5

Thx,

I did some more calculations (more milliamps for powering an Arduino Pro Mini) and I should indeed be ok if I use one twisted pair for Vcc and a pair for GND over 125 meters, with either 23 or even 24AWG FTP cabling. Expecially since I will use up approx. 50mA per 10 meters and not the whole sum over 125 meters.

Next stop, researching cable :slight_smile:
It needs to be FTP not UTP (shielding for RS485 reliability), that much I know, but not sure if solid core copper would be more optimal for power transport or flexibel core is sufficient. There won't be much movement in the cables and it won't be outside for long, so (expensive) outdoor cabling won't be necessary.

And maybe add a capacitor at each arduino to smooth everything a bit on startup of the 12V power supply?
(Which shouldn't be a very heavy one... 1 or 2 Amps should be enough for the whole bunch I think)
Not sure that I should actually do this or especially not.

6

jdiderik:
Thx,

I did some more calculations (more milliamps for powering an Arduino Pro Mini) and I should indeed be ok if I use one twisted pair for Vcc and a pair for GND over 125 meters, with either 23 or even 24AWG FTP cabling. Expecially since I will use up approx. 50mA per 10 meters and not the whole sum over 125 meters.

Next stop, researching cable :slight_smile:
It needs to be FTP not UTP (shielding for RS485 reliability), that much I know, but not sure if solid core copper would be more optimal for power transport or flexibel core is sufficient. There won't be much movement in the cables and it won't be outside for long, so (expensive) outdoor cabling won't be necessary.

And maybe add a capacitor at each arduino to smooth everything a bit on startup of the 12V power supply?
(Which shouldn't be a very heavy one... 1 or 2 Amps should be enough for the whole bunch I think)
Not sure that I should actually do this or especially not.

  1. Use the twisted pair as nature intended - make the 'solid' wire in each pair 12V and the 'stripe' wire ground. Using the pairs like you suggested is a bad idea.

  2. Flex or solid won't make any electrical difference for your application. I would choose flex, since this setup is likely to be moved.

  3. But lots of capacitors will increase the inrush current when you switch it on. The regulator at each Arduino will take care of this for you. There's a capacitor on the 5V side, so the Arduino chip will only see clean power.

7

Excellent, thank you for your help.
I will make sure to use your advice on the use of the pairs and not adding capacitors.

I love this community, willing to help with patience and educate the newcomers.

It is quite the learning curve. I'm a experienced programmer in many languages, trying to get my head around the logic of electronics :slight_smile:

8

use 9 or 12 vac (or less) from a wall wart and rectify at each arduino

9

use 9 or 12 vac (or less) from a wall wart and rectify at each arduino

That's what I would do.

Or

12 - 24DC then feed to SMPSs at each location

10

Greensprings:
use 9 or 12 vac (or less) from a wall wart and rectify at each arduino

Would you care to explain as to why you would first transform 220V to a lower AC voltage and convert to DC at the arduino side? Instead of converting to DC right away?

I would think converting to DC first would save me some components at the Arduino side, since I can run the DC straight into the RAW input of the Pro Mini.

11

I'm using something similar - 12 boards, each with ATmega328P , two DS18B20 thermometers, and RS485 line. Line lenght is 340 meters, power voltage is 12V. For power and RS485 I'm using 4 core, 0,5mm square, "alarm cable" - it's not twisted or shielded. Each board has 5V voltage regulator. This setup is running 24/7 since 2012 without any problem.

12

jdiderik:
Would you care to explain as to why you would first transform 220V to a lower AC voltage and convert to DC at the arduino side? Instead of converting to DC right away?

I would think converting to DC first would save me some components at the Arduino side, since I can run the DC straight into the RAW input of the Pro Mini.

There's less power loss when using AC. I don't think, however, that power loss will be a problem for you over that distance.

13

Not true. The power loss will be proportional to the square of the current. The RMS current of 12v AC will be pretty much exactly the same as 12v DC.

AC is a good idea for an outdoor system. If there's any moisture in the cable or connectors, the DC will tend to accelerate corrosion. AC won't corrode any faster than if it was unpowered. That's one of the reasons why AC is used for mains power distribution.

14

...now I wonder why PoE has Vcc on the both blue and GND on both brown...

15

Use POE module:

http://forum.arduino.cc/index.php?topic=312340.msg2165874#msg2165874

Input voltage range 36V to 57V, standard is 48V.

daisy chained POE module together, use existing cable, connector (cat 5), junction box.

16

sonnyyu:
Use POE module:

Input voltage range 36V to 57V, standard is 48V.

daisy chained POE module together, use existing cable, connector (cat 5), junction box.

I'm basicly creating my own Power Over Ethernet... since I'm using FTP cabling and putting power on some pairs... :slight_smile:

No need to use specific PoE components, will only complicate things and add to costs and more components. And my footprint is small and basic.

But thank you for pitching in idea.

17

jdiderik:
I'm basicly creating my own Power Over Ethernet... since I'm using FTP cabling and putting power on some pairs... :slight_smile:

No need to use specific PoE components, will only complicate things and add to costs and more components. And my footprint is small and basic.

But thank you for pitching in idea.

Not really, to use 24 AWG cat 5 cable at 240 m, we need feed high DC voltage (~48V) to reduce power loss.
DC-DC converter for convert it back 5V feed Arduino. Since POE module are mass produced and price is fair.

POE module:

  • DC-DC converter
  • Voltage regulator
18

sonnyyu:
Not really, to use 24 AWG cat 5 cable at 240 m, we need feed high DC voltage (~48V) to reduce power loss.
DC-DC converter for convert it back 5V feed Arduino. Since POE module are mass produced and price is fair.

You are absolutely right....but to overcome that challange I'm gonna do it now in such a way that I will put power on the FTP cable in the center of the installation.

That way, I will have to supply approx 60 meters left and right, thus reducing the length and therefore the voltage drop.
I figured it will be a lot easier to cross the distance to the center of the installation with 220V/AC (180mtrs from the control station) with proper outdoor cabling etc, which I checked and will be available at the event and convert to 12V DC there.