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====== Overview ======
In this article we roll out all of the information we have about Crowbox power consumption, and what we know about options that would allow you to run a Crowbox from a portable power source. 

We studied this problem quite a bit during prototyping, so we have some good firsthand information to share with you here.

Solar Power is a topic that's pretty popular in the [[http://groups.google.com/group/CrowBoxKit|Crowbox Google Group]]. We've done some basic research on the subject but we have never actually run any Crowbox prototypes on solar power. We'll share what we know but please realize you'll be a pioneer if you decide to try running a Crowbox on Solar Power. 

====== Power Consumption ======
During prototyping, we did a thorough analysis of Crowbox power consumption because we knew this information would be important when designing a portable power solution for the Crowbox.

Power consumption was measured using an isolated ammeter with its own power supply.

**IDLE** - A Crowbox spends the vast majority of its time being //idle//. This means the Crowbox is just sitting there waiting for a bird to land on the perch and/or drop a coin into the coin slot. During this time the Crowbox draws about **47 milliamperes** of current.

**ACTIVE** - The only time a Crowbox consumes more than 47mA is when the servo motor is being used to open or close the sliding reward lid. While the sliding lid is in motion, the Crowbox **consumes 680-720 mA of current**. If the servo has to work harder to open and close the sliding lid due to friction or other factors, more current will be consumed.

The obvious point here is that the Crowbox uses very little energy when **IDLE** and quite a bit when **ACTIVE**. The busier your Crowbox is, the more power it will consume over the course of a day.

We do realize it would be helpful to further reduce the **IDLE** power consumption but it's unlikely that we would be able to reduce this by more than a further 20%. We are looking into updating the CrOS software to put the Arduino UNO into 'sleep' mode if the Crowbox hasn't been visited in a while, but the Arduino's power LED consumes a little bit of power, too, and there's no way for us to turn that off without physically modifying the Arduino board.

====== Running on Battery Power ======
===== Overview =====
The text on this page is important, so please read it before you consider this Crowbox modification. 

In addition to the information here, you can view our instructional video on converting a Crowbox to run from a USB Power Bank [[https://www.youtube.com/watch?v=Jq9xL0tjDSg|here]].

===== USB Power Banks =====
We had some great success running Crowbox prototypes from a USB Power Bank. **BUT BUT BUT** There are two very important features that a power bank must support in order to work properly with a Crowbox:

  - Rated to deliver at least 2 amps (2A)
  - //MUST// have "Always on" feature

This means you **can not** hop onto Amazon and buy any old power bank! Most power banks these days meet requirement #1, but power banks that meet requirement #2 are uncommon.

Before going any further I'll point out that power banks made by Voltaic Systems were the only power banks we tested that worked perfectly with the Crowbox. This is because Voltaic's power banks have the "Always On" feature that is required. 

https://voltaicsystems.com/battery-packs

If you're interested in the technical reason behind this, I can explain: The vast majority of USB power banks on the market use identical circuitry for voltage regulation and power delivery. One function of this circuitry is to detect when devices attached to the power bank have finished charging, and shut off the power bank. Since the Crowbox uses very little power, most power banks see it as a device which has finished charging and shut themselves down. The cut-off point for most power banks seems to be below somewhere between 60 and 90mA, and a Crowbox draws only 47mA which will cause almost all power banks to shut themselves off. 

A power bank with the "Always On" feature will continue to deliver power even when connected devices aren't using very much energy, and that's what we need.

NOTE: The "Always On" feature is also sometimes called "No Auto Off" or "No Auto Shutdown"

==== How long will it run? ====
Simple math can be used to figure out how long a particular power bank will run a Crowbox. Only two steps are required:

=== Estimate actual available power ===
The practical energy capacity of a USB power bank device is always less than the bank's 'rated capacity'. Let's say you have a power bank rated for 10,000mAh. While the power bank's internal battery may be an actual 10,000mAh battery, we don't get to use all of that power. Power banks are designed to prevent their internal battery from discharging completely -and- we lose some energy to the power bank's internal voltage regulation circuitry. This means we don't receive all 10,000mAh of juice.

Our research and hands-on tests indicate that we can use about 64% of a power bank's rated capacity before the bank shuts itself off and wants to be recharged. To figure out how much usable power we'd get out of a 10,000mAh power bank, we multiply the bank's rated capacity by .64:

  10,000mAh x .64 = 6,400mAh

We can expect to receive around 6,400 practical usable milliampere-hours of power on a single charge from a '10,000mAh' power bank.

=== Compute Crowbox runtime ===
To figure out how many hours a device will run from a battery, we use this simple formula:

  runtime in hours = battery capacity in mAh / device consumption in mA

Which, in our example, simplifies to:

  runtime = 6,400 / 47

Giving us an expected runtime of about 136 hours, or about five and a half days before the power bank would need to be swapped or recharged, depending the environmental conditions that usually affect battery performance (such as very hot or very cold weather). Also, the Crowbox's power consumption is much higher during the times when the sliding lid is being opened or closed so this will add up over the course of a day if your Crowbox sees a lot of activity, lowering expected runtime.

It's generally considered a good idea to be pessimistic when making these sorts of estimates. On a personal note, I like to round up the power consumption of the device and use a conservative estimate that any given power bank will deliver 60% of its rated capacity. This is how I'd make my own, more conservative estimate:

  True power bank capacity at 60%:
  10,000mAh * 0.6 = 6,000mAh

  Crowbox power consumption at 50mA instead of 47mA

  estimated runtime: 6,000mAh / 50mA = 120 hours (five days)

==== Hooking up a Power Bank ====
To connect a USB Power Bank to a Crowbox you'll need a USB Breakout. This is a little USB jack that plugs into the power bank's USB port and has terminal blocks which allow you to 'break out' the USB power and ground wires so you can connect them to the power terminals on your Crowbox's breadboard.

There are many different styles of USB breakout. We strongly recommend you choose one of these two types:

^ USB Breakout Jack ^ USB Breakout Cable ^
| {{ :kit:parts:usb_breakout_plug.jpg?nolink&400 |}} | {{ :kit:parts:usb_breakout_cable.jpg?nolink&400 |}} |

As you can see, the business end of these two breakouts is the same- a terminal block which will make it easy for us to wire up USB power to our Crowbox without soldering. Choose whichever you prefer but I'll say that we lean towards the breakout cable.

**You can view our instructional video on converting a Crowbox to run from a USB Power Bank [[https://www.youtube.com/watch?v=Jq9xL0tjDSg|here]].**

===== 12V Power Sources =====
We have successfully operated multiple Crowbox prototypes using two different types of 12 volt power sources- Lead-acid batteries and Lithium Polymer (LiPo) batteries.

One of the reasons we studied 12 volt power is because there are some extremely high-capacity 12 volt options such as automobile batteries that would run a Crowbox for a very long time before the battery would need to be swapped or recharged.

Our tests with 12 volt (3 cell) LiPo batteries (12 volt/3S) went very well, but high-capacity LiPo battery packs are the most expensive battery option by far, so it feels safe to assume this will not be a popular option.

No matter which 12 volt source you choose, you’ll need to add a component called a ‘DC to DC Buck Converter’ to reduce the battery’s 12 volt output to the 5 volts required by the Crowbox. We have tested two different types of 12 volt to 5 volt buck converters and ended up with one favorite:

The model EA15-5V 12V->5V/3A buck converter from “Tobsun” is our top pick. It’s simple to install (no soldering required) and we found them to be reliable and highly-efficient at converting voltage without much loss. If you Google using the search term "EA15-5V" you'll find multiple vendors that offer this part. Cost is usually between 8 and 10 USD.

^ Part Description ^ Part Image ^
| TOBSUN EA15-5V 12V to 5V DC-DC buck converter | {{:kit:parts:tobsun_ea15-5v.jpg?nolink&400|}} |


FIXME Discuss installation of Buck Converter

  We're currently preparing documentation on how to install one of these buck converters
  and run a Crowbox from 12V power sources.


====== Solar Power ======
There's a lot of interest in the [[http://groups.google.com/group/CrowBoxKit|Crowbox Google Group]] on the subject of running a Crowbox from solar power. This is not something we have tested ourselves, but there are no obvious problems with the idea. The main issue is that you want to provide steady, regulated power for the Crowbox so any solar panel setup should also include a battery or power bank.

As we stated earlier, Voltaic brand power banks are a good, reliable source of portable power for a Crowbox. Voltaic also offers solar power kits which include a solar panel and an 'always on' power bank. This setup should be perfect for a Crowbox but, as I said, we have not yet tested these ourselves.

In mid-January we'll begin testing this Voltaic solar power kit with the Crowbox:

https://voltaicsystems.com/2-watt-kit/

Since Crowbox power consumption is under 1/2 watt most of the time, our hope is that a 2W solar panel combined with a 6,400mAh power bank will run a Crowbox indefinitely on solar power during spring and summer in most locations. We will publish our observations in the [[http://groups.google.com/group/CrowBoxKit|Crowbox Google Group]], including accurate measurements on the practical output of this particular solar panel. 

  NOTE: We have no relationship or other affiliation with Voltaic Systems. It just happens that they
  make the type of power equipment that the Crowbox requires. We pay out of our pockets to buy the
  Voltaic products that we are testing.