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kit:mod_battery_power

This is an old revision of the document!


January 19, 2019 - This article is still being authored. This information is not 
yet ready for use!

Introduction

Converting a CrowBox to run from battery power is an easy thing to do and makes it possible to deploy a CrowBox in locations which do not have easy access to mains power.

CrowBox Power

Before we talk about the modifications required to run a CrowBox from battery power, we should briefly talk about the CrowBox's power consumption details.

  • The CrowBox runs on 5 volt DC power
  • An idle CrowBox consumes about 50 milliamperes of current
    • This power is consumed by the Arduino UNO
  • When the CrowBox's sliding lid is moving (opening or closing) the CrowBox consumes about 800 milliamperes of power
    • It is possible for the CrowBox servo motor to consume more power when opening or closing the sliding lid, theoretically up to 2000 milliamps (2 amps) but we have never seen the servo consume more than around 750 milliamps.

Usage cases

We've divided battery-powered CrowBox configurations into two categories, covering what we believe are the most common requirements.

Short term battery power

This is probably the configuration most users will be interested in. Short term battery power describes a CrowBox installed on or around your home, school or workplace, or put simply, any place where the operator has easy access to the CrowBox and visits the CrowBox frequently to check up on it.

We call this 'short term' power because it will be necessary to swap the CrowBox's batteries every few days or so, depending on the size of the battery used.

As we'll discuss in a moment, we suggest the use of a USB power bank to power a CrowBox on short term power.

Long term battery power

Long term battery power would be suitable for a CrowBox which is installed somewhere that is not readily accessible to the operator and is not checked on very often. This type of installation requires a larger battery and may employ solar panels or other strategies to extend the working life of the battery.

A CrowBox running on 'long term' battery power might be deployed in the middle of the woods or at the far edge of large field or farm.

For now this article won't discuss long term power options in further detail. This is mainly because we are unaware of any users who require long term battery power. But the ideal solution probably involves the use of a large 12 volt battery such as an automobile or motorcycle battery. A DC-to-DC buck converter is also required to step the battery's 12 volt output down to 5 volts, which is the voltage the CrowBox requires.

Short Term Power Plan

This section describes what you'll need to do in order to convert a CrowBox to run on short term power.

Required Parts

Here's a good thing- you only two need parts to convert a CrowBox to run from a USB power bank. Even better, one of these parts is the power bank itself! We'll talk more about choosing a power bank in moment.

The other part you need is called a “micro USB breakout board” or “micro USB pinboard”. This is a small micro USB socket with some standard pin headers attached to make it easy to wire up to projects like the CrowBox so that you can plug in a power bank. This is very inexpensive part and they are easy to find on amazon and eBay. These are so inexpensive that you usually have to buy 10 or more in a lot for around $5 USD, so you'll end up with some extras.

NOTE: Be sure that the USB breakout boards that you buy are “micro USB” and that they come with the header pins! Also, some minor soldering is usually required. The item you are looking for looks like this:

Choosing a power bank

Due to the enormous popularity of smartphones, tablets and other devices which are recharged through a USB cable, portable batteries with USB ports (USB power banks) are also extremely common and relatively inexpensive. USB power is 5 volts, the same as our CrowBox, which is very convenient for us.

There are a couple of important features you must look for in a power bank and we'll go over those after a discussion on energy capacity.

Power Bank Capacity

USB Power Bank capacity is expressed in milliamp-hours, or mAh. For our application, 5000 mAh is the minimum you should consider. High-capacity power banks may provide 30,000 mAh or more.

Capacity matters because it determines how long your CrowBox should run off the power bank before the power bank must be removed and recharged. Here's how you figure out how long a CrowBox should run on a given power bank:

[Hours of continuous operation] = [power bank capacity in mAh] / 50

This computation assumes the CrowBox is idle most of the time. Depending on the level of activity, particularly how many times the sliding lid is opened and closed each day, more energy will be used and the power bank may need to be removed and recharged sooner.

This computation also ignores power that may be consumed by the power bank itself. Power banks contain voltage regulation circuitry and many of them use one or more LED's to indicate power or status. These items consume some of the power bank's battery power during use. To compensate for these unknown factors in our power consumption it's a good idea to be conservative and recharge the power bank sooner than this formula would suggest. Let's look at some examples:

If you are considering a 5000 mAh power bank, our formula says that a CrowBox should run for 100 hours before the power bank is dead. (5000 / 50 = 100 hours). This works out to 4.16 days (100 hours / 24 hours = 4.16 days).

A high-capacity power bank providing 30,000 mAh should be able to power a CrowBox for around three weeks!

However! These computations assume ideal conditions and must be made more realistic. To figure out how long you should actually try to run a CrowBox from a power bank before recharging, use a modified version of our formula which attempts to take into account the extra power consumed by the power bank itself:

[practical hours of operation] = [power bank capacity in mAh] / 75

Using this updated formula, here's how long you should actually expect to run a CrowBox off of a given power bank before stopping to recharge the power bank:

  • 5,000 mAh - 66.6 hours or 2.77 days
  • 10,000 mAh - 133.33 hours or 5.3 days
  • 22,000 mAh - 293.3 hours or 12.2 days
  • 30,000 mAh - 400 hours or 16.6 days
kit/mod_battery_power.1547950197.txt.gz · Last modified: 2019/01/19 18:09 by steve