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Smart Charging your phone, tablet, and other 5v USB devices.

P1030804I have several devices that are charged with a USB 5v charger. Most have a warning on them “Disconnect charger when charged to save energy”. Why? Because most 5v chargers do not know when the batteries are charged, so they keep charging, wasting energy, producing excess heat, and reducing battery life (and the life of the charger).

This weekend we got a USB Smart Charger. This device stops charging when your device is fully charged, and displays a green light to let you know it’s done. Handy for my Kindle Fire which gives you no notification that it’s finished. This devices saves energy, and will extend the life of my devices, and itself.

At 2 Amp output, it’s fully capable of charging the most demanding 5v device, whether it’s a tablet or a phone, or a usb powered device with no onboard battery, like an Arduino.

Velvetwire Introduces First-Ever Apple HomeKit Device Smart Charger

Powerslayer Blu Eliminates Energy Waste and Allows for Customized Charging of Devices

SANTA CRUZ, CA – September 30, 2014 – Velvetwire, a leader in smart energy technology, today announced the winter availability of Powerslayer Blu, its Apple HomeKit-enabled USB charger. The Powerslayer is a cleverly designed intelligent smartphone charger that integrates a first-of-its-kind device-aware software for a more energy efficient charging process as well as a surge protector for keeping both consumers and gadgets safe. Now with added Bluetooth low energy (BLE) connectivity, Powerslayer Blu is compatible with the HomeKit-controlled ecosystem, allowing for customization and enhanced control of the charging process in addition to reducing energy waste.

“Our vision for Velvetwire arose during a two-year sailing trip around the world, where we realized the vital importance of conserving energy. Powerslayer is our first endeavor at tackling energy waste and creating a smarter energy future for the modern consumer,” said Jennifer Lee, co-founder and COO of Velvetwire.

Powerslayer Blu is a unique, eco-conscious way to charge devices. By turning off automatically when charging is complete, the device prevents overcharging and protects the battery life of USB devices. It also eliminates vampire power – the energy constantly consumed by electronics even in standby mode – while looking stylish.

“We are proud to be among the first group of companies to produce HomeKit-compatible devices,” said Eric Bodnar, co-founder and CEO at Velvetwire. “By integrating Bluetooth technology into the Powerslayer, we’re offering customers a new way to interact with their devices and be part of Apple’s HomeKit. Velvetwire is committed to developing intelligent, energy-efficient devices that allow users to live more consciously without sacrificing convenience. We look forward to sharing Powerslayer Blu and future generations of our power-saving devices with the world.”

Powerslayer Blu’s customization features include the ability to select between high power boost-mode charging and eco-mode to maximize battery life as well as the ability to receive a variety of device notifications. The charger interacts wirelessly with Apple devices through a Bluetooth-powered iOS application developed by Velvetwire and can interact with other HomeKit applications. The app allows users to visually see and monitor relevant information about the level of charge their device is receiving. By tailoring charging power levels to suit their situation, users are provided a whole new level of interaction with the charging process.

Pricing and Availability:
Powerslayer Blu is available Winter 2014 for $89. To sign up to learn more about Powerslayer Blu and become alerted when available, visit

About Velvetwire:
Based in Santa Cruz, California, Velvetwire produces intelligent technology products that help eliminate energy waste. After two successful startup exits, co-founders Eric Bodnar and Jennifer Lee journeyed on an extensive sailing trip around the world where they realized the preciousness of conserving energy – upon return they launched Velvetwire. The company is now at the forefront of wireless and mobile innovation with deep-rooted commitment to rethinking the way modern society consumes energy. For more information about Velvetwire, visit

For regular Velvetwire updates follow us at or

Introducing Powerslayer from Velvetwire on Vimeo.


Product Spotlight – Super Powergate 40S Backup Power Switching and Charging System

The perfect complement to a 400 watt inverter, this unit is ideal for the ham shack, Home Office computer system, or off grid cabin or RV.


* A Super PWRgate is a 12 volt backup power system that can supply up to 40 amperes continuously from either a Power Supply or a Battery, and can also charge the battery with its high performance charger.
* Connected equipment will instantly switch to battery during a power blackout or power supply failure. No glitches.
* The circuit uses two 80 ampere Schottky diodes as an OR-Gate to isolate the battery and power supply from each other. Forward voltage drop of less than 0.3 volts at 20 A.
* To keep the battery fully charged and ready for use, the Super PWRgate has a built-in four-stage battery charger with selectable current rates of 1, 4, 7 or 10 amperes.
* The circuit is optimized for use with GELLED & AGM type batteries, but will keep flooded lead acid and marine type batteries near full charge as well.
* The Super PWRgate and the power supply may also be used to charge a battery that is powering the radio, as described by W1ZR in QST.

Super Powergate 40S Backup Power Switching and Charging System


RENEWABLE POWER FOR AMATEUR RADIO (and other electronic devices)

RENEWABLE POWER FOR AMATEUR RADIO (and other electronic devices)
by Larry D. Barr, K5WLF

About the author: Larry D. Barr is an Amateur Extra class amateur radio operator, first licensed in 1966. He is uniquely qualified to write on this subject, having lived offgrid for 19 months with the majority of his electricity provided by a Wincharger 1222H wind generator. Larry is a journey level electrician, an alternative energy systems designer and the former editor of Energy Self Sufficiency Newsletter. His pickup mounted, solar powered ham radio installation was featured in the American Radio Relay League’s “We Do That” video series and on their website. Currently employed as the Planetarium Manager for Tarleton State University in Texas, Larry continues to be active in renewable energy and looks forward to living offgrid again in the near future.

Because of my interest and involvement in renewable energy, I’m often asked by other amateur radio (ham) operators about the best way to run their stations on renewable energy sources. Most of these queries pertain to solar, or photovoltaic (PV), sources, but we’ll also mention wind and minihydro in addition to PV in this article.

The good news is that modern, solid state ham rigs lend themselves extremely well to renewable power. They draw relatively little current at a nominal 12 VDC, and therefore require fairly modest expenditures in generating devices.

The bad news is that hams who like the old vacuum tube (hollow state) rigs will not be able to power those old “boat anchors” without a serious layout of funds for PV panels or a much larger than usual wind generator. The old rigs simply draw too much current to be practical for operation on a renewable system.

So, let’s look at the practicality of running a modern, 100 watt, solid state transceiver like my Yaesu FT897D on a PV system. It’s easy to do – and at a relatively low cost for the solar setup.

First, let’s consider the power required to operate the radio. There are two distinctly different current requirements for the unit. One is the power required for the radio to receive incoming signals. That’s about one ampere (1A) at a nominal 12 volts direct current (12 VDC). Nominal 12VDC turns out to be somewhere in the vicinity of 12.6 VDC, for a fully charged 12 volt battery, to around 13.8 VDC which is the output of an average vehicle alternator. We’ll mostly stick with 12 VDC for this article just to make the calculations easy.

The other requirement is 22A while transmitting at the full 100 watt output level. Well, you’d think that wouldn’t take long to run down a battery, and you’d be right. But think a minute. We don’t transmit all the time. Actually, the ratio of transmit to receive in normal ham operation is right at 1:9. 10% transmit and 90% receive.

Now, we need to figure out how many Amphours (Ah) we’ll use per clock hour in normal operation. Amphours is the numbers of amps, the current, consumed over a period of one hour. It’s the way the battery capacity is rated. As I said earlier, normal radio operation is generally calculated at 90% receive and 10% transmit.

So, in 1 clock hour we’re consuming:
(1A X 0.9h) + (22A X 0.1h) = (0.9Ah + 2.2Ah) = 3.1 Ah

Figuring our 100Ah battery at 50Ah, because we don’t ever want to take the battery below 50% depth of discharge, we divide:
50Ah / (3.1Ah/hour) = 16.129 hours

Which is about 16 hours and 8 minutes from a fully charged battery. I run two 100 Ah sealed lead acid (SLA) batteries in my battery banks for a rated 200 Ah capacity and a ‘real world’ capacity of 100 Ah. That doubles my run time to about 32 hours and 16 minutes.

There are those who will disagree with me about my advice to never exceed 50% depth of discharge in a deep cycle battery. They are welcome to do so. And I will never loan one of those folks my batteries. Your batteries will last much longer and provide better service to the end of their life if you follow my advice. Each time a battery is drawn below 50% charge, it gives up a small part of its longevity. Personally, I can’t afford to replace batteries before the natural end of their life. So, I treat them well. My shack and pickup batteries are over six years old and still operating at peak efficiency.

I must mention here that manufacturers base the capacity ratings of their batteries on the assumption that the discharge will be made at a constant rate. That rate is assumed to be one twentieth (1/20) of the published Amperehour rating of the battery. In the case of our single 100Ah battery, the rate would be 5A. For our 200 Ah bank, it would be 10A. This relationship is called C (capacity) / 20. You’ll see it published simply as C/20 or ‘the C/20 rate’.

Any deviation from this C/20 rate, especially discharge rates which exceed it, will result in a different amount of power available from the battery. If we exceed the C/20 rate, the capacity of the battery will be less. In many cases, much less. It depends on the extent to which we exceed the C/20 rate of discharge.

In the case of our 100 Ah example, since our calculated rate of discharge was 3.1Ah/hour (or 3.1A), we were below the C/20 rate of 5A and should get at least the run time we calculated. However, if we were to exceed the C/20 rate, our run time would be less. How much less would be proportional to the amount above the C/20 rate that we imposed on the battery. If our discharge rate is below C/20, we may get a bit more. But let’s figure for worst case and not count on it. This phenomenon has been well documented by a gentleman named Peukert and his analysis of the effect is known as Peukert’s Theorem.

We should note, and must accept, that this does not indicate that the battery is faulty. It’s simply reacting in accordance with the laws of physics and chemistry that batteries operate under. To draw an analogy — if you bought a car and the manual stated that you could expect 25 MPG at 50 MPH, it would be unreasonable to expect that same mileage at 120 MPH. You’ve changed one of the variables in the equation and you can’t expect the result to be the same.

Now, let’s look at the PV panels and other gear required to support our FT897D on a solar electric diet.

My system consists of two UniSolar US64 amorphous panels rated at 64 watts each. They’re connected in parallel for a total of 128 watts. With the Xantrex C12 charge controller set at an output voltage of 14.2VDC – it seems high, but it’s right for the SLA batteries – that gives me about 9.01 amps to the batteries. Let’s just call it 9 amps. So, in one clock hour, I’ve put 9 amphours back into the batteries. That’s almost a 3:1 ratio of input to output.

Truth be told, I usually see about 7.4 amps, more or less, from the panels going into the battery bank. But that’s more than twice what I’m using and certainly explains why, on occasion, I’ve gone out on a radio mission with less than fully charged batteries, worked on the air for four hours or so and returned home with a fully charged battery bank. And all free, from Mother Nature.

My UniSolar panels aren’t available anymore. Unisolar has decided to dedicate their manufacturing capability to mainly Building Integrated PhotoVoltaic (BIPV) and has discontinued their line of discrete PV panels. We recently mounted a Kyocera 235 watt panel on our local ham club’s tower trailer, and if I were buying now that’s what I’d get for myself.

Let’s look at the total cost of a PV system to run the radios using the Kyocera panel.

The PV panel will run you about $375, the Schneider/Xantrex C35 controller with the CM digital display (recommended) is about $165, and a pair of PowerSonic 100 Ah SLA batteries will round out the system for $275 each or $550 for the pair. That’s a total of $1090 for the system. With proper care, the panel and the controller will last you for a lifetime. The life span of the batteries depends on you. I’ve been running mine for about six years now, and they’re still doing their job, and doing it well. If you abuse them, by discharging them below 50% capacity, or over or under charging them, their life span will decrease.

Now, let’s talk about wind power for a minute. If I were buying a wind generator today, I’d get an Air 30 turbine made by Southwest Windpower. It’s a 400 watt unit and has all the controller circuitry built in. At peak output, it’ll give you somewhere around 25 amps, and because of the integral controller, it interfaces seamlessly with a PV system. Cost is somewhere in the neighborhood of $600. If you live where wind is one of your most prevalent natural resources, you might get by with just the Air 30, but I really recommend a hybrid system that uses more than one source. Wind and PV is a great combination, for many times when the wind is blowing the most, the sun is obscured.

Minihydro is a wonderful power source if you have a year round watercourse on your property. If you don’t, just forget about it. My dream is to find a property with a year round stream on it, but unless I win the Lotto and maybe leave Texas (not likely), I’ll never find it. Don’t even fret over hydro unless you can provide your system with a reliable and continuous source of water. There aren’t many locations available with that resource and it’s best to not even think about it unless you already own it. If there’s a call for it, I’ll gladly write about minihydro at length in a future article.

OK. let’s summarize. I’ve explained how to calculate the draw of your radio. We’ve discussed the factors that control battery run time and battery life. We have talked about the initial cost of a PV system, and considered adding a wind turbine to the system. It’s easy to add other 12VDC devices, such as lighting or entertainment devices, to the system. Just do your calcs and ensure that you’re not drawing your battery bank below 50% capacity. Be sure to follow all appropriate wiring codes and make damn sure that your wiring is safe and overload protected. Enjoy the free energy that Mother Nature provides. ldb

Off grid info and components available at

Discuss Amateur radio and alternative energy topics at


What is an Off Grid Power System?

Most of our installations are for clients who want to live in remote locations where the Solar ROI can be immediate. These locations are either not served by the electrical power grid, or poorly served with frequent outages, due to weather or other reasons. Some of these systems are mobile, as in boats and RV’s.

While adding solar to an on grid home is certainly doable, and admirable, it’s an expense not easily justified, as the grid is typically very cheap to install and hookup. However, there is a monthly electric bill, and prices are not known to decrease, or even stay static, but increase over time.

An off grid home is insulated from grid outages, and increasing energy costs. A remote home which would require power to be brought in from long distance can show an immediate Return On Investment (ROI), the the cost of the solar power system is typically less than the installation charge to bring the grid in. Remote property is typically less expensive than property serviced by the grid, offering more opportunities for savings.

An off grid power system typically consists of Solar Panels and/or Wind Turbines, but also may include micro hydro and generator systems. The charging sources fill battery banks with regulated power for 24/7 operation, even when the sun or wind is not in operation. The batteries can power low voltage devices directly, and regular household appliances though AC Inverters.

Conserving power by using energy efficient appliances, and time shifting heavy loads to times of generation, can greatly decrease the total cost of the system by reducing the size of the system needed. This process does not mean reducing services. An off grid home can have the vary same conveniences and services of an on grid home, just done in slightly different ways to meet the power and financial budget of the owner.

Off grid power systems can be professionally installed, or homeowner installed, and may qualify for state and federal rebates and incentives, improving the ROI even further.

For free information on how to design and build your own off grid power system, rain water harvesting, and other off grid tech, see



A Torqeedo-powered electric boat won the 9th annual Wye Island Challenge, an electric-only boat race held in St. Michaels, Maryland, on October 2. Captain Todd Sims, owner of EPower Marine in Boynton Beach, Florida, piloted his 23′ Calypso Launch to victory with an average speed of 6.5 mph. The 24-mile course extended from the Miles River Yacht Club, across the Chesapeake Bay and around Wye Island. Winds averaged 15-20 mph, while 3′ breakers stirred in the open water.

“The first leg of the course was straight into the wind and waves, but the Torqeedo Cruise 4.0 electric outboard pushed the boat through the weather like a tractor,” said Captain Sims. “This kind of race demonstrates the viability of electric propulsion in real-world conditions. I couldn’t be more pleased with the performance of the boat and motor.”

“These are all off-the-shelf parts available to anyone. The Cruise 4.0 has this kind of power right out of the box,” continued Captain Sims.

With thrust equivalent to a 9.9 hp gas outboard, the Cruise 4.0 R achieves an efficiency of more than 50%. It operates on a 48V lead-gel, AGM battery bank or two high-performance lithium manganese batteries from Torqeedo’s Power series.

Founded in 2005, Torqeedo’s high-tech outboards have won numerous awards. Environmentally-sound, they offer unrivalled strength and efficiency for superior range.

EPower Marine specializes in electric propulsion solutions for the marine industry. Located in South Florida, EPower Marine is a sales and service dealer for system components, turnkey packages and purpose-built electric boats. Recreational users and commercial fleet operators have utilized EPower Marine’s expertise and broad vendor relationships to design, source and deliver the best electric propulsion systems available. Captain Todd Sims can be reached at 561-613-2737 or for more information.

Contact Torqeedo Inc., 171 Erick Street Unit A-1, Crystal Lake, IL 60014. 815-444-8806; Fax: 815-444-8807.;


Green Trends for 2011

Amazing Green Trends to Watch For 2011 – by Eric Carlson

As 2010 comes to a close and 2011 begins there are some definite trends and changes that you are going to want to keep an eye on in the coming year. With most media companies focusing their attention on new gadgets and technologies that are hitting the market in the New Year, there are others that are quietly taking hold behind the scenes that are making huge impacts in our lives. While green technology may be mainstream in the media right now, the work and advancements that are happening are left by the wayside, and these changes are happening in unlikely places such as satellite TV networks and the manufacturing hub of the world.

  • Changing The Face Of Power

Over the last year there have been some huge improvements and breakthroughs in the areas of solar power. While this may seem to be trivial to you, think for a moment what this means to your wallet. Traditional power sources such as coal and oil are depleting and though we are in no danger of running out right now, the prices only keep rising. The cost of mining, then producing the power from the resources is getting astronomical and that cost is passed on to us as a consumer. Now what if there was a way to produce large amounts of power for a fraction of the cost that it takes to produce power from coal or oil? That would mean a huge reduction in the costs for the consumer, both in the energy and the service. While nuclear power was supposed to be the power alternative it has proven to be just as expensive if not more so, albeit cleaner energy. This brings us to the huge advances that have been made in solar power. You may have noticed that there are solar panels going up everywhere from peoples roofs to farmers fields. These solar panels are taking them off the grid partially if not completely and providing cheap clean energy. This is just the beginning of the advances in this form of energy and is something to keep an eye on.

  • Technological Efficient Upgrades

With this green imitative has come some interesting tends that are helping to reduce the use of energy by making our lives more efficient. Imagine your fridge sending you a message telling you what you need to pick up on the way home from work, so that you don¡¯t have to waste the time and energy later to go out again and get it. While the technology is not completely there right now it is getting there.

Ford has started with the SYNC service in its new cars, which incorporates music, news, weather, GPS, hands free cell phone, and many other features built into one unit in the vehicle. While this may just seem to be a convenience, think about it this way, you will not need to purchase a GPS unit, which saves you money and reduces the amount of resources used in producing that unit. The GPS and weather service, along with the traffic alert service, will help to get you where you need to go in a timely fashion, meaning you are on the road less, burning less gas and helping the environment as well as your wallet at the same time.

  • Manufacturing Going Green

The manufacturing hub of the world is going green both in the processes they use in development and the technologies they produce. We are of course talking about China. Being the manufacturing hub of the world has given them an interesting advantage in the green market. They get to implement the technology first hand and lead the way. Also they are making huge advances in the green energy field as well, as they have a high population and not a lot of space to put everyone.
Investing In Tomorrow

With green technology and energy taking off, there have already been some huge investments made, but there needs to be more. Many companies around the world and specifically America have been calling for substantial investments to be made now for tomorrow. Such investors and advocates include Bill Gates, founder of Microsoft, and Bank of America Chairman, Chad Holiday. Only with the investments now can we change the face of the world tomorrow.

  • Taking Transportation Green

You may or may not remember the electric car. It was a big sensation when it was first introduced years ago, and was also quite the controversy. It faded from media coverage as well as production after only a few years for many different reasons. It has started to make a comeback though and looks like the innovations in the technology are making waves as well. With the Chevy Volt and the Nissan Leaf taking hold in the American market, the rise of the electric car is in motion.

Analysts predict that within a few years as electric transportation develops that most of our public transportation will also make the switch and thus become a cheaper solution to commuting to and from work.

  • Changing The Grid

With the advent of green energy, the grids that transport our power have undergone some major overhauls recently. These improvements have not only upgraded the system, allowing for a better distribution of power, but also made them more efficient. These changes are further proof of the advancement in green technology.

  • Green Entertainment

At last count there were enough televisions in the United States to put 3 televisions in every persons home and still have a surplus. This is a staggering number when you consider the population of the United States. Television is mainstream entertainment for everyone and everything about it uses an immense amount of energy. From the production of a movie or show, to the distribution and the final viewing of that show, the drain on our power systems continues to rise. There have been many advancements in the technology that the networks and satellite distributers have made that have lowered the energy needed and changes continue to be made all the time.

These are only a few things you are going to want to keep your eye on. With 2011 only just begun, there are sure to be many breakthroughs and great technologies that come onto the market.

About the Author

Eric Carlson is the Publisher of He lives in San Francisco, CA with his family. He is passionate about everything to do with satellite TV providers and can often be found discussing the different changes and advancements that the Satellite TV network has to offer. Keep your browser turned towards his blog for an interesting and fresh perspective on the world of satellite TV.


Wireless Solar Charging Made Easier

19 June 2012—Anybody with a smartphone dreads the low-battery warning that initiates a mad search for an electrical outlet. But engineers at Princeton University are developing technology that could lead to widespread wireless charging stations for all our electronics. Along the way, this technology could also help build better sensors to monitor the health of both humans and buildings.

Wireless chargers operate through inductive or capacitive power transfer. An alternating current creates an oscillating electrical or magnetic field, which induces power at the receiver. “We’re looking for an opportunity to create ubiquitous charging stations,” says Naveen Verma, an assistant professor of electrical engineering at Princeton.

Verma and his team presented the work last week at the IEEE Symposia on VLSI Technology and Circuits, in Hawaii. The research focuses on using the same material—thin films of amorphous silicon—both to make solar cells and, for the first time, to build circuits to handle the electricity the solar cells produce. The combined solar cells and circuitry could be made on large sheets of plastic that could be molded or wrapped around everyday objects, from buildings to patio umbrellas. Amorphous silicon has its limitations. For one, it’s not as efficient at converting light to electricity as crystalline silicon is. But unlike crystalline silicon, it can be processed at relatively low temperatures, allowing production over large areas on plastic substrates. Amorphous silicon also produces transistors with much lower performance than crystalline silicon. The reduced speeds result in low-quality inductors, which are typically a key component in creating the oscillating fields used in wireless power transfer. What’s more, it is usually possible to build only n -type thin-film transistor (TFT) devices, but not both n- and p-type at the same time, as needed in the complementary logic of computers.

So Verma’s team designed a circuit containing two solar cells, capacitors, and n-type TFTs, skipping the p-type TFTs and inductor. The TFTs switch the current so it flows to the capacitors first from one solar cell and then the other (which is wired in reverse), thus turning the direct current produced by the cells to the desired alternating current.

Verma says the charging system can provide a device with up to 120 microwatts of power at a transfer efficiency of up to 22 percent under indoor lighting. An iPad, which uses power in the tens of milliwatts, wouldn’t benefit much from that, but there should be ways to increase the charger’s capability. A larger energy-harvesting surface can provide more power, and larger capacitors raise both power and transfer efficiency; increasing their area from 5 by 5 centimeters to 10 by 10 cm increases power by a factor of four. Verma is also interested in replacing the amorphous silicon circuits with metal oxide semiconductors, such as zinc oxide, which may work better and is compatible with the silicon processing.

In the meantime, he says, “there are a lot of devices that consume very little average power.” Some medical sensors, such as those worn on the body to monitor heart rates or other signals, need only a few tens of microwatts. And in other research presented at the conference, Verma and his colleagues propose combining thin-film solar cells with thin-film electronic circuitry for power management, readout, processing, and communications in a new type of structural sensor for buildings.

Today, sensors for monitoring strain in buildings and bridges often consist of an optical fiber connected to a detector. If a bridge bends more than a certain amount, that bends the fiber, which alters the light hitting a detector at one end. Verma would like to replace that design—which senses strain in only one dimension—with an array of sensors, powered by photovoltaics. “The kind of sensors we’re envisioning are much more functionally diverse,” he says. “This technology provides sensing capability on a scale that no technology we have now could provide.” He’s hoping to install a prototype of such a system on a bridge on the Princeton campus.
About the Author

Neil Savage, based in Lowell, Mass., writes about strange semiconductors and amazing optoelectronics. In the April 2012 issue of IEEE Spectrum, he reported on molybdenum disulfide, a potential rival to graphene in nanoelectronics.


Is it power, or is it energy?

What’s a Watt?

The differences between power and energy are a great mystery to a lot of folks, and we answer this question a lot. I’ll try to do this again for those out there still confused.


Work (energy) = force x distance

Let’s say I have a door on my house that’s 1 meter from the hinges to the door knob. If I have to apply 50 newtons of force to the door knob to open the door, and I rotate the door so that the knob moves 1 meter along the arc, I’ve applied 50 Newton-meters (Joules) of work, or energy.


Power (Watts) = Work (Joules) / Time (second)
Energy (Watt-hours) = Power (Watts) * time (hours)

Power is Work divided by Time. If I take 1 second to open that door, I’ve expended (50 joules / 1 sec) = 50 Watts of power. If I take 2 seconds to complete the task, I’ve expended (50 joules / 2 seconds) = 25 Watts of Power, even though I’ve still applied 50 Joules of Work.

If I have a 50 watt lightbulb, and I keep it lit for 1 hour, it uses 50 watt-hours. If lit for 2 hours, it uses 100 watt-hours, even though it’s a 50 watt bulb and it takes 50 Watts to light it at rated brightness. So, Watt-hours = Power (Watts) * Time (hours), and is a measurement of energy. 100 Wh = 100 Joules/second * 3600 seconds = 360,000 Joules.


Torque = Force x Distance

Torque is a force applied to an object that causes a turning motion. In the above example, the door turns on its hinges, the axis of rotation, and since we applied 50 newtons of force to the door handle, and the handle was 1 meter from the axls of rotation, it also happens to be 50 newton-meters of torque. If the doorknob was at the midpoint of the door instead of the edge, or .5 meters from the hinges, I’d have to apply 100 newtons of force to open the door, but that would still be 50 newton-meters of torque.


The above examples were done in metric, and some parts of the world still use English standards, so for ease of understanding, I’ll give the conversion units.

50 Joule = 36.8781088 foot pounds
50 Newton = 11.2404471 pounds
1 meter = 3.2808399 feet
1 kilowatt-hour = 3.6 million joules

For more conversions, see


Measuring Power Consumption

Living off-grid, either in an RV or a renewable energy powered home, there is a great need to be able to measure the power consumed by various devices. This is necessary in order to size your power generation devices, like PV Panels, your distribution devices, like inverters, and your storage batteries.

Even in an on-grid home, a Kill-A-Watt is good to help you conserve energy by comparing energy comnsumption of various appliances for purchasing decisions.

For 120vac devices, we use a Kill-A-Watt to monitor and predict daily power consumption. This unit monitors Volts, Amps, Watts, VA, HZ, PF, kWh, and hours used.

For DC devices, we use a “Watt’s Up” watt meter which replaces an ammeter, voltmeter, wattmeter, Amp-hour and Watt-hour meter:

Watt's Up Meter (Color: Blue, End Configuration: Powerpole Ends)


Homebrew Wind Power

Our favorite (and in our opinion, the best) DIY guide to off grid power systems and DIY wind turbine construction has to be “Homebrew Wind Power” by Dan Bartmann & Dan Fink. It’s a complete guide to low voltage dc power systems and a good electronics tutorial in addition to being a step by step guide to producing free electricity with the power of the wind.

“Have you ever wondered how wind turbines work and why they look like they do? Are you interested in adding wind power to your off-grid electric system, but have been put off by the high cost of equipment and installation? Well, now you can build and install your own wind turbine!

Harnessing the wind can be a tricky business, but in this groundbreaking book the authors provide step-by-step, illustrated instructions for building a wind generator in a home workshop. Even if you don’t plan on building your own turbine, this book is packed with valuable information for anyone considering wind energy. It covers the basic physics of how the energy in moving air is turned into electricity, and most importantly, will give you a realistic idea of what wind energy can do for you–and what it can’t.”

Get the book here

Homebrew Wind Power

and if you email us your Amazon order confirmation, get the DIY ebook package of your choice from

absolutely free.

To learn more about electronics, and how to monitor off grid power systems and control devices, see