FAQ

General

Q: What is the EnerJar?
A: The EnerJar is an open source watt-meter. It measures the amount of energy an appliance is using. You can use it to find out just how much energy it takes to run a microwave, TV or Laptop. Figure out what requires the most energy and give it a break. Or see if you can figure out how to use it in a way that requires a little less energy. Try measuring how much energy your TV uses while it is off. You might be surprised!

Q: When will these be available?
A: Kits to build these yourself will be available in the near future. The design is posted here for those of you who can find all of the parts yourself and have a PIC Programmer and some basic soldering skills. There are currently no plans for commercial mass production, but we are still investigating how we might distribute these and are open to suggestions. We would like to make them available to as many people as possible.

Q: How hard will this be to build?
A: The only tool required will be a soldering iron, required for nearly all DIY projects of this sort. A drill, voltmeter and a little knowledge or willingness to learn basic electronics are a plus, but we hope, not required. Our primary goal is to make these as accessible as possible so we will work on making it simple. However, remember that the EnerJar's circuitry involves 120-volt AC power, which can hurt or even kill you if you don't take the proper precautions. Never touch any of the wiring or circuitry when the EnerJar is plugged in.

Q: How much will they cost?
A: We are still working out the details. The current goal is to give away as many of these as we can afford. Yes, thats right, free hardware. There will be a cost to send out the parts and then a partial or full refund when you send a picture of your working EnerJar. We encourage those of you who can pull parts from old electronics to do so. If you only need some of the parts, we plan on custom shipping only what you need to reduce waste.

Q: How can hardware be free?
A: Partly because we got money from the Greener Gadgets design competition. Partly because, we'll ... we're working on it. Donations to subsidize the cost for people who can't afford this wouldn't hurt!

Technical

Q: Does the EnerJar work with 240-volt AC?
A: It sure does! The only change required to make the EnerJar 240-volt compliant is that the R6 resistor should be changed to about 1.5M. The exact value is not critical because of the calibration process.

Got a question? Ask in the comments below!

Cool idea

This is such a cool idea. I had no idea that these things even existed. I just found out that our TV uses almost as much energy when it is off, and so this would help with cutting cost for electricity and heating.

how cool

This is a really neat idea. I think with this green era we are in, this product will be very useful. You have gone above and beyond by showing us all how to make our own. Thanks.

Measuring wasted energy

How safe is it to use as part of a School project to outline how much energy we all waste in our homes. Going to build one with my daughter or do I need permission before hand?

Cheers
Khaled

First of all,

First of all, congratuations! This device is creative. I would like to know what is the maximun current the device can measures?

Thanks and I wait the answer.

mpcoc

Have you guys thought about

Have you guys thought about using a hall effect ammeter inline with your small piece of extension cord in the same form factor to provide the same watt measuring (assuming the person understands they are running either 110 or 220) ability, but without the hazard issues?

mpcoc

Accurate readings

When will the calibration instructions be posted on the site, or doesn't it need to be calibrated?

Preprogrammed Chip

This is a great project. I am thinking of making this but I have little knowledge about programming. Any chance you guys making/selling preprogrammed chips?

Sign me up for the kit

Hey,
Is there a way to sign up so I'd be notified when the kits a ready to roll out?

LCD Connection

Please can you tell me how the 4-digit LED segmented display was connected.which of the pins are common cathode and which of the pins are common anode.
please reply immediately.
thank you

Brilliant! Since I do not

Brilliant! Since I do not have any skill, can you tell me Where can I buy the divice? Thank you.

School Project

I would like to build the enerjar for my daughter for a school project. Do you have any objections? We will make all your details availble as she has to do some research as part of the project. I would appreciate any help that you can offer. Do you have detailed photos of the various stages of the building process. In South Africa we have 240V power. I had some electronic experience at school and are a civil engineer.

Regards
Louis Geyer

Calibration

What is the best method of calibration?

already calibrated

The device does not need any calibration it will be totally hands off (my guess).
- Chili Bonus

Current

First of all, congratuations! This device is creative. I would like to know what is the maximun current the device can measures?

Thanks and I wait the answer.

What about using a hall effect ammeter to avoid inline issues?

Have you guys thought about using a hall effect ammeter inline with your small piece of extension cord in the same form factor to provide the same watt measuring (assuming the person understands they are running either 110 or 220) ability, but without the hazard issues?

Hall devices are notouriously difficult to use

Hall devices are notouriously difficult to use and to calibrate and keep calibrated. The measurement accuracy will be low. The mechanical construction becomes an important factor, as coupling to the power conductor and de-coupling to the environment are important.

A hall effect device could

A hall effect device could be a non-contact replacement for the shunt for measuring current (as could a current transformer), but you still need to measure line voltage to be able to calculate power.

What about non polarized AC outlets?

Many countries in Europe use non polarized AC outlets. Thus you cannot know which wire is live and which one is neutral. Does the EnerJar work with such plugs with the current sensing R7 in series with neutral instead of live? Could currents slipping into the earth ground make this device inaccurate?

If you have significant

If you have significant ground leakage currents, then I fear you have more to worry about than the accuracy of the power reading! Whether or not the live (hot) and neutral are swapped, ground leakage is still going to make the reading inaccurate.

A device with current sensors in live, neutral and earth connections could be useful to detect leakages back into the power ground, or via another path, but would increase cost and complexity and becomes more of a diagnostic tool than a simple power meter.

Ground leakage

If you have any significant amount of ground leakage, you've got way worse problems than anything an EnerJar can solve.

In fact, current home wiring standard in Germany requires a ground-leak fuse which will turn off the power instantly when Ground is connected to Neutral anywhere. (Including in a circuit which has Live disconnected, which can be very very annoying when you need to work on your mains wiring.)

To sum it up, there's no problem whatsoever with switching Live and Neutral in any well-designed device, much less one that has UL / CE / whatever approval.

Absolutely fantastic!

This is an absolutely fantastic device. I am subscribing to the RSS for this immediately so I can be kept abreast of the development. I am not financially all that well endowed so I will be paying especial attention to the possibility of free hardware. Major Kudos guys!