Matt's blog

A note to visitors

Dear visitors:

As you have probably noticed, it's been a while since the EnerJar site has been updated. As much as I'd love to attribute my neglect entirely to schoolwork and projects, there has been quite a bit of foot-dragging going on as well. We recently discussed the future of the EnerJar, to try to get back on track, and both of us were nagged by a concern that had been brought up to us many times: the EnerJar isn't very safe.

Several comments on this site as well as emails we have received describe several significant issues with the design. Most of the problems stem from a lack of isolation between the AC line and the low-voltage circuitry. Some students at Cornell designed a device inspired by the EnerJar, taking into account many of these safety concerns. Their design is quite clever and I encourage anybody interested in building a safer EnerJar alternative to read through their documentation. However, their design also requires two power supplies and does not achieve the precision that we feel is necessary in an all-purpose power meter.

We explored other alternatives, including hall effect sensors and signal transformers. None of the solutions we found produced the desired sensitivity, and all of them added considerable complexity and cost to the design. After considering these options, and the ethical responsibilities of an engineer, we have decided to stop supporting the EnerJar project.

We're sorry to everyone who was waiting for an update. The design problems are just too big. If any talented DIY'ers out there think they can make the EnerJar safe and easy-to-use while staying cheap and simple, please, prove us wrong and make a better power meter.

Thanks for all the comments and support,

Matt Meshulam and Zach Dwiel

Progress page and more

I just added a Progress page where we will keep track of what still needs to be done.

Also, we've gotten a few questions about the possibility of a 240-volt international version of the EnerJar. To make the EnerJar work on 240 volts, all that is needed is to change the value of a single resistor. The code will be exactly the same, because of the calibration that we are working on.

In response to another question, at the moment, we are not planning on selling prebuilt EnerJars. We may reconsider after the design is completed and we begin sourcing parts, but if you want an EnerJar but have no soldering skills, we recommend making friends with an electronics geek. They are pretty handy to have around.

Welcome to!

Well, we've finally launched a real website! As you can probably tell, we're not totally done with the site but we have posted preliminary schematics and source code. We will be updating the site as we solidify more of the design. If you want to stay updated on our progress, subscribe to our RSS feed or leave a comment below saying that you want to be on our mailing list. If you run into any issues with the site, email: admin {at) enerjar [dot} net.