A note to 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