Trick a smart meter into working on the bank

When the widget you’re working on is powered by a battery or USB charger, it’s probably pretty safe to use on the couch. But when the object of your reverse engineering wish is a residential electricity meter, things can get a little tricky.

Not that this increased danger level has been preserved [Hash] from exploring the mysteries of smart meters. Still, with the desire to make it a little safer, he came up with a neat trick to safely power electric meters on the couch. [Hash] found that the internal switching power supply on the backplane of the meter was simple enough to feed back from a 12-volt bench power supply, rather than supplying the meter with the full 240-volt AC power it normally gets when on a meter base (These are meters for the North American market, where split phase 240 volts is the norm for residential connections.) But that wasn’t enough for the meter – it started up, but stayed in a reset state without going completely off to start. It took more to bring the meter to full life.

That something turned out to be a small AC signal. Normally, a resistor network divides the 240 volt supply to about 3 volts, which is used by the sensing circuit in the meter. [Hash] found that injecting a 60 Hz, 600 mV sine wave signal with about 3 volts DC bias into the sensing circuit was enough to fake the meter into thinking it was connected to the meter base. The video below gives an overview of the hack and some nice shots of the inside of the meters he has worked with.

[Hash] has been working with these meters for a while and some of the things he has learned are pure gold. Be sure to check out his 2021 Remoticon lecture on meter hacking for all the fascinating details.

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