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DIY Energy Monitor

Discussion in 'Charging Standards and Infrastructure' started by Haxster, Apr 4, 2017.

  1. Haxster

    Haxster Member

    Apr 4, 2016
    Silicon Valley
    For under $50 you can build a plug & play energy monitor for your EV that lets you check voltage, current, Watts, and kWh.


    Here’s what I used: DROK Digital Multimeter AC Voltage Amperage Power Energy 4in1 Meter 80-260V 100A Volts Amps Testing Gauge 22kW 9999kWh Power Energy Monitor Red Digital Tube Display: Industrial & Scientific Camco 55215 18" PowerGrip Extender - 50 AMP: Automotive

    The meter is pretty nice. It has a recessed button to reset the accumulated energy consumption. And if power is lost, it doesn’t lose this reading. It consumes less than a Watt and auto-ranges the displays to provide more resolution. It’s perfect for a 40 Amp home charger and could be used for the Tesla High Amp Wall Connector (with different connections).

    At 40 Amps, there’s about a 3% current difference between the meter and the charger readings. I haven’t tested the meter with a calibrated 40 Amp load to see who’s right…and I don’t plan to. Close enough.

    The short 14-50 extension cable was spliced inside the plastic box (one hot wire cut) to get at the 240V needed for the meter and a to run one of the legs thru the current sensing transformer for the meter. There are open frame transformers that would eliminate the need to cut & splice the wire, but this meter didn’t come with one.

    If anyone’s interested, the Tesla Mobile Connector draws an average of 3 Watts in standby.
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