• State of the art - Reuse the hardware you already have!

    Mastro Gippo04/30/2022 at 11:33 0 comments

    If you’re a smart engineer or even anyone with a working brain cell, you might be asking why car manufacturers are not making their charger to be bidirectional already:

    After all, (almost) all the required power electronics for a 7kW (or more!) converter is already included in the car charger! It’s just a matter of replacing secondary side diodes with a bunch of mosfets and writing some software to make it bidirectional: 

    A standard cheap EVSE could then negotiate the energy transfer and connect the car to the grid. There are only a few drawbacks for this approach:

    • carmakers will not be able to sell more overpriced hardware to the users
    • grid configuration and regulations are different from location to location (this can be solved by sending the configurations and parameters to the car via the overengineered ISO 15118)
    • some car batteries may have a voltage that’s too low for the DC/AC converter when they are discharged

    Turns out, a few carmakers are starting to offer V2L (Vehicle to Load) to power utensils but still forbid V2H (Vehicle to Home). In this category we have the Mitsubishi Outlander, the Ford F-150, the Hyundai Ioniq 5 and the Kia EV6. Look at that cool adapter!

    The crafty hacker can now make a suicide cable and power its house, yay!

  • State of the art - Bidirectional AC/DC converter

    Mastro Gippo04/29/2022 at 16:46 0 comments

    Car manufacturers are hesitant to allow users to use the battery energy for anything other than driving for various reasons, like battery warranty or not wanting to compete with other products they’re selling like the Powerwall.

    Only the Nissan Leaf historically offered bidirectional energy transfer capabilities since 10 years ago, and a few bidirectional chargers popped up to support this using the CHAdeMO connection standard. CHAdeMO allowed CAN bus communication between the vehicle and the EVSE, and bidirectional power transfer could be requested.

    It must be noted that this is simply the same procedure as DC fast charging: the car and the charger negotiate a session, and the car directly connects the battery bus to the terminals. In a DC charging session, the charger would start the current flow to the car. But the battery voltage is directly available at the connector, so we can just connect any 400VDC load and we’re good to go! Unfortunately all modern cars interrupt the session and disconnect the contactor as soon as they detect energy flowing out of the battery, so that’s a no-go. But there's still hope! There’s a standard called ISO 15118 that describes the new communication method for DC charging (CHAdeMO is deprecated). I will rant about this standard in a followup post, but suffice it to say that it supports many Bidirectional Power Transfer modes! Unfortunately no car has implemented it yet, so we’ll have to wait at least for a software update if EV manufacturers are generous enough to provide one.