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Close call, almost drove off while plugged in!

Plugged in?

Plugged in?

I had a close call last week where I almost drove off in the electric MR2 with the cord plugged in…luckily disaster was averted.

I normally don’t have this problem, because the charge port is on the driver side. Because of its location, I am always able to see the charge cord, and can unplug it before driving off.

However, I was in a hurry and had to run out of the house late in the evening. In my effort to save some time, I decided not to turn on the lights in the garage and fumbled quickly to get into the car. As I started to drive off, I noticed my problem and quickly stepped on the brakes. Luckily, there was no damage done.

It looks like I am not the first one to have done this; this a DIY question wants to know how to build a motor disabler when the cord is connected.

Manufactured electric cars like the Nissan Leaf, Chevy Volt, and the Tesla Model S all have safety features built in, such that the car can not be driven while the cord is plugged in.

I decided to install this safety feature using a $6 magnetic reed switch from Amazon. Here’s a video of the mock up:

I ended up wiring the magnetic switch right above the inertia switch in the following schematic.

wiring schematic

Magnetic switch connected right above the Inertia switch, which disables the car if ever in an accident.

This worked for a few minutes before the switch failed in the closed position. I think it is due to some back voltage from relay. A friend suggested that I put a one way diode between relay lead 85 and lead 86 to prevent this back voltage. I’ve invested in another $6 magnetic switch and will test with the diode in place and will make a comment below when complete.

Please comment if you have any suggestions. Thanks!


Posted in MR2EV

7 Responses to “Close call, almost drove off while plugged in!”

  • Ken says:

    The new switch with the diode didn’t work either, after a couple of weeks of driving, the magnetic switch melted…

    I am driving without the safety feature again…

    • Chris Bonaci says:

      I did not get your name,
      Anyway, for the reed switch you need a circuit with a transistor and a resistor. When I get home I will send you my diagram. What voltage are you using between the reed switch?


  • Chris Bonaci says:

    Dear Ken,
    Attached please find the reed circuit diagram. This diagram is for a 240V, obviously you will need to replace the 1K resistor to suit your needs, either for 110V or 12V.


    • Ken Chiang says:

      Hi Chris,
      I can’t find the attachment. I am not sure if it is possible to attach files in the comments section on this site. Can you email it to me at ken[at]mr2ev[dot]com?
      Thank you very much!


  • Doug Brentlinger says:

    For the guy that stripped a post hole on his battery: I did the same and installed a Helocoil thread replacement, works fine. Call if you want more info. 510-304-5001

    • Ken Chiang says:

      Hi Doug,

      Thanks for the tip, I was able to fix the bad battery terminal by retapping to an M12. My first attempt to tap to an M10 failed because I used the incorrect sized drill (it was too big). Lesson learned, when retapping a terminal, don’t just eyeball the opening and pick the closest match, use a tap chart like this.

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