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Modify MC240 for 40A Charging?

Discussion in 'Roadster' started by supersnoop, Apr 22, 2014.

  1. supersnoop

    supersnoop Tesla Roadster #334

    Mar 24, 2014
    I have the older model mobile connector, MC240, which is limited to 30A. I know that the newer version, the UMC, supports 40A with the NEMA 14-50 plug. I've been reading through the forums and see reference to modifying the MC240, often with mention of the Roadster Foundry Mobile Charger, which seems to be the basis for Tesla's updated UMC.

    I've seen a post or two mention that the MC240 can be modified; that the only reason it was limited to 30A was because that's the largest GFI available at the time it was made. There was reference to simply removing the GFI to enable full 40A charging. Event through I'm neither an electrician nor an engineer, that just doesn't seem right. Are there any instructions available to enable more amps out of the MC240?
  2. jeremyz

    jeremyz Member

    Apr 5, 2013
    Just taking out the GFCI wouldn't make it charge at 40A. There's a circuit board next to the GFCI that generates a pilot signal that tells the car what the maximum available charging current is. The charger in the car limits the amount of current it draws based on that pilot signal. If you changed the pilot signal (by changing its duty cycle) to advertise a maximum charging current of 40A, the Roadster would try to suck 40A out of it. I'm not sure if that would blow up components in the MC240 or not. The wiring seems up to the task of 40A charging, but I'm not sure about the other components.
  3. qwk

    qwk Model S P2681

    Dec 19, 2008
  4. Pantera Dude

    Pantera Dude Member

    Mar 18, 2012
    Long Beach, California
    A company or someone had listed at one time that they could do the conversion of the MC240 to 40 amps for maybe $800? It may have been in the parts for sale section? This was a number of years ago IIRC.
  5. ernst

    ernst 't is een grijze.

    Nov 1, 2010
    Im already using one of Chris Howell's older evse boards for a long time. Not sure if it fits in you old box but you cable and plug are the most valuable parts anyway. It does not have a fancy automatic amp dail with different adapter cables also not $1500. How many different places do you expect to charge your car to begin with? If its a lot you have to get to used to be careful on what you can really expect from a socket to charge your car on critical moments. Its not to difficult to get basic adapter made for this setup or make them your self.
  6. hcsharp

    hcsharp Active Member

    Jun 7, 2011
    The OpenEVSE boards would fit but wouldn't be safe. The problem is the UMC has to be able to automatically reduce the amps based on what adapter you are using. OpenEVSE does not do this (at least not the same way that the UMC does). You might think "Oh I'll just remember to limit the amps on the VDS..." but it will be easy to forget and you may not be the only person who uses that cord. Someone else might not know and start a serious fire. You would have to re-program the firmware for OpenEVSE then test it. At least OpenE has a GFI circuit that works better than the MC240 GFI.

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