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Thread: How to make a 30 amp J1772 extension cord for public charging

  1. #41
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    Quote Originally Posted by hcsharp View Post
    I just spent a lot of time writing comments/questions to your previous post and then I saw this!
    Sorry. I was kicking myself too..

    I can't see doing this without the micro but maybe it's possible.
    Possibly some special cases (like the 70A->80A example) would be feasible, but I agree there's still too much complexity in the general case.

    Why do you think the dummy load would stay on when the car disconnected? We're using a one-shot triggered by the falling edge of the pilot to turn on the dummy circuit. Wouldn't the dummy load get turned off at the end of our timing sequence the same as any other time?
    It's only an issue with the really stripped-down (analogue) version - as you point out, the problem is actually worse than that since there need to be two different dummy loads for connected-but-not-charging and charging-active cases, and it needs to transition from one to the other (as well as the case of transitioning to none at all which is what I was worrying about).

    The fact that the very short stretch 'just works' without any dummy load at all (because the power supply reservoir acts as a kind of sample-and-hold, remembering what the level was at the end of the high pulse) maybe suggests other approaches.

    For a wacky approach, the micro can create dummy load by running the ADC at maximum rate and modulating the CPU clock speed to achieve the required voltage - as it happens, the CPU running at max speed consumes just over the amount of current we need to burn.

    Could we solve the glitch problem by using silicon transistors instead of FETs to transition to and from the dummy load? Instead of switching on a new circuit of resistors, transistors could manage the current. As I think about this, it would be more complicated and introduce other problems. A filter approach might be better.
    Another idea to fix the glitch (maybe half-baked, I've only just thought of it): the power supply reservoir in practice tracks the level of the high pilot, so we can provide another FET to drive the output from our power reservoir - turn this on momentarily to cause the transition on the output, then turn on the main FET once input and output are at approximately the same level.

  2. #42
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    Quote Originally Posted by TonyWilliams View Post
    Secondly, I actually called my home owners insurance company, USAA, and posed this specific scenario. I was absolutely assured that my company would pay the claim provided there wasn't intentional malice (intentionally trying to burn the house down).
    I would appreciate if you could town down the attacks ("internet blather"), only because your own statement is just as much. When you get a written letter from a claims decision-maker, I'll concede that there is one insurance company that doesn't care if you violate the NEC. Otherwise, side by side with your hypothetical call with USAA, I will tell you that I know a homeowner whose claim with another company likely larger than USAA was impacted with electrical code violations. There, Tony 1, FlasherZ 1. We don't know who gave you the opinion - a front line sales rep, a claims rep, a claims decision maker, etc., and we don't know how you characterized the question.

    It doesn't really matter which forum it is. A technical forum should include safety issues, which include both bodily harm and property protection, which brings in risk management associated with that as well. The fact it is illegal is indeed important to the situation.

    That said, my warning is here - I post it in each thread with a connection to the FAQ because search engines dumping someone into this thread may not convey the risk.

    If you don't like the posts, feel free to ignore me on the board, my posts won't appear, and you'll be happier. I'm sure others have. It won't break my heart, really.

    I won't add to this thread anymore, so you can continue to build your extension cord. However, like your "safe" Easy240 design from the other thread, it is technically illegal to use the device. I don't mind you producing one and trying to make it as safe as possible, just tell people that it violates the NEC and that may include liability and insurance risks. Simple as that.
    Last edited by FlasherZ; 2013-09-27 at 09:02 AM.

  3. #43
    Senior Member wycolo's Avatar
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    Flasher: Well said & words to live by. Your expertise is extensive and pretty much unique in this forum; something we appreciate.

    I viewed this thread as 'public' meaning exclusively 'outdoor away from home'. But we must consider the likelihood that sooner or later a device that we have become used to using on a regular basis will work its way homeward and end up getting plugged into our garage EVSE for a visiting car parked alongside the house, etc, etc. Since 'stuff happens' eventually, there you go: a major loss occurs and someone is left holding the bag.

    It is a nice solution to the ICEing problem, however!!
    --

  4. #44
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  5. #45
    Senior Member hcsharp's Avatar
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    Quote Originally Posted by wycolo View Post
    Flasher: Well said & words to live by. Your expertise is extensive and pretty much unique in this forum; something we appreciate.
    +1. @FlasherZ: I'm sorry that you are being repeatedly attacked by somebody that you are only trying to help. Keep in mind that the vast majority of us here on TMC appreciate your generous contributions to our community.

    Quote Originally Posted by wycolo View Post
    I viewed this thread as 'public' meaning exclusively 'outdoor away from home'. But we must consider the likelihood that sooner or later a device that we have become used to using on a regular basis will work its way homeward and end up getting plugged into our garage EVSE for a visiting car parked alongside the house, etc, etc. Since 'stuff happens' eventually, there you go: a major loss occurs and someone is left holding the bag.

    It is a nice solution to the ICEing problem, however!!
    --
    Well said. A couple years ago I would have said "C'mon, I know how to be careful with extension cords..." But who's going to borrow your car or cord who doesn't know they have to scale the amps when charging at my house (70 & 80A chargers)? The risk is obviously small but pretty soon there will be millions of EVs on the roads and the risk will be multiplied dramatically.

  6. #46
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    Thanks, I appreciate the kind words. I've taken my answer to this question to the FAQ where I referenced this thread and listed my own experience with the question to the insurance company. I'll stop cluttering the thread with safety concerns and let you get back to figuring out how to make it safer.

    - - - Updated - - -

    Quote Originally Posted by wycolo View Post
    I viewed this thread as 'public' meaning exclusively 'outdoor away from home'. But we must consider the likelihood that sooner or later a device that we have become used to using on a regular basis will work its way homeward and end up getting plugged into our garage EVSE for a visiting car parked alongside the house, etc, etc. Since 'stuff happens' eventually, there you go: a major loss occurs and someone is left holding the bag.
    That's also why I say "liability", because it may not be a denial of a claim but rather a liability claim against you.

    Have a great weekend, all.

  7. #47
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    Quote Originally Posted by FlasherZ View Post
    .... I don't mind you producing one and trying to make it as safe as possible, just tell people that it violates the NEC and that may include liability and insurance risks. Simple as that.
    Well, now we're getting to the heart of the problem... you think I need your approval. No, I don't. Simple as that.

  8. #48
    Senior Member wycolo's Avatar
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    Just a "30 amp J1772 extension cord" - how hard can that be, really?? I keep asking myself that as I read thru these detailed variations on this simple theme. But reflecting on my experience with HF Radio where success was as much art as science. Gives pause to the expectation that Tesla will come up with a Chademo Charging Adapter 'real soon now'. Why does my head hurt whilst reading thru this? Thanx to all who are contributing to this effort.
    --

  9. #49
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    Just an update - I have now designed all the analogue pieces of this circuit and simulated them successfully, so I'm convinced this will work; unfortunately got swamped with Real Work so haven't got round to drawing the whole schematic yet.

    The glitch on the input pilot when the output switches did look quite nasty in simulation (using the J1772 figure of 2n2 for car/cable load capacitance - no idea how close to real-world this is). The fix with an additional FET to drive the transition from our supply reservoir rather than the input pilot solves it nicely.

    Will try to get back to it shortly.

  10. #50
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    Quote Originally Posted by arg View Post
    Just an update - I have now designed all the analogue pieces of this circuit and simulated them successfully, so I'm convinced this will work; unfortunately got swamped with Real Work so haven't got round to drawing the whole schematic yet.

    The glitch on the input pilot when the output switches did look quite nasty in simulation (using the J1772 figure of 2n2 for car/cable load capacitance - no idea how close to real-world this is). The fix with an additional FET to drive the transition from our supply reservoir rather than the input pilot solves it nicely.

    Will try to get back to it shortly.
    Awesome work! Looking forward to testing your design.

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