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Thread: SAE DC fast charge retrofit?

  1. #1
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    SAE DC fast charge retrofit?

    I'm not very knowledgeable in this area technically, so here goes:

    Would it be possible to retrofit an earlier SAE J1772-equppied car to accept the new SAE DC fast charge coupler?

    Supposing you could source the vehicle end connector, would using DC fast charging on a vehicle which was not originally designed for it, fry the battery?

    For just one example, if you had the right connector, could you DC fast charge a Think City, without any harmful effects? Or does the battery pack have to be "set up" for it?

    Or would it not matter?

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    It wouldn't be possible.

    For a car set up with the J1772 connector the type of power it's designed for is very different from what is supplied with the DC system. Square peg in round hole.

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    What would happen? Would it cook the battery?

    From my understanding, the SAE DC fast charge standard is simply the J1772 with an extra connector. This way a car set up for SAE DC fast charge (like the new Spark) can still accept a level 2 J1772 connector at the same port.

    My thinking was that one could just get a DC fast charge port and hook it up where the existing port is, and there you go, a 5 minute recharge for a Volt.

    From your answer I take it that the onboard charger is the issue? If you could explain the "square peg round hole" thing for me on a technical level, I'd appreciate it.

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    S85 - VIN:P05130 - 3/2/13 jerry33's Avatar
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    Quote Originally Posted by mattjs33 View Post
    From your answer I take it that the onboard charger is the issue? If you could explain the "square peg round hole" thing for me on a technical level, I'd appreciate it.
    Any DC charging system bypasses the on-board charger(s) (which convert AC from the EVSE to DC) so the on-board chargers don't enter into the picture. DC charging requires special circuitry to connect directly to the battery. An adapter would have to mimic the Supercharger on the car side and the J1772 DC charger on the EVSE side and might require bulky (and heavy) parts to do so.
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    Jerry, you've confused me (an easy thing to do) with your mention of the Supercharger, which is a proprietary Tesla technology.

    I'm speaking of the new SAE DC fast charge hookup, which incorporates a J1772 connector in one unit which can do both Level 2 J1772 charging as well as DC fast charge. I think there's a few extra contacts, and a specific socket?

    In any case, if DC fast charge does indeed bypass the car's onboard chargers, then couldn't a sufficiently talented person simply rewire a vehicle-side SAE DC fast charge socket in the place of the J1772 socket of a vehicle so equipped? Since the SAE DC fast charge socket also incorporates J1772, no capability would be lost. From what you say a direct circuit to the battery would be required, if I understand correctly. As I'm theorizing, I wouldn't be needing any adapter at all.

    Forgetting for a moment the method in which you would hook up -- Could the batteries in the current generation of EVs on the road handle the current without problems?

    If SAE DC fast charge stations take off, you could imagine a cottage industry of retrofitting charge sockets to take advantage.

  6. #6
    Senior Member stopcrazypp's Avatar
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    Quote Originally Posted by mattjs33 View Post
    I'm not very knowledgeable in this area technically, so here goes:

    Would it be possible to retrofit an earlier SAE J1772-equppied car to accept the new SAE DC fast charge coupler?

    Supposing you could source the vehicle end connector, would using DC fast charging on a vehicle which was not originally designed for it, fry the battery?

    For just one example, if you had the right connector, could you DC fast charge a Think City, without any harmful effects? Or does the battery pack have to be "set up" for it?

    Or would it not matter?
    If you want an "easy" SAE DC charging retrofit, the car must have DC charging equipment in the first place! As others have said, the DC charger bypasses the AC charging circuit. The major difference between the two is that a DC capable EV at minimum has high power contactor(s) that can connect and disconnect the battery from the DC port, the onboard charger, and other power electronics. In addition, the car will have beefed up wiring between the DC port and the battery.

    For this reason, it'll be much easier to convert a car with a different DC charging standard (for example a Leaf with Chademo port) to SAE J1772 DC, than it is to convert a car without any DC charging.

    And having a normal J1772 port isn't going to help you much, because even though the J1772 DC port is backwards compatible in regards to AC (a car with a new J1772-DC port can use existing older J1772 chargers), J1772 is not necessarily forwards compatible (aka upgradeable) esp. with respect to DC. And you WILL have to upgrade the software/charging protocol in the car to handle the new DC protocol (which was just finalized recently). There may also be new hardware necessary to handle the PLC (power line communication) that the DC protocol uses.

    Quote Originally Posted by jerry33 View Post
    Any DC charging system bypasses the on-board charger(s) (which convert AC from the EVSE to DC) so the on-board chargers don't enter into the picture. DC charging requires special circuitry to connect directly to the battery. An adapter would have to mimic the Supercharger on the car side and the J1772 DC charger on the EVSE side and might require bulky (and heavy) parts to do so.
    This is very OT, but Tesla is pin-to-pin compatible with J1772-DC because J1772-DC doesn't use the two AC pins when charging in DC. So all Tesla needs for the Model S is a simple physical adapter to work with J1772-DC (just like the small one it has for regular J1772). The only difference is the extra two large DC pins in J1772 DC will connect to the power pin of the Tesla connector (rather than the AC pins), plus you probably can't use the same adapter to charge in AC mode.
    Last edited by stopcrazypp; 2012-12-05 at 07:24 PM.
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    Quote Originally Posted by stopcrazypp View Post
    ... This is very OT, but Tesla is pin-to-pin compatible with J1772-DC because J1772-DC doesn't use the two AC pins when charging in DC. So all Tesla needs for the Model S is a simple physical adapter to work with J1772-DC (just like the small one it has for regular J1772). The only difference is the extra two large DC pins in J1772 DC will connect to the power pin of the Tesla connector (rather than the AC pins), plus you probably can't use the same adapter to charge in AC mode.
    Interesting! So a J1772-DC to Tesla-SC adapter sounds could be on the drawing boards already!
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    I'll try and make this simple. The bottom line is that a car can't handle SAE DC fast charging unless it was designed to do so.

    Why?

    The prior SAE standard was about "level 1" and "level 2" charging which is all AC, not DC. To use fast DC charging, the car needs:

    1) to know what to tell the DC charger to tell it how fast to charge, when to slow down, etc. This is a "control protocol". Without this, the charger will burn out something in the car. Essentially the car and charger need to understand a common language. The language for SAE level 1 and 2 charging is different from the language used to control SAE DC charging. DC charging needs a richer control language so the car can tell the charger what to do and when to keep the charger charging fast but so fast that it burns out the car's battery or charging circuitry.

    2) to be able to talk to the charger (electrically) in the first place. The car and charger need the moral equivalent of a phone line so they can talk to each other. I don't know if this is the same or not for SAE AC and DC charging. But it doesn't really matter because of #1 and #3.

    3) the proper charging circuitry so the car can safely swallow the power sent by the charger. SAE level 2 charging is electrically different from SAE DC fast charging so the car needs different power paths from the charging port to the battery to handle both.

    So if the car isn't designed ahead of time to support SAE level 1 and 2 charging and SAE DC charging, the odds are essentially zero that you can practically and safely retrofit the car to do so. The car manufacturer might be able to develop and produce a retrofit kit but the cost to do so would be high enough that it's simply not worth it. The cost to the consumer for the kit+installation would likely be so high that it wouldn't make financial sense.

    About "Supercharging":

    Tesla's proprietary fast DC charging (aka Supercharging) is supposedly compatible enough with SAE DC charging that Tesla should be able to provide a reasonably priced adapter. But that's because Tesla knew enough about the SAE standard in advance (and probably influenced it) and designed their charging circuitry and control protocol to be compatible. But Tesla has a nicer plug .

    I believe that SAE and Chademo (a competing DC fast charging technology used by the Nissan Leaf) isn't compatible even though both are DC. #3 is probably (close enough to) the same for both. As I understand it, the challenge is #1 and probably #2 -- the control protocols are different enough as is the communication connection that a car can't handle both unless it was explicitly designed to do so. To my knowledge, no car in existence has been.

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    Quote Originally Posted by rcc View Post
    I believe that SAE and Chademo (a competing DC fast charging technology used by the Nissan Leaf) isn't compatible even though both are DC. #3 is probably (close enough to) the same for both. As I understand it, the challenge is #1 and probably #2 -- the control protocols are different enough as is the communication connection that a car can't handle both unless it was explicitly designed to do so. To my knowledge, no car in existence has been.
    #3 is going to be virtually the same for all DC charging protocols, since DC charging is basically just a connection from the battery and external charger (with a high power contactor in between for safety and heavy wiring to handle the current).

    #1 is not that big a challenge if the charging logic is programmable, plus you can always add a micro-controller to do some "translating" if it isn't.

    #2 is the definite big issue with SAE vs CHAdeMO. CHAdeMO uses a CAN bus and some analog control pins for charger control. SAE just uses PLC for charger control. The number of pins (and function of them) are completely different between the two, so a direct physical adapter is impossible.
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    Thank you StopCrazyPP and RCC for explaining that to me, in terms even I could understand!

    Based on the size of the battery, how long do you guys think it would take to charge a Volt battery at DC fast charge? I wonder if there are any plans to outfit it for that type of charge?

    Now that the SAE DC standard is out, and the Spark is the first to take advantage, I can't think of any reason for any plug-in vehicle made for the U.S. market to not be built to handle this technology. Especially when one can still use the J1772 already in many places.

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