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DIY DC->DC Charging Station

Discussion in 'Model S: Battery & Charging' started by wk057, Feb 26, 2015.

  1. wk057

    wk057 Senior Tinkerer

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    So, a long term goal of my off grid solar project is DC->DC charging for my Model S. Should be more efficient, should be able to do at least the same power level at the HPWC, or even twice as much.

    Since the CHAdeMO protocol appears to be more readily available than Tesla's Supercharger protocol, using the adapter plus a custom made CHAdeMO station would seem to make sense.

    I found one company that sells the charging station plug... and they want $1500 for just the plug, which is pretty steep for just the plug, IMO. It would probably be better, for my purposes, to gut a Tesla CHAdeMO adapter and not actually use the CHAdeMO plug.

    The power conversion side of things probably wouldn't be cheap either, especially with my setup where I would need to bump ~48VDC to ~400VDC with regulated voltage and current. To do 40kW that'd be ~830+A power draw on the input side, and 100+A output on the output side, and I envision many large HV capacitors and copper bus bars... so, not cheap either.

    Feeding directly from high voltage PV would likely be more ideal.

    I'm guessing that for the moment this is probably out of reach of my DIY skills, but probably possible long term when/if some more DC charging standards work with the Model S. When Tesla is done with their CHAdeMO adapter backlog, I'll probably buy a second one to gut and see what I can do, even if it is a low current demo.
     
  2. islandbayy

    islandbayy Active Member

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    I was thinking same thing. Also, maybe a CHAdeMO to CHAdeMO adapter. A box in-between to shuttle charge between two cars. Would allow cars to share a charge in emergency, as well as increase compatability to do so between brands. IE, Tesla can "Jump" a leaf. Leaf could, uh, might provide enough power to get a model s off the free way.
     
  3. wk057

    wk057 Senior Tinkerer

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    I think a company already makes something that does this... ORCA Inceptive

    Looks a bit bulky, though.

    For myself, I just want a personal 40kW GreatCharger (not quite "super" ;) ) preferably one that can run from low voltage DC input between 40-50V.

    - - - Updated - - -

    Actually, looks like that same company makes chargers that take DC input, but they not super efficient. Looks like 54kW input for 50kW output, so 92.5% efficient. So if I bumped my low voltage DC to high voltage DC at those current levels, the used one of those units, probably no better efficiency than using my DC-AC inverters and the onboard chargers. :(
     
  4. islandbayy

    islandbayy Active Member

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    Accually, I'm most interested in some sort of low power V2G. If I can eliminate my day time power usage, I'd save about $100/month if that power could be shifted to off peak.
     
  5. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Could you serialize some of your modules with nice 'n' chunky cables without needing a DC-to-DC converter? I realize it would limit your module increments, but perhaps that would get you cheap HV?
     
  6. wk057

    wk057 Senior Tinkerer

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    I don't think my 48V inverters would appreciate that too much. :)
     
  7. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #7 FlasherZ, Feb 26, 2015
    Last edited: Feb 26, 2015
    Well, duh. :)

    I was thinking the 48V inverters would remain at 48V from the +/- of each individual module; but using separate cables you'd serialize the modules to give you the 400+V you need to your DC/DC charger. It means isolated grounds on the DC side of your inverters and between modules, and I don't know enough about those inverters or your setup to know if that's possible or not.

    ------------------------------------------------ to DC charging neg
    |
    --- to inverter 1 neg
    MOD 1
    +++ to inverter 1 pos
    |
    --- to inverter 2 neg
    MOD 2
    +++ to inverter 2 pos
    |
    [...modules 3 through 7...]
    |
    --- to inverter 8 neg
    MOD 8
    +++ to inverter 8 pos
    +++++++++++++++++++++++++++ to DC charging pos
     
  8. wk057

    wk057 Senior Tinkerer

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    If I didn't have a ground/neutral/dc-negative bond anywhere, this technically could work. Doubt the NEC would approve though.

    Even if it did work, though, the issue would become imbalance in the SoC of the modules. The way the inverters I have work, most are powered down/sleeping waiting for a load. As the load increases, more inverters come online. There are technically 16x 4 kW inverter modules that can be either on or off in my setup. At 2kW, the next module comes online. at 4kW the next, 6kW the next, etc etc until we hit 32kW and all 16 modules are online for up to 64kW continuous load. Somewhere around 50% being the most efficient conversion I believe. (I plan on rotating out the order in which this happens so that they get a relatively equal usage using software, except for the primary inverter which needs to be physically switched to a different physical port which I will do periodically).

    But anyway, I would have to leave all of the modules online all the time for this to work evenly, which is a huge parasitic load all together (cant recall the exact number, but it's something like [edit] 272W with all modules active and idle [EDIT: found exact wattage]).
     
  9. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Yeah, just put shrink wrap around the whole room and call it an appliance and then the AHJ can't complain. :)

    It seemed like a long shot, and I figured there'd be balancing issues somewhere / sometime... But it's simpler than finding an 800A DC-DC step-up converter. :)
     
  10. wk057

    wk057 Senior Tinkerer

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    Received a response from a CHAdeMO station manufacturer. They claim they can customize one of their units to accept the low voltage 40-50V DC input from my battery bank for 40-50kW output to the Model S with > 90% efficiency............ for $30k.

    As cool as that would be, I think I'm going to have to pass on that one.....
     
  11. davewill

    davewill Member

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    There's a project over on the Nissan LEAF forum working on a home sized CHAdeMO.

    Mini-QC Rapid-Charger (RC) Project for LEAF QC Port

    They are working on a 240v AC powered device, but the project is broken up into three pieces, a DC power supply, a DC-to-DC converter to make the correct voltage as needed, and a CHAdeMO interface module. In particular, they've been working on their own CHAdeMO plugs.
     
  12. wk057

    wk057 Senior Tinkerer

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    Guess it can't hurt to post over there. :)
     

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