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High Power Charging Ideas

Discussion in 'Roadster: Technical' started by richkae, Sep 5, 2009.

  1. richkae

    richkae VIN587

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    When you charge the roadster a certain portion of the power is spent cooling the battery. If you try to do a fast charge in an hour at higher voltage and current like 50 kW ( 500 volts 100 amps? ) there will be a lot of heat to dump.

    Why not have a second loop through the radiator to do a higher efficiency heat exchange. This second loop is normally empty and penalizes the car with an extra couple pounds of copper or aluminum. Then you have a second umbilical that runs coolant through this heat exchanger. The car doesnt need to waste any of the juice it gets running fans, only running the pumps.

    If you are charging at 50 kW, then you have the charge station have a powerful cooling system to cool this fluid.
    Even if you are charging at a normal power, you could run fluid through a big heat sink and then you would charge faster because you dont waste power running the fans and you should be able to run the pumps less because you are getting rid of the heat more efficiently.
     
  2. Jeremy

    Jeremy New Member

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    Most likely the cost and complexity would not justify this sort of endeavor, especially since the vast majority of the time Tesla owners are going to be charging from home or elsewhere with power limitations around the 70 amp level anyway. If the infrastructure for public charging comes into play in the future, then 440-ish volts and high amperages will be a reality for rapid charging.

    Keep in mind, though, that the power to run a fan and the coolant pump is truly inconsequential when compared to the amount of juice the battery pack can hold, and in terms of what it essentially 'robs' from the charging process. If you left your Roadster unplugged and in an area where it had to run the coolant pump 24/7, it would go for months and months before the battery discharged fully. The cost to your electric bill to run that pump while charging, if it's even necessary when charging, would almost certainly never add up to how much it would cost to add additional features and capacity to the cooling system.

    A lot of people also ask about solar panels on the car and the fact is that even if the entire surface of the car was covered in them and you left it outside in the sun all day, you might add 2 miles to the range. Boils down to the same answer -- it's just not cost effective and the benefit isn't worth adding the complication, weight, etc...

    Jeremy
     
  3. raymond

    raymond Member

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    Wasting Energy like Two Really Nice Refrigerators « Tesla Founders Blog says it's more like 16 days. And since Martin actually measured his findings I think 16 days (14 kWh in 4 days = 56 kWh in 16 days) is pretty accurate.
     
  4. vfx

    vfx Well-Known Member

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    When I have left the car unplugged I logged about 3 miles lost each day.

    My car came hundreds and hundreds after Martin's so I'm sure things got changed as a result of that blog.
     
  5. ra-san

    ra-san Member

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    Much as I'd like to say all is great, the truth is a little more nuanced than that. Basically, if the battery is cool and no pumps or fans are running, then 1'ish percent per day discharge is pretty accurate (maybe 2%). If the pack is warm though, Martin's numbers still hold true. My own tracking shows a bit more consumption than Martin's, but certainly on that order of magnitude. Your pump will rarely run while just sitting there if you've been charging on 240V, thanks to the built-in cooling phase. Not so lucky with 120V, currently.

    Some people (vfx maybe :) ) seem to have more luck than others with getting their packs cool enough, even with 110, to not run the pump continuously, but the general rule is 240V good, 120V convenient maybe, but not so good.

    Should be noted that Martin's original observation was from tracking while charging with the 240V HPC, and that had indeed been improved since Martin's post, by tweaking the trigger point for the coolant pump to run.
     
  6. Palpatine

    Palpatine Banned

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    That was based off of any older version of the firmware that ran the pumps much more often while the battery was above 50% charge even when just sitting in your garage.

    Now the pumps only run when you are above the standard charge into the range/performance charging zone.
     
  7. BBHighway

    BBHighway Member

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    I look forward to getting that firmware upgrade. My pump runs when the charge is over 50%.
     
  8. ra-san

    ra-san Member

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    #8 ra-san, Sep 16, 2009
    Last edited: Sep 16, 2009
    The 2010's may well be different, but for the 2008's, I'm current as far as I know, and as far as has been tracked on the owner's board at 3.3.1.17.

    All the versions near that release and several earlier have the same trigger supposedly. The lead firmware guys said this:
    I have also been told that instead of ~87F, the number is actually 27C (~80.6F). I don't know which is right, just know that with 120V charging, it's almost always above it and the pump is on. This is what drove my suggestion in the firmware update thread elsewhere on this site.
     
  9. vfx

    vfx Well-Known Member

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    I heard there was to be a new release last week.
     
  10. DaveD

    DaveD EVs Kick Gas!

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    Numeric versions are beyond my comprehension. They should give it a name - something like Snow Leopard, eh? :biggrin:
     
  11. richkae

    richkae VIN587

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    waste heat

    I suggested a higher efficiency cooling loop not because I am worried about the wasted power running fans, I am worried that a little tiny radiator and fans cant remove the heat fast enough for really high power charging.
    With a separate cooling loop to a big water heat sink and humungous radiator you should be able to remove heat a lot faster.
    The faster you can remove the heat, the faster you can charge, right?
     
  12. TEG

    TEG TMC Moderator

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    That "cooling loop" could power some sort of small generator (Sterling Engine?) to recapture some of the energy that is otherwise being wasted as heat...
     
  13. richkae

    richkae VIN587

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    physics challenge

    Ok suppose you use 60 kWh to put 50 kWh of charge into your car and you have 10 kWh of waste heat. How much will that energy heat up 50 gallons of water, assume that it starts at 60F.

    Calculator watches and slide rules.... go!
     
  14. doug

    doug Administrator / Head Moderator

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    #14 doug, Sep 18, 2009
    Last edited: Sep 19, 2009
    Heh.. a nice quick back of the envelope exercise in unit conversion. If you didn't have a way to look up the constants, you can get pretty far by remembering some things in non SI units. You can approximate the mass density of water as 1 oz/fluid oz, which leads to 1 gallon weighing 8 lbs (I assume US gallons). Knowing the definition of the calorie gives you the specific heat capacity of water, etc. There are only 2 significant figures anyhow.

    I did break down and look up the number of calories in a kWh and the C to F temperature conversions.

    So I got a 45 Kelvin increase in temperature, resulting in a final temperature of 61 C or 142 F.
     

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