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How much power does the the Roadster's AC use?

Discussion in 'Roadster' started by benji4, Jul 16, 2011.

  1. benji4

    benji4 Roadster 2.5 #0476

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    Today it was pretty hot, around 30 degrees C, so I decided to leave the soft top on and just use the air con today. Anyway, I set off driving with a full standard charge (190 ideal miles) and reset the trip counter as I normally do. Anyway, after driving for awhile, I noticed that my ideal miles was all the way down to 150, and I had averaged 458 Wh/mi for the first 20 miles of my trip! It was a bit shocking to see that as I have never done anything close to that badly before. At that rate the car would use up a whole standard charge in less that 100 miles (not counting the reserve of course).

    Anyway, I turned the air con off, opened the windows, reset the trip counter, and for the next few miles of my trip I was able to average a much more normal 225 Wh/mi. I was in stop and go traffic and did spend probably an hour or so in the car, so maybe an hour of using the air con is what did it. The PEM, motor, and battery were all in the blue range so no problem there. Question is, should the AC really be using that much power, and do I need to have Tesla take a look at it?
     
  2. Sparrow

    Sparrow S105/ Roadster 189

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    My AC seems to cut my range by up to 20% so I am getting between 300 and 350 Wh/mile while using the AC on a regular basis. I have been surprised by those numbers because the RAV4 EV seems to drop range by less than 10%.
     
  3. Eberhard

    Eberhard #421 Model S #S32

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    #3 Eberhard, Jul 16, 2011
    Last edited: Jul 16, 2011
    Its not possible to say how much is the consumption of the AC per 100km. Its more kW per hour and depends on heat and humidity as well. I guess it sucks around 3-5kW including the cooling of the battery pack.
     
  4. Doug_G

    Doug_G Lead Moderator

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    That seems extreme to me. In my experience the A/C takes a very modest amount of power.
     
  5. NigelM

    NigelM Recovering Member

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    Ignition on and car stationary the dash shows a draw of 1 Amp; turn on the A/C and it rises to 6 Amp and seems to settle on 5-6Amp. Maybe someone smarter than me can translate that to a likely effect on the battery power and therefore to average range impact?
     
  6. Doug_G

    Doug_G Lead Moderator

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    4.5 amps at 400 volts is 1.8 kW. Run the A/C for an hour at that power and it will consume 1.8 kWh (higher math there!).

    That is 3.4% of the 53 kWh pack capacity. Assuming a full pack = 385 ideal km that means you would consume 13 km range in an hour.

    Like I said, it consumes a very modest amount of power.
     
  7. Doug_G

    Doug_G Lead Moderator

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    Going back to Benji's original question...

    If your A/C consumed anywhere near that much power it would be on fire. The excess consumption you are reporting has absolutely nothing to do with the A/C.
     
  8. tennis_trs

    tennis_trs 2010 2.0 Roadster Sport

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    If benji4's 458Wh/mi and 225Wh/mi were accurate and the only difference was due to the AC being off and it was 1hr with the AC on, then I believe that would indicate:
    458-225=233Wh/mi due to AC
    (233Wh/mi)*(20mi)/1h= 4660W average power for the AC

    Looking at NigelM's data:
    About 5A for AC
    If assume 400V then
    5A*400V=2000W

    I believe there are other threads where people have indicated estimates of power usage by their AC, but I only did a quick search and didn't see any.
     
  9. Sparrow

    Sparrow S105/ Roadster 189

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    When my AC is running in my 1.5 Roadster, the amp reading goes from 1 or 2 to about 9 or 10 amps.
     
  10. Doug_G

    Doug_G Lead Moderator

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    I'm believe the 1.5 A/C system is different from the 2.0/2.5 version. As I recall my 2.0's numbers are in line with NigelM's.
     
  11. WarpedOne

    WarpedOne Supreme Premier

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    8 A at 370V gives about 3kW. Sounds right.
     
  12. ChargeIt!

    ChargeIt! Member

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    And there's also a "Power Share Adapter Installation" TSB for 1.5 Roadsters I am aware of. Don't know if this applies to 2.0+. And I don't have before/after data. Supposedly helps with the way A/C is shared between ESS and passenger cooling. This may affect the amount of power draw, so ... when quoting usage, it may be helpful to know whether the TSB has been implemented on the car.
     
  13. markwj

    markwj Moderator, Asia Pacific

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    Charging 240V @13A is ~3.2kW. AirCon + Fans seems to use less than half of that when charging in hot climates.

    Idle, with AirCon running, I get 2 to 3 amps (@400V) shown on the vehicle display of my 2.5.

    My own estimates are between 1kW and 1.5kW for AirCon + Fans.
     
  14. Doug_G

    Doug_G Lead Moderator

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    My 2.0 produces identical results. Stationary, A/C on, fan hi.
     
  15. hcsharp

    hcsharp Active Member

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    That would be the same as my experience with v. 2.5. It adds 1 or 2 amps depending on fan setting. Negligible effect on mileage unless you're driving really slow.
     
  16. benji4

    benji4 Roadster 2.5 #0476

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    If the AC uses 5-6 amps @400V, doesn't that mean the battery would drain completely after 24 hours of continuous use? That seems extremely inefficient to me since even my whole house does not use that much power... Another way to look at it, if you drove for 2 hours at an average of 10 mph (which unfortunately happens a lot in Tokyo), your Wh/mi indeed would nearly double from the 200's to the 400's as I saw the other day. Very easy to get into the mid 400's in that type of scenario. I suppose the moral of the story is that if you are forced to drive at very slow speeds but have distance to cover, leave the AC off!

    Anyway, does the AC really use just 2 or 3 amps, or does it use 5 or 6? At 5 amps / 400V, here is the approximate additional Wh/mi you lose at various speeds.

    10mph 200
    20mph 133
    30mph 67
    40mph 50
    50mph 43
    60mph 33
     
  17. Doug_G

    Doug_G Lead Moderator

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    It's hard to know exactly, but the A/C appears to use something shy of 2 kW with the fan on high.

    FYI, I don't believe the fan itself is responsible for any significant power draw. The Roadster backs down the heater power if you turn down the fan; that's immediately obvious if you adjust the fan with the heater on. I also suspect it reduces cooler power to the cabin with a lower fan setting.
     
  18. NigelM

    NigelM Recovering Member

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    I guess (as with my home AC) that less power is required to run the compressor to cool the air, than is required to heat the air with any type of radiator elements?
     
  19. TEG

    TEG TMC Moderator

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    Typically in an EV the heater uses more power than the AC.

    Similar old discussion here:
    HVAC power usage

     
  20. Doug_G

    Doug_G Lead Moderator

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    Thermodynamically speaking...

    Resistive heaters are always 100% efficient, because fundamentally any efficiency losses would come out as heat.

    Heat pumps, on the other hand, can be more than "100% efficient", because they are moving heat around not creating it.

    In the real world...

    Real heat pumps never achieve their theoretical efficiency. And of course any heat pump (real or theoretical) generates its own waste heat.

    For both heating and cooling there is efficiency loss due to heating in the battery pack and wiring. But that can be ignored in a comparison since it is the same for both (ignoring second-order effects like different pack temperatures).

    I think the biggest reason the resistive heaters take more power is that they are simply more powerful. I know that sounds circular, but the air conditioner simply cannot produce as much delta-T as the resistive heaters. I suspect that if it was sized to do the same delta-T it would take more power.
     

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