14.47 kwh per full charge

Discussion in 'Clarity' started by JulianClarity, Aug 14, 2019 at 3:13 PM.

  1. JulianClarity

    JulianClarity Active Member

    Finally I got free charge at work on chargepoint, and I found the capacity is more than I wad told before.
     
  2. Robert_Alabama

    Robert_Alabama Active Member

    Capacity and charging kWh consumed are two different things. If the battery was ever fully depleted, Capacity would reduced by charging losses as compared to charging consumption. But the battery isn't ever fully depleted before charging. The battery at full capacity is advertised at 17 KWh. Assuming that the battery is depleted to 20%, that would mean charging would be approximately (17*.8*1.065) or 14.5 kWh. (assuming 6.5% losses from EVSE to battery). (I'd normally have just thrown 10% at losses, but I chose the 6.5% to make the math work for your reported charging kWh.) Also, someone may have told you that the usable capacity of the battery is (17kWh *.8) or about 13.6 kWh. This is essentially correct from what I have been able to observe. Occasionally some report their cars slippling below the 20% reserve level, but I don't think that is often. Again, the 13.6 kWh used from the battery would require more like 14.5 kWh to replenish due to losses. And I know you charged free at work, but if you did this at home, you would have been billed for losses on top of this (wiring losses from your meter to your EVSE), so you may have had to pay for 15 kWh (depends on your wire size and charging amperage and voltage).
     
    Last edited: Aug 14, 2019 at 4:04 PM
  3. Geor99

    Geor99 Active Member

    According to my kilowatt meter on a 120V outlet with a 50' cord that is 12 gauge, I used 16.3kW hrs to charge my car on Friday (the only time that I measured it.)
    It seemed a little high even on 120V.

    The kilowatt meter was a $9.99 Ebay special, so perhaps it's not the world's most accurate meter:)
     
  4. JulianClarity

    JulianClarity Active Member

    Thank you guys for the info!
     
  5. Robert_Alabama

    Robert_Alabama Active Member

    Had a minute so I used google. #12 copper is about 1.588 ohms/1000 ft. So 50' is 0.0794 ohms. To EVSE and back on the extension cord (current has to flow on both legs), that is 0.1588 ohms (r). At 16A charging (i) , i squared r is 40.6 W/hr. Assuming 10 hours to charge, that is about 400W lost to the extension cord. Maybe a little more due to heating at contacts, round up to say 500W. So that would reduce the 16.3 kWh to 15.8 kWh. The charging losses for the EVSE are also more for the 120V vs 240V (twice the voltage is 25% of the losses). So given the earlier example, I wouldn't be surprised for total losses (even including battery charging) to be double that of the 240V charging. In the example above, we assumed 0.9 kWh at 240, so maybe 1.8 kWh at 240. So 13.6 + .5 + 1.8 = 15.9 kWh estimated at 120V. It's very likely I was a little too optimistic at just multiplying the losses at 2, or maybe your car was a little more discharged (13.6 was too low in the equation above) or a combination of both. But I'd believe the 16.3 kWh from your meter. Did this in a hurry so y'all don't hate on me too much if I messed it up....
     
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  6. Geor99

    Geor99 Active Member

    I believe that those charts assume the round trip so you dont need to double the ohms/distance constant.

    Otherwise Thanks for the calculating:)
     
  7. Robert_Alabama

    Robert_Alabama Active Member

    I didn't pull the value from any chart, just googled resistance per foot for #12 copper. I am pretty sure it hasn't been adjusted for any single phase application/3 phase application assumption. So I believe it should be doubled for both neutral and hot leg losses. But I have been known to be wrong (occasionally).
     
  8. Geor99

    Geor99 Active Member

    Gotcha. Those online calculators normally ask if single phase etc and even note that a roundtrip is assumed.
     
  9. KentuckyKen

    KentuckyKen Well-Known Member

    Historically on other threads, the most reported charging kWhs have been in the ~14.2 to 14.4 range on a Level 2 EVSE with no extension cord. This makes sense since the BMS keeps some buffer at the top and bottom of the SOC to ensure battery health. The 14.2 to 14.4 kWhs range is the usable amount of the total 17 kWh battery pack that the BMS allows.
     
  10. Robert_Alabama

    Robert_Alabama Active Member

    Yes, I think I'll buy that. 14.2-14.4 kWh from the level 2 EVSE would be about 13.3 to 13.5 kWh of useful battery capacity after subtracting 6.5% losses (very close to 80% of 17 kWh). Maybe this is making me feel even better with the 6.5% loss assumption for level 2 charging. I guess this is at 32A? Maybe charging at 16A level 2, the loss percentage would be more like 3.2% (losses are 1/4 per hour, but charging time is doubled)?
     
    Last edited: Aug 14, 2019 at 5:57 PM
  11. Geor99

    Geor99 Active Member

    Next time I'm on 0.0ev miles, I'll get on the Honda app to get my battery % prior to charging. This may help figure the numbers.
    I'll also steal my wife's parking spot and ditch the 50' extension cord. According to your math, even with my 12 gauge cord, I'm wasting more juice than I would like.
     
    Robert_Alabama likes this.
  12. Bender

    Bender Member

    That's always for me.... It's at 12% now and it's been charging for over an hour already.
    HOWEVER, *reporting* below 20% does NOT mean it's actually below 20%. They are reading voltage(s) and converting to the charge (or usable charge) percentage with a formula.
     
  13. Robert_Alabama

    Robert_Alabama Active Member

    You're right, the 2 bars/1 bar/0 bar may be as good a guess as we can get. Hondalink may just be reporting percentage of usable battery.
     
  14. fotomoto

    fotomoto Active Member


    There's also any conditioning losses from the battery thermal system in the noise; especially this time of year and/or charging in the heat.

    FWIW
     
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  15. KentuckyKen

    KentuckyKen Well-Known Member

    This is true, buts it’s analogous to preconditioning when plugged in. It does cost some energy, but it doesn’t affect how much charge the battery ultimately receives and so your SOC and range are also unaffected.

    From what I’ve read on this forum and some Internet searches, the on board charger (AC to DC converter) reportedly loses about 6 to 12% to that dastardly Law of Thermodynamics.
    So let’s call it 92% efficient.
    Then 14.2 to 14.4 max reported kWh input (Level 2 EVSE, no extension cord) at 92% = ~13.1 to 13.2 kWhs actually entering the battery pack. For a fresh 17 kWh battery pack, that’s about 77 or 78% usable capacity, giving a buffer of around 23% that is split between top and bottom of the SOC. We just don’t know for sure how that is split up. If we assume the bottom buffer is 10%, then there is 13% at the top. Again, that’s an assumption.
    The approximate 23% total buffer, or 77% usable part of the total 17 kWh battery pack seem to be in the ball park using the total Voltage of the battery pack and the nominal 55 Amp hour number from the PDI.

    So the BMS does a good job protecting our battery pack from thermal overheating, overcharging, and over depletion and thus many are happy to let the BMS do it’s thing and just plug and drive. Some of us want to treat our battery packs extra nice in order to prolong their life and range, and within the bounds of convenience, try various strategies like not charging to 100% (usable) whenever possible.

    That’s too much mental math for my poor pea brain since neither Honda or ChargePoint make it possible to charge to a user selectable %SOC. All I’m doing is scheduling charging early in the morning so I’m not charging a just used, possibly hot battery and reducing the time spent at 100% SOC. I also cleaned out the garage and for the first time in my life am parking in my garage to try and reduce large temperature swings. (That and preconditioning and ceramic tint really keep my range up.) Additionally, I usually don’t let the SOC go much below half and don’t charge if I haven’t driven much that day in order to reduce depth of discharge and number of charge cycles. I’m not obsessing over it though. I’m just doing a few simple things that are easy to do. Those with longer commutes will have to charge every night and those with only Level 1 charge most of the night.

    So, bottom line, who knows if all these machinations will have a significant effect or not? I’m guessing that no matter how much effort you put into “babying” your battery pack it won’t make more than a few % difference since the BMS is pretty good. Of course we’ll all have to compare notes in 8 to 10 years to really know but by then it will be too late.

    I freely admit that I am not an EE or licensed electrician and don't even play one on TV, so will the more knowledgeable members out there please correct anything I may have gotten wrong.
     
    2002 likes this.
  16. sniwallof

    sniwallof Active Member

    I get home, plug in, and charge until it stops (EV full charge) (chargepoint 32A).

    Hopefully soon many of us will have our $60 Autel - @MrFixit tool, then we can compare battery numbers over the years.
     
    Last edited: Aug 15, 2019 at 2:11 PM
  17. Mikesmith78

    Mikesmith78 New Member

    I measured 16.35 Kwhr using my kill-a-watt meter for a full charge from EV = 0 to 100%. This is with the provided level 1 charger. Does this seem high?

    If 14.47 kwhr is from a level 2, then level 1 wastes about 1.88 kwhr of energy more than level 2.
     
  18. fotomoto

    fotomoto Active Member

    As a ballpark rule of thumb? No, that seems similar to reports from other PHEV's owners I've seen. For example, Volts with 10.5 kWhr report 12.x kWhr's, C-Max when new is 5.7 kwhr report 7ish, etc. Every EVSE and onboard charger have different efficiency ratings and temperatures play a big role too so don't read a lot into these values.
     
  19. metabubble

    metabubble New Member

    My Honda charger only pulls 10.9A
     
  20. Robert_Alabama

    Robert_Alabama Active Member

    True. I forgot that the level 1 only has a rated level of 12A. When I get a minute, I will redo this post for the lower amperage. Thanks for catching that. That will lower the losses for the extension cord for @geo99 a good bit.
     

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