When to pull the plug?

Discussion in 'Clarity' started by Ken7, Jan 4, 2018.

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  1. Ken7

    Ken7 Active Member

    When I'm not driving my Model S, I leave the charger plugged in the car. The Tesla will periodically turn on the charger as the 'phantom drain' continues from the draw of the onboard electronics. Once you've lost about 6-7 miles of range from this phantom drain, the car automatically charges back up to full.

    Now with the Clarity, I haven't noticed that this automatic recharging behavior nor have I seen the stated range drop on the phone app, even if the car remains parked for a period. Now that might not mean the range isn't actually dropping, as all batteries will lose charge over time, especially in a relatively cold garage, but I haven't seen it.

    So without confirmation that the Clarity's charger periodically kicks in on a parked car, is there any reason to keep the charger plugged in the car after the charging has stopped? I observed the same behavior on our PHEV Sonata. We never saw the charger kick in again after charging initially stopped.
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  3. jdonalds

    jdonalds Well-Known Member

    When our Clarity is fully charged I sometimes pull the plug just to get the cord out of the way. I haven't noticed any drop in the battery level, but then the car doesn't sit unused for more than 20 hours at a time.
  4. dstrauss

    dstrauss Well-Known Member

    Only for the convenience of starting the Climate Control if you are hooked to a Level 2 charger so it doesn't drain the battery warming up.
  5. Ken7

    Ken7 Active Member

    That's actually a good point and a good reason to plug it in. In the summer, not so much.
  6. Ken7

    Ken7 Active Member

    There were times the Sonata was sitting in our garage for 3 days and we didn't notice a single mile dropping off the range. I wasn't prone to believing that.
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  8. dstrauss

    dstrauss Well-Known Member

    I wonder though, down here in the desert SW, whether it might not be a good idea when pre-cooling as well?
  9. Ken7

    Ken7 Active Member

    ^ That's true too.
  10. Tiralc

    Tiralc Active Member

    I think the Volt (esp. Gen2) did all sorts of minor housekeeping, like charging routines for the 12V battery (including an odd pulsed pattern for extending battery life, desulfation i think), or possibly a little heating of the HV battery on really cold days, or some fluid pumping when very hot. It often made all sorts of odd noises you could hear while walking by it in the garage. So, I always left if plugged in, except for summer thunderstorms.

    Other than climate pre-conditioning, our Clarity does not seem to do much else once fully charged?

    Definitely unplug for thunderstorms. Odds of a nearby strike may be low, but the right transient on the 240V line can do a lot of damage.
    Last edited: Jan 4, 2018
  11. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    1. Is this the Clarity Electric (BEV), or the Clarity PHEV?

    1a: If it's the PHEV, then likely there's no good reason to leave it on the charger all the time. The PHEV doesn't have a built-in battery heater, so that won't keep the battery warm even if you do leave it plugged in all the time.

    1b: If it's the BEV, then you are advised to keep it plugged in at night anytime the outside temperature is going to drop below freezing, so the car can run the battery heater as necessary to keep it warm.

    2. Generally speaking, you shouldn't be charging any BEV to 100% on a daily basis; that's bad for battery life. The usual advice is to charge it to 80%, unless you need to maximize the car's range the next day. If you want to get down into the weeds (WARNING: What follows is very definitely "inside EV engineering", so skip the rest of this paragraph unless you're a STEM geek like me) of doing everything you can to maximize battery life, then you should be selecting a charge level balanced around a 50% SoC (State of Charge). That is, you should select a charge level that will allow your car to start the day as far above 50% as it will end it below 50%. (For example, if your daily drive uses 40% of the battery's capacity, then you should charge to 70% and discharge to 30% by the end of the day.)

    Unfortunately, according to some recent discussion here on this forum, it appears not all BEVs are built to allow the driver to select the charge level. I know the Tesla Model S allows you to select whatever level of charge you want; I'm told the Leaf gives you no control at all (another reason to avoid buying a Leaf!); I dunno about the Clarity Electric.

    * * * * *

    There are other issues related to this topic. If you're going to leave a BEV sitting for a month or longer, then ideally you should discharge the pack to 50% but leave it on the charger. That's possible in Tesla's cars, but I dunno about other BEVs. I find it shocking that not all production BEVs allow you multiple options on setting the level of charge :eek:, but apparently that's the case.
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  13. jdonalds

    jdonalds Well-Known Member

    I've always assumed the cars are designed to have a range of charge shown to the consumer that is less than the actual charge on the battery. That way the "fully charged" battery shown to the driver is actually less than a 100% charge; this to prolong the life of the battery. I remember from someone's earlier post that only something like 14kW is required to fully charge the 17kW battery.

    Is this not true?
  14. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    Yes, it's true. Tesla cars (sorry to keep talking about them, but those are the EVs I know the most about) have about 4-8% reserve, depending on the size of the battery pack; 4-8% difference between usable capacity and full capacity. I'm not an engineer, but I am getting the impression (not fact, but a hopefully informed guess) that other BEV makers are also engineering their BEVs to use most -- over 90% -- of the full capacity of the battery pack.

    No BEV maker is going to engineer their cars to use the full 100% of the battery capacity as rated by the battery cell manufacturer. Repeatedly charging a cell to 100% of rated capacity, or draining it to 0%, will age the battery cells quite rapidly.

    Bottom line: What you need to keep in mind, as you charge and discharge the battery pack in your car, is that you're not interacting with the battery cells themselves; you're interacting with the car's BMS, the Battery Management System. When you charge your PEV to what the car's instrument panel reads as a "100% charge", it's not actually 100% of what the battery cell manufacturer rates as its full capacity. A PEV's BMS is programmed to not allow the pack to fall below a certain level of charge, and that level will be displayed as "0%". Likewise, whatever the BMS is programmed to use as the maximum charge level will be displayed as "100%", altho it may actually be only 92% or 94% or 96% of the battery cells' full capacity.

    It seems that PHEVs are noticeably different. The Volt has such a large margin of reserve that at last report, not even the oldest Volts have shown any decrease in range due to capacity loss! I hesitate to make blanket statements regarding a subject on which I'm far from an expert, but early evidence re other PHEVs leads me to suspect that they also have a larger portion of their full capacity held in reserve. That is, a larger percentage reserve; the actual kWh of reserve may be no larger than is typical for a BEV, because the average battery capacity (total kWh) for a PHEV is far lower than it is for a BEV. So, when the Volt's instrument panel reads "100% charge", then what is the actual level of charge? Googling the subject, I see reports that a "full charge" of a Volt's originally 16 kWh battery pack took 12-13 kWh. That indicates the usable capacity was only ~78% of the full capacity when the cars were new.
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  15. JyChevyVolt

    JyChevyVolt Active Member

    From 2011-2015, the Volt used 16, 16.5, and 17.1 kWh battery packs. GM only allowed 65% of the battery to be usable, to guarantee 150,000 miles and 5000 cycle.
  16. dstrauss

    dstrauss Well-Known Member

    A "know nothing" here, but it was my understanding from using Li in laptops, tablets, and phones for years that many manufacturers only charge within a 60% band - not letting it go below 20% or charge beyond 80% capacity to avoid battery degradation. Could this be a part of the EV equation as well?
  17. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    May I ask what your source is for that figure?

    I've seen a great deal of controversy and argument over just how much reserve GM used. In fact, so far as I know, to this day GM even refuses to acknowledge that there is some reserve built in. I've even seen at least one person who ought to know better, claim that GM has engineered the pack not to lose capacity over time, as if that was physically possible!
  18. Tiralc

    Tiralc Active Member

    Last edited: Jan 4, 2018
  19. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    I don't at all doubt what you say is true. Let's keep in mind that not all li-ion batteries are created equal, nor are all li-ion battery packs. Different types of li-ion battery cells use different chemistries. Some are optimized for high cycle life; others are optimized for maximum power (used in PHEVs) or maximum energy (used in Tesla's cars and likely in other BEVs.)

    Laptops use only a very few (I think it's 3-5?) li-ion cells. Obviously they can't allow even a single cell to fail; if one does, then the battery pack would need to be replaced. At the other extreme, Tesla cars are engineered so that if a few cells fail, they are automatically cut out of connection with the rest of the battery pack, so the failure of a handful or less is pretty insignificant.

    The charging standard for stationary/ home energy storage using li-ion batteries used to be 80% DoD (Depth of Discharge); cycling between 10%-90% SoC (State of Charge). That used to be the rule-of-thumb recommendation for anyone using li-ion cells; even for do-it-yourselfers building their own conversion EVs.

    But obviously production BEVs are engineered to allow a greater percentage of the car's battery pack to be used; the usable capacity for BEVs in general, I think, is 90% or higher. But that doesn't mean drivers of those cars should be charging their cars to the max every day! Every expert on the subject advises charging to a lower percentage if and when it's practical to do so, to extend the life of your car's battery pack. (And that's why I'm shocked that Nissan and perhaps other BEV makers force BEV drivers to charge to the max the BMS will allow.)

    I think it's pretty clear why BEV manufacturers have optimized their cars' battery packs to allow more of the capacity to be used. If a battery pack costs $10,000, then you don't want to waste 20% ($2000) of that on unused reserve capacity! Packs probably don't cost so much these days, but a few short years ago they did, and the initial engineering of the packs was done back when they did cost that much.

    dstrauss, I realize I have not fully answered your question. But I tend to get myself into trouble when I start talking beyond the edges of what I really understand, so I think I've said about as much on this subject as I should. Perhaps others can expand on the differences in engineering between li-ion battery packs in consumer electronics vs. plug-in EVs.
  20. Pushmi-Pullyu

    Pushmi-Pullyu Well-Known Member

    WARNING: This is an "inside EV engineering" post. If you're not interested in the details of EV engineering, then don't read any further.

    Okay, that agrees with the ~78% figure that I found in a very brief Google search. But that does not necessarily mean JyChevyVolt is incorrect to cite 65% as the true usable capacity figure. It may be that (to use my earlier figures) using 12-13 kWh of energy to charge a nominally 16 kWh was measuring that 12-13 kWh from the wall, and not what the battery pack actually stored. If you lose 15% of the energy from charging inefficiency, then for a use of 12.5 kWh that indicates a loss of ~1.9 kWh, which means the pack is only storing ~10.6 kWh in a 16 kWh pack, which comes to ~66.25%... which certainly appears to be within experimental error of JyChevyVolt's figure of 65%.

    In fact, my guess is that the reported kWh figures for charging the Volt's battery pack are almost certainly measuring the kWh drawn from the wall, and not the actual charge level of the pack. I've read enough on that subject to know that it's very, very difficult to measure the exact charge level of a li-ion battery pack. That's a challenge even for someone specializing in EV/battery cell electrical engineering. On the other hand, measuring how much energy is fed into the charger in the car is dead easy; all you need is the right meter between the wall plug and the car.
  21. Viking79

    Viking79 Well-Known Member

    PHEVs use a lower percentage of the battery to prevent damage from over-voltage while the generator is running. BEVs don't have this issue. The design goals are very different for a BEV and PHEV. A BEV might only need to last 500 to 1000 cycles to go a few hundred K, but a PHEV might need 5000 cycles to do the same. I imagine they are slightly different chemistry between the two in order to optimize them for their use case, but that is speculation on my part.
  22. JyChevyVolt

    JyChevyVolt Active Member

    2013 Chevy Volt
  23. Viking79

    Viking79 Well-Known Member

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