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Lowering Amps to Improve Battery Life

Discussion in 'Model X: Battery & Charging' started by tarponman, Aug 31, 2016.

  1. tarponman

    tarponman New Member

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    Just picked up our Model X 75D this past Friday and having a blast. When I asked about battery maintenance, I received a circumspect answer about staying within daily limit. But, they suggested lowering the home charging amps from 40 to 30 or even 20 (saying that you get a more even charge - like filling an ice tray with less water pressure), and lowering them even further when on vacation to trickle charge. The forums that I have read have a lot of discussion about optimal daily charge (80% or less unless needed) and 50-60% range when on vacation, but little on charge amps (a couple of old threads on lowering it). Thoughts and recommendations? Thanks
     
  2. shokunin

    shokunin P85 & S40

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    Even at 240v and 40amps it's a relatively slow charge (7h charge). I have a ton of 18650's that I use for flashlights and other projects and I don't think I've ever charged any of them that slowly.

    Now, I have dialed down charge rate from 40 to 36 because i was having issues with multiple UMC's (Universal Mobile Connector) failing.
     
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  3. robby

    robby Member

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    Yeah, and be sure to charge at high altitude to minimize gravitational pull on the electrons.
     
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  4. Rocky_H

    Rocky_H Member

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    I'm going to agree with @shokunin. Considering that the battery can charge at over 100kW power level, the less than 10kW of the mobile connector is nothing to the battery, so it will not care a bit. However, I also have my amps turned down from 40A for regular daily use because the mobile connector does get a little hot at that maximum level, and heat (and especially hot/cold cycles) is the main thing that degrades and shortens the life of electronics, metal solder joints, etc. I want to make my UMC last as long as possible, and I don't care if it takes another hour charging while I'm sleeping.
     
  5. David99

    David99 Active Member

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    The statement about charging being 'more even' is nonsense. The electricity goes into the entire battery at the same time at the same rate. The analogy with filling an object with water is wrong. Tesla keeps the cells and modules in balance regardless of how you charge or drive. It's a process that is always active and works extremely well. After almost 100k miles on my car the differences between the modules are 0.1%!

    Charging at 40 Amp is absolutely safe for the battery and fine. Lowering the rate does not help your battery. It also doesn't help with efficiency as the charger is actually less efficient at partial load and most efficient at full load. Tesla's website used to show that, but they changed this a while ago.

    One good practice is to use the charge time and set it so the charging finishes just before you use the car again in the morning. This way you keep the battery at a lower state of charge for a longer time (which is good for the battery) and charging will warm up the battery so when you start driving in the morning, you have no issues with performance or limited regen. Charging at night also help smoothing out the load on the grid.
     
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  6. mal_tsla

    mal_tsla Member

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    Range-readiness is probably more important than any tiny longevity benefits that charging slowly might produce.

    What happens when you have to make an unexpected trip in the middle of the night and your charge is suboptimal because the car was set to slow-charge?

    No thanks! When our car is parked in the garage, it is always plugged in and charging to 90% daily limit as fast as it can.
     
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  7. number12

    number12 Member

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    What about high amp charging?

    Also what if you plug a 100amp breaker hpwc into an non high amp charging car?
     
  8. mal_tsla

    mal_tsla Member

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    We have a 100 amp HPWC (really 80amp). The X charges from it at 72. A standard charger equipped X will charge from it at 40.

    The car is charger. The HPWC is just a connection to the power. You can hear relays click to flow high power after the car recognizes it.
     
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  9. number12

    number12 Member

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    So it will not hurt loaner for instance?
     
  10. brkaus

    brkaus Member

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    The car will take as much as possible per it's configuration or manual setting if less than max, up to the setting on the HPWC (which is determined by wiring, breaker, overall panel capacity).
     
  11. number12

    number12 Member

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    So what about people with the high amp charging option! I see now that it was a clear waste of money (coming previously from a leaf with 80 mile range it made sense).

    But moving on what is the best practice?
     
  12. brkaus

    brkaus Member

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    No reason to lower amps on vacation. It's going to hit the
    High amp charging option would be beneficial for trips. You could use and free up a destination charger quickly, either for someone else or to get back on the road. It would also be good for quick turnaround at home. Come back from travels and need to run lots of errands for example.

    I personally would probably set the car at 40a when at home for normal use. No need to over-warm things. Bump it up to max in "emergency" if/when needed.

    I would leave the HPWC set at the max the circuit would support.
     
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  13. bhzmark

    bhzmark Active Member

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    Best practice is minimizing the chance that you will be caught in a low charge state when you need more range. So charging all the time to 90% whenever you can as fast as you can is best practice. So far experience has shown that there's no-hit to battery degradation with that practice
     
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  14. wycolo

    wycolo Active Member

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    If the newest batteries cannot withstand high amp or SC rates then that car's firmware should already have the proper limits in place.
    --
     
  15. Saghost

    Saghost Active Member

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    There might be a small argument that a slower rate might extend the charger's life - but this is liquid cooled solid state electronics and were told it's the same hardware that's in 72A cars, so even that is generally running way below capacity and should be subject to minimal stresses.

    As other folks have said, the fastest AC charge rates the car gives you are still very, very slow charging for a lithium chemistry.

    Also, cars that are supercharged daily aren't showing higher rates of degradation than cars that aren't - there's a car that's driven from L.A. to Las Vegas every day, supercharged to 100% every day, and has gotten 200,000 miles in a year and a half - and it is apparently showing 6% capacity loss after that 200k.

    Tales from a Tesla Model S at 200k miles
     
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  16. Rocky_H

    Rocky_H Member

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    Not necessarily a waste of money, as @brkaus pointed out, but it does depend on where you you drive how much use you would get out of it. Here are a couple of for instances from near where I live. The most commonly traveled route if people are driving between the San Francisco bay area and Boise Idaho includes using U.S. highway 95 from Winnemucca up through the edge of Oregon to get to Boise. That is a long stretch that is not very reasonable to do in one charge (really not doable going south with the elevation gain). So what are the charging options along the way? Well, people used to use an RV park in Jordan Valley at 40A, and it would take about an hour to hour and a half to have enough to get through.

    Someone donated a high power J1772 charging station to a casino in McDermitt, right at the Nevada border that supplies 80A. If you have the higher amp charger in your Model X, you can suck juice from that at 72A instead of 48A, so it makes the charging stop shorter. There is a similar situation going from Boise to Bend Oregon. If you take highway 20, there is a high amp charger in Burns. If you take highway 26, there is a high amp charger in John Day. So you are generally correct that it doesn't really matter for home use when the car is going to charge while you are sleeping, but for routes that don't have full Supercharger coverage, it can be very useful. I only have the old 40A charger in my car, so those routes take more planning/patience for me, and at this point, I don't think it's worth the extra $2,000 to get the upgrade to my car to the 80A charger.
     
  17. Rocky_H

    Rocky_H Member

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    No, it's all fine because the car and the station communicate with each other. The station announces how much power is available, and the car requests how much it wants, not forced by the station. It's like if there is a big food buffet. The buffet doesn't dump on you and bury you under a pile of food if you approach it. You come with your plate, and you start taking what you want. There is more available, but you are deciding how much to put on your plate.
     
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  18. mal_tsla

    mal_tsla Member

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    #18 mal_tsla, Dec 1, 2016 at 8:38 AM
    Last edited: Dec 1, 2016 at 9:02 AM
    The owners manual states that best practice is to plug the car in whenever you are not driving it, if possible.

    Less frequent or slower charging is never better. Charge as fast as you can as often as you can. It isn't going to hurt your car. The only thing that hurts the car is charging above 90% regularly. If you're going to charge over 90% (before a long trip) try to do it close to your departure if possible.

    Trust Tesla's guidance on their own technology more than people online saying you should charge only while you sleep and only to 50% or whatever you need in "normal" conditions. Do you want to be low on charge when an emergency trip is suddenly needed at 3AM because you usually keep the car at 50% and charge overnight only? Not me

    We have high amp charging upgrade, because we want the car as "range ready" as it can be, always, just like a traditional gas car is (given that refueling is available anywhere and in just a few minutes) and we want 48mph charging instead of 27mph charging from things like destination chargers that we might use on trips.

    This means we let the car charge however it wants (it chooses 72 amps at home), set to the recommended 90%, and we plug it in every time we park it at home, even if we only drove it 20 miles on an errand. This does not hurt anything, in fact, the owners manual says to do it this way: "plug it in when not driving it"

    A connected Tesla is a happy Tesla.

    EDIT: just a quick note to say that we have an HPWC at home, as I believe the Mobile Connector is meant as just that -- something that lives in the car in case it is needed. I don't think it is designed for constant/daily home charging. So the above might not make sense if you're planning to use the UMC full-time at home. If we were using the UMC at home as our primary means of charging (e.g. with a NEMA 14-50 outlet), I might be tempted to adopt different charging habits to possibly protect the UMC from excess wear, or at least specifically ask Tesla if charging "at every opportunity" at the full 40A is fine for the UMC.
     
  19. Rocky_H

    Rocky_H Member

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    Well, I'll just offer a little balanced perspective. If you look at the recommended daily set point for charging, it is not AT 90%; it is a section of battery range from 50% to 90%. Choose as you see fit. Considering that the car will start warning you that it's not a good idea if you set it for 91% or more, I don't see how 1% less than that is magically perfect. I use around 75 to 80% to keep it a little farther from that unrecommended area. Also, that is fine for us since most days we don't use more than about 20 or 30 miles, so it's never really low anyway, even if we've gone a day or two without plugging in. I do understand Tesla's recommending to keep it plugged in. It's a new experience for people if they are used to driving a gas car, and they want people to build that habit and have that range confidence, not forget for a few days and then they realize their car is low and they are stressed because they need to leave for work. Also, they do want to assure people that it is not at all bad to keep it plugged in as much as you want.

    For the sudden emergency movie-scenario trip at 3AM, that might come up once in a decade or two, do you have Superchargers near you? If that were to come up, and my car isn't at 90% in the middle of the night because I have it set to start charging at 1AM, I have options. I can still probably make it to the Supercharger 2 hours away, or I could hit the Supercharger here in town for 5-10 minutes before heading out.
     
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  20. mal_tsla

    mal_tsla Member

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    Nearest supercharger is about 100miles away. I definitely envy those of you with that extra flexibility that you can hope to encounter one on any random trip, but I bet it's the minority case.

    Lithium ion batteries aren't going to be damaged by being charged to 90%. Tesla has already built in the safety margin by making the "trip" range 90-100. It's not that 91 is a magic number where it's bad... it's that they've chosen 90-100 as the "bad range." Charging to 70-80 is just doubling margins. Most lithium batteries can tolerate charges above 95% without issue.

    The real issue with 100% charging is when the car is left to rest at 100% for prolonged periods. It's bad for the battery chemistry to sit at max charge. Imagine a balloon inflated to JUST under the point that it pops and then stored that way.

    By discouraging charging above 90%, Tesla is reducing the likelihood of that happening to almost zero. But charging to 90% or less as often as you want, as fast as you want, that's fully endorsed.
     

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