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Free Charging @ Work -vs.- Daily Charging @ Home

Discussion in 'Model S: Battery & Charging' started by Brian, Apr 27, 2013.

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  1. Brian

    Brian New Member

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    My roundtrip daily commute is only 25-30 miles, and I have access to free J1772 charging at work. However, we're expected to move our vehicles from the company chargers shortly after our charge is finished (to let others use them), and I've been following Tesla's advice of plugging the vehicle in every night and charging to standard charge. As a result, I don't take much advantage of the free charging at work, since I would need to move the vehicle after just 45-60 minutes of charging.

    It would save on the electric bill for me to *not* plug in my Model S at home and wait for the charge to get down to 40-50%, and then complete a standard charge of the battery for free one or two days a week at work. But will this behavior cause accelerated degradation of the battery? Any advice from the battery experts out there?
     
  2. joshuaeven

    joshuaeven Member

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    I'm no expert, but I'd charge at work.
     
  3. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Charging at work is fine. I'd do it daily though.
     
  4. Brian

    Brian New Member

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    My problem is that charging daily at work is inconvenient, because the chargers are far enough away that it's a pain to move the vehicle after just 45-60 minutes of charging.

    My point here is -- do we *really* need to charge daily if the daily use is <30 miles, or will it harm the battery life to wait a few days in between charges?
     
  5. MichaelS

    MichaelS Member

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    My employer allows me to charge at work, for quick I am very grateful.

    Li-Ion batteries like best to be kept around 50% SOC. You didn't say if you have a 60 or 85 kWh car.

    I typically charge every other day with my MS60. Sometimes every third day. And at 100 to 188 mile charge takes about 5 hours on the 200V 30A circuit I have or 17 MPH charging.

    And once the really hot weather hits I will manually terminate the charging at 80% to keep the batteries cooler. Another good option is to time your charging so you leave right after the car finishes charging.

    So no, this will not degrade you battery pack.

    I've been driving pure electric since 1997 starting with a GM EV1.
     
  6. joshuaeven

    joshuaeven Member

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    Should be no issues at all with skipping days between charges. You could probably charge on Monday and Friday and be set for the week.
     
  7. Kipernicus

    Kipernicus Model S Res#P1440

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    Yes workplace chargers tend to be the 6kW variety (unless Brian you are lucky and have some high powered stuff at work), so a 25-30 mile round trip, plus nightly vampire losses, would mean 2.5 to 3 hours charging every day.
    What may be more of a factor is whether you can reliably get a charger at work. At mine we only have 4 to share among many plug-ins, some who really need a charge to get home, and I don't get in that early so usually have to try my luck in the afternoon.

    But to the OP, yeah I try to charge at work as much as possible (about 2-3 times a week), and I don't think it's going to harm the battery.
     
  8. Apoclyps

    Apoclyps Member

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    I have been charging daily at work. I wait for the non-S cars to do their charging before I try accessing them (6 J chargers and usually free by 3 pm). I work late (6:30 or 7 pm) so this is perfect for me. We are allowed 3 hours of charging a day (about 50 miles). My commute is about 40 miles plus vampire drain, so enough to keep the battery near full by Friday afternoon. The only time I plug in at home is the weekend, where I am taking it down past 50% charge and want to make sure I have enough to run errands and get back to work on Monday.

    I have had the car for only a week and am doing daily charging at work so that i will have enough charge to go on an extended weekend to Palm Springs. My Excel spreadsheet tells me I need to do the daily charging and one Range charge so that I have enough Juice to get to Palm Springs. I only have 110v at home (working on getting the 240v in, but gotta check with HOA and a decent Electrician). After this trip I may go with every other day charging.
     
  9. pete8314

    pete8314 Vendor

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    My daily mileage is about 30 miles typically. I charge at work once a week (they installed a NEMA 14-50 outlet for me) on a Wednesday normally, and then at home on a Sunday (I get free power on Sundays with my current plan). Generally my battery doesn't get below about 80 miles remaining (85kwh), but occasionally it'll get into the orange. So, free power, and it's an easy routine.
     
  10. EarlyAdopter

    EarlyAdopter Active Member

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    I'm in the exact same situation. I did the math and worked out that charging exclusively at work would save me a whole $25 a month in electricity versus charging at home. Not worth the hassle of the J1772 adapter, manually popping the charge door, and moving my car afterwards. I just grab the UMC when I get home each day. The convenience is worth the $25 a month.
     
  11. Ven Rala

    Ven Rala Member

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    I have a 14-50 installed at work (since I own my own business, getting the ok was easy), but my HOA has not yet approved my parking lot 10-30 outlet. So I guess for now my plan is to charge at work, and not to overdo weekend driving. I still have about 4 weeks to get this done before my delivery date.

    I thought it was recommended to charge daily? Is it better to get it down to 50% SOC before recharging?

    since I can charge any time of day at work (no one else for now needs the charger), should I charge at the end of the day?

    would it be a bad idea to range charge every Friday to get me through the weekend? (I am aware of the battery degradation issues with range charging, but it is not clear to me how often is too often).
     
  12. mknox

    mknox Well-Known Member

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    Tesla recommends plugging the car in whenever possible. They seem to know what they're doing when it comes to this technology, so I won't be second guessing them.

    I'm going to be installing a 90 amp J1772 charger at my office and will primarily charge there, but will plug in at home too.
     
  13. J in MN

    J in MN S60 P12635

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    Also consider that, in the USA at least, electrical infrastructure capacity is constrained during the summer day time peak, while there is significant available capacity at night. If EV adoption takes off in the way that most of us here want and expect, and a significant portion of people choose to charge during the day, additional infrastructure will need to build, probably at great expense, and will therefore lead to higher electricity rates for everyone.

    Therefore my rule of thumb is to charge at night, and only charge during the day if you need the extra range.
     
  14. mknox

    mknox Well-Known Member

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    That is actually a fair statement and worth keeping in mind. Here in Ontario, Canada we have Time-of-Use rates pretty much across the board, so it also becomes an economic consideration. In theory, at least, the higher rates should encourage off-peak charging, and those who do pay the premium are helping to fund infrastructure improvements to support added daytime loads.
     
  15. digitaltim

    digitaltim Sig737 VIN628

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    In theory...

    TOU was implemented more so to try and shift load from peak (generally day time) to off-peak (generally night time) to avoid having to build out the transmission/distribution system to handle higher peaks. It is more of a cost avoidance incentive versus generating revenue for infrastructure investment.
     
  16. rolosrevenge

    rolosrevenge Dr. EVS

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    If you've got the 85 kWh pack, I wouldn't charge at work. You clearly have plenty of capacity to make it there and back and if there are other EVs with smaller packs that need the charge more, I'd let them take it. Plus as you mentioned, it's inconvenient. Also, the less peak charging that occurs, the better for the power grid, so charge it up over night.
     
  17. mknox

    mknox Well-Known Member

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    A bit of both, really (I am a VP at an electric utility responsible for TOU rates and Smart Metering). As a rate regulated utility, we can't simply say sorry, we've run out of power, or the Regulator would likely revoke our distribution license. If on-peak usage rises to the point where additional infrastructure is needed, it gets built and paid for through the electricity rates we all pay. Incentives (such as TOU rates) do defer such infrastructure build as do conservation and demand management efforts that utilities promote.
     
  18. montgom626

    montgom626 Active Member

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    I would enjoy the walk after 45 minutes to move my car from a free charger. Great exercise. Then, I can remotely cool or heat my car before I leave work for home and know I have a lot of power left to get home. Standard charge would be best.
     
  19. digitaltim

    digitaltim Sig737 VIN628

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    #19 digitaltim, Apr 30, 2013
    Last edited: Apr 30, 2013
    I hear ya...20+ years in the industry myself as a VP in controls & commodities related technologies...I just see the build getting funded by an overall rate increase versus TOU. In our control area, it is the distribution/transmission charges that cover the build out, TOU is to reflect the cost of the energy supply which is all about what generators have to run to support the load - more load and higher cost generation has to come online.

    I know you know all that...

    PS - To be on topic, in my 5 months of ownership, I have rarely charged outside of the house but for using the supercharges in the east coast corridor. I like the convenience of not having to charge on the go and letting charge while I sleep.
     
  20. yobigd20

    yobigd20 Well-Known Member

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    I actually had a conversation with an expert on the energy industry last week who studied this very thoroughly. He said that if every single car in America was swapped out with an EV today, it would only increase the load on the power grid by 2%. Our electrical infrastructure is more than sufficient to handle 100% electric cars in America as it stands today without even having to any new power plants.
     

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