Mar 18, 2012
Pantera Dude What is the recommended way to use the battery? Should it be fully charged every night or is it preferred to run them down to 20% or so before charging? I'm thinking that if I am only using say 25% of the battery's charge on a normal day, that would only require 6 or 7 hours per night to charge it with 110, am I correct about that? I guess I could start off going the 110 route and then spring for the 220 if I'm not happy. Is the battery life compromised in any way by using the 110 instead of 220?�
Mar 18, 2012
TEG Many of your battery questions are debated.
What I recollect:
Recharging/topping off after short trips is good. Letting it go down to 20% on purpose is not so helpful. But, charging to 100% is not so great either. If you charge in "standard mode" (instead of range mode) then it doesn't fill to 100% so you are in good shape.
So, basically - leave it plugged in whenever possible in a "standard mode" charge.
"Range mode" or "Performance mode" should be saved for special occasions, and it is best to time it so you use the car right after one of those "full" charges. Also, best not to do "Range mode" or "Performance mode" charges on a really hot day.
There really is little/no "memory effect" so letting the pack run down by missing charging opportunities isn't really useful.
Charging from 120V is somewhat wasteful as a relatively higher percentage of the electricity is used running accesories and charging equipment and less makes it into the battery pack than you would get if using 240V.�
Mar 18, 2012
Doug_G The important take-away from TEG's message is: Plug it in every night and charge in Standard mode.�
Mar 18, 2012
NigelM +1
Pantera, sounds like I'm in the same situation as you....There are days when I drive 5 miles and days when I drive 150 miles. I've discussed it with several Tesla people and they all told me: "Plug it in, regardless of miles driven" Over time, the battery pack will balance itself just fine. The only caveat is that if you're not going to drive for a few weeks,still plug it in but change to storage mode.�
Mar 18, 2012
Pantera Dude Sounds good, thank you!�
Mar 18, 2012
Timothy My understanding from talking to some of the guys at Tesla that plugging in every night is not necessaryand not helpful. I've been told to plug in once the battery is 50% discharged. I usually drive about 100 miles per week, so I charge every Sunday night.�
Mar 18, 2012
TEG Yeah, keeping above 50% is probably good enough. (Although if you had some unexpected emergency, you might have wished it was left plugged in.)
There are still some people who got "trained" from the Ni-Cad days to think you are supposed to drain your battery before recharging.
Probably not such a good procedure for Li-Ion. I think it is "happier" if you never let the SOC get very low.�
Mar 19, 2012
dsm363 They have always recommended keeping it plugged in when you are not driving. That could be just so if you forget it's not left at a low SOC but it's not supposed to be harmful charing every night in standard mode according to Tesla. I guess it could be better for it to stay at 50% SOC but it's easier to just plug it in each night.�
Mar 20, 2012
Pantera Dude Thanks guys!�
Mar 20, 2012
hcsharp That depends on where you live and how you drive. While keeping your SOC high all the time has a minor impact on battery life (minor because it's never above 90% in std mode), there are other factors resulting from not charging every day that can impact it more. Heat and high amperage draw are worse for the battery than leaving at 90% SOC. If you drive with the same speed and acceleration at 50% SOC as you do at 90%, it will draw more amps and heat up the battery a lot more. If you never drive the car very hard then this may not be much of an issue.
The other issue is extreme cold or hot weather, which you don't have in Santa Barbara. Storing the battery at a high SOC while it's cold has almost no impact on its life. But driving in extreme cold is hard on it, especially at a low SOC. If you keep it plugged in then it never gets so cold that it's affected by this.
And to add to what TEG said, it's nice to be able to dump the gas-car model that you're used to. Charging every day is ultimately more convenient because it's always full for unexpected trips.�
Mar 20, 2012
Timothy Hrumpff! It does SO get cold here--42 degrees one night earlier this week!(But 70 in the daytime.) For me, unexpected trips are always expected, so I can charge extra if I need to. But once a week works great 95% of the time and I rarely get below 50% SOC.
�
Mar 20, 2012
vfx Agreed on this Timothy. Word from battery engineers at the factory (somewhere in these pages we have a quote) is plug in every night.�
Mar 21, 2012
dsm363 There have been a few owners charging in standard mode for 3 years now with very little drop in ideal miles after a charge. It really is better and a good habit to just plug in when you get home. Even if I'm going going to be home for a few hours I still plug in. That way I rarely forget.�
Mar 21, 2012
Doug_G You mean +42? How about -42???�
Mar 22, 2012
TEG As you may have noticed, some have contradicted that somewhat saying that nightly top-off (in stanard mode) is preferable.
I was just noticing this:
Model S Facts | Tesla Motors
�
Mar 22, 2012
hcsharp The cathode in Li ion batteries forms defects (microcracks) due to stress caused by expansion and contraction relative to neighboring materials. It is simply bigger or smaller depending on whether it's charged or discharged. The more you discharge it, the more it changes size. And the more it changes size, the more microcracks it gets. These microscopic cracks lower the battery's capacity. That's one reason why smaller cycles, more often, contribute to longer battery life. That's why you should plug it in every night.
Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life. And guess what? Your battery heats up more when used at a lower SOC because it requires more amps to keep your car going 65mph than it does at a higher SOC. That's why you should charge it every night.
Capacity fade also comes from the build-up of non-soluble deposits on the anode and cathode. This chemical process happens faster when the battery is warmer. It also happens faster when at a high SOC. But the process slows to a crawl when you drop the SOC to 80 or 90%, and slows only a tiny bit more at 50%. So if you are going to drive your car, keeping it charged in std mode has less impact on battery life (lower amps, less heat) than driving at a lower SOC. But if you're not going to drive your car for a few days, there are no amps or heat to worry about. That's when Tesla recommends putting it in storage mode, which keeps it at a lower SOC.
end of science lesson.�
Mar 23, 2012
bonnie Wow, thanks. That is the best explanation I've heard on this, by far.�
Mar 25, 2012
Timothy Too much science for a non engineer! But if you live in a temperate place (my house has a weather station and the low in the last year was 40 [yes, plus 40!] and the high 87--though never that high in my garage) and you drive 10 mi avg a day and charge in standard once a week (sooner on the rare instance I drive longer and get a SOC under 50%) is it STILL worth charging daily? I have had the car 11 months and there has been ZERO drop in the range after a standard charge since day 1. Not that it is that big a deal, but it is somewhat of a pain to plug it in daily if I really only need to do so once a week!�
Mar 26, 2012
hcsharp @Timothy: Most people setup their chargers so it's not a pain to plug it in every day. Takes about 5 seconds generally. When I first got my Roadster I treated it like a gas car for a couple of weeks like you are doing. Eventually I realized the electric paradigm was better for battery life and more convenient. If you want to keep doing it the way you are, I'd drive gently when the battery gets down near 50% SOC.
My elderly parents live in Santa Barbara. My mother was an organic avocado rancher for many years. The climate is quite nice! I'll bet some of those roads like Mountain Dr and Gibralter Rd are fun in a Roadster.�
Mar 26, 2012
dsm363 Tesla recommends plugging it in every night so that is what I do. If that was detrimental to the battery, they probably wouldn't recommend it.�
Mar 26, 2012
Dragon Most probably you could optimize the charging by plugging it in and taking consideration of a lot of parameters (ambient temperature, battery temperature, state of charge, driving needs next day, etc.). But is it worth the effort? If you do that for 5 years just to have 5-10 miles more on your ideal range, probably not.�
Mar 26, 2012
dsm363 That's kind of how I look at it too. I'm sure it's possible to outsmart Tesla's engineers but I'd imagine the savings will be very small as you said. It also takes one of the EV advantages away which is leaving home with a full 'tank' each day, even if you rarely need it.�
Mar 26, 2012
vfx Hmmm....�
Mar 27, 2012
dsm363 I meant more in the theoretical sense. If you took all factors into account you might be able to come up with a charge method that was slightly better than simply plugging in every night but I doubt it and it probably wouldn't be worth all the effort to save a very small change in ideal miles over 5+ years. It's safer and easier to simply plug in each night.
I didn't mean to imply that the Tesla engineers weren't doing an amazing job. I think the Roadster has been great and the Model S looks to be even better.�
Sep 3, 2012
Raffy.Roma Can I ask you by taking these precautions after eight years what is the efficiency of the batteries?�
Sep 3, 2012
wiztecy >Can I ask you by taking these precautions after eight years what is the efficiency of the batteries?
hcsharp reported in the battery log thread that he still gets 245 miles in range mode, so I think his charging practice is working for him
>Heat aggravates the microcracking process, so keeping your battery cool contributes to longer battery life.
@hcsharp to contradict that for sake of argument, if you don't need to charge then why charge it? Ignoring the fact of emergency miles... Since heating will result in heating the pack up. So wouldn't be better to not charge it if you don't need to and are over 50%? I think its also key to charge at a lower ambient temperature if possible.
I don't want the SOCs to be sitting higher than 50% with nothing to do (if you know you're not driving the roadster til the morning). So for me I have the Roadster begin its charge so that its completed 1 hour before I leave for work. The one hour gives time for the pack to equalize and cool. Anytime you can allow the pack to cool is a good thing. Then I drive 35 miles to work, for which I pull the SOC down from 185 ideal miles to 150 (81% SOC). The roadster sits unplugged all day, I then commute back home another 35 miles and my ideal miles is at 115 miles (62% SOC). I then plug the roadster, where charge is not initiated until the next morning, in where the cycle starts again where my charge initiates 1hr before I need to depart for work. Over the weekend I don't do too much driving since I live in Santa Cruz and its a resort for me, beaches, bike rides, sun and kayaking in the ocean
I know the LiPo battery packs tested in consumer electronics favor the 50% SOC in longevity tests I've seen and reviewed with a battery engineer I work with (who's also an EV enthusiast).�
Sep 3, 2012
Doug_G The thing about leaving the battery at lower SOC is that the cell voltage slumps a bit. That means that the car has to draw more current to maintain the same power level, which would mean more heating and stress on the battery. So storing the car at lower SOC is better for the battery, but operating the car at lower SOC is not.�
Sep 3, 2012
wiztecy Thanks Doug and for the background on the battery science technology Henry. Makes sense and very good points to keep in mind. Another thing to consider is AMPs to charge. I believe Tom did an analysis on what Amps are the most efficient to charge at and his curves showed 30Amps ( I need to revisit it if that was the exact Amps, I believe so). Any lower and its inefficient in terms of cost to push the amps across the line. I believe above 30 Amps you start building up heat and heating up the battery packs more than necessary. When I charged at Tesla down in Santa Row they had the 70amp quick charger. I wasn't in a hurry and my charge not too low so I dialed it down to 30Amps in the Roadster.�
Sep 3, 2012
Raffy.Roma Does it mean that by treating carefully the batteries of a Tesla Model you could still have an efficiency of almost 100% after eight years?�
Sep 3, 2012
wiztecy There's the factor of time that batteries have a constant shelf life. But it does mean your battery should be more reliable and healthier if you understand the battery technology as well as the physical and electrical principals that are tied to it. The battery logs research is a big part of this and I encourage all to participate. I know every time I stop at Tesla to have anything done they pull my logs. I'm sure they're doing the same and much more analysis on this data as we are to understand battery and charging characteristics based on multiple variables.�
Sep 3, 2012
spleen Think it was 40 amps, based on what I saw in Tom's blog.
Tesla Roadster Charging Rates and Efficiency - Tom Saxton's Blog�
Sep 3, 2012
hcsharp Actually it varies from 245 to 247 miles in the summer with 246 being the most common. It's been driven daily for over 14 months approaching 13k mi. But these numbers assume that Tesla's algorithm for calculating the ideal miles is accurate. They've adjusted it a few times in the software. I find the latest revision to be fairly accurate but it might be slightly optimistic.
You didn't contradict what I said. And in fact you answered the question yourself with your comment about temperature. What you need to keep in mind is that storing the battery at 85 or 90% SOC is only slightly worse than storing at 50% SOC. A far bigger factor is storage temperature.
The problem with your theory that it's better to get home and wait before charging is that a long-ish commute like you have will warm your battery up, especially at freeway speeds. Immediately charging will kick on the roadster's thermal management system and cool the battery down during the first few minutes of charging. That is especially true if charging at very low amperage. That will be much better than letting it hot-soak for several hours. The ideal behavior would be to get home and charge at 12 or 16A for about 30 - 45 minutes to cool your battery off. Then charge as you normally would in the middle of the night at 32 or 40A. That's why I installed a button on my DIY EVSE that, when pressed, will charge the car for 40 min at 16A, then stop, and resume charging at the normal time and amps. If I get home on a warm day, I plug in and press that button. You can do the same with a Tattler if you don't want to build your own HPC.
I don't take credit for this idea. It really belongs to Scott451 and others who developed log parsers. Scott noticed that his roadster would hot-soak until he started charging. One of the best reasons to get a Tattler or OVMS is to help manage your battery temperature and SOC for maximum longevity.
True, except that I'd much rather have it sitting at 90% SOC if it's at a lower temp, even if only a couple of degrees lower.
Are you asking about efficiency or capacity? Very little is known about efficiency changes over time independent of capacity. As for capacity, near 100% would be unrealistic in 8 years. The fact that many Roadster owners didn't lose enough to count in the first year or two doesn't mean you can extrapolate from that what will happen in 8 yrs. There's a lot of evidence that the Roadster battery will degrade faster with age, just the opposite of your laptop. See the discussion elsewhere about the failure runaway theory. The best way to prevent that is to keep your battery charged and balanced. And cool�
Sep 3, 2012
strider Keep in mind that Tom's research had nothing to do w/ battery health. It looked purely at the most efficient charging rate - where the least amount of energy from the wall is lost due overhead. I know that's what you said in your post but since this is a thread about battery health, I didn't want someone to extrapolate Tom's efficiency research into the realm of battery health.�
Sep 4, 2012
PRJIM I believe the plug-it in always mantra is due to Tesla not wanting to be liable-or bad press- if an owner forgets the plug in the vehicle (ala bricking story). By preaching plug it in always, it helps avoid customer confusion. I have a friend who owns a roadster and only plugs in his car once the range is <90 Miles. He still gets 189 miles with 23,000 miles on the odo. There are certain circumstances where plugging it in is probably not very helpful. If it is very hot, it is not particularly helpful to have a high SOC or to charge your vehicle.�
Sep 4, 2012
wiztecy Lots of good points bought up in this thread, I now feel better educated which is always good
Also a very good point hcsharp pointed out using the thermal management of the Roadster to cool the pack down after long drives and hot days. I don't see my battery temp really move above the 2nd block. It always stays there, ambient (60-75 degrees F) and higher. If it gets over 90 degrees and I'm doing a long drive or sprinted the car it will move up but not much. Happy with that. I really wish there were numbers and real temps though, that'd be way more useful for temps and the state of the components.�
Sep 4, 2012
strider That kind of data is only going to come with time. I'm sure Tesla has done a bunch of simulations but ask Nissan how well that's going for them. There simply isn't a replacement for actual data. That's why we should all support Rich's study. From that hopefully we (and the OEMs) can learn how best to care for batteries in this application.�
Sep 5, 2012
Botbldr45 With a Tattler what would be a good cooldown target temp for temp management of battery??? My battery sits at around 30 to 36C.... is that too hot???�
Sep 5, 2012
Doug_G The car's cooling system tries hard to keep the battery under 40C. I would think that is an upper limit, and it's better not to have it sitting that high while parked. It's not unusual for mine to be close to 40C by the time I get home, due to a combination of driving and sitting in the sun all day.
Probably an ideal temperature would be 20C; however, that's often well below garage ambient in summer. That said, you can cool past ambient and it takes a long time to soak back. Then again cooling takes power. My compromise has been to set the target for 25C, and leave the time limit at 45 minutes (I think that's the default). If it's a hot day it might end up at 30C to 32C after 45 minutes, which is better than sitting at 40C. At 2 AM full charging starts and that typically cools it down some more.�
Sep 5, 2012
Botbldr45 Outstanding! Set the Tattler and 992 is cooling as I type. Maryland summer is much hotter than normal ......no Global Warming right!! This is monumental for me ... First time the pack has cooled to under 35C all summer! Wish I had picked up this info last year. Better late than never�
Sep 9, 2012
daniel If the Roadster does not cool the battery pack until charging begins, then why is there a very loud whirrrring sound when I shut off my car after driving hard or on a hot day? I figured that's the car cooling the batteries.
BTW, any talk about X miles driven and Y ideal range remaining needs to be seen in the context of the age of the car. We won't know what the battery can do at 8 years of age until we have batteries that are 8 years old. I doubt that we can really extrapolate from a one- or two-year-old car. When some high-mileage cars are five years old I think we'll just begin to get an inkling.
One of the reasons I chose the Roadster is that at 50% battery capacity I'll still have more range than I need. I'm betting I'll be too old to drive before that happens. I think it's poor planning to buy an EV that has only slightly over the range you need on a regular basis.�
Sep 9, 2012
hcsharp It depends on what's making the whirring noise. If it's the fans in front then it's cooling the battery down. The rear fans are only cooling the PEM and motor. Regardless, when you shut off your car it will not cool the batteries down as much as it will if you plug it in and start charging, especially at a low charge rate. This has a big impact on battery life.�
Sep 9, 2012
wiztecy The whirling sound is most likely the normal operation of the coolent being circulated thru the battery pack. Its not kicking on the fans in the front which means the condenser is not being used. That takes energy and like Henry said, to initiate that you need to plug the roadster in. Otherwise the car wants to conserve the battery and won't start the condenser unless its a dire situation.�
Sep 10, 2012
hcsharp Somebody please correct me if I'm wrong but I don't think the fans in front only come on when the AC condenser is on. I think sometimes they are used to cool the battery coolant without using the AC.�
Sep 10, 2012
donauker As far as I know the fans in the front are only for the AC condenser. I have never seen my front fans run when the AC compressor wasn't running.�
Sep 10, 2012
wiztecy Johnny at Menlo park said the roadster will drop the driver's comfort and tend to its critical needs first meaning no AC for the driver and only for the roadster and this is if the battery is really really hot, in that case the condenser will fire up and fans will run. I think this is an extreme case.�
Sep 10, 2012
donauker This happens regularly here in PA. All output of the AC compressor is taken to cool the battery pack when it's temperature reaches 40C. When the outside temperature climbs into the upper 90s and the dark colored car is parked in the sun all day the AC will actually come on when the roadster is off and the pack temperature goes over 40C. In those conditions it is normal to have no AC available for cabin cooling for the first 10+ minutes of driving.�
Sep 10, 2012
daniel The whirring I hear when I shut the car off is the same noise I hear after I open the door or the trunk or unplug the car. In that case, I don't think it's cooling the PEM or motor, which have been sitting idle in my cool garage. I assume it's pre-cooling the battery pack. And I assume that the forward fans only run if the coolant running through the condensers is over a defined temperature, as the condensers will dissipate heat even without the fans running.
Charging the car produces a significant amount of heat, causing the cooling system to run harder. But I cannot imagine that Tesla would have neglected to have the car cool the pack as soon as the car is plugged in if that would make a significant difference in pack life. I have the car set to charge at 1:00 a.m., when I presume it's easier on the grid. I'm not going to futz around every day, starting the charging, then stopping it, and then having it charge at night.
I figure that if it was that important for battery longevity to do a brief charge immediately after driving, they'd have given the car firmware to allow me to program it to do that. It would be a simple matter.
Anyway, Spokane is a mild climate, and I'm gone (with the car plugged in and in Storage mode) for the hottest part of summer.
Next time we have a really hot day (probably next year) I'll look at the temperature gauge after driving. I don't remember ever seeing it particularly high, though.�
Sep 10, 2012
hcsharp Your battery can be almost 95 deg F and only be on the 2nd blue bar. If you turn off the car it won't do anything to cool itself. But if you plug it in and start charging at a low rate, low enough that the charging itself wont generate heat, the cooling system will cool the battery down another 10 - 15 deg F in about 30 minutes (give or take). You can deny it all you want but that will make a big difference in battery life if you live in a mild or warm climate.
I agree that it's a PITA to get home and manually charge for 40 min at low amps, futzing around to use your words. That may be the best reason to get a Tattler. That's why I built my own HPC with "one button cool down" feature.�
Sep 10, 2012
donauker I totally agree! It was rather disturbing to me to discover that my pack would sit for hours at over 100F after returning to my garage after a normal summer day of parking in the sun and driving 20 miles to home. With no active AC cooling that big pack looses very little heat in a 80+ degree garage. The circulator pump will run but that just keeps the pack temperature even throughout. I feel the cooldown mode is one of the most valuable features of the Tattler and the thing I really miss with OVMS since I am now back to manual charge control for cooldown.�
Sep 10, 2012
dsm363 Couldn't Tesla easily do this in firmware? Glad the Tattler does it and OVMS is working on it.�
Sep 11, 2012
strider That's not exactly true. The car will continue to run the pump and circulate coolant through the pack until it cools down (as I mentioned in my post above I haven't hung out in the garage long enough to figure out where it cuts off). However it won't run the A/C unless the pack is over 40C. So if the pack is at, say, 36C when you come home, the coolant pump will run so it will cool the pack (Assuming your garage is less than 36C) it's just slower than kicking on the A/C. Bottom line is that we (and Tesla) are all learning about how best to take care of these packs. The Tattler's cooldown function does cool the pack more quickly than just running the coolant pump but then who knows what lots of starting and stopping charging does to things like pack balance? Lots of trade-offs...�
Sep 11, 2012
drees Yep, and keep in mind that lithium batteries typically follow Arrhenius equation which means that (approximately) every 10C reduction in temperature, you double the calendar life of the battery.
If this means you get home at 7pm in the summer and don't start charging until 1am to take advantage of off-peak rates, this is like adding 6 hours of life to your battery every day - or about 25%. So if doing nothing results in your battery degrades your battery to 80% in 5 years, now you might get 6.25 years before you reach 80% capacity.
Since battery calendar life is also extended by keeping them at low SOC in addition to keeping them cold, ideally you could configure the car to cool the battery pack whenever you plug in in addition to using an end-time timer (say at 6am) so that the car automatically starts charging in time to finish charging by 6am regardless of the starting SOC.�
Sep 11, 2012
dsm363 Even though I have no off peak charging I've always charged at 2AM to be nicer on the grid. Maybe I should just charge at 24A or so on plug-in during the summer at least.�
Sep 28, 2013
markwj Now Advanced Charge Control and Cooldown is here for OVMS, here are my settings for home (where I do 99% of my charging):
1. Cooldown on plugin. Target 28C for 60mins maximum.
2. Charge at 40A (to limit pack heating and be easy on the grid).
3. Limit charge to 90% standard mode SOC.
My reasoning is:
The car will run that little pump when max brick is above 31C (approximate), and (most importantly) won't even bother monitoring temperature below that. Cooldown will reduce max brick temp by about 1C per 10 mins. I guess Tesla know what they are doing, and figure I'll just help them to get battery temperature down below the level they don't care about it.
The efficiency difference for charging 40A vs 70A is minimal, so I choose the former. Easier on the grid and car, although I don't think it makes much practical difference.
I don't need extreme range, day-to-day, so limit to 90% standard mode SOC, to avoid storing the car overnight and at work (where it is unplugged and hot) at highest SOC. Standard mode is already conservative, so this gives it a little bit more conservatism.
I am concerned about balancing, and whether the above practices impact that negatively. I'm keeping a close eye on it.�
Sep 28, 2013
wiztecy
Thanks Mark, Been waiting for this for a long time!!!!
Mark. I don't think this will impact balancing for a conscience user. That's up to the Driver/User to manage balancing and understand those dynamics. If we can get feedback from the balancing grid in Diags that would be great, but I'm sure that's not avail via the CAN bus. Something Tesla should have made public.
The key is to always do std mode charges when you use your roadster and allow at least 30 min (my avg) or 1 hour to balance. More if you do partial charges allot. I make sure not to do little charges and know they'll throw you pack out of balance... and users must understand the Pack WILL NOT balance if you're under 80% SOC.�
Sep 28, 2013
markwj My concern is the forced charge stop before 100% complete. The car is still plugged in, but the charge has been stopped, so not sure if the car will balance or not. Does it balanced after an interrupted charge, or only when 100% complete?
The diags balancing grid is available on the can bus. I'll be keeping an eye on it.�
Sep 29, 2013
wiztecy From what I've observed and recall from Tesla, the pack will balance whenever its above 80% and never when its below that threshold. From all the times I've used "manual" cool-down I've never seen my balancing becoming worse. I do a cool-down every time I arrive home from work, pulling the pack down from 35C down to 23-26C. On the weekend I'll do 1-3 cool downs if I've done a few trips and noticed the pack's above 26C. When I initiate a cool-down it its typically between 50-65% SOC. Upon each view of the grid once the Roadster had time to balance after my next full Std. Mode charge (which would be always on a Monday, I'd leave it at 50-60% SOC over the weekend, I've never seen my pack become out of balance. My pack would / will always take 15-30 min tops to fully balance after a full std. charge. Even Tesla commented how balanced my pack was.
Tesla noted that the packs they see that become out of balance are from people who never allow the Roadster to sit 30-60 mins after a full std. charge to allow this balancing and that they just typically drive off. They say you can do many under 80% SOCs but to always give the pack time when its above 80% to balance. They also told me that they've seen packs that always charge off 110v to be out of balance. I don't think that's a 110v issue but rather impatient Roadster owners driving off too soon!
Cool on access to the balancing grid on the Can-Bus. Would be super if we can display that on the OVMS. If not possibly an alert to notify the user that they need to perform a balance on the pack and how they can do that.
Thanks!�
Sep 30, 2013
asgard Wiztecy, do you use tattler to do all this?�
Sep 30, 2013
shrink Outstanding! Thanks so much, Mark!
Has the iOS app been updated yet with this feature? Hard to tell now that iOS 7 updates in the background automatically.�
Sep 30, 2013
wiztecy No, I do everything manually... Appears I'll be soon managing it with OVMS�
Apr 5, 2014
lmore Top-charging (100 %). I never top-charge my Roadster. A Tesla employee where I live rented the Roadster from me, although I told him (and wrote in the contract) to never top-charge the car and never charge at higher rates than 30 Amp, he top-charged at 60 Amp... Sometimes I don't understand what goes on in peoples minds. He was fully aware of that I could monitor everything he was doing (via log-files and OVMS). This rent was obviously ended because of lack of trust.
He claimed that this charging was not harmful for the battery. He let the battery sit at 100 % charge only 2-3 hours before driving. And I have read on the Model S forum that it is better for to charge at high speed. This was a bit of a shock for me to read, is that so for the Roadster also? Ambient temperature never gets much higher than 20C (room temperature) where I live and is half year around freezing point.
What about top-charging, is that not harmful at all if it stays 100 % only 2-3 hours?
This summer I am planning to rent the Roadster to a very enthusiastic woman for 50 days (I have several other EV's that I need to focus on fixing). She plans to drive a lot, 4000 km, several long trips (>400 km) but she can stop to charge after 200 km. I want the battery of my Roadster to live as long as possible. Would the optimal for this be to:
* always keep the car in Standard mode
* not go below 30 %
This will limit her usage of the car somewhat, but she told me she has plenty of time. She has already installed the OVMS on her phone and I remember that a notification can be set there when the limit gets at a certain point.
I plan to charge around USD 3000 for the rent, what would you estimate the maintenance/degradation cost of the Roadster to be per km/mile?�
Apr 5, 2014
djp The Plug In America Roadster Battery Study shows the main factor in degradation is mileage. The occasional range charge doesn't seem to hurt capacity.
http://www.pluginamerica.org/surveys/batteries/tesla-roadster/PIA-Roadster-Battery-Study.pdf
The danger is in leaving the pack at 100% for a long period of time, especially in the heat. The BMS chills the battery during a Range charge to protect it, and limits the actual max SOC to 95%. The effect of a single quick range charge is minimal, but to be safe you should time the charge to finish within a few hours of departure to minimize the amount of time at full charge.
Keeping a buffer of 30% is not a bad idea, but more for unplanned events like unexpected headwinds or broken charger stations on the road trip. Going below 30% won't noticeable degrade the battery - the risk is in going to absolute zero.
Don't worry about charge rate, even the max current from an HPWC is nowhere near the max C rate of the battery.
In terms of fair price for the degradation, as a rough guess you can take the rate from the PIA study of 0.15% loss per thousand miles driven. That works out to 0.37% over 4000km. If you assume the pack is worth zero after 30% capacity loss and costs $40,000 to replace, then the 0.37% loss is worth $493.�
Apr 5, 2014
Doug_G +1. 100% agree with everything djp said.
The first renter was correct that you really don't need to be concerned about an occasional range charge or the charge rate, but since it is your car you have every right to decide how it is used.�
Apr 5, 2014
bart513 I had my car parked in the garage at about 95% SOC. It sat for almost 2 weeks without being plugged in and held a charge quite well going down to about 80%, possibly higher. Because I had a 135 mile drive to make I plugged it in the night bofore, drove to NJ and charged it to 62% SOC getting a CAC of 154.86 on April 2nd. The CAC on March 13th was 155.13 when I had the car plugged in on a regular basis.�
Apr 5, 2014
hcsharp I pretty much agree with everything djp said. The charging rate at 70A is still very gentle on the battery. Regarding charging speed and the comments in the Model S thread, I don't think the readers were interpreting the study properly WRT how it applies to these cars. When somebody later clarified with one of the authors of the study, he responded that it's probably marginally better to charge at a slower rate, but not much difference. I'm not sure why the "charge fast is better" myth continues to propagate. Tesla's charge management tapers down at the end of a charge in such a way that charging faster does not keep the battery at a higher state of charge for a shorter period of time the way it might with a computer or cell phone BMS.
If I were writing the Roadster rental agreement, I would not put any restrictions on charging rate. As far as top charging, I would include a limit on the number of times she can do it during the rental period. A reasonable max number might be 3 to 5 over 4000 km. That might actually be better than not doing any at all because it will help keep the battery balanced.
My guess is that you will wear out tires at almost the same rate that you wear out the battery.�
Apr 5, 2014
lmore Thanks for the great help (again). Tire wear is also a good point. I usually drive with 16" back wheels which reduces tire wear, they might last as long as the battery. The 17-inch standard tires didn't last more than 10000 miles.
I might add that what I am not that worried about the battery capacity dropping a few percent. The big fear is the battery going bad and needs to be replaced. So the car usage should reflect that. From what I have understood, the risk for a defect battery is higher if the battery is deeply discharged (often) since the risk for single battery cells will go bad is higher if they are dropping to a low voltage.�
Apr 5, 2014
wiztecy How do 16" rear wheels lower tire wear over 17"? 16" should wear faster actually due to a quicker snap of the tire off the line.�
Apr 5, 2014
jerry33 The main reason would be that the tires aren't the same from 17" to 16". Even if they are the same brand and model tire, they will likely be different. In addition, the taller sidewall allows the the 16" tire to absorb road and alignment irregularities better.�
Apr 5, 2014
wiztecy Thanks. So with a higher sidewall you're gaining side to side slop in the rear. I think I'd take more tire wear over side to side slop, especially where its being rented, pushed most likely hard around turns, and possibly could end up in an accident. The car wasn't designed for 16" rears. If it were me I'd put the best performing tires on the car for the car's safety as well as the renters and increase the rental rate. They are renting it for the "Tesla Roadster" experience and not some scaled down version. Again increase the price, state the car is a performance vehicle andclearly state to use/appreciate it safely, and lastly keep close to the specs the car came with. If it was your daily driver you'd learn the way the car drives with the 16's, but your audience is not and assuming the car will be setup close to the way Tesla sent it out of the shop. If I did anything close to this I'd make sure my good lawyer has spent a good bit of time reading over the contract to protect myself as well as my assets in the worse case scenario, which do occur.�
Apr 14, 2014
smorgasbord OK, back to battery charging.
I don't know why I can't find it, but I remember reading about how every now and then one should do a Range charge and then drive without turning the key off until the battery SOC is below some number (like 20%?), and then charge back up to full (Standard mode?) in order to get the pack balanced.
Can someone explain precisely what the procedure is/isn't?�
Apr 14, 2014
Doug_G I've never been convinced that it is necessary to do this without turning off the key, but that's what "they say".�
Apr 15, 2014
smorgasbord So, should I take a second key and if I need to leave the car for a bit, put the car in Park (but still on), and use the other key to lock/unlock the door? Assuming I'm in a safe area, of course.
Unfortunately, for the trip down, the best thing for me is to Range charge, drive 60 miles to Monterey, get breakfast and some power at a ChargePoint, then take off down the coast. So, if I don't charge to Range Full again in Monterey, I can't do this, right? Or, does the drive from not quite Range Full to almost empty in SLO count?�
Apr 16, 2014
wiztecy Taking a 2nd key is a good idea, its a pain not being able to leave the Roadster. You have OVMS, so you could also lock your doors that way too and not feel as worried since you can track your Roadster as well as shut it down if someone broke a window out then drove away.
> So, if I don't charge to Range Full again in Monterey, I can't do this, right? Or, does the drive from not quite Range Full to almost empty in SLO count?
From what I heard you don't need to do a Range Mode charge to have the pack recalibrate the ideal miles to CAC. I heard the pack needs to do a 70% pull down to redo the calulations. That being said you could charge in std. mode to 84% SOC and pull the pack down to at least 14% SOC on one key turn, then your charge needs to be at least a full std. mode charge. I just feel like doing a Range Mode charge helps out with the calculation better and logically to me makes sense if I have the time. But I've never read the specs nor seen the code, just did lots of shop talk at Menlo Park with managers and techs to make sense of it all. I even caught a few of them getting confused with this
This would be a great request to make at the next TesLive. To ask if Tesla could assign an engineer to validate and create a Wiki on these tips we've pulled together on maintaining the packs, etc.... I don't think that would be too much to ask nor take that much time and money.�
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