enough range to make it home for the first time?

[doug]

However with 35 miles to go i got a message that the battery was almost depleted and the range calculation was inaccurate. The 35 miles remaining of charge indication went to zero and the car shut down 4 miles later. not a big deal.

Ah... not sure what mode you were in, but you might have been able to unlock a bottom few % of the battery that could have got you home. Nonetheless, great that you made it and hopefully you have the car plugged in right now. Cheers!

 

[S-2000 Roadster]

However with 35 miles to go i got a message that the battery was almost depleted and the range calculation was inaccurate. The 35 miles remaining of charge indication went to zero and the car shut down 4 miles later. not a big deal. AAA brought a flat bed in 15 minutes and finished the journey.

Hopefully, you plugged it in the instant you arrived. Actually, this can be a "big deal" because if you run the Tesla Roadster battery until it stops and then do not immediately recharge, you can ruin the battery and will void the warranty in the process.

The car had not been used much the prior few months and the Tesla rep said that you need to ballance the cels to get accurate range by cycling them a couple of times.

Balanced cells will happen if you charge the car and keep it plugged in. That just takes a little time.

However, you absolutely do not want the "cycle" the battery a couple of times. In standard battery speak, cycling means to fully discharge and then fully recharge. The Tesla batteries do not like to be fully discharged. You really should avoid running it until it stops. Normal use is enough to recondition the battery. It's far, far better to stop somewhere appropriate before you reach your destination and charge for a while rather than run it dry and tow it to a charger. There are many discussions on this forum with more details, and you should trust your Owner's Manual as written by Tesla Motors.

 

[ysrman]

Yes I immediately got it back on charge in the hangar and am letting it charge fully before driving it again. The problem with this trip is when i arrived to pick up the car the guy had not fully charged it so i waited until it said 205 miles and figured that would give me some cushion to get it home(184 miles). The tesla help desk later said that if you come out of storage mode and do not fully top it off the calculation on range can be innacurate because the cells are not all ballanced. anyway lesson learned. Thank you for the assistance

 

[Roger Reid]

...I did manage to get it home today with the help of AAA for the last 30 miles... the Tesla rep said that you need to ballance the cels to get accurate range by cycling them a couple of times...

The Tesla rep told me that there are 11 sheets of batteries. Standard mode runs 2 sheets at a time with performance mode using 3. When a sheet is depleted to a certain level it will switch to other sheets. So with different sheets being used to different charge levels, when charging is finished, not all the sheets will be at the same charge as the highest charge sheet will determine when you are done. Occasionally charge using range mode, possibly several times back to back to get all the sheets at the same charge level. I did this to mine and got 10 indicated ideal miles added to my range.

 

[TEG]

Can anyone confirm that? I always assumed that current was drawn from all the sheets at the same time, just more quickly when in performance mode.
It seems like it would be harder on individual cells to let some sit idle while others shouldered all the load.

 

[vfx]

It seems like it would be harder on individual cells to let some sit idle while others shouldered all the load.

Yeah, unless they cycled them, those two sheets would get worn out a heck of a lot faster than the rest.

 

[S-2000 Roadster]

The Tesla rep told me that there are 11 sheets of batteries.

That one sentence is the only true statement. The rest is highly doubtful.

Standard mode runs 2 sheets at a time with performance mode using 3. When a sheet is depleted to a certain level it will switch to other sheets. So with different sheets being used to different charge levels, when charging is finished, not all the sheets will be at the same charge as the highest charge sheet will determine when you are done.

The Tesla Roadster needs all 11 sheets to reach the nominal 400V that runs the HVAC and, of course, the motor. As far as I know, all sheets are in use at all times. I was told that two sheets were used in early model ESS systems to run the 12V subsystem, but that not only doesn't add up, it was also shot down on this forum. Seems like the Tesla reps do not understand the technology all that well, because I've heard many things directly from "Tesla" that turned out not to be true.

It's entirely possible that charging in Standard Mode works on 2 sheets at a time while charging in Performance Mode works on 3 sheets at a time - there's certainly the option of charging only parts of the battery pack. As I said, though, the whole thing is engaged when driving.

The real reason that cells become unbalanced is not because the Tesla firmware uses only part of the cells - they're using all of them - but because the chemical reactions in each cell are impossible to perfectly match. Even with liquid cooling and advanced firmware, it would be impossible for 6,831 cells to perform exactly the same at all times, whether charging or discharging. It seems like your Tesla rep was looking for a complicated explanation when chemistry and physics are enough to explain why this occurs.

Occasionally charge using range mode, possibly several times back to back to get all the sheets at the same charge level. I did this to mine and got 10 indicated ideal miles added to my range.

It probably isn't necessary to charge in Range Mode if you want the battery balanced. It should be sufficient to charge in Standard Mode, wait an hour, and Top Off if you want to allow time for the cells to balance. But I admit that there might be something I missed here.

 

[hcsharp]

It uses all 11 sheets at once while discharging. S-2000 you are correct that it discharges with the sheets in series to get over 400v. It also charges them all at the same time, but not in series. That's because it needs to monitor the individual cell voltage carefully while charging. The cell voltage might be slightly different from one sheet and brick to another. The cells in each brick are parallel and charged that way. In std mode the bricks are charged until the highest voltage in one of the bricks or sheets reaches 90% SOC. Not all the other bricks will necessarily be that high, but it will stop charging. In range mode it continues charging each brick until it reaches 4.15 volts. That is called balancing because every brick ends up at the same voltage when it's done. It continues balancing from one cell to another after it finishes charging. This takes a few minutes or hours depending on how far out of balance it is.

ysrman's car was not only badly out of balance, but he never completed the range mode charge which would have continued to charge the lower-voltage cells. Further, he didn't let it sit after the range mode charge to let the cells self-balance which would have allowed him a chance to top it off again. To help his battery life and performance, he should do a range mode charge and let it sit for a few hours, drive it to about 50% SOC, and then do another range mode charge, let it sit a couple hours, and then drive it again.

Good luck ysrman.

 

[S-2000 Roadster]

In range mode it continues charging each brick until it reaches 4.15 volts. That is called balancing because every brick ends up at the same voltage when it's done. It continues balancing from one cell to another after it finishes charging. This takes a few minutes or hours depending on how far out of balance it is.

Are you certain that all bricks will be a 4.15V at the end of a Range Mode charge? If they're not all at 4.10V when a Standard Mode charge ends, then why would they all be at the same voltage after a Range Mode charge? My understanding is that the first charging session in any mode is not very balanced, and you have to wait a while and Top Off to get better balancing. It's true that balancing continues after the charge is finished, but I do not believe there is any charging mode that could force all bricks to the same voltage.

The OEM battery specifications state that the cells are full at 4.20V, but Tesla Motors avoids the true "full" charge in order to extend their lifetime. I have seen the VehicleLogs show the brick voltages covering a span of voltages until they get close to the end of the charge. However, Range Mode and Standard Mode do not seem to have a substantial difference in the span of voltages. In other words, they both are fairly balanced at the end, but neither charge mode appears to be more balanced than the other. Maybe I should increase the resolution on my log viewing application to see whether Range Mode does a slightly better job of balancing voltages.

ysrman's car was not only badly out of balance, but he never completed the range mode charge which would have continued to charge the lower-voltage cells. Further, he didn't let it sit after the range mode charge to let the cells self-balance which would have allowed him a chance to top it off again. To help his battery life and performance, he should do a range mode charge and let it sit for a few hours, drive it to about 50% SOC, and then do another range mode charge, let it sit a couple hours, and then drive it again.

Do you have confirmation that discharging to 50% SOC and other driving has any effect on balancing? My understanding is that you can simply pick Standard or Range Mode, then charge, wait an hour, charge again, and perhaps repeat that a few times. I assume that charging alone is enough to balance the bricks/cells. If there's any official word that discharging the cells can help in any way to balance them, then I'd appreciate more information.

 

[Fabrizio]

This thread has been very helpful as I am planning on a trip from Phoenix to San Diego and it seems that the most convienient RV parks along the way are in Yuma, AZ - about 180 miles away. Additionally, the highways in AZ have a 75 mph speed limit and most every one drives faster than that. You can get run over doing "only" 75 mph. May need to find some secondary, scenic roads to keep my speed down and extend my range.

It was mentioned earlier in the thread about the effects of aerodynamic drag on energy consumption. To help reduce aerodynamic drag, wash and give your car (any car) a coat of good wax. Above 65 mph it does make a difference.

Another tip I received from Tesla is after charging in standard mode, to charge in Range mode for 20 minutes. This cools the batteries further, adds range, but because it does not charge to 100% it does not affect battery life as charging fully in Range mode.

 

[rsquared99]

In January 2010, I made the trip on I-10 from Surprise, AZ to Blythe, CA in one range mode hop, where I recharged at an RV campsite. I don't remember now what kind of spare range I had when I got to the RV site. You do feel like a mouse in a herd of elephants with the truck traffic, but I stayed in cruise control at 65 and made it with no problems. Coming back to Surprise, I used the same RV campsite and, aside from an electrical problem getting charged (a camp wide power outage), I made it back in one charge despite it being dark and raining the whole way (sights and wipers). In the dark, you really feel like a mouse in the herd, but I made it without screaming too much.

 

[JRP3]

I don't know exactly how Tesla does balancing but usually it works like this. The cells or sheets in series charge in series until a preset voltage, then charge is bled off the cells that hit "full" first, allowing the other cells to catch up. Current is lowered during this phase, it may even stop completely for a bit, and then come back on, until all the cells hit the same voltage. Stopping the charging, driving for a bit, and charging again should not be necessary and I don't think it could serve any purpose, all the balancing should be happening near the end of charge. As describe the different charging modes simply change the finish voltage, allowing more or less capacity in the cells. Electrolyte breakdown voltage is a little above 4.2 volts, I think the cell structure is under more strain at higher voltage, and it's less stable, all good reasons to avoid "full".

 

[hcsharp]

...
Do you have confirmation that discharging to 50% SOC and other driving has any effect on balancing?

No not 50% necessarily but his batteries needed some cycling. If you were using the car regularly you wouldn't need to do this. Some cycling is helpful to get all the cells behaving/reacting the same way to both charging and discharging.

My understanding is that you can simply pick Standard or Range Mode, then charge, wait an hour, charge again, and perhaps repeat that a few times. I assume that charging alone is enough to balance the bricks/cells. If there's any official word that discharging the cells can help in any way to balance them, then I'd appreciate more information.

Range mode does more balancing than std mode. You may not notice it if your bricks are all pretty close in voltage.

 

[JRP3]

Some cycling is helpful to get all the cells behaving/reacting the same way to both charging and discharging.

By what mechanism? As far as I know balancing only takes place near the end of charging as I described above. I suppose it's possible that there is a time constraint, such that even if not fully balanced the charging shuts down, so that discharging the pack somewhat and then charging again would allow further balancing. Ideally the charger would stop charging and let the cells settle for a while then start charging and balancing again on it's own, repeating this cycle as necessary, but it may have been more practical to get it close enough and then complete it in subsequent charges.

 

[TEG]

They say that the brain is good at making up details to fill in gaps of information if you don't have all the facts.
It is amazing how many different "theories as facts" people have about how the battery packs behave.
Over at the mynissanleaf forum was a long debate about how to best manage pack SOC for long life with many different opinions about what is best.
My Nissan Leaf Forum View topic - Optimal Portion of Battery to Use for Longest Battery Life?

See also:
Tesla Roadster Battery Care

Perhaps the mods might want to move some of these "How does the ESS keep the cells balanced?" posts to a different topic from "how do I drive optimally to get the range I need for a 184 mile trip?"

The fact that ysrman's pack was (apparently) unbalanced was (apparently) due to having the car sit for a long time, not due to how he drove on the trip.

 

[JRP3]

The fact that ysrman's pack was (apparently) unbalanced was (apparently) due to having the car sit for a long time, not due to how he drove on the trip.

Which is relevant to why he didn't make the expected range, and is part of the answer to the question of do I have enough range for the trip. An unused car may have an unbalanced pack which might mean you don't have enough range. Seems relevant to the thread.

 

[TEG]

Yes, relevant, but not generally descriptive enough for people in future who might be searching on battery balancing.

 

[Doug_G]

Are we all getting rather too fancy with all these theories about battery balancing? Tesla's own efficiency spreadsheet gives a range of 181.5 miles at 70 mph. That leaves a negative margin for his trip.

Personally I would have done a trip like that closer to 60 mph, to ensure a sufficient margin. Maybe 65 with drafting.

 

[JRP3]

He said he did it around 58 mph, and still ended up being 30 miles short. So I think the balancing issue was the problem, or his pack has issues.

 

[Doug_G]

Ah, okay then. I guess I should have reviewed more of the thread before commenting.