Time for a new HV Battery

[howardc64]

@howardc64, balancing kicks in approx 4.0V (80%, give or take) Oftentimes lower, depending on overall balance, brick capacity, etc. #becausealgorithms

Thanks. Good to know. But with many variables and no clear signal or evidence of rebalancing, its basically a mystery haha

Been trying different SOC points 80%, 90%, 95%, 99.7% (drove immediately afterwards on 90+ SOC to bleed off high SOC) to see if any rebalancing on my 2013 battery pack @75kmi. Pack always return to the same 22mV imbalance whenever at 70% SOC so don't really see any evidence of rebalancing. Perhaps some early warning signs on my old pack.

> 80% SOC runs pumps and battery chiller constantly per @aerodyne in post #176 and #177 on this older battery pack. So I'm left with the mutually exclusive choice of charge to 70% SOC (no constantly running chiller + pump) or 80%+ SOC (try to get rebalance but no evidence while accepting constantly running chiller+pump)

Since no evidence of rebalancing, the natural choice becomes accepting 70% SOC for topping off at home.

Anyway, an old pack so perhaps guidelines somewhat different than a newer or more balanced pack?

 

[henderrj]

Thanks. Good to know. But with many variables and no clear signal or evidence of rebalancing, its basically a mystery haha

Been trying different SOC points 80%, 90%, 95%, 99.7% (drove immediately afterwards on 90+ SOC to bleed off high SOC) to see if any rebalancing on my 2013 battery pack @75kmi. Pack always return to the same 22mV imbalance whenever at 70% SOC so don't really see any evidence of rebalancing. Perhaps some early warning signs on my old pack.

> 80% SOC runs pumps and battery chiller constantly per @aerodyne in post #176 and #177 on this older battery pack. So I'm left with the mutually exclusive choice of charge to 70% SOC (no constantly running chiller + pump) or 80% SOC (try to get rebalance but no evidence while accepting constantly running chiller+pump)

Since no evidence of rebalancing, the natural choice becomes accepting 70% SOC for topping off at home.

On May 85, which is a December 2014, if I charge to 75% the cooling pumps don't run afterwards. I have noticed that as long as it gets below somewhere between 80 and 90%, and it's been parked for a long time and not awoken by access from some app, the pumps do shut off anyway.

 

[howardc64]

On May 85, which is a December 2014, if I charge to 75% the cooling pumps don't run afterwards. I have noticed that as long as it gets below somewhere between 80 and 90%, and it's been parked for a long time and not awoken by access from some app, the pumps do shut off anyway.

Yes, I think I also see pumps shutting off after sometime > 80% but haven't spent the time to track down the algorithm. Maybe its time, maybe its temperature, maybe its reducing SOC. No idea. < 80% SOC is about the only observed guarantee to keep pump+chiller off after topping off.

 

[thefrog1394]

avoiding charge levels that regularly hover around 50%.

Avoid leaving your battery below 30% - 40% for long periods of time. Keep it topped up regularly, preferably daily.

Any data to support those two assertions? I understand there's the pack balancing stuff, so periodically charging high enough to allow balancing makes sense. But every study I've seen suggests that lower SOC is better to decrease calendar aging. And that low SOC is only an issue if you let the battery fully discharge. And Tesla keeps around 5% below 0 as a buffer, further increasing the safety of low states of charge.

 

[aerodyne]

So, some comments from owing a 85 pack for several years with SMT and Teslafi tracking.

You can avoid "pumpgate" by AC charging to as high as 78% SoC in cool conditions, 77% for sure. For SuC in high temps, 75% is a better bet.

Consider there is a difference between rebalancing and BMS calibration. The former can be seen at high SoC, over 93%, as drawing more power than the pumps would. Rebalancing might increase pack capacity slightly, but I only saw about a mile of range increase.

BMS calibration seems to be done all the time, most effective when going from say 75% to 25% SoC, but still in my case only added at most 5 miles of RR after 2 months in sheltered storage at 57%.

 

[howardc64]

So, some comments from owing a 85 pack for several years with SMT and Teslafi tracking.

You can avoid "pumpgate" by AC charging to as high as 78% SoC in cool conditions, 77% for sure. For SuC in high temps, 75% is a better bet.

Thanks. Make sense pumpgate has a few degrees variation with ambient temp. Been using 70% SOC top off target for years.

Consider there is a difference between rebalancing and BMS calibration. The former can be seen at high SoC, over 93%, as drawing more power than the pumps would. Rebalancing might increase pack capacity slightly, but I only saw about a mile of range increase.

BMS calibration seems to be done all the time, most effective when going from say 75% to 25% SoC, but still in my case only added at most 5 miles of RR after 2 months in sheltered storage at 57%.

Yes, understanding the difference between rebalancing and BMS recal. Still get like 24x miles on 100% charge from original 25x so not trying to recover range. Just trying higher SOCs to see if can reduce 22mV imbalance at 70% SOC. So far, nothing like worked with any > 80% SOC on my old 2013 RevB pack. So probably just going back to my usual 70% SOC top off target.

 

[Recell]

As with most things, there are diminishing returns in maintaining charge levels below 70%.

Pack longevity, convenience, performance and passing power, and yes, even the life of your coolant pump, are all in play when setting charge levels.

Take for example performance. While performance is of course subjective, 50% vs 80% results in an immediate 10% drop in performance and passing power for an EV. A lower charge level means lower on-demand power.

50% is a great level for storing your car. We recommend to owners that 80% is a great level for driving your car.

#getoutanddrive

 

[NV Ray]

As a frame of reference -my other car is a Toyota Prius Prime PHEV with an 8.8 kWh lithium ion HV battery, When the charging meter is at 100% and 0%, the State of Charge is actually 84% and 14% respectively.

Unlike Tesla, Toyota doesn't allow the user (there is no slider to adjust State of Charge) to go to either 100% or 0% State of Charge.

 

[tubaprde]

As with most things, there are diminishing returns in maintaining charge levels below 70%.

Pack longevity, convenience, performance and passing power, and yes, even the life of your coolant pump, are all in play when setting charge levels.

Take for example performance. While performance is of course subjective, 50% vs 80% results in an immediate 10% drop in performance and passing power for an EV. A lower charge level means lower on-demand power.

50% is a great level for storing your car. We recommend to owners that 80% is a great level for driving your car.

#getoutanddrive

but what if you normally only use only 25% charge every day? for longevity of the battery I would think you'd want to charge to 50% each night, draw down to 25%, and then charge up to 50%

 

[tubaprde]

As a frame of reference -my other car is a Toyota Prius Prime PHEV with an 8.8 kWh lithium ion HV battery, When the charging meter is at 100% and 0%, the State of Charge is actually 84% and 14% respectively.

Unlike Tesla, Toyota doesn't allow the user (there is no slider to adjust State of Charge) to go to either 100% or 0% State of Charge.

interesting, are you saying that toyota caps their batteries on both the high and low end so the user doesn't have to worry about such things, with the only downside that customers get to use less of their battery? sorry for the dumb question. i wonder if the new rav4 prime works the same way?

 

[NV Ray]

interesting, are you saying that toyota caps their batteries on both the high and low end so the user doesn't have to worry about such things, with the only downside that customers get to use less of their battery? sorry for the dumb question. i wonder if the new rav4 prime works the same way?

Yes, it's my understanding that the RAV4 Prime works the same way.

 

[aerodyne]

but what if you normally only use only 25% charge every day? for longevity of the battery I would think you'd want to charge to 50% each night, draw down to 25%, and then charge up to 50%

Yes, the shallower the charge cycle, the less stress on any battery.

 

[vcor]

Consider when you have a small battery in a PHEV, it is charged and discharged far more times than a large battery in an EV. You have to have a different strategy in the PHEV to make the battery last as long as those in an EV.

 

[NV Ray]

Consider when you have a small battery in a PHEV, it is charged and discharged far more times than a large battery in an EV. You have to have a different strategy in the PHEV to make the battery last as long as those in an EV.

Good to know, thx. However, to me makes no difference - both are Lithium Ion batteries and are getting discharged/charged just as frequently by either regen or wall charging. Unless you have other evidence...

 

[Rocky_H]

Good to know, thx. However, to me makes no difference - both are Lithium Ion batteries and are getting discharged/charged just as frequently by either regen or wall charging. Unless you have other evidence...

They ARE different. It's two different strategies for trying to protect from damage and degradation. Either the manufacturer can reserve and hide some of the capacities, and then the user gets no choice, and there is simply EMPTY and FULL, and they don't get to adjust the usage, because they don't have to. The manufacturer has already taken it out of their hands to prevent the worst case degradation behavior. Or as Tesla does, the users do get to have access to (almost) all of the battery capacity, but then the interface needs to give coaching and advice to the user to manage their usage to try to stay away from some of those worst case treatments of the battery.

 

[NV Ray]

They ARE different. It's two different strategies for trying to protect from damage and degradation. Either the manufacturer can reserve and hide some of the capacities, and then the user gets no choice, and there is simply EMPTY and FULL, and they don't get to adjust the usage, because they don't have to. The manufacturer has already taken it out of their hands to prevent the worst case degradation behavior. Or as Tesla does, the users do get to have access to (almost) all of the battery capacity, but then the interface needs to give coaching and advice to the user to manage their usage to try to stay away from some of those worst case treatments of the battery.

You're right, Tesla and Toyota have two different owner options (strategies) for battery management.

 

[ucmndd]

They ARE different. It's two different strategies for trying to protect from damage and degradation. Either the manufacturer can reserve and hide some of the capacities, and then the user gets no choice, and there is simply EMPTY and FULL, and they don't get to adjust the usage, because they don't have to. The manufacturer has already taken it out of their hands to prevent the worst case degradation behavior. Or as Tesla does, the users do get to have access to (almost) all of the battery capacity, but then the interface needs to give coaching and advice to the user to manage their usage to try to stay away from some of those worst case treatments of the battery.

I think it also boils down to a the different objectives and use cases for a BEV vs. PHEV.

The entire goal of the hybrid system in a PHEV is maximizing efficiency. Large top/bottom buffers ensure that there's generally capacity available to both capture regenerative braking energy and/or provide a bit of temporary oomph from the electric motor if there's a sudden need - even if the battery is "fully" charged or discharged. This is a reasonable compromise for most situations and provides a more consistent driving experience. I'm sure there are also long-term health implications for the much smaller battery that will rack up cycle counts much more quickly than a BEV.

BEVs are all about the range with no backup ICE so it's unsurprising that they expose more usable capacity for propulsion.

 

[NV Ray]

I think it also boils down to a the different objectives and use cases for a BEV vs. PHEV.

The entire goal of the hybrid system in a PHEV is maximizing efficiency. Large top/bottom buffers ensure that there's generally capacity available to both capture regenerative braking energy and/or provide a bit of temporary oomph from the electric motor if there's a sudden need - even if the battery is "fully" charged or discharged. This is a reasonable compromise for most situations and provides a more consistent driving experience. I'm sure there are also long-term health implications for the much smaller battery that will rack up cycle counts much more quickly than a BEV.

BEVs are all about the range with no backup ICE so it's unsurprising that they expose more usable capacity for propulsion.

Well put, thx. What are your thoughts on my comment #194 ?

 

[ucmndd]

Well put, thx. What are your thoughts on my comment #194 ?

I think @vcor is generally correct in his insight that much smaller hybrid batteries (PHEV batteries are like 12-20kwh these days) will experience more charge cycles over the same amount of driving because of their smaller capacity. Charge cycles are one of the primary aging factors for lithium batteries, so it would make sense to me to implement other battery health measures like larger buffers in the name of longevity.

 

[tubaprde]

I think @vcor is generally correct in his insight that much smaller hybrid batteries (PHEV batteries are like 12-20kwh these days) will experience more charge cycles over the same amount of driving because of their smaller capacity. Charge cycles are one of the primary aging factors for lithium batteries, so it would make sense to me to implement other battery health measures like larger buffers in the name of longevity.

So, if i generally charge my p85d from 25% to 50% daily, after four days is that considered the equivalent of 1 charge cycle?