Preserving battery life: short or long charges?

[Johan]

What about speed of charging? Is it better to charge nightly for say 8 hours at 10-15 Amps or 2-3 hours at higher amps?

I know I can buy the wall charger and just leave everything at default. (that's what we do with our Volt)
I'm wondering if I would gain a few percentage points over 4-5 years if I charged more slowly or say plugged into 110 instead of 220.

I'll typically drive 20-40 miles per day with the occasional 100 mi (across town) and the occasional 200+ mi out of town trip.

It's been said about the Roadster that the "sweet spot" for charging is 30A... Guess pretty much the same would go for the Model S? Also remember that charging at very low current will give you a bigger % of "wasteful charging" - i.e. difference between power out of the socket v.s. power gone in to the battery. Over time that can actually add up to substantial differences.

 

[Robert.Boston]

It's been said about the Roadster that the "sweet spot" for charging is 30A... Guess pretty much the same would go for the Model S? Also remember that charging at very low current will give you a bigger % of "wasteful charging" - i.e. difference between power out of the socket v.s. power gone in to the battery. Over time that can actually add up to substantial differences.

That "sweet spot" is about most efficient power use. The OP was inquiring about battery life. I think that the general rule is slower is always better, but it seems likely that the difference between 10A and 30A is unimportant for battery life.

 

[jerry33]

That "sweet spot" is about most efficient power use. The OP was inquiring about battery life. I think that the general rule is slower is always better, but it seems likely that the difference between 10A and 30A is unimportant for battery life.

My guess would be that because 10A charging is fairly inefficient, you'd lose as much or more in additional electricity charges that you'd save in battery life. And anyway, once you get to those small numbers (probably less than 5%) driving style and environmental factors would overpower the difference between 10A and 30A charging. This is something that I'm not going to lose any sleep over.

 

[Cottonwood]

My guess would be that because 10A charging is fairly inefficient, you'd lose as much or more in additional electricity charges that you'd save in battery life. And anyway, once you get to those small numbers (probably less than 5%) driving style and environmental factors would overpower the difference between 10A and 30A charging. This is something that I'm not going to lose any sleep over.

Remember that all those numbers are for a Roadster with its 53kWh battery. These charge rates scale with battery capacity. C/P is the correct scaling; C is battery capacity, P is charge power, so C/P is hours to full charge. For an 85kWh pack with new, improved batteries, I am sure that regular 40A charging from the UMC or even 80A charging from the HPWC is going to be just fine for the batteries. Even the Supercharger should not be too bad. It seems that the real issues with degradation come from high charge rates at a high state of charge; that is when the most thermal power is dissipated in the batteries. The Tesla chargers seem to be very careful with this. If you read carefully about the Supercharger, Tesla talks about very fast rates for half the capacity of the battery. When the Superchargers come on line, I would really like to hear from some of the California folks about details, at what states of charge does the max charge current ramp down and to what levels.

 

[jerry33]

Remember that all those numbers are for a Roadster with its 53kWh battery. These charge rates scale with battery capacity. C/P is the correct scaling; C is battery capacity, P is charge power, so C/P is hours to full charge. For an 85kWh pack with new, improved batteries, I am sure that regular 40A charging from the UMC or even 80A charging from the HPWC is going to be just fine for the batteries. Even the Supercharger should not be too bad. It seems that the real issues with degradation come from high charge rates at a high state of charge; that is when the most thermal power is dissipated in the batteries. The Tesla chargers seem to be very careful with this. If you read carefully about the Supercharger, Tesla talks about very fast rates for half the capacity of the battery.

Right. Like I said, this is not something I'm going to lose any sleep over because a few full power starts when the battery is below 25% will more than overcome the small difference in degradation from charging as long as the charging rates are in the normal range. The Roadster owner who lost 30% of capacity in 200,000 km (125,000 miles) often raced his Roadster so that's pretty much a worst case. The Model S should have far less degradation.

 

[VolkerP]

The biggest contribution to Li-ion battery degradation is sitting at high SoC in high temperatures (e.g. 100°F/40°C pack temp).

-> charge at 208/220/240V@30-80A is to be preferred over 110/120V@12-15A. The car can divert some electric power to the A/C to cool the batteries then.
-> charge with the minimum power to finish a standard mode charge near the time you want to leave. Add 1h for the car to balance the pack.

Tesla is still working on the in-car software for charging scheduling. I expect that Model S will have a "complete charging by #:## hours AM/PM" feature with one of the next firmware updates.

 

[Johan]

The biggest contribution to Li-ion battery degradation is sitting at high SoC in high temperatures (e.g. 100°F/40°C pack temp).

-> charge at 208/220/240V@30-80A is to be preferred over 110/120V@12-15A. The car can divert some electric power to the A/C to cool the batteries then.
-> charge with the minimum power to finish a standard mode charge near the time you want to leave. Add 1h for the car to balance the pack.

Tesla is still working on the in-car software for charging scheduling. I expect that Model S will have a "complete charging by #:## hours AM/PM" feature with one of the next firmware updates.

... and also if we assume that the thermal management is efficient but not 100% efficient (i.e. there will be an increase in battery temp during charging, even if small, and probably this increased temperature will not be completely evenly distributed in the whole pack) and if we assume that the liquid cooling of the Model S is able to keep temp stable even when charging at higher amps, then it's good to charge with higher amp since the battery spends less time actively charging.

 

[EdA]

This charging every night is a blow to me because I planned on driving my Model S all week and recharging via my solar array on weekends. So much for my plan to rule the world...

 

[Johan]

This charging every night is a blow to me because I planned on driving my Model S all week and recharging via my solar array on weekends. So much for my plan to rule the world...

Are you on a smart grid? Sell the solar back and charge from the net at night? People talk about electrons flowing this way and that way. In my opinion the same electrons are in my wires now as the day I bought them, it's just a question of what is pushing on them and from what direction, at any given time. I.e: let the grid push on them at night (thus pushing power in to your battery) and then at weekends let your solar array push the other way (in to the grid). This argument makes sense, just at Elon's argument about the Superchargers with solar arrays makes sense: So long as they produce the same or more than is consumed, it doesn't matter much when (or for that matter where) the production/consumption takes place.

 

[EdA]

Are you on a smart grid? Sell the solar back and charge from the net at night? People talk about electrons flowing this way and that way. In my opinion the same electrons are in my wires now as the day I bought them, it's just a question of what is pushing on them and from what direction, at any given time. I.e: let the grid push on them at night (thus pushing power in to your battery) and then at weekends let your solar array push the other way (in to the grid). This argument makes sense, just at Elon's argument about the Superchargers with solar arrays makes sense: So long as they produce the same or more than is consumed, it doesn't matter much when (or for that matter where) the production/consumption takes place.

I pay about $0.18/kWh but that is split about evenly between generation and transmission.
When the electrons flow back into the grid I only get back the generation charge. Needless
to say my March electrical bill was $6.43 and I had no charges until July which was $1.94!
Fall and Winter aren't so fruitful though...

/Ed

 

[aviators99]

Tesla is still working on the in-car software for charging scheduling. I expect that Model S will have a "complete charging by #:## hours AM/PM" feature with one of the next firmware updates.

I hope they get it working soon...especially since their web page says this feature comes with the car.