# Wished mobile app can change rate of charge



## HappyDad (Jul 14, 2018)

Anyone wished they could change the rate of charge (i.e. incoming amperage) from their Tesla mobile app? I lowered my charge amperage to 10A just to keep a slower charge for battery health and my short daily commute. However there are times when I use up more during the day, it would be nice to be able to look at my app when charging starts at 11pm to see how much time to reach my preset charge % and adjust higher charge rate/amperage if necessary.


----------



## garsh (Apr 4, 2016)

HappyDad said:


> I lowered my charge amperage to 10A just to keep a slower charge for battery health


This is actually BAD for battery health.
For anything other than supercharging, it's best to reduce your time spent charging as much as possible.


----------



## Metasequoia (Nov 17, 2018)

What is optimum charging amperage for longest battery life?


----------



## Ed Woodrick (May 26, 2018)

How many years are you wanting? 20? 30? 
Just drive the car and stop worrying about the battery. Tesla builds the car as a car, not something that has to be treated special.


----------



## MelindaV (Apr 2, 2016)

Metasequoia said:


> What is optimum charging amperage for longest battery life?


Hi Battle Ground  
as high as is available. The charging system automatically lowers it as it needs for the battery health (IE when nearly full). Otherwise, it's fine to keep it at the max you have available.


----------



## HappyDad (Jul 14, 2018)

garsh said:


> This is actually BAD for battery health.
> For anything other than supercharging, it's best to reduce your time spent charging as much as possible.


Any technical info or links you can share on why slow or long charging is bad?


----------



## garsh (Apr 4, 2016)

HappyDad said:


> Any technical info or links you can share on why slow or long charging is bad?


Let me see if I can find the relevant posts...
Found them! 

First, Here is a post where it was found that Tesla says to keep the charging rate below about 200 amps to keep from causing battery degredation. Since the Model 3's built-in AC charger maxes out at 48 amps, there's no issue maxing out your Level 2 charging rate.


garsh said:


> https://www.tesla.com/blog/bit-about-batteries
> 
> A couple of tidbits from this article:
> 
> ...


Then there was this video of Professor Dahn (Lithium battery guru at Dalhousie University, who has since been hired by Tesla to run their battery research). In this lecture, he presents his test results that show that battery degradation is related more to the length of time of charging, rather than the rate of charge.


JeffC said:


> Turns out charging too slowly is also bad, in general. Here is Professor Dahn's lecture on battery degradation:
> 
> 
> 
> ...


----------



## JeffC (Jul 4, 2018)

garsh said:


> Let me see if I can find the relevant posts...
> Found them!
> 
> First, Here is a post where it was found that Tesla says to keep the charging rate below about 200 amps to keep from causing battery degredation. Since the Model 3's built-in AC charger maxes out at 48 amps, there's no issue maxing out your Level 2 charging rate.
> ...


It's a bit more complex than that. For some battery chemistries, slow charging can be bad since it can allow more time for parasitic side reactions to happen. However Tesla uses battery chemistry and additives that measured least affected by this. (Both are mentioned in Dahn's lecture.) So the effects of slower charging on Teslas will be much less than other batteries.

I chose as a lower limit of C/24 charging because that's where Dahn's data shows significantly less effects. The actual optimum may be higher. C/25 would be 75 kWhr / 25 hours = 3 kw = 12.5 Amps at 240 volts. (Actual charge power would need to be a bit higher due to various losses before it actually gets to the battery.) Again the effects of slower charging for Tesla packs is least of the types they tested. so trying to charge faster than C/24 is for an abundance of caution and not much actual need.

There is definitely a point where higher power charging will degrade the battery pack. Ordinary 120kw Supercharging will do it if done often enough, so an optimal charging rate is definitely lower. 72 kW Urban Supercharging may be marginally better.

The 200 Amp mention for Roadster probably is less relevant because of changes to the battery chemistry, thermal management, etc., since then, though it has some general relevance that higher power can degrade batteries.

A more useful reference from Martin's first blog post above is C/2 (a 2 hour to full charge date) which is slower than Supercharging. Supercharging a 75 kWhr Model 3 pack at 120 kW is C/1.6. So for the Roadster batteries, Supercharging would degrade them. Done often enough, Supercharging could also degrade the Model 3/S/X packs, which is why Tesla recommends against Supercharging a lot and will reduce a given car's Supercharging power if done too often.

Bottom line: most practical charging should be fine. 10 Amps at 240 Volts should be ok. Based on Dahn group's research, I'd recommend higher than 3kW charging power and much less than Supercharging.


----------



## SMITTY (Jan 24, 2019)

Interesting article stating that Tesla slows down the rate of charge at Superchargers once the "vehicle has seen significant DC fast charging" to prevent degradation of the battery pack...

https://electrek.co/2017/05/07/tesla-limits-supercharging-speed-number-charges/


----------



## garsh (Apr 4, 2016)

JeffC said:


> It's a bit more complex than that.


It always is. But people are mostly interested in general guidelines.


> Again the effects of slower charging for Tesla packs is least of the types they tested. so trying to charge faster than C/24 is for an abundance of caution and not much actual need.


I'd argue the other direction: that charging slower than 48 amps is unnecessary and provides no benefit to battery lifetime. And as a more practical matter, charging at slower rates is a little less efficient.

Given that charging at faster AC rates is both more efficient and results in less battery degradation (again, not a whole lot of difference, and you'll most likely not notice much difference over the lifetime of the vehicle due to Tesla's excellent battery chemistry), it makes no sense to dial down the rate of charging for either of these reasons.

If you have another goal in mind (such as keeping the battery warm all night by slowing down the rate of charge so that it finishes right before you leave in the morning so that you have more available regen) then I think lowering the charge rate is fine. Again, all indications are that there won't be much noticeable difference to a Tesla over the lifetime of the car.


----------



## JeffC (Jul 4, 2018)

garsh said:


> It always is. But people are mostly interested in general guidelines.I'd argue the other direction: that charging slower than 48 amps is unnecessary and provides no benefit to battery lifetime. And as a more practical matter, charging at slower rates is a little less efficient.
> 
> Given that charging at faster AC rates is both more efficient and results in less battery degradation (again, not a whole lot of difference, and you'll most likely not notice much difference over the lifetime of the vehicle due to Tesla's excellent battery chemistry), it makes no sense to dial down the rate of charging for either of these reasons.
> 
> If you have another goal in mind (such as keeping the battery warm all night by slowing down the rate of charge so that it finishes right before you leave in the morning so that you have more available regen) then I think lowering the charge rate is fine. Again, all indications are that there won't be much noticeable difference to a Tesla over the lifetime of the car.


There are tradeoffs.

Faster charging is good for less time exposed to parasitic side reactions, BUT, Tesla's battery chemistry is probably the most inherently immune to those, so arguably less benefit there.

Slower charging is better for the grid and has lower current related losses such as resistance and induction. Current related losses are significant since for example resistive losses are the square of current. Twice the current is quadruple the resistive losses, not double. These losses are very significant due to the square law.

There are some relatively fixed losses in the system, so higher charging power is better to reduce those as a proportion of the energy actually getting stored in the battery.

All of the above balance each other out at some optimum, but the actual optimum is highly complex to calculate.

Very fast charging such as Supercharging will degrade the battery pack (any non-phosphate Lithium ion battery, which no one uses in vehicles due to lower energy density) if done often enough.

That all said, any typical Level 2 charging from about 3 kW to 11 kW should be fine, so it's really not a big deal. Due to Tesla's excellent battery chemistry any long term effects of anything other than Supercharging should be tiny.

Would definitely recommend above 3 kW charge power.


----------



## garsh (Apr 4, 2016)

JeffC said:


> Current related losses are significant since for example resistive losses are the square of current


Unless you have a 500 ft or longer run from the breaker panel, the wire resistive losses are swamped by the charger's constant overhead. I ran through the math here.


----------



## JeffC (Jul 4, 2018)

garsh said:


> Unless you have a 500 ft or longer run from the breaker panel, the wire resistive losses are swamped by the charger's constant overhead. I ran through the math here.


There are resistive losses everywhere in the system (really any electrical system), including in the car itself, such as battery cells, battery wiring, charger transistors, internal wiring, internal connectors, etc.


----------



## garsh (Apr 4, 2016)

JeffC said:


> There are resistive losses everywhere in the system (really any electrical system), including in the car itself, such as battery cells, battery wiring, charger transistors, internal wiring, internal connectors, etc.


Yep. And if all those lengths added together are less than ~500', then the resistive losses will be less than the constant charger overhead.


----------



## JeffC (Jul 4, 2018)

garsh said:


> Yep. And if all those lengths added together are less than ~500', then the resistive losses will be less than the constant charger overhead.


The losses in a transistor aren't the same as the losses in copper, etc.


----------



## garsh (Apr 4, 2016)

JeffC said:


> The losses in a transistor aren't the same as the losses in copper, etc.


What are you trying to argue at this point?

If you have a long run of copper wire, then resistive losses dominate. If not, then the car's charger (which contains most of those resistors) appears to exhibit roughly fixed power loss regardless of the charging rate, and those losses dominate.


----------



## JeffC (Jul 4, 2018)

garsh said:


> What are you trying to argue at this point?
> 
> If you have a long run of copper wire, then resistive losses dominate. If not, then the car's charger (which contains most of those resistors) appears to exhibit roughly fixed power loss regardless of the charging rate, and those losses dominate.


The point is that charging current still matters due to the laws of physics.


----------

