Home Charging Rate - Fast or Slow

[jdcollins5]

I understand that on trips you want the fastest charging rates possible. How about at home, is slower better than faster if you can get the needed charge during Off-peak hours?

The UMC is limited to 32A but you can always lower the current limit: @32A ~ 30 mph, @20A ~ 20 mph and @10A ~ 10 mph. Say I drive 60 miles on a given day. I can recharge in 2 hours @32A, 3 hours @20A or 6 hours @10A.

It seems logical to me that it would be better to charge at the slower rate. Less heat generated in the battery, less heat generated in the home electrical system, and a lower Off-peak KW.

Does this make sense or am I overthinking this?

 

[SSedan]

The charge rate PER CELL at 32amps is still very low so battery heat is not a factor at this level. Honestly at this level I think charger cooling is necessary but not so much battery.

Also there is some fixed electrical overhead with the onboard charger and electronics, go too low and charging becomes inefficient due to keeping all this running way too long. As it related to S and X I had seen some comments 24amps at 240volts was most efficient. Minimize time spent with charger and controls active vs not so fast as to cause cooling to use much energy.

Far as home wiring, it is a 50amp circuit only being run at 32amps, you aren't exactly leaning on it hard.

If it makes you feel better to run it at 20amps go for it but I wouldn't bother going below that, also once the weather turns cold, battery heating is going to become a factor if your garage is unheated, I would let it have all 32amps then. Last winter I "got by" on 24amps from a 30amp outlet near Green Bay with my MS and battery heating was a big factor in charge time and if warming the battery and cabin it could actually still consume a few miles warming up while plugged in but this is a colder climate. I am hoping that with the HCWC now it can heat and charge more efficiently.

 

[Darmie]

The Efficiency of the charge rate is going to be lower when you have a slower charge. This comes from the amount of power going in battery vs being consumed by car during a given time. Wouldn't think it matters.

 

[ewoodrick]

The Efficiency of the charge rate is going to be lower when you have a slower charge. This comes from the amount of power going in battery vs being consumed by car during a given time. Wouldn't think it matters.

I have real problems with this statement. I do not believe that their is an efficiency difference.

If I have a car plugged in for 48 hours, with a charge rate at 10A or 40A, do you believe that it will use different amounts of electricity? I say no.
Yes, because there is a low current drain, the charging rate of a 40A is not 4 times that of a 10A, but that's not efficiency.

 

[SSedan]

at very low charge rates like 15amp 120volt the charger and computers make up a meaningful portion of the electrical usage.
According to the Tesla adapter chart 15amps 120volt is 3mph on a Model 3 but 15amp 240volt is 11mph.
Explain how doubling power nearly triples charge rate?
It has to do with standard electrical overhead to run the charger and computers that need to be active during charging, probably coolant pumps too.

Now if you charge so fast real cooling is needed running fans and AC compressor then I can see charging efficiency dropping at the high end or charging rates

 

[Kirby64]

at very low charge rates like 15amp 120volt the charger and computers make up a meaningful portion of the electrical usage.
According to the Tesla adapter chart 15amps 120volt is 3mph on a Model 3 but 15amp 240volt is 11mph.
Explain how doubling power nearly triples charge rate?
It has to do with standard electrical overhead to run the charger and computers that need to be active during charging, probably coolant pumps too.

Now if you charge so fast real cooling is needed running fans and AC compressor then I can see charging efficiency dropping at the high end or charging rates

120V 15A (12A) is actually closer to 4-5mph, the Tesla chart is inaccurate for 120V 15 and 20A.

Efficiency wise though, you are taking a hit by powering on all the electronics vs. higher rates. To OP, the best charging rate is likely to be fastest. Charging at 10A is definitely going to incur a penalty for having all the electronics on. Between 20A and 32A, it's probably a wash. You aren't stressing the battery out as others have said, so I'd say charge as quickly as possible. Better anyways than having to think about it!

 

[Darmie]

I have real problems with this statement. I do not believe that their is an efficiency difference.

If I have a car plugged in for 48 hours, with a charge rate at 10A or 40A, do you believe that it will use different amounts of electricity? I say no.
Yes, because there is a low current drain, the charging rate of a 40A is not 4 times that of a 10A, but that's not efficiency.

Good point.
On our teslafi charging charts, it appears they are referring efficiency as to how much power actually goes into the battery over time.

See the article below. Now, is there any truth to a Tesla battery having better longevity if fast charged vs slow charge?

Want lithium-ion batteries to last? Slow charging may not be the answer

 

[Big Dog]

I have real problems with this statement. I do not believe that their is an efficiency difference.

Thank you for raising this point. The "efficiency" argument has been posted many times on tmc, and the physics (and math) never made any sense. I'm surprised it has taken this long for someone to point out the obvious.

To the OP, I charge at 32 amps at home with my WC. The Mobile Service guy who here a couple of weeks ago said that he charges at ~38 amps at home.

 

[Big Dog]

It has to do with standard electrical overhead to run the charger and computers that need to be active during charging,

That is the only thing that make sense from an efficiency standpoint. (Cooling may or may not be a factor. If charging at 48 amps, the cooling system is more likely to come on than if charging at 30 amps.) So the real question is, how much extra juice does it take to keep the M3 'awake' while its charging v. being asleep?

 

[SSedan]

I don't know about the AC/DC conversion and if there is a fixed percentage loss there or if there is an efficiency curve.

 

[jdcollins5]

My take away from this thread is that most agree to charge at 32A and forget about it.

If I do reduce the charge rate do not go below 20A due battery cooling/heating and other car overhead.

 

[desiGeek]

How about using the Model S/X Corded Mobile Connector to charge Model 3 LR at 40 Amps?
Will Charging at 40 Amps degrade the Model 3 LR battery?

I am thinking of getting this Corded Mobile Connector and have it permanently plugged in my garage. So that I can set it to daily charge at 32 Amps and use 40A occasionally when you are short on time. Also this will allow me to leave the UMC (that came with the car ) and the adapters in the car so that they are readily available on trips when needed.

 

[jdcollins5]

How about using the Model S/X Corded Mobile Connector to charge Model 3 LR at 40 Amps?
Will Charging at 40 Amps degrade the Model 3 LR battery?

I am thinking of getting this Corded Mobile Connector and have it permanently plugged in my garage. So that I can set it to daily charge at 32 Amps and use 40A occasionally when you are short on time. Also this will allow me to leave the UMC (that came with the car ) and the adapters in the car so that they are readily available on trips when needed.

That is definitely an option and no it should not degrade the battery. The HPWC can charge at 48A.

 

[Sophias_dad]

How about using the Model S/X Corded Mobile Connector to charge Model 3 LR at 40 Amps?
Will Charging at 40 Amps degrade the Model 3 LR battery?

I am thinking of getting this Corded Mobile Connector and have it permanently plugged in my garage. So that I can set it to daily charge at 32 Amps and use 40A occasionally when you are short on time. Also this will allow me to leave the UMC (that came with the car ) and the adapters in the car so that they are readily available on trips when needed.

Why would you go that route instead of the HPWC? With a little searching, you can find a HPWC for $400 or so, and it comes with 24' of cord and a convenient way to hang it. Of course, if you already have an appropriate outlet, that changes things a bit.

 

[Rocky_H]

How about using the Model S/X Corded Mobile Connector to charge Model 3 LR at 40 Amps?
Will Charging at 40 Amps degrade the Model 3 LR battery?

You never need to worry about that with home charging. It helps to get some understanding of the paradigm here.

At Superchargers, the cars can be receiving about 110 kilowatts or more. They do some cooling to manage it, but they handle that power level just fine.
The 240V 40A you are talking about is 10 kilowatts. It is a tenth of the speed of Superchargers. Any level of charging your house could supply is going to be so low that the battery will have no problem.