Should you charge slower with your wall charger in the summertime?

[A-Wimoweh]

I picked up my new 75D late last November, and have been charging at 48 amps to 80% every morning before leaving for work. My thinking was charge the battery quickly and have it ready just before I leave in the morning, so on cold winter mornings I have full regen starting out, and don't need to use the battery to heat the battery.

But now that it is warming up and my battery does not need the extra heat, would I be better off charging longer at a lower amperage, like 32 vs 48? Thinking that would keep the battery temp down while charging at home. Would this affect the efficiency of the charger, either positively or negatively?

 

[Electric700]

If charging close to 30 A (240 V) won't negatively impact your range needs, I think it will be fine. Lower current = less heat.

Congrats on your car!

 

[TexasEV]

Stop obsessing over the battery. The difference between charging at 32A and 48A (7.6 or 11.5 kW) is trivial compared to the power a supercharger provides. On the other hand, charging at 32A makes the charging circuit run 50% longer than when you charge at 48A. If you can charge at 48A, charge at 48A.

 

[sorka]

It's not how long your charge but how long your battery stays warm vs time:

So it's tricky. If charging at 60 amps results in the battery rising to 100F but charging at 80amps results in the same 100F because the cooling system kicks in to keep the battery from getting warmer, then it would be better to charge at 80 amps because your spent less time at 100F.

I'm not saying that's what happens with this exact scenario. Just pointing out at some point something like this could happen. When you supercharge, you spend very little time charging and the battery stays relatively cool because the AC is actively keeping the battery from going above about 110F in the worst case scenario. So is 110F for 30 minutes worse or better than 100F for 4 hours?

 

[David99]

As for battery health, it really makes no difference charging at 48 Amps vs 32 or whatever you want to set it to. The heat generated makes no difference to battery health one way or another. Don't worry.

One thing to consider when charging at a lower rate. When charging at a lower rate, you are charging longer. This means supporting components like battery pump, fans and other things are running longer using a little more energy of the longer time. So overall it is a little less efficient. Another thing to keep in mind is that power electronics (like chargers) are often most efficient at the rated power and less efficient at partial load. So charging at partial load is a little less efficient. The 48 Amp chargers are made from two 24 Amp modules, though. So 48 and 24 Amp is most efficient. Anything in between is less efficient. 72 Amp chargers are made from 3 24 Amp modules.

But all of this is small differences. Don't worry, charge as you used to. Using a charge timer or app to charge just before you leave is a good idea (I do the same). It keeps the average state of charge over time lower without any compromise of using the car or range.

 

[jerry33]

If you want to help the grid, you can set the timer to charge early morning. That will also reduce the amount of cooling the car has to do. The battery won't care.

 

[ewoodrick]

No.

Drive Car, Enjoy car, forget about battery. That's the way it is designed.

 

[Rocky_H]

These levels of home charging are about one tenth of the power the car would get at Superchargers. So this little difference you're considering about 32A versus 48A is meaningless as far as trying to "go easy" on the battery. But the factor @David99 mentioned is a real thing. Some of the degradation takes place based on how long the battery stays in that chemical state of recharging. So getting it over with and then letting it go back to resting is a little helpful. This 32 or 48 is again not much of an issue, but I've heard of people talking about turning it down to 5 or 10A, so it can go really slowly, which triples or quadruples the charging time, and that's probably not a good thing long term.

The only good reason people might turn things down some is to give a little room to maximum load creating excess heat in the charging cables, but that wouldn't apply to your wall connector situation here. There had been some issues with the old mobile connectors running at their maximum 40A rate all the time or the wall connectors running at their maximum 80A rate all the time. There were some melted connections or blown fuses on some of those. So I might have that same thought at the newer UMC version 2 that is built a little smaller and rated for 32A maximum. If it were me, I might turn it down by a few amps for the regular daily use. But since you're talking about 32 or 48A from a wall connector rated to 80A maximum, this isn't an issue on your setup.

 

[sorka]

As for battery health, it really makes no difference charging at 48 Amps vs 32 or whatever you want to set it to. The heat generated makes no difference to battery health one way or another. Don't worry.

One thing to consider when charging at a lower rate. When charging at a lower rate, you are charging longer. This means supporting components like battery pump, fans and other things are running longer using a little more energy of the longer time.

All depends on ambient temperatures and actual charge rate. If you charge at 40 amps when it's 50 degrees outside, your cooling system will never turn on to cool the battery.

Conversely, charging at 80 amps in when it's 90 degrees out will cause not just the fan to turn on but the AC to occasionally turn on as well.

 

[David99]

All depends on ambient temperatures and actual charge rate. If you charge at 40 amps when it's 50 degrees outside, your cooling system will never turn on to cool the battery.

Conversely, charging at 80 amps in when it's 90 degrees out will cause not just the fan to turn on but the AC to occasionally turn on as well.

The question was if reducing from 48 to 32 Amp would make a difference in terms charging efficiency. I don't think I have ever heard the AC turn on when charging on AC, even on very hot days. Surely not after the car has been sitting over night for many hours.

 

[SSedan]

Another way to demonstrate you are worrying about nothing.

Your cell phone charging in an hour generates a bunch of heat right bit with no active cooling or even circulating coolant to disperse heat evenly.

If you could throttle it to take 10 hours the way a Tesla would at these charge rates how much heating do you think there is? Then consider it circulates coolant so no localized hot spots.

 

[A-Wimoweh]

Interesting points about charging for longer periods causing more wear on the charging system...

As for those saying I am worrying about nothing... Its not like I am loosing sleep and waking myself up in the middle of the night to go down to the garage and start my car charging. If I had to do that, no way. I'd rather sleep better than get some small minuscule gain in the battery longevity. But all it takes is a little time to figure out how these systems work, apply it to your situation, and then set the charging schedule. Then you're done.

By delaying the start of the charge, you're helping the grid, your car, and your finances if you have a TOU electric plan. The only downside is sometimes I will wake up in the morning and see there is an update, and have the car interrupt charging to install it. But my commute is such that even if I did not charge at all one day, I'd still have plenty of juice the next day.

 

[bob_p]

Tesla has a lot of data they've been collecting from S/3/X since 2012.

It's good practice to keep charge between 10-90% and avoid keeping the battery outside of that range for extended periods.

The only case where Tesla has identified charging as a major risk to the batteries is with 3rd party DC fast chargers - and when the software detects a potential issue, evidently it will limit use of those chargers.

Otherwise, owners shouldn't worry about using HPWCs at up to 72-80A or 14-30/14-50 at lower amps. The software and hardware is designed to protect the battery - and keep the battery at a safe temperature while charging.

Keep it simple - read the owner's manual - and don't worry about it...

 

[Rocky_H]

I'd rather sleep better

In the jungle, the quiet jungle...

 

[sorka]

The question was if reducing from 48 to 32 Amp would make a difference in terms charging efficiency. I don't think I have ever heard the AC turn on when charging on AC, even on very hot days. Surely not after the car has been sitting over night for many hours.

Yes, but I was responding directly to this in your quote of me:

One thing to consider when charging at a lower rate. When charging at a lower rate, you are charging longer. This means supporting components like battery pump, fans and other things are running longer using a little more energy of the longer time.

...and my point is that it's just the opposite. The slower you charge, the less likely you are to use any pumps or fans at all.

 

[SSedan]

I don't know what they do but I would hope the pumps run at least intermittently, can't get accurate pack temp measurements otherwise, even a dozen temp sensors scattered.around would leave big gaps in coverage that can be filled by circulating the coolant and equalizing everything.

 

[Big Earl]

Charging more slowly will decrease your charging efficiency. The car has fixed overhead consumption while charging, so if you reduce the power available for charging, that fixed overhead becomes a higher percentage of the total energy pulled from the wall.

 

[sorka]

When charging at the same voltage, there's very little difference in charging efficiency. If anything, it's a little less efficient at 80 amps because the pumps and fans are sometimes going:

I have hundreds of charging sessions logged from 20 amps to 80 amps and unless the cooling system turns on, it's always right around 90%.

Some might confuse longer charging with efficiency since that's often associated with lower voltage. Charging at 110v *IS* way less efficient because the inverter's overhead to step it up to 400v is far higher than stepping up from 245 volts.

Over 50+ charging sessions at work on 110v, my average efficiency is about 71%.

 

[Big Earl]

When charging at the same voltage, there's very little difference in charging efficiency. If anything, it's a little less efficient at 80 amps because the pumps and fans are sometimes going:

View attachment 396170

I have hundreds of charging sessions logged from 20 amps to 80 amps and unless the cooling system turns on, it's always right around 90%.

Some might confuse longer charging with efficiency since that's often associated with lower voltage. Charging at 110v *IS* way less efficient because the inverter's overhead to step it up to 400v is far higher than stepping up from 245 volts.

View attachment 396176

Over 50+ charging sessions at work on 110v, my average efficiency is about 71%.

Very interesting. Thanks for that data.

 

[sorka]

Very interesting. Thanks for that data.

BTW, it doesn't mean there isn't a fixed overhead for running the charger regardless of your charge rate, but I think it's so small that it doesn't factor in more than a fraction of a percent with other factors being far larger.