Slow (but not trickle) charging

[f308gt4]

In the world of mobile phones, I think it’s generally accepted that charging slowly is better for the battery. Does this also apply to our batteries?

I have a NEMA 14-50 outlet that charges my Model 3P at 32A, and notice that you can change the amperage on the main screen. Would it have a beneficial effect over the long term to lower the amperage so that it takes longer to charge?

 

[SSedan]

When thinking charging speed think of hours from empty to full.

Your UMC at 32amps is going to take what 8+ hours to charge from empty to full on a standard range.........

That is trickle charging.

 

[smatthew]

There is some research that suggests that the amount of time spend charging is relevant. They believed that charging at around the urban supercharger rate would be optimal for the batteries long term health.

That would seem to indicate that lowering the charging amperage does not help the battery.

 

[user212_nr]

The Model 3 battery has 3,000+ cells inside of the battery pack. Each of those cells has more power, about 18wh, than two cell phones, about 10wh.

So imagine that you are trickle charging 6,000 cell phones off one electrical outlet. Not much power is going to each cell. Even 32 electrical outlets does not provide a large charge to each battery cell.

It is possible that there is also a concept of "too little" being a disadvantage if the cells get cold. Many find that they are not even able (or barely able) to charge the Model 3 off a standard wall outlet when the weather is too cold. That is not good for the battery certainly.

 

[jjrandorin]

In the world of mobile phones, I think it’s generally accepted that charging slowly is better for the battery. Does this also apply to our batteries?

I have a NEMA 14-50 outlet that charges my Model 3P at 32A, and notice that you can change the amperage on the main screen. Would it have a beneficial effect over the long term to lower the amperage so that it takes longer to charge?

For our car batteries, Supercharging = "fast". Anything we are doing at home basically is "slow" (even at 48amps for a LR / P).

 

[1.21GW]

If you aren’t supercharging, then it is all relatively slow charging. Batteries are researched based on C rates. (1C = empty to full battery in 1 hour, 2C = empty to full in 30 minutes, etc...). When we go empty to full in 8 hours, we are 0.125C. This is essentially trickle charging for the battery.

Additional, not relevant info. Batteries are capable of discharging at high C rates , but only charging at low C rates (<2C). This is why your regen gets limited in cold weather but your acceleration does not.

 

[Rocky_H]

From the perspective of the car or battery, no, if won't make a bit of difference. You're question the difference of like 5kW versus 7kW, when the car can handle over 100kW. Home is always "slow" charging.

The only place it can make a useful bit of difference is with your charging equipment. With the mobile charge cables or the wall connectors, they are built to handle a certain maximum amps, and they can sometimes get pretty warm running at maximum level like that. Thermal cycling is the main thing with that of how much the temperature swing is every single day when it gets hot charging, and then cools down. Those kinds of daily hot/cold cycles can be hard on electronics and the solder joints in them and can cause them to fail sooner. So turning the amps down a few from the maximum level can keep it from getting as hot and reduces the temperature swing distance of your daily charging, and can help your charging equipment last longer.

 

[smatthew]

From the perspective of the car or battery, no, if won't make a bit of difference. You're question the difference of like 5kW versus 7kW, when the car can handle over 100kW. Home is always "slow" charging.

The only place it can make a useful bit of difference is with your charging equipment. With the mobile charge cables or the wall connectors, they are built to handle a certain maximum amps, and they can sometimes get pretty warm running at maximum level like that. Thermal cycling is the main thing with that of how much the temperature swing is every single day when it gets hot charging, and then cools down. Those kinds of daily hot/cold cycles can be hard on electronics and the solder joints in them and can cause them to fail sooner. So turning the amps down a few from the maximum level can keep it from getting as hot and reduces the temperature swing distance of your daily charging, and can help your charging equipment last longer.

Except now you're talking theoretics. The equipment that gets warm during charging is the PCS which is in the battery pack, and that has coolant to moderate its temperature. Remember, the Mobile Connector and Wall Connector are just smart switches. There is no power conversion circuitry (ok, technically there is a tiny power supply in there to power the microcontroller and the leds) in an EVSE. They're basically a big honking relay with support circuits. 120V or 240V in, the same voltage out. And the mobile connector is designed and manufactured to be used outdoors in basically any weather. The gen2 mobile connectors are pretty reliable.

 

[Rocky_H]

Except now you're talking theoretics. The equipment that gets warm during charging is the PCS which is in the battery pack, and that has coolant to moderate its temperature. Remember, the Mobile Connector and Wall Connector are just smart switches. There is no power conversion circuitry (ok, technically there is a tiny power supply in there to power the microcontroller and the leds) in an EVSE. They're basically a big honking relay with support circuits. 120V or 240V in, the same voltage out. And the mobile connector is designed and manufactured to be used outdoors in basically any weather. The gen2 mobile connectors are pretty reliable.

Uh, no, not talking theoretics. I'm talking reality. I'm talking the actual inline electronics box in the UMC cord. I'm talking about the plug heads at the outlet. I'm talking about the charging handle plug that goes into the port. I'm talking about all of the connection points of those along the way where they are attached to each other. I'm talking soldered points of dissimilar metals with different thermal expansion coefficients. They get noticeably pretty warm when running at high currents, near their maximum rated levels. It is directly observable in reality to the touch that they do not get as hot if they are used a lower current levels. This is a fact in electronics that less differential of heat cycling in a very high number of cycles is less stress on the materials and helps to extend the operating life of them.

I know it's not doing voltage conversions in there, but it is a wire, and it is passing high current through it, and Tesla does like to use what they can get away with for wire thickness, so they are usually pretty hot from the resistance when running at max current.

 

[smatthew]

Uh, no, not talking theoretics. I'm talking reality. I'm talking the actual inline electronics box in the UMC cord. I'm talking about the plug heads at the outlet. I'm talking about the charging handle plug that goes into the port. I'm talking about all of the connection points of those along the way where they are attached to each other. I'm talking soldered points of dissimilar metals with different thermal expansion coefficients. They get noticeably pretty warm when running at high currents, near their maximum rated levels. It is directly observable in reality to the touch that they do not get as hot if they are used a lower current levels. This is a fact in electronics that less differential of heat cycling in a very high number of cycles is less stress on the materials and helps to extend the operating life of them.

I know it's not doing voltage conversions in there, but it is a wire, and it is passing high current through it, and Tesla does like to use what they can get away with for wire thickness, so they are usually pretty hot from the resistance when running at max current.

And Tesla designed the UMC so that it will work successfully in all weather. Let's check the manual:
"Caution: Do not operate the Mobile Connector in temperatures outside its operating range of -22°F to +122°F (-30°C to +50°C)."

If you can hold your hand to the UMC for more than 5 seconds, it's operating within normal design parameters.

And the UMC has temperature sensors. If any part were to get too hot it shuts down.

BTW - there are NO solder joints in the main power path of the UMC. Tesla knows what they're doing.

 

[Uncle Paul]

There is no difference that you would notice.

 

[SSedan]

The newer owners seem to suffer a lot of delusion believing that no ICE means no wear, car lasts forever.

I for one have a 96k mile S that has had more, and more expensive repairs than any other sub 100k mile car I have ever owned. The original UMC to car plug that I repeatedly cleaned with electronics cleaner still runs warmer at 32amps than my wall connector does at 72amps. The UMC was the power source for the first 80k, the HCWC for the last 25k. The UMC plug to car is simply worn, I avoid using it at 40amps due to the temp rise. It is the backup and travel solution now.

Plus even if you drink the koolaid and think the Tesla parts are pure perfection, the heat cycling of the home circuit has caused problems for more than one or two folks. Little else puts the sustained load on a circuit a car does, hence the 80% rule in the US and 75% for Canada. On the other side slow down too much and you waste power keeping the electronics and coolant pumps needlessly active. Tradeoffs to everything.

 

[Rocky_H]

And Tesla designed the UMC so that it will work successfully in all weather.

...and I still am not talking about the weather.
I am talking about current flow through resistive wires heating things up--daily heat cycling.

 

[MXLRplus]

If the car needs to fire up the cooling fan to charge, or the cabling gets warm, you can save electricity by charging at a slower rate.
As far as battery life goes, you hear 100 different stories, and in all likelihood, those stories will be different next year.

Think about this. Even though it cost Tesla almost nothing to stop selling the cars with a L2 connector (14-50), they did do it. And many other other cars come with just an L1 EVSE. Many cars will kick on their cooling at ~6 kW.

Perhaps the mfrs know something?

But? The reason to buy a 250+ mile EV is so you DON'T have to worry about the range and battery.

 

[SSedan]

The L2 connector not being included was about getting an extra $35 zero chance it was about extending battery life with slower charging. Implying that is absurd at best.

I haven't paid attention but if I were designing the system I would run the coolant loop when charging just to keep temp balanced, can't have thousands of sensors for each cell.

 

[camalaio]

And Tesla designed the UMC so that it will work successfully in all weather. Let's check the manual:
"Caution: Do not operate the Mobile Connector in temperatures outside its operating range of -22°F to +122°F (-30°C to +50°C)."

If you can hold your hand to the UMC for more than 5 seconds, it's operating within normal design parameters.

And the UMC has temperature sensors. If any part were to get too hot it shuts down.

BTW - there are NO solder joints in the main power path of the UMC. Tesla knows what they're doing.

Thermal cycling still occurs without needing to trip the sensors for thermal maximums. This is probably worse in winter where the UMC itself could be very cold then warm up as it charges.

While the main power path may not have soldered joints, there's still a populated PCB in the same thermally cycling enclosure and the power contacts themselves are potential higher resistance points. Like you said, I'm sure Tesla has considered these things but the OP would not have a completely false worry about thermal cycling. It's just unlikely to cause issues on any particular unit.

Anecdotally, mine doesn't seem warm at 24A but sure is toasty at 32A. I charge at 24A because I'm paranoid about warm electrical things, which is a mostly unfounded fear (and I'm OK with that, it charges fast enough for our needs anyways).

If the car needs to fire up the cooling fan to charge, or the cabling gets warm, you can save electricity by charging at a slower rate.
As far as battery life goes, you hear 100 different stories, and in all likelihood, those stories will be different next year.

Think about this. Even though it cost Tesla almost nothing to stop selling the cars with a L2 connector (14-50), they did do it. And many other other cars come with just an L1 EVSE. Many cars will kick on their cooling at ~6 kW.

Perhaps the mfrs know something?

But? The reason to buy a 250+ mile EV is so you DON'T have to worry about the range and battery.

Minor corrections, these are good to know though:

• The car consumes 250-300W or so while charging regardless of heating/cooling, which is significant.
• Cooling on L1/L2 charging is exceedingly rare. You'd have to be hot off the track on a hot day, and even then it wouldn't be cooling for long.
• Heating on L1/L2 is more likely depending on ambient temps, and can draw significantly more power.

For probably 99.9% of people, charging slower just means consuming 300W for a longer amount of time, wasting energy to running the computers and pumps. For the cases where heating or cooling is needed, it needs to run that regardless of charge rate. At L1/L2. the power going to the battery isn't really sufficient to heat it like a Supercharger does. We're talking less than 0.1C; it'd be like hooking your phone to a very old, slow 5V/250mA charger - you'd never notice the waste heat from that.