Cold weather charging / battery heating / loss of range (THEORY INSIDE!)

[Chris TX]

Cold weather charging / battery heating / loss of range (un-orignal THEORY INSIDE!)

Normally, I would plug the car in at night reduced down to 20A for a nice, slow charge. That's fine, nice for the battery, gets me nice range due to better pack leveling.

However, these past few days have been 10+ degrees below freezing and we get the "Battery is heating, performance is impacted blah blah blah..."

So I had an idea:

What if I bump the charging to the 40A max, but delay it to a few hours before we leave in the morning? That way, the battery is already warmed by the charging AND the battery is finished charging. Then, you have a pre-warmed / full range drive for the day!

It's supposed to be cold in the morning, so I'm going to try this theory. I searched, but couldn't see if anyone else thought of this, yet.

I'll post my results on whether this works or not.

 

[islandbayy]

Normally, I would plug the car in at night reduced down to 20A for a nice, slow charge. That's fine, nice for the battery, gets me nice range due to better pack leveling.

However, these past few days have been 10+ degrees below freezing and we get the "Battery is heating, performance is impacted blah blah blah..."

So I had an idea:

What if I bump the charging to the 40A max, but delay it to a few hours before we leave in the morning? That way, the battery is already warmed by the charging AND the battery is finished charging. Then, you have a pre-warmed / full range drive for the day!

It's supposed to be cold in the morning, so I'm going to try this theory. I searched, but couldn't see if anyone else thought of this, yet.

I'll post my results on whether this works or not.

This has been covered a few times.

Here is what you do, as I have played around with this extensively.

When it gets super cold out, the pack heater kicks in. Charging at 20 amps is not enough power to provide power to the pack heater and still charge the battery. After the pack heater turns off, it will start to charge, but the lack of power from the wall to the car (as you say, limited to 20 amps) means that the pack heater also TOOK power from the battery. Also, the lower the charging amperage, the less heat is generated by the charging process.

I've found, during these cold months, charging at the full 40 amp (or possiably a wee bit below as in 37-39 to reduce resistance in the wiring a bit), generates just enough heat to keep the pack heater off. Thus keeping you from wasting power heating the pack, when the charging process could be doing that for you and killing 2 stones with one bird. You would be better off delaying it a bit. But still, make sure you keep a safety margin in their, as if temps get too cold, or winds pick up and keep the car from building up enough heat on it's own through charging, that the car has enough time to finish the charge.

 

[stevezzzz]

Good thinking, but certainly not original to you. Here's a recent post from one of TMC's resident cold-weather hypermilers:

Tesla Cross-Country Trip - Page 25

 

[Chris TX]

OK, so it looks like my good idea isn't unique. But at least it's a good one

We don't get many days like this down in Texas, so it's a fun adventure every time. If my new thread shows someone else how to save some electricity this winter, it's worth it.

I've got about 60 miles left before the battery is charged to normal level (80%) so I've got it started charging 2 hours before we leave for our first errand. I'm looking forward to NOT seeing the dreaded, dashed orange line in the morning!

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Good thinking, but certainly not original to you. Here's a recent post from one of TMC's resident cold-weather hypermilers:

Tesla Cross-Country Trip - Page 25

I just searched the Battery and Charging section for this, since it falls directly into this section. That's a good read, though. Thanks!

 

[islandbayy]

OK, so it looks like my good idea isn't unique. But at least it's a good one

We don't get many days like this down in Texas, so it's a fun adventure every time. If my new thread shows someone else how to save some electricity this winter, it's worth it.

I've got about 60 miles left before the battery is charged to normal level (80%) so I've got it started charging 2 hours before we leave for our first errand. I'm looking forward to NOT seeing the dreaded, dashed orange line in the morning!

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I just searched the Battery and Charging section for this, since it falls directly into this section. That's a good read, though. Thanks!

Sorry to tell ya, you will see the dashed line or no line at all (regen disabled) regardless if it was just charging at 40 amp. It all depends on the temps. The car tries to keep the battery just warm enough to safely charge (Charging a lithium battery when it is at or below 32*F (Freezing) will cause permanent capacity loss due to electroplating the anode inside the cell which is why we get limited or no regen when cold).
Although, your timing may help keep the pack more at the borderline, so when you do start to drive, it will reach full operating temps quicker.

But also factor in, delaying the charge, will also let the pack cold soak, so it will still need to heat the pack to a minimum temp before charging will start. So make sure you factor in the "Fudge" time for the pack warmer.

 

[jerry33]

Charging at 32 amps and then preheating at 26.5 (non-range mode) for 1.5-2.0 cycles will get the regen dashed line to about 30 kW and no power limiting at -8 (parked outside--Texas). If the charging isn't quite complete when the pre-heating is started, the charge rate goes way down, but doesn't entirely stop (e.g. goes from 30 minutes remaining to 4 or 5 hours remaining). When driving switch to range mode and the dashed line goes away in ten miles. No heat while driving required till after 25 miles.

 

[Chris TX]

An update for this theory:

My estimated time to start charging was only off by 7 minutes (which couldn't be set anyways). At the time of our departure, the car was still charging and the coolant pumps were still whirring, so that was a good sign. It was below freezing when we left, but I didn't get the dashed, yellow line once during the whole trip.

As for cold soaking the battery pack, the car sits in my garage which can get down to the mid-20s if the outside temps are far below.

All-in-all, everything worked out as expected. I'll be adjusting it back down to the lower amps with no start time once the weather warms back up.

 

[efusco]

You'll improve the effectiveness of keeping the pack warm if you're sure to turn off Range Mode. I never remember to do that, but when you do it dedicates more juice to the pack.

 

[Todd Burch]

By the way, you're not doing the battery any favors by charging at 20A vs. 40A. Even 40A is only about 10 kW. Even with a 60 kWh battery that's a 1/6 C charge rate. If you're not aware of what that means, the battery can easily handle 1/6 C charge rate without any damage. In fact, you make things worse by charging at 20A, because that is actually less efficient than charging at 40A. You will use more electricity charging at 20A vs. 40A.

 

[rlang59]

By the way, you're not doing the battery any favors by charging at 20A vs. 40A. Even 40A is only about 10 kW. Even with a 60 kWh battery that's a 1/6 C charge rate. If you're not aware of what that means, the battery can easily handle 1/6 C charge rate without any damage. In fact, you make things worse by charging at 20A, because that is actually less efficient than charging at 40A. You will use more electricity charging at 20A vs. 40A.

That may be the case but a continuous load of 20A is going to be easier on the grid than one at 40A.

 

[NigelM]

It's an interesting math problem but I'm not sure that I buy it as a real world problem. I'm guessing that in Dallas it doesn't get that cold very often so I think I'd just leave my car plugged in at max amperage and let it take care of itself on those occasions. Plus, as Todd mentions you're reducing efficiency to the point where it's actually going to cost you more.

At risk of starting a different conversation about charging rates, I'll confess that I always leave it up to Tesla to determine what is best for my batteries. I've just plugged in my Roadster every night for three years to take whatever amps it could draw and I've seen zero degradation (I do an occasional range 3-4 times per year, just whenever I have a long drive, which helps balance). I've been doing the same thing on Model S for 18 months now (26,000 miles) and seen no real degradation. I know there are different points of view but if it ain't broke, why fix it?

Caveat: neither of my cars has ever experienced temperatures below 40F.

That may be the case but a continuous load of 20A is going to be easier on the grid than one at 40A.

The OP is charging at off-peak anyway.

 

[rlang59]

The OP is charging at off-peak anyway.

I know but that still doesn't change the fact that 20A continuous is easier on the grid than 40A. I was only adding a "pro" for not increasing the amperage.

 

[GDH]

killing 2 stones with one bird.

HA!

 

[Todd Burch]

I know but that still doesn't change the fact that 20A continuous is easier on the grid than 40A. I was only adding a "pro" for not increasing the amperage.

Although I'm not an expert, power stations would prefer to have a constant continuous load. Nighttime load is *so much* less than daytime load that, for a very good while into the future, charging at your max rate is probably BETTER for the grid than worse--because it helps bring it closer to the daytime usage--less of a difference between day and night.

Grain of salt: I'm not a grid expert.

 

[Chris TX]

I'm charging slower to be easier on the battery. I don't care about the grid (in this case) and lower amps means less heat/resistance loss through the little 50A circuit. It's also easier on the battery (in warmer weather) to charge at lower amps for better pack leveling.

 

[Todd Burch]

I'm charging slower to be easier on the battery. I don't care about the grid (in this case) and lower amps means less heat/resistance loss through the little 50A circuit. It's also easier on the battery (in warmer weather) to charge at lower amps for better pack leveling.

Actually, charging at lower current is resulting in larger losses. See post #9 in this thread. Tesla's very own charging calculator shows higher currents to be more efficient on their website. And 5 kW vs. 10 kW charging with a battery this big makes no difference. Even 240V 80A is easy for the battery to handle.

 

[mknox]

Although I'm not an expert, power stations would prefer to have a constant continuous load. Nighttime load is *so much* less than daytime load that, for a very good while into the future, charging at your max rate is probably BETTER for the grid than worse--because it helps bring it closer to the daytime usage--less of a difference between day and night.

Actually, not quite. Utility capacity planning is built around some diversity in loads from house to house, appliance to appliance, and much of the distribution system depends on nighttime cooling of transformers and equipment. Having said that, loads are generally a lot lighter at night than in the day, so that is obviously preferred for EV charging. The real bottleneck is not at the generator or transmission level, but at the local distribution level on your street. A Tesla Model S with twin chargers can look like 4 houses to the utility from a demand perspective.

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When it gets super cold out, the pack heater kicks in. Charging at 20 amps is not enough power to provide power to the pack heater and still charge the battery.

I only have a 20 amp circuit in the garage and charge my car at 16 amps continuous. Works fine for me so far at temps as low as -15 F. The pack heater will come on first, and will indeed use a bit of battery capacity plus the shore power at first, but it fairly quickly tapers off and charging will ramp up to the same 11 Rated Miles per Hour that I get in the summer.

 

[Todd Burch]

Actually, not quite. Utility capacity planning is built around some diversity in loads from house to house, appliance to appliance, and much of the distribution system depends on nighttime cooling of transformers and equipment. Having said that, loads are generally a lot lighter at night than in the day, so that is obviously preferred for EV charging. The real bottleneck is not at the generator or transmission level, but at the local distribution level on your street. A Tesla Model S with twin chargers can look like 4 houses to the utility from a demand perspective.

OK, so I know you work in the electric industry...I don't remember where I read it or which power source it was (maybe nuclear?), but I remember reading that some power stations actually end up dumping (wasting) power at night because they're unable to taper back to the low nighttime levels quickly enough. Does that ring any bells? In that case, for now anyway it would seem that you're not really being any better to the grid by charging at 20A vs. 80A in the middle of the night.

 

[rlang59]

OK, so I know you work in the electric industry...I don't remember where I read it or which power source it was (maybe nuclear?), but I remember reading that some power stations actually end up dumping (wasting) power at night because they're unable to taper back to the low nighttime levels quickly enough. Does that ring any bells? In that case, for now anyway it would seem that you're not really being any better to the grid by charging at 20A vs. 80A in the middle of the night.

The issue isn't with the power plant it is with the local distribution. The transformers need to cool at night but if you are pulling 40-80A they don't have the chance to do that.

 

[mknox]

OK, so I know you work in the electric industry...I don't remember where I read it or which power source it was (maybe nuclear?), but I remember reading that some power stations actually end up dumping (wasting) power at night because they're unable to taper back to the low nighttime levels quickly enough. Does that ring any bells? In that case, for now anyway it would seem that you're not really being any better to the grid by charging at 20A vs. 80A in the middle of the night.

I work in electric utility distribution at the municipal level. At the generation level, there are baseload generators (i.e.nuclear, hydro), peaking generators (typically gas turbine) and now a lot of renewables that are intermittent by nature (i.e.wind, solar). Grid operators balance supply and demand by dispatching (switching on or off) those sources that can quickly respond like the gas plants. Further, transmission systems are interconnected with neighboring jurisdictions, so imports and exports can also take up or make up the slack. There are economic models around all of this as well. Power doesn't get dumped/wasted so much as it may get exported to a neighbor at a low price or a gas plant doesn't spool up and its operator doesn't get paid.

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The issue isn't with the power plant it is with the local distribution. The transformers need to cool at night but if you are pulling 40-80A they don't have the chance to do that.

^^This. Further, the continuous load of an EV charger (or worse, multiple EV chargers on a single distribution transformer) can cause havoc at the local level as well.