Charging at 120V/20A versus 240V/30A in cold weather

tencate

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#1
Max has now seen a couple of winters and has spent the last year charging at home with a 120V/20A outlet. I tried a standard 15A outlet for a week or so but never got quite enough charge for my day-to-day needs so I found another outlet which actually had a 20A breaker and the correct wiring and I've been using it all the time. Perfectly adequate for my needs, only a couple of times over the past year+ did I wish I had faster charging at home. Even during the coldest days last winter and now, I'd simply plug in the car when I got home and when I woke up next morning, I'd preheat the car, unplug, and off to work I'd go. No issues, seldom saw the blue snowflake and regeneration was mostly normal, even on single digit mornings. I was happy but always thinking that I wasn't charging efficiently with 120V.

Recently I decided to charge more efficiently. I tapped into an unused circuit in my panel and now have 240V/30A charging for Max. But I'm running into bizarre issues. Last night the car was charged up and done charging before 2 AM (which is pretty great). However, this morning I drove away with a blue snowflake and zero regeneration. Moreover, I drove around for about 60 miles this morning running errands and the snowflake only went away when I pulled into my driveway. Very little to no regeneration the whole time. Ambient temperature reached about 25F at the end of the driving. I'm very unhappy about that. What to do?

Suddenly all the discussion about how the car heats the battery and starting a charge session at 3 AM instead of when you get home now makes more sense to me. I kinda miss the days of just plugging in at night, juicing up at 120V @ 16 amps and driving away with about 60 miles of added range and zero regeneration issues or blue snowflakes. I'm almost inclined to go back to 120V/20A for the rest of the winter and use the 240V only for emergencies.

Any suggestions? I suppose I could dial back the current on the 240V charging (maybe 18 amps instead of 24?) to keep it charging longer, for more of the night??? That might eliminate some of the cold battery issues I'm having? Or am I way off base in thinking of doing that. And how much efficiency would you lose doing that way anyway? Inquiring minds want to know. I kinda like my 240V charging but not if I'm gonna lose regen during winter!
 

Lovesword

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#2
Sounds like your charging is getting done much quicker (as expected) and then the remnant heat left over from charging that is warming the battery slowly dissipates until you have none, leaving you with a cold soaked battery when you go to leave in the morning. I have this in my garage as well as it's connected, but not insulated or heated. I try to preheat in the mornings but that's more for me as half the time my car isn't the one on the charger.

I think you have the answer to your question within own your post as you mentioned scheduled charging. That, IMO is the way to go. If you can schedule it to start so that when you leave it's been charging, you'll no doubt have a battery that's warm and full regen on your brakes.
I plan to do this once I have the garage set up where both my wife and I can charge instead of sharing one. My only "concern" is that I've also heard it's good for the battery to charge after driving... so, when I get home, versus starting it from the dead cold of night after it's been sitting for quite some time. Not sure I've read enough on this topic to scare me away from trying the scheduled charging I plan to, but I do want to mention it.

Sounds like it's a trade off one way or the other:
1 -Charge right when getting home. Pro: battery is warm. Con: Gets done way before the car is needed, allowing battery to get cold before using the next day.

2 -Schedule the charging for the morning before leaving for work. Pro: Leave with a warm battery and full (or close to full?) regen. Con: Starting battery charging after it's been sitting and is cold soaked. (any truth to this being "bad" for the battery?)

3 -Utilize the lower amps or go back to the 120V. Pro: I havent done this myself but sounds like it keeps the battery warm enough to have no snowflake and have regen. Con: Efficiency??

Great thread @tencate , I'm very interested in others feedback on this.

Edit: some clarifications
 
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joelliot

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#3
Sounds like your charging is getting done much quicker (as expected) and then the remnant heat left over from charging that is warming the battery slowly dissipates until you have none, leaving you with a cold soaked battery when you go to leave in the morning. I have this in my garage as well as it's connected, but not insulated or heated. I try to preheat in the mornings but that's more for me as half the time my car isn't the one on the charger.

I think you have the answer to your question within own your post as you mentioned scheduled charging. That, IMO is the way to go. If you can schedule it to start so that when you leave it's been charging, you'll no doubt have a battery that's warm and full regen on your brakes.
I plan to do this once I have the garage set up where both my wife and I can charge instead of sharing one. My only "concern" is that I've also heard it's good for the battery to charge after driving... so, when I get home, versus starting it from the dead cold of night after it's been sitting for quite some time. Not sure I've read enough on this topic to scare me away from trying the scheduled charging I plan to, but I do want to mention it.

Sounds like it's a trade off one way or the other:
-Charge right when getting home. Pro: battery is warm. Con: Gets done way before the car is needed, allowing battery to get cold before using the next day.
-Schedule the charging for the morning. Pro: Leave with a warm battery and full (or close to full?) regen. Con: Starting battery charging after it's been sitting and is cold soaked. (any truth to this being "bad" for the battery?)
-Utilize the lower amps or go back to the 120V. Pro: I havent done this myself but sounds like it keeps the battery warm enough to have no snowflake and have regen. Con: Efficiency??

Great thread @tencate , I'm very interested in others feedback on this.

Edit: some clarifications

Third option would be to preheat the car in the morning. It does seem to heat the battery enough to get rid of the snowflake. This seems pretty quick when plugged in, but maybe it’s the lack of cold air blowing under the battery. (I’ve only done a couple preheats in the cold unplugEd)
 

Lovesword

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#4
Third option would be to preheat the car in the morning. It does seem to heat the battery enough to get rid of the snowflake. This seems pretty quick when plugged in, but maybe it’s the lack of cold air blowing under the battery. (I’ve only done a couple preheats in the cold unplugEd)
This is the way I'm leaning as well, once the garage is set up the way I want it (where both my wife and I can plug in and do this by scheduling the charging to start in the morning). I'll edit my post above because this is actually my "point 2" but it's not worded clearly and is jumbled together a bit.
I definitely appreciate the feedback and hearing about your experience, I'm anxious to get my garage situation solved to get this implemented! :)
 

tencate

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#5
Third option would be to preheat the car in the morning.
I did that before I left. I usually do that every morning. About 30 min. Had the snowflake and almost no regeneration the entire morning. Scratch that option for me. I scheduled charging last night to start at 3 AM. We'll see what happens today.
Edit: My car sits outside in my driveway overnight.
 

tencate

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#6
OK, this is one morning's datapoint. Outside temps were 14F this morning and I'd scheduled the car to start charging at 3 am last night instead of when I got home. This time no snowflakes and a decent amount of braking regeneration was available. So, unless I need a lot of charge, I'll keep the schedule for 3 am and see how I make out.
 

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#7
Don't have the cold weather challenges that many of you do but I wouldn't suggest going to 120v if you have 240v charging capability. There is a substantial efficiency difference of greater than 20% between the two.
 

tencate

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#8
difference of greater than 20% between the two
At 120V/20A? I've done that for over a year, since I've owned the car. (I have 120V at 20 amps not 15A.) I know ~20% is the claimed efficiency difference for a 120V/15 Amp circuit to a 240V/30A but I get almost 2 kW from a 120V/20A circuit. So far I haven't really seen all that big a difference with my new 240V line. Here's what I think I see happening: when the 240V kicked in last night, a bunch of juice was "wasted" getting the cold soaked batteries warm enough to accept charge (0 miles added for a while even though the car started charging) but once the batteries were warm, only then was the charging efficient. I'm going to try and quantify that tonight, may have to sleep in the car or something or stay up and watch it. :) I guess I really need to install a meter/logging device of some sort to really carefully compare. But I don't get the feeling I'm seeing all that much difference in overall efficiency so far. I'm sure 240V is more efficient, not questioning that, and I'll be doing that in the summertime for sure, but I don't think I'm ready to dismiss using 120V/20A overnight when it's cold out. I'm guessing someone has measured things like this though? I keep hoping they'll pipe up :) Meanwhile, I'll keep taking observations as long as it stays cold out. Level 1 charging all night might not be as efficient as Level 2 but you never spend any of that energy heating up the battery either. Mind you, we're probably talking a few dollars difference in my monthly electricity bill here. :)

Edit: and I'll bet it's different for people in the great white north where temps are seriously negative all the time. Might be that a 120V/20A circuit isn't enough to keep the batteries warm enough for a charge at all! My morning temperatures are mild compared to some who post here regularly.
 

JasonF

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#9
Watts is a less confusing index to tell you how quickly the battery is charging:

110v@12A = 1320W
110v@18A = 1980W

220v@12A = 2640W (for comparison, 220v/15A is rare) - Double 110v@15A (2x 110v)
220v@18A = 3960W (for comparison, 220v/20A is rare) - Double 110v@20A (2x 110v)

220v@28A = 6160W - Common dryer outlet (4.5x of 110v@12A, 3x of 110v@18A)
220v@32A = 8800W - Max for Mobile Connector plugged into 14-50 - about 6.5x charging speed of 110v@12A, 4.5x of 110v@18A
 

tencate

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#10
Yes, Watts are best for these sorts of comparisons, P=iV. I have a somewhat unconventional 240V charging solution (I'm using an RV generator cord with a 14-50 adapter) so I simply dial up whatever current I want, up to 24 amps which is the limit of the breaker and wiring. Today I was seeing 247 Volts on that circuit. I also plugged into an RV circuit this afternoon at our local dog park where I was getting 240 Volts at 32 amps. Charging quickly is nice. But after that the battery mostly sits around and gets cold overnight. So I think programming it to start charging at 3 am is so far my best solution. YMMV!
 

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#11
Any suggestions? I suppose I could dial back the current on the 240V charging (maybe 18 amps instead of 24?) to keep it charging longer, for more of the night??? That might eliminate some of the cold battery issues I'm having? Or am I way off base in thinking of doing that. And how much efficiency would you lose doing that way anyway? Inquiring minds want to know. I kinda like my 240V charging but not if I'm gonna lose regen during winter!
I would strongly suggest sticking with 240V and reducing the current. 240V at any current level is about 15-20% more efficient compared to 120V, because the boost converter doesn't have to work as hard to get to battery 400V. You can see it in your mi/h or km/h display quite clearly. You'll see the incoming watts with a little math (V*A) and if you made them equal, you'll get way more range out of 240V. (eg. 240V 8 amp ~2KW is faster than 120V 16 amp ~2KW despite being the same amount of power)
Just reducing your charge current to the equivalent watts should drag the charge time into the morning so you have a warm battery...
 
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tencate

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#12
Thanks I'll try that. I've already done something similar. Instead of L1 charging last night at 120V/16A I tried 240V/8A. Same wattage as I've been charging with all year but I'm curiously not entirely charged this morning with the 240V 8 Amp setting. Watts wise I'm the same but clearly the charging is different. More fun with 240V coming. :)
 

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#13
Watts is a less confusing index to tell you how quickly the battery is charging:

110v@12A = 1320W
110v@18A = 1980W

220v@12A = 2640W (for comparison, 220v/15A is rare) - Double 110v@15A (2x 110v)
220v@18A = 3960W (for comparison, 220v/20A is rare) - Double 110v@20A (2x 110v)

220v@28A = 6160W - Common dryer outlet (4.5x of 110v@12A, 3x of 110v@18A)
220v@32A = 8800W - Max for Mobile Connector plugged into 14-50 - about 6.5x charging speed of 110v@12A, 4.5x of 110v@18A
Good summary but your 20A lines are too high at 18A. Max draw should be 80% so should use 16A for those lines. But yeah the Watts are probably easier for most people and it really shows the difference quickly
 
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#14
I have a 240V/30A circuit (30A breaker, 24A max continuous draw) in my unheated, detached garage.
We've had a cold snap over here with temperatures from -20 to -32 C lows the last couple of weeks.

I've recently put in a power meter but have not analysed the usage to this extent yet. Before the meter I have experimented with plugging in when I get home (charging when battery is already warm) and scheduled charge (to start with a warm battery when I leave for the morning. Until this discussion I settled on charging immediately when I got home, but (particularly since I have the meter now) it merits testing the various options. Previous to now, I have not tried a lower charging rate yet but upon second thought it might be a good thing to test for very cold temperatures..

Note that due to temperatures in my region, I have almost never experienced full regen since I got the car in September (I've only had full regen on a handful of days). I expect I will get it back in spring and summer though.
The car is not plugged in at work, so no matter what regen level I have in the morning due to charge level, it is cold soaked and always has regen dots and often has the snowflake symbol on the drive home in the evening. "Consistent" driving in the fall/winter would actually be if I had no regen in either direction.
As such, starting the day with regen isn't a high priority for me at least in the winter months.

Here are my thoughts:
If the car is really cold, once charging stops, it will use the battery for critical heating (this is NOT to allow regen, nor is it specifically to keep the snowflake off, it is just to ensure that the battery is above the minimum safe battery temperature). No shore AC power is drawn for critical heating (unless it draws more than the threshold (5%?) of your max charge limit), this is drawn directly from the battery resulting in a lower than expected charge level in the morning.

If the car is only slightly cold, when charging stops, there isn't a need to use the battery for critical heating, so you start with a full or nearly full charge. However regen will be limited, and you may have the snowflake indicating that the battery is cold when you start, since the battery was neither charging nor was it being heated.


Specific examples:

Cold temperatures (below -10 C)

If you plug in immediately, and charge at full rate:
In this case the battery is warm when charging so you charge at full rate until the battery is at your charge level (90% in my case). After the battery reaches charge level, the battery will start to get cold soaked. The battery heater (motor in heating mode) will run as necessary to keep the battery above the critical limit, but this does NOT use AC shore power, it uses battery power. This results in you starting in the morning with 3-4% less than your charge limit (car has 86-87% charge rather than 90% charge).
- Pro: Since critical battery heating was active, no snowflake in the morning
- Neutral: No battery pre-heating before charging is required, but critical heating is needed for the battery (as below). Not sure if this is slightly more or slightly less efficient (or about the same) as either of the below options until testing.
- Con: Since critical battery heating was active, and AC was NOT used, you start with less charge in the morning
- Con: Reduced starting battery level due to critical heating is therefore lost energy and lost efficiency
- Con: Regen severely limited, dots go all the way to just left of "k" in km/h, power limit is about 4 dots.

If you have scheduled charging timed so that charge ends near when you will use the car, and charge at full rate:
In this case, the battery gets cold soaked initially and will likely have to do some critical battery heating to keep the battery above criticial temperature. At the scheduled charging start, the battery will then need to use shore AC power to heat up enough to charge, then when it is sufficiently heated, it will need to charge. The time to reach cold soaked until full charging is about 1-1/2 to 2-1/2 hours, so that is 1-1/2 to 2-1/2 hours extra charge time required. This is not at full current, so I will need to use my meter to find out how much extra energy is used for this.
- Pro: Since charging was active immediately prior to driving, there is no snowflake in the morning.
- Pro: More regen on morning commute since battery is warmer. Note even if I have a 6 hour charge, the battery is still not warm enough for all the dots to disappear, it will still be 1/4 way to 1/2 way to the center. Usually however there is no power limit dots on the right side
- Con: Between the time you arrive, and the time that scheduled charging starts, the battery may become sufficiently cold soaked to require critical heating. This will draw some energy from the battery for this, which will have to be extra energy added during the charge cycle.
- Con: Additional loss of energy and therefore efficiency due to having to heat the cold soaked battery at the start of scheduled charging
- Con: You have to guess at the best start time each day depending on the charge level you have left before charging and the temperature, and it isn't always easy to guess how much extra lead time for both critical heating plus the battery charge pre-heating you need to add. If you didn't add enough heating time in your scheduled start time, you will start with less charge than your desired charge level.

If you plug in immediately but charge at slow rate:
(possibly with a schedule so the charging starts BEFORE the battery gets cold soaked yet ends either when you use it or at least before it gets cold soaked between the time charging stops and you drive off)

In this case the battery is warm when charging so no pre-heating is required, and you charge at the lower rate until the battery is at your charge level or until you drive off. If the charge is slow enough and schedule is set right, you should still have a warm battery when starting.
- Pro: Likely no extra shore power energy is used to pre-heat the battery for charging, and likewise no extra battery energy is needed to keep the battery above critical temperature.
- Pro: More regen on morning commute (but likely still limited)
- Pro: No snowflake since battery was kept heated by charging
- Con: May have energy loss due to longer charge period (minimum current draw by charging circuit?)
- Con: May have to guess at both charge current and/or scheduled start to end charging near drive time.
I have not tried this method yet however so this is just a guess.

Moderate temperatures (+10 C to -10 C)

If you plug in immediately, and charge at full rate:
In this case the battery is warm when charging so you charge at full rate until the battery is at your charge level. Battery is above critical heating level so does not need the battery heater.
- Pro: This is probably the most efficient charge, no wasted battery heating before charging is required and charging is done in the minimum time.
- Con: Starting your drive, the battery may have the snowflake symbol indicating cold battery
- Con: Regen will be limited, dots going from 1/2 way to 3/4 way to center. May have some power limit when starting as well.

If you have scheduled charging timed so that charge ends near when you will use the car, and charge at full rate:
In this case, the battery gets cold soaked initially. At the scheduled charging start, the battery will need to use AC shore power to heat up, then when it is sufficiently heated, it will need to charge. The time to reach cold soaked until charging is about 1 hour, so that is 1 hour extra charge time required.
- Pro: Since charging was active immediately prior to driving, there is no snowflake in the morning
- Pro: More regen on morning commute since battery is warmer. There will likely be 4-6 regen dots (up to about 1/4 to 1/3 of the way to the center). Likely no power limit dots on the right side
- Con: Loss of energy and therefore efficiency due to having to heat the cold soaked battery before scheduled charging
- Con: You have to guess at the scheduled start time each day and may end up with less expected charge if you guess wrong.

If you plug in immediately but charge at slow rate
In this case the battery is warm when charging so you charge at the lower rate until the battery is at your charge level or until you drive off.
- Pro: Likely no extra shore power energy is used to heat the battery for charging
- Pro: More regen on morning commute (but still likely limited)
- Pro: No snowflake since battery was kept heated by charging
- Con: May have energy loss due to longer charge period (minimum current draw by charging circuit?)

Summary:
The "best" method will not only depend on your priorities, but whether the temperature will get cold enough to trigger critical battery heating if cold soaked, so you may have two or even three "best" methods depending on the weather.
 

JasonF

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#15
Simple suggestion: Turn on climate about 30 min before you leave. That will draw power from battery to run either the A/C compressor or heater, and the charger will try to refill the battery at the same time. That should cause gentle battery heating, as well as making the cabin more comfortable.
 
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#16
Simple suggestion: Turn on climate about 30 min before you leave. That will draw power from battery to run either the A/C compressor or heater, and the charger will try to refill the battery at the same time. That should cause gentle battery heating, as well as making the cabin more comfortable.
From what I've experienced, if you are plugged in, climate control (or at least heating) comes from shore power and does not draw from the battery (unless your charging voltage/current is less than the 4-5 kW to cover the cabin heater and defroster). Thus if you previously charged and reached your charge limit this session, and your battery is lower than your charge limit but not low enough past the "low" threshold to start charging again, it does not charge the battory thus does not (directly) heat the battery other than possibly the cabin itself indirectly warming the battery below it. I would think that this would be fairly inefficient as opposed to actively charging/heating the battery, as there are un-necessary losses of heat to the outside through the un-insulated windows and cabin during the 25+ minutes you don't actually need the cabin heated.

It would be nice if Tesla gave us a direct option to pre-heat the battery, independent of cabin heating and charging, and preferably on a schedule.
 
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#17
Edit: I charge at 240v/32a

As Xelloss said, the Tesla charging management system seems to be designed this way. It only cares about one thing, and that is the % limit you set charging too. As long as this is fulfilled, the car does not care about the snowflake icon or limited regen. There is a caveat to this however, because I see my charge drop below my set limit all the time (its 90% and sometimes I get into my car which was plugged in at 88 or 87%) and I don't know if there is a 'threshold' Tesla sets to start charging again, and if there is, I have not seen it based on TeslaFi charging data.

I schedule my charging so that it is done at or a few hours before I have to leave for work. This way I should not have a snowflake icon and have SOME regen, which is good enough for me.
 

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#18
Another anecdote to add

Last night and tonight I brought my UMC to work since I'm parking outside...plugged into the block heater outlets at work I set it to 10A instead of 12 to give a little extra room in case someone plugs in next to me... Drawing ~1200 watts... I charged at 0km/h for 12 hours and arrived to a 'warm' no snowflake battery...but it gained zero charge at -15C temperatures.