Brain dead Model S in cold region

[mswlogo]

I used to live in MA with an attached insulated garage. And didn’t have much problem. Rarely dropped below 40F.

Now I’ve moved to NH with an un-insulated detached garage. Lucky if it’s 1 degree warmer than outside. I hope to insulate in the future.

Anyway I’ve noticed it “topping” off often now (like every day). And it’s heating the battery for 40 minutes and charging for 10 minutes to add a few miles. This is stupid. Nothing is on (no sentry, cabin protection or anything). Battery had not dropped that much. A couple miles. But it wanted to top back up.

I suspect it’s because my phone key got near it that triggered it. Maybe.

Now after I get home from a trip I have to make sure it’s on 80% charge. Then after it’s done charging drop it to 70%. Then before I want to head out raise it to 80%.

What a PITA.

I should be able to set how I want it to behave. How much to drop by or to not top off at all.

 

[SilverGS]

Why exactly is it a PITA? I'm just curious.

You're not actually doing anything - the car is taking care of itself automatically already..

I set mine to charge to 70% and if I don't drive for about 3 days, charging kicks in and it tops up (my garage is not insulated either and temps are similar to yours). If I have to drive and I know I will need more than 70%, then I set the limit to 80 or 90 % the prior night.

 

[gaswalla]

The car is smart enough to not charge when the temperature would damage the cells, hence it warms it first. OP seems bothered by the car doing its best to maintain SOC at prescribed level, and has found a way to bypass it. Moving on

 

[beatle]

Seems wasteful for the car to pull so much power to warm the battery only to charge a very small amount.

I wonder if this is also exacerbated by the swing in available battery energy when the temperature drops. This compounds the normal phantom drain.

 

[DerbyDave]

I often hear what I am assuming is the coolant pump running in mid winter when I walk by the car in the garage with no key or anything for it to detect my presence. I assume while it is plugged in, the battery takes better care of itself in cold weather. If the wall connector is supplying power, it is low amp and not charging the battery, but just running necessary car stuff. I have set the car to start recharge at an off-peak hour in the middle of the night.

 

[vcor]

Perhaps some don't realize if the car were to charge the battery when the battery is below freezing, it destroys the battery. The battery must be heated first and even at low temperatures (below 60-70F) it can only be charged slowly (i.e home charging). I might remember wrong, but the Ideal charging temperature is 90F, and if you're driving to a Supercharger via Navigation, it will pre-heat the battery so it can safely accept the fastest charge.

This is not specific to Tesla, but all Lithium-Ion batteries. Tesla figured this out 10 years ago, and others are still trying to figure out good battery design and charging. Hopefully, most other automakers, new to EVs, will figure it out.

 

[beatle]

It sounds like that's part of the issue with frequent top-ups in the cold. The battery may only need 3-4% to come back up to its total, but it may also take 3-4 kwh of heat just to allow it to accept a charge. When the battery finishes its charge, it cools off rapidly in the cold ambient temperature. Less energy is available as a result which causes the perceived SoC to also drop more rapidly. (This is different from phantom drain.) This may trigger a "premature" top-up.

OP said the car tops up daily. My car in an attached, partially insulated garage tops up every 3 days. I'd be curious to see what the total difference in power use is if the desired SoC is lowered to prevent top ups vs. topping off every day.

 

[David29]

This has me curious. My car is parked outside all year, and it is some distance from my condo, so I have no idea if it "tops up" or if any of the fans or pumps run when I am not nearby -- How would you know? Is it only if one happens to be in the car's vicinity? Or do you have to have one of the after-market apps that you plug into the car's data port?
My only issue with leaving it outside was last winter when the coolant heater failed, so I began to have trouble charging at home, and it would not charge at all at a Supercharger (when I tried to as a test). I suppose my heater (and pumps) are running without my knowing it, which adds to the effective energy use per mile. I will say that it does not run enough to avoid restrictions on regenerative braking.
I guess I am in the camp of being glad that the car is "taking care of itself," even if it costs me some kWh.

 

[beatle]

You can use a data logging service like TeslaFi or TeslaScope to see and log charging activity. It doesn't tell you how long the pumps run, however. I don't think it logs battery heater use during a charge, but it does track overall charging efficiency and battery heater use when driving.

Though it is annoying and "wastes" power to preheat the battery, I think battery health is more important than a few kwh here and there, and there really is no way for the car to know not to top itself up if you're not going to be leaving the next day. Seems like a necessary evil to maintain battery health and ensure you can leave with a battery that is within a few % of your desired SoC.

 

[PCMc]

I actually believe there are two separate functions here. One is the battery charging behavior and what triggers the car to top up to the SOC charging limit which has been set. The other is the battery thermal management where the car will do what it needs to do to keep the battery in a safe temperature range, whether heating when cold or cooling when hot. My experience is that battery thermal management does not automatically trigger charging.

One key piece of information that @mswlogo did not provide is how does he have scheduled charging or pre-conditioning set, versus both of those are turned off. My conjecture is that both may be turned off. In this situation the car will start charging whenever the battery SOC drops below the charging point, even if that's just 1% SOC.

However, if you have scheduled charging set, let's say for grins set to start charging daily at 5 am, then the SOC can drop down below the charging limit but will not activate charging to top up until 5 am the next morning. In this case the car may still be trigger thermal management to maintain the battery temperature, but not actually expend the energy needed to charge the battery. If you were running a logger sampling frequently enough you would likely still see some external current draw, but not see charging state reflecting "charging" status.

One caveat ... there does appear to be a "tolerance" of around 5 hours or so on the daily scheduled charging start time. I tripped upon this a few years ago when I was always using scheduled charging. What would happen is I'd have scheduled charging set for like 6 am, typically only needing it to charge for about an hour. If I went out and ran a couple short errands, say at 8 am to pick up coffee, buy something at the hardware store, get back a couple hours later and plug car in then it would immediately start charging. However, if I waited and not plug it in until say lunch time, it would not charge and wait until the next morning to top up. It seemed like the tolerance window as something like about 5 hours per memory, but I've not actively tested this out for a couple years, which is an eternity in Tesla software updates and changing behaviors without any explanation or notification.

The behavior of the car topping up the charge when all scheduled charging was shut off appeared to change a couple years. Prior to that everyone typically talked of a 3-4% tolerance before charging would kick back in, but that's not what I see now.

So if my conjecture is correct, and @mswlogo does have all scheduled charging turned off, it might be an interesting experience to turn scheduled charging on and see if they observe a difference in the charging behavior.

Just my two cents worth as someone that lets there car sit for 2-4 months at a time and remotely monitors battery SOC, charging, and car wake-up behavior from overseas while on expat assignment using my own custom written data logging program.

 

[DerbyDave]

@PCMc FYI:
Scheduled Charging: When you set a
scheduled charging time, Model S displays
the set time to begin charging when you
are parked at the scheduled location. If, at
the scheduled time, Model S is not
plugged in at the location, charging starts
as soon as you plug it in, provided you
plug it in within six hours of the scheduled
time. If plugged in after six hours,
charging does not start until the
scheduled time on the next day.

 

[BPeter]

This sounds like a bug I had in ~2021 with my 2018 P100D. The bug lasted about a year before a subsequent update fixed it.

I also started lowering the charge threshold so it wouldn't do that. Big waste of energy. It would wake up constantly when it barely lost any energy to top off. It hadn't even dropped 1% before it started topping off. I think it was waking 8 times a night to top off. It would use more energy heating the battery than it put into the battery.