Is preconditioning before DCFC really worth it?

[JacobAZ]

To what battery temperature does the Rivian heat to during pre conditioning?

On my Gen 2 preconditioning warms battery to 105 if given enough time. When cooling it appears to target about 107

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[Skeldog99]

Here is a bug I found that can be an issue.
26 Gen 2 R1T

1. I manually turned on precondition and was driving around.
2. Went home and forgot to turn off precondition.
3. noticed on my WiFi that my vehicle wasn’t sleeping and in the app I was losing battery %. It was going for over a few hours
4. Had to go to the vehicle and turn it off. Motors were at 181 degrees, battery was 90 something.

I thought all these settings would turn themselves off once you leave the vehicle.

 

[Scotsol]

So I took my '22 R1T LE out to try to DCFC for the first time locally. We're going on a trip this weekend and I just wanted to see how it worked and ensure that it did. Drove about 5 miles from my house to a Supercharger. The truck was preconditioning and clearly cooking extra electrons as I was getting about 0.9mi/kwh on a drive I would normally get about 2.3mi/kwh and burned off about 5% battery in 5 miles. Battery started at 50F and on arrival was... 51F. Ambient temp was mid-30F.

I only charged for about 5 minutes but it worked flawlessly, plug and play and auto charged my Rivian account with an EV Supply Co NACS to CCS1 adapter. Put 10kwh in, basically what I used driving there at $0.59/kwh. So in ten minutes I used nearly 5kwh to add 1 degree to the battery.

It got me thinking, preconditioning essentially used nearly $5 worth of electricity (more like $2.50 since my efficiency was halved). I can't imagine being on a road trip and it preconditioning for an hour and using up $15+ in energy just to warm the battery, especially since it was almost a negligible amount. The 5 min DCFC session heated the battery from 51 to 61 degrees in 5 minutes while charging at 124kw.

I guess the point of this ramble is why bother preconditioning? It uses a large amount of energy and the fast charging itself will heat the battery up much faster anyway? Since you're paying per kwh at the DCFC you're spending a lot to save maybe a few extra minutes waiting for the battery to have a more optimal charge curve essentially? Does the preconditioning efficiency improve over the longer it runs? Extrapolating my experience, it could take nearly 50kwh to get a 10 degree gain in battery temp, which would cost nearly $25 in DCFC charges...

Not on Topic but if you plan to use the TESLA Network look into the subscription it can save you more than it costs on a long trip, but to get the savings you need to initiate the charge from the Tesla app.

 

[carsly]

In temperate conditions (50-100 F), if you don't mind spending another few minutes at the charger then don't precondition and save some juice and money.

If you're at/below freezing temps the pack will need to warm up in order to DC fast charge anyway. You can heat up before you get to the charger or at the charger but either way you'll have to warm the pack in order to DC fast charge.

Otherwise AC charging is your best bet for efficient charging/energy usage.

 

[Dave Cundiff]

Charging heats the battery anyway, whether or not preconditioning is simultaneously going on.

From my informal observations, @carsly has it about correctly. If time is not an urgent issue, it seems more efficient to arrive at a DCFC at a lower temperature (as long as it's 50 or above) than at the 90 degrees or so that preconditioning might achieve.

Later in a DCFC, the Rivian must cool the battery. Unless the energy cost of cooling the battery is negligible, that would waste energy to save our time.

It seems to be a balance. Waste energy to save time, or waste time to save energy? The best answer to the question, when posed that way and without numbers, is, "It depends." I never want to waste a lot of time to save a little bit of energy, and I don't usually want to waste a lot of energy to save a little bit of time.

Best to all!

 

[Billyk24]

On my Gen 2 preconditioning warms battery to 105 if given enough time. When cooling it appears to target about 107

My Ford Mach E only heats to 59f (battery temperature). Owners believe it is related to concerns about battery health as DCFC will warm the battery significantly. Next question: how warm does the battery get while dcfc? Seeking information on how well Rivian provides thermal regulation.

 

[Rural1T]

In temperate conditions (50-100 F), if you don't mind spending another few minutes at the charger then don't precondition and save some juice and money.

If you're at/below freezing temps the pack will need to warm up in order to DC fast charge anyway. You can heat up before you get to the charger or at the charger but either way you'll have to warm the pack in order to DC fast charge.

Otherwise AC charging is your best bet for efficient charging/energy usage.

This ^ is important to know.

Also know that 5 miles is a VERY short distance to precondition the battery and will result in a large energy expenditure (especially if the vehicle is cold) for very little benefit. Preconditioning is much more efficient and effective when navigating to a distant charger. Sometimes on road trips the vehicle might start preconditioning two hours before reaching the charger. This allow the vehicle to create a large battery temperature change over a long period of time and doesn't use much extra energy.

 

[josh0]

I'm not asking if a warm battery charges faster/better, but rather does preconditioning have a significant enough impact to offset the extra energy use and cost?



Yes, some of that was heating the cabin but I've driven plenty of short drives all winter in much colder temps and get just under 2mi/kwh with heat, two heated seats, and the heated steering wheel running so still was eating up around a kwh every mile to precondition

Right, so the answer is: it depends. What temperature you're starting at, how far/long it will take to get to the charger, how much of a charge you need, how much time you can/must spend once you get there. If you're in a hurry, a warm battery absolutely makes a difference, but if you're starting cold and with a low SoC, preconditioning might not be able to raise the battery temp enough to matter. There is no simple yes/no answer to the question.

 

[carsly]

This ^ is important to know.

Also know that 5 miles is a VERY short distance to precondition the battery and will result in a large energy expenditure (especially if the vehicle is cold) for very little benefit. Preconditioning is much more efficient and effective when navigating to a distant charger. Sometimes on road trips the vehicle might start preconditioning two hours before reaching the charger. This allow the vehicle to create a large battery temperature change over a long period of time and doesn't use much extra energy.

Good insights here.

To add, if you hurriedly precondition you'll introduce thermal gradients (hot spots and cool spots) in the pack, especially a Rivian pack. Ultimately your rate-limiter on DC fast charging will be the area of the pack that's spiking in temps. If you gradually precondition over a longer duration, as suggested, not only is energy usage lower but you're more likely to arrive with a pack that's roughly the same temp across all the cells optimizing the speed of your fast charging session since they can all accept power roughly equally.

 

[Mellowyellow]

My family and I spent the weekend at a resort in the Poconos. No EV charging there. When we left Sunday, the battery was 17F. I stupidly drove to the closest L3 charger and plugged in so we could drive home. It took me over an hour to get the charge enough to get home (and we only needed a little bit more!). Initial charge rates were <15kw. In retrospect I should've just driven it and preconditioned along the way and stopped to charge when I absolutely had to. That would've cut down so much on time!

 

[JacobAZ]

My Ford Mach E only heats to 59f (battery temperature). Owners believe it is related to concerns about battery health as DCFC will warm the battery significantly. Next question: how warm does the battery get while dcfc? Seeking information on how well Rivian provides thermal regulation.

In my experience DCFC does not warm the battery a lot. At high outdoor temps (110+) the battery holds its temp steady ( under 110+)while charging, but you can hear the R1 cooling. In cold weather it warms slowly. A 10 min charge will not warm the battery much.

 

[Dave Cundiff]

In my experience DCFC does not warm the battery a lot. At high outdoor temps (110+) the battery holds its temp steady ( under 110+) while charging, but you can hear the R1 cooling.

During DCFC charging, our Rivians will cool the battery aggressively to keep it from exceeding 110-113 degrees Fahrenheit. Even when charging would otherwise warm the battery quite a bit, battery cooling won't let it.

In cold weather it warms slowly. A 10 min charge will not warm the battery much.

Sometimes our battery warms very quickly with DCFC, sometimes only somewhat quickly. Seems to vary mostly on charging speed and starting temperature, but sometimes also on what seem to be random factors.

Best wishes!

 

[Billyk24]

With the Rivian at 100f at the start of a dcfc what will the peak kW be at 20%? 20 to 80% fill time remains around 28 minutes for a 100kWh battery?

 

[Dave Cundiff]

With the Rivian at 100f at the start of a dcfc what will the peak kW be at 20%? 20 to 80% fill time remains around 28 minutes for a 100kWh battery?

Your question is relevant to preconditioning, but answering your question might take this thread way into the technical weeds.

I perceive SO many more variables than you have listed, @Billyk24, such as: Which battery chemistry and size? (most important); Beyond the battery temperature, what are the inside and outside temperatures? What software version? What will the charger perceive as its limitations and the vehicle's limitations? What other, seemingly random, factors will confound the measurement?

So I would caution you against expecting a knowledgeable GENERALIZABLE answer from anyone.

However, some Rivian owners may be able to give you averages like that from THEIR vehicles under conditions SOMEWHAT SIMILAR to your conditions. Verify that their battery chemistry and battery size match yours, and even then take them with a grain of salt, but estimates like that will be better than nothing.

I hope this is helpful. Best wishes!

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