satchel prefect
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- Sep 2, 2022
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- South Florida, USA
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- Crusty old PHEV
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To investigate the effect of low ambient temperature on battery capacity (and by extension, range) I have been gathering battery temperature and capacity data using Car Scanner. With some readings from my own car and some from @21FE , I have some interesting results to share. It's not micrometer perfect, and it is largely based on my car (with a lower temp reading provided by 21FE), but probably close enough to support what many have been reporting anecdotally, including some of us who have been surprised and alarmed by number shown on the car's "Guess-o-meter".
TLDR: Winter range is lower not only because you're using more power to drive and heat, but also because you lose battery capacity
The data suggests that the ER battery will have around 77kwh when ambient temperature is around 13F, and will gain about 2.6kwh per 10F until it reaches full capacity.
I found the strongest correlation between HVB Min (F) and estimated capacity. HVB Min tended to be consistently 7F above ambient when ambient was below 50F, provided the car was parked and not charging or preconditioning for a few hours beforehand. Let's consider a chart showing what this implies--again, at least for my car:
When ambient temp was 50 or below, HVB Min temp was consistently about 7F warmer than ambient temp. This was true both for 21FE and myself, and I was fortunate enough to take readings with temperatures ranging from the low 40s to the mid 80s over a 3 week span. So, for example:
Here is a chart of the data, along with the transfer function and R-squared value:
Think of this as just a fun exercise. As someone mentioned earlier, there's of course a lot more to the picture than just temperature. But it seems temperature alone is not a terrible predictor of battery capacity. This may not in fact be a linear relationship across its entire range. In fact, we know it tapers off, as no one would expect to have 105kwh capacity at 130F for instance. But with a 95% r-squared value, I was content to roll with it for the temperature range most of us are likely to encounter.
Even if these numbers are off, hopefully they help paint a picture of why winter range can drop so dramatically. Let's say you have only 84% of your battery capacity and 65% of your running efficiency when it's below 20F, and you're heating the cabin, seats, windshield, and steering wheel. Under those conditions, your range could very well work out to (.84 x .65)= 55% of your mild weather range.
New owners: The good news is, as many members have said repeatedly, the car is probably fine, and you probably got the right battery. The range will revert to a more attractive number as the temperature goes up. (It's important to also consider that the range displayed on the Guess-o-meter may not respond immediately to nicer weather because it seems Ford tends to be very conservative and has some type of smoothing built into their calculation.)
If you have data points you'd like me to plug in, I need HVB Min, HVB SOC, and Energy, and whether you have the ER or SR battery. For consistency, this should be captured as soon as possible after starting, with a 4-5 hour downtime beforehand with no charging, driving, or preconditioning. Car Scanner shows these readings on this screen:
Thanks all.
TLDR: Winter range is lower not only because you're using more power to drive and heat, but also because you lose battery capacity
The data suggests that the ER battery will have around 77kwh when ambient temperature is around 13F, and will gain about 2.6kwh per 10F until it reaches full capacity.
I found the strongest correlation between HVB Min (F) and estimated capacity. HVB Min tended to be consistently 7F above ambient when ambient was below 50F, provided the car was parked and not charging or preconditioning for a few hours beforehand. Let's consider a chart showing what this implies--again, at least for my car:
When ambient temp was 50 or below, HVB Min temp was consistently about 7F warmer than ambient temp. This was true both for 21FE and myself, and I was fortunate enough to take readings with temperatures ranging from the low 40s to the mid 80s over a 3 week span. So, for example:
- At 38F ambient, HVB would be approximately 45F. At that temperature, battery capacity is around 83.6kwh, which is a 9.1kwh reduction from max, leaving 90% available. My personal consumption in that temperature range is 2.9mi/kwh, yielding an actual driving range of 242 compared with the 330-340 I usually see in tropical South Florida.
Here is a chart of the data, along with the transfer function and R-squared value:
Think of this as just a fun exercise. As someone mentioned earlier, there's of course a lot more to the picture than just temperature. But it seems temperature alone is not a terrible predictor of battery capacity. This may not in fact be a linear relationship across its entire range. In fact, we know it tapers off, as no one would expect to have 105kwh capacity at 130F for instance. But with a 95% r-squared value, I was content to roll with it for the temperature range most of us are likely to encounter.
Even if these numbers are off, hopefully they help paint a picture of why winter range can drop so dramatically. Let's say you have only 84% of your battery capacity and 65% of your running efficiency when it's below 20F, and you're heating the cabin, seats, windshield, and steering wheel. Under those conditions, your range could very well work out to (.84 x .65)= 55% of your mild weather range.
New owners: The good news is, as many members have said repeatedly, the car is probably fine, and you probably got the right battery. The range will revert to a more attractive number as the temperature goes up. (It's important to also consider that the range displayed on the Guess-o-meter may not respond immediately to nicer weather because it seems Ford tends to be very conservative and has some type of smoothing built into their calculation.)
If you have data points you'd like me to plug in, I need HVB Min, HVB SOC, and Energy, and whether you have the ER or SR battery. For consistency, this should be captured as soon as possible after starting, with a 4-5 hour downtime beforehand with no charging, driving, or preconditioning. Car Scanner shows these readings on this screen:
Thanks all.