this post was submitted on 08 Dec 2024
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I have a 2021 prime and also concluded that gasoline is cheaper than running on electricity. I actually only charge up when charging is free. I don’t live in extreme cold, but most of the issue is electricity is so expensive near me that it actually negates any savings.
You have a lot better math than I did though, so Kudos.
With a 32% loss between wall and miles-driven, (assuming Toyota's battery meters in the car are accurate) there's clearly something going on here. I'm thinking L1 chargers are extremely inefficient. It is well known to anyone charging their car that the battery fans + heater turns on when you plug it in the winter. You can literally hear the battery conditioning turn on.
L2 chargers are faster, meaning battery conditioning (be it fans for cooling, or heat for the winter) will be run less. Ex: If you charge 3.5x faster on L2 there will be 3.5x less battery conditioning, leading to more efficiency.
Its a fools errand to "try to save money" through this however, as buying new L2 chargers will likely cost you $thousands, and the Prius Prime already cost $thousands more than a regular Prius. So do this because you're a believer in electricity (ex: lower emissions, nuclear/solar power use, reduction in oil and/or geopolitical issues with the Middle East, yadda yadda). But DON'T necessarily do any of this to save money, the math just isn't adding up for me yet.
I just did some napkin math using Google research numbers. On average L2 charging appears to be 7.3% more efficient than L1. (83.8% efficient for L1, 89.4 for 2.. and the percentage increase is not subtraction problem for anyone wanting to poke at my math).
So using your electricity-only efficiency numbers, you would still only get: 12.5 * 1.073 = 13.41 miles/dollar.
It's partially subtraction.
The 100W heater (or whatever it is....) to condition the battery in the winter is a subtraction problem, not a multiplication problem. The heater needs to run during the winter when charging or when driving.
1100W L1 charger - 100W heater is less efficient than 3500W to 10,000W L2 charger - 100W heater.
Now there is another component of multiplicative losses (the inductor and/or voltage conversion coil + MOSFET switch resistance). So it's partially subtraction and partially multiplicative losses. Ultimately I'll need to just test the damn thing to find reality, we can't math this out on paper. (100W losses I assumed earlier was just that, an assumption. I have no idea how much the battery conditioning circuits / pumps / etc. uses up in practice)
The real problem is that I'm not aware of any Kill-a-watt model for 240V circuits. I'll have to rely upon the charger to give me accurate readouts. But all the theory (and apparently some internet testing) suggests that the
You can look into a current clamp meter as a stand in for the kill-a-watt. If you're willing to tinker a bit and like automation, you can use one of those and an esp32 board to make a remote power monitoring system for your 240v circuit.
If you're less willing to tinker you can get some off the shelf stuff that you run the wires through or a clamp style variant to do something similar.
(Note: I can't provide any recommendations on off the shelf products, I just bought the clamps and am working on tinkering it together).
Hmmm, current is the bulk of it. But voltage drop is also important as that'd measure wire losses. (All wires have resistance and it adds up the longer the wire runs get).
But yeah, good idea. I'm actually into electrical engineering so ESP32 is right up my alley. I mean, I prefer AVR but any uC can be used in that circumstance.