Battery charge / discharge Q

Not to get off topic. I just learned in this chat that a Level 2 charger is approx 20% more efficient. I always thought that it was just for quicker battery charging.

 

Yes, indeed. The closer the supply voltage is to the battery voltage the more efficient the system can be. The 2023 Prius Prime cells are nominally 266 volts.

Interesting explanations about charging efficiencies: Is your EV battery getting all the energy you pay for?

Our 2023 Prius Primes charge at a very conservative 3.3kW maximum and at either 1kW for level 1 EVSE at the 8A default setting, or 1.44kW (12A) at the "maximum" charge setting which I use.

 

That 10.6 kWh you deduced is not quite empirical. It assumes that the car's internal watt–hour meter that calculates mi/kWh is accurate (owner's manual says that it isn't) and assumes that you know how the car calculates mi/kWh.

It is not to mention that you are trying to obtain three significant figures using two significant figures as the input (mi/kWh), which is not possible. 4.1 mi/kWh could be anywhere between 4.05–4.14 kWh, which actually gives a range of 10.5–10.8 kWh instead of 10.6 kWh dead-on.

That said, 10.6 kWh sounds about right or perhaps it is slightly underestimated (up to 0.4 kWh or so).

The only empirical value will be if you install an accurate watt–hour meter on your EVSE. Yes, that also corresponds to what you actually pay. If the battery-output watt–hour meter is accurate, you can perhaps access it using a third-party app.

I am surprised that your Level 1 efficiency is that bad. I was getting 6.90 kWh on Level 1 vs. 6.34 kWh on Level 2, the latter of which is identical to the EPA value for Gen 4.

 

Hmm, default for Gen 4 is 12 A, and 8 A is an option.

Thinking about it, the charge rate (C rate, the inverse of charge time in hours) for Gen 5 is about half as for Gen 4, which could be why Gen 5 charging is less efficient.

 

Efficiency vs battery lifetime. The lower the current you charge with, the more charge/discharge cycles. I would assume that the higher voltage level 2 charger charges faster because it has higher current, therefore it may be more efficient, but may shorten the lifespan on the cells. Unless there is something I am not understanding.

 

Indeed level 2 at 3.3kW would be 266v at 12A where the level 1 is at 4A, but perhaps both levels are conservative when it comes to life?

Could it be the life warranty costs that Toyota designs for that limited the chargers to 3.3kW?

This “how to extend the battery life” thinking outside of Toyota has also included suggestions to keep (actual) SOC between 20% or 30% and 80%. When I view my Recurrent battery state chart it makes it look like I am blatantly ignoring that guidance but Toyota is supposedly managing the charge levels to maximize life and maximize range over that life, such that I can charge to 100%. The question becomes is Toyota managing so that the battery life is safely longer than the warranty, or so that battery life is truly maximized?

 

raqball et al,

I had a similar question. I had a full charge showing 100% and when I went about 42 miles on EV it showed ---%. I then charged it up and my History on the app showed it went from 30% > 100%. I read somewhere that the battery kept a reserve so I assumed that was why it showed 30% or thereabouts before I plugged it in to charge.. The app also showed charging of 7.21 kWh taking almost 11 hours to bring it back to 100%

Without getting technical, is the 7.21 kWh a reasonable estimate of the kWh needed to bring it to 100% from ~30%? Is 7.21 kWh a fair estimate of how much kWh is needed to charge for driving 42 miles on EV. I am less interested in knowing if the 30% is what it would read after going 42 miles on EV.

I live in Los Angeles and the off peak charging rate is ~$0.40/kWh from SCE currently so of if it takes ~7.21 kWh to charge from ---% to 100% then my cost for the charge is $2.88 for that 7.21 kWh. Is that about right?

Thanks much!

 

To get an accurate read, get a good watt meter which will tell you how many kWh it really takes to bring the charge to full. It will even tell you the cost of the charge up.

 

No, the app numbers are just bogus (apparently - don't use it myself). They reflect neither the useable amount nor the actual SoC.

Top of "---" is about 14% of real SoC, and "100%" is about 91% of real SoC, as reported by OBD output. That gives about 10.5kWh of EV capacity, and that's consistent with measurements lots of people have done here.

It's not clear what the app is doing, but that 7.21kWh is nonsense. Scaling it up by 100/70 to try to cancel out the "empty=30%" gets you 10.3kWh, which seems more correct, but still a bit off.

No. To get from --- to 100% means adding at least 10.5kWh of actual charge, and charging losses could mean that requires 13kWh on the least-efficient 100V level 1 charge. Level 2 will be more efficient.

It will be at least $4.20 for 10.5kWh. On a level 2 charger, you should be looking at around 11.5kWh consumed, so $4.60.