Real time indication of Miles/kwh

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DoctorTubaUF

Member
Joined
Apr 17, 2017
Messages
10
When I complete a trip in my Rav the information display on the right side of the instrument cluster shows me the trips average miles/kwh in decimal form. While Im driving I see I can cycle through the various displays and I can see the bar graph of my miles/kwh instantaneous and average. However that bar graph is difficult to see to get an accurate number. Is there is display either in the instrument cluster or the main display that shows me my average miles/kwh in decimal form as Im driving and not just at the end of a trip?
 
How to use the 2012-2014 Toyota RAV4 EV Range Chart:

https://www.dropbox.com/s/n8bhjas2wk5ryzd/JdeMOhowToUseRangeChart.pdf?dl=0

Download and print the Range Chart:

https://www.dropbox.com/s/3bcv212xxsfd2vr/Rav4rangeChartV90.2.pdf?dl=0

On the car:

A. Reset Consumption meter:

1) Press mechanical "home" button below the center of the navigation screen.
2) Press "EV" softbutton
3) Then press "Energy Monitor"
4) Select "Past Record"
5) Press "Update"

B. Display Energy Consumption during Map display mode:

1) Press mechanical "home" button below the center of the navigation screen.
2) Select "MAP"
3) Select "Map Mode" in lower left corner of screen. If this is not available to select, press "On", then "Map Mode".
4) Select "Energy Monitor"
5) Press the "go-back symbol" in the upper right corner
6) Confirm that "Consumption" is at the top-right of the display. If it says "Past Record", change to "Consumption". At the bottom-right of the display, it will show the average consumption. This will read 0.0 miles/kWh if it was properly reset. If not, go back and repeat step A.

C. Then, reset the trip odometer (black mechanical button between speedometer and energy gauge):

1) Press and release until desired trip meter is displayed
2) Press and HOLD button until miles go to zero

After you have completed these steps, you are ready to plan your trip.

First, let's stipulate that the "GOM" / estimated range on the dash is not to be used. This seems to be the hardest thing to overcome for many people.

The controlling value for range are two values:

1) Average miles per kWh
2) Available stored kWh onboard

If you need to travel 120 miles, and the battery is fully charged, you'll start with about 37kWh with a typical somewhat degraded RAV4 EV battery, therefore:

120 plus a 15% buffer equals 138 miles range required.

138 / 37kWh = 3.7 miles per kWh required to complete the trip with a 15% reserve.

That's about 55-60mph, on cruise control, according to the chart, but it could be a higher or lower speed. There are MANY factors that affect range, and the ONLY thing that matters is the "Average Miles/kWh" from reset.

If you drive 40 miles or so into your trip, and you're no where near 3.7 miles per kWh for this planned trip, YOU NEED TO SLOW DOWN!!! (Or find an alternate charging spot).

I recommend starting this trip with the cruise control on 60mph. If after 40-60 miles (just prior to the halfway point) the Average Miles/kWh are holding mostly steady at 3.4 miles/kWh for this example, the you MUST slow to 55mph.

If the Average Miles/kWh do not start climbing above 3.4 when you have reduced the speed by 5mph for the next 20 miles, you probably need to make sure that the heater is off, or start planning to find an alternate charging location. Slowing to 50mph on public freeways / high speed highways is probably dangerous.

Again, the GOM does not matter. If your battery is cold, it will consume more power to warm it up. If you run the cabin heater, you will consume more power. There may be a headwind. You may have a tire with low pressure. You may have a dog strapped on the roof. This is why the speed NOT a controlling factor in range... Average Miles/kWh is.

How will you know how much energy that your battery will hold? Do the "Tony-Test" to determine your approximate degradation:
 
Ok, here was a test I ran where I reset the energy use at the beginning of the day. I drove 76 miles which included starting high going 1800' to sea level, then after a bit of flat, back up to 1800', down to 500' flat driving, then back up to starting point at 1800'.

I got exactly 3 miles/KWHr on graph.

Original charge was regular, recharge same.

Juicenet reported 32.695 KWHrs for a distance of 77miles = > or 2.3551 Miles per KWHr.

So why the huge difference between 3.0 and 2.3551?

I did use AC a fair amount of the time but the energy use should have reflected that.

This is why I worry about relying on the efficiency meter.

Could it be there is energy lost during charging batteries? BTW I purposely slow charge at 25A rather than 40A since it is likely easier on them.
 
laguna_b said:
Juicenet reported 32.695 KWHrs for a distance of 77miles = > or 2.3551 Miles per KWHr.

So why the huge difference between 3.0 and 2.3551

Slowing the charge rate reduces efficiency. I recommend charging at 40 amps AC.

I have no idea what meter the Juicenet folks are using, but I'll guess that it's not expensive or uber accurate. But, taken at face value, then:

3.0 / 2.3551 = 1.27

Is there a 27% loss of energy? Maybe. If it was uber hot while charging, the air conditioner would be running the whole time, and for a lot longer time, since you reduced the charge rate.

Normally, I would expect about 15% loss.
 
Ok, another test from yesterday.... 47 miles driven 19.841 KWHr used. Efficiency metered at 2.9
Assuming full efficiency charging that would yield 2.37 Miles /KWHr actual versus predictive 2.9

The Juicenet is actually VERY accurate as it is certified to be used as a secondary meter in the PGE EV-B charging tariff. (The one where you get off the tiered rates ONLY for your EV but get a "free" charger)

I charge at night in an open garage with ambient temps between 50 - 60 due to marine layer. So, one COULD argue that rather than AC to cool the battery, it might use a heater if it has one.

I am not sure why you think 40A is better than 25A but curious as to why since it is the inverse of the DCFC issue which is that it reduces battery life thus it implies slower increases it. Could you elaborate?
 
fromport said:
laguna_b said:
I am not sure why you think 40A is better than 25A . Could you elaborate?


This is for the built-in charger of a nissan leaf, so not 1:1 comparable with a tesla charger:
http://www.mynissanleaf.com/viewtopic.php?t=8583

This is a pdf link :
https://avt.inl.gov/pdf/fsev/SteadyStateLoadCharacterization2015Leaf.pdf

Thanks for this info!

Wow, this is interesting....both clearly point to higher efficiency with higher charge rates. I suspect the reasons are that since the charger in the vehicle had to reduce charge rates when operating below max, it does so by using switching like a thyristor or similar device to switch on and off which would create lots of harmonics and some heat loss. It is hard though for me to imagine that they charge with anything close to smooth DC (perhaps Tony knows) since the low impedance of the battery would dictate massively huge caps. But I suppose they could use switchers to raise the effective frequency of the charging current so caps would not have to be nearly as large....all my theoretical speculation.

So, I think the efficiency issue is answered and thus my NEXT experiment will be to run a multi-mile test like before and see what impact 40A charging has on the total consumption. I suspect it will fill a big part of the gap between theoretical m/KWHrs and what I have been seeing based on charging. I have a trip tomorrow likely stretch out over 150 miles where I can put the efficiency meter to the test as well. (expect one top up stop)
 
laguna_b said:
Wow, this is interesting....both clearly point to higher efficiency with higher charge rates.

I googled some more.
In this thread : https://forums.tesla.com/forum/forums/charging-efficiency-0 they have some interesting information.
Among which:

I charged yesterday at a ChargePoint location. The total drawn was 6.250 Kw and energy into the car showed 5.081 from their information. That gives an efficiency of 81%.

It's still early to account for all the variables like battery heaters coming on, vampire load, etc, but so far I am seeing about 86% efficiency (ie, 86% of the energy that comes from the wall makes it into the battery) charging at 40A/240VAC.

We have had our car for 18 days. We have logged 1070 miles. The car has always been charged at home on a dedicated meter.
Total kWh used per meter is 462
Total kWh used by car trip B (never been reset): 340
Charged up every night.
74% charging efficiency (including vampire loss at night)

Another thread with charging efficiency is here:
https://teslamotorsclub.com/tmc/threads/home-charging-efficiency.73181/

Those numbers should be closer to our scenario.
Looking forward to your data.
 
The energy used by the charging process has a significant fixed component, mostly coming from the cooling systems. The slower the charge rate the bigger the fixed part is as a percentage of energy used.
 
So we can model that as 2 questions in 2 unknowns. (I cant help it, i'm an Algebra tutor for kids...)

If we assume that the numbers above are correct:
5.081KW added to battery with a 6.25KW input
8.256KW added to battery with a 9.6KW input

we model that as two equations:

6.25 = fixedLoss + 5.081 * efficiencyFactor (30A @ 208V)
9.6 = fixedLoss + 8.256 * efficiencyFactor (40A @ 240V)

Solving for this using conventional algebra (substitution method) gives us:

0.888 KW = fixedLoss
105% = efficiencyFactor (note this is actually the INVERSE of efficiency)

The efficiency of conversion is 95% (1/105) which is well within the range of "normal" for switching power supplies - this would be the efficiency of the on-board charger in this case).

The most important source of error might be temperature during charging - if the a/c was running on one but not the other, we'd be off here.

Thinking about this, it may well be ok (i was thinking that 888watts of fixed load was ridiculous, becuase how would we EVER charge at 1.1KW (120V) with that much dead load). However, its probably the cooling system running, which normally wont run very much when charging at 120V (maybe not ever, although i think i hear it start up every time i plug in for 120V charging but normally my car is very quiet when being charged at 120V which i do almost all the time when i'm in Fremont, since its a pain to hook up the 240V charger cord and i can generally get away with 120V down there. So the equation may very well be different for 120V. (what probably isnt different is the 95% efficiency of the power supply in the onboard charger. Thats likely the same for any voltage).
 
davewill said:
The energy used by the charging process has a significant fixed component, mostly coming from the cooling systems. The slower the charge rate the bigger the fixed part is as a percentage of energy used.

The problem I have with this is that if the charging rate is slow enough, convection cooling should be enough to cool the battery.......which of course assumes that ideal charging temperature is above ambient.

I did seem to verify there was a positive impact on efficiency when I went from 24A to 39A (max for this RAV4). I lost the numbers I used for the calculation but the apparent driving efficiency (indirect measure of charging efficiency) went up about 10 - 15%.

Yesterday I did what was gong to be a great test of range where I went from home to Monterey, to Garapata and home. The total drive 144 miles. In Monterey I got a top off of 1:40 at a charger that USED to deliver 30A. No it is on a 30A breaker and a Clipper Creek DCS-40 (rated for 30A) but apparently delivering about 1/2 that based on the relatively small charge I got. I wish I had better data on that extra charge to be able to calculate my overall trip but no.

Why would they drop the charging rate down like that????? Don't they realize that time is the critical component in charging and that it is like cutting the number of chargers by half? The charging infrastructure, other than proprietary Tesla network, has hardly budged in 3 years I have been EV. (end of rant)
 
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