Quantifying Regeneration and Consumption

[JoeS]

About a year ago I had concluded that our Power Gauge was simply a damped ammeter, and proceeded to 'calibrate' the red-needle interval settings on that gauge, shown earlier in this thread.

After reading a very detailed Argonne Advanced Powertrain Research Facility report about the Leaf, I began questioning my previous conclusion and now think that a series of current measurements at various states of charge (voltage levels) of our battery pack should be made in order to validate/disprove my previous assertion. I won't be doing this until I implement a decent isolated scheme for measuring our traction pack voltage, but hope our CAN bus developers can get get to the point where we have a useful tool to do the same.

It all boils down to whether it is power or current that our iMiEV not only displays on that gauge, but actually uses which parameter to control what's coming out of the battery pack. My previous presumption that it is current has been put in doubt.

For those technically inclined, here's the AVTA report - fascinating reading with lots of data and graphs.

There's a discussion of this over on the Leaf Forum, with one of the apparent conclusions being that the "Pulse and Glide" ICE hypermiling technique is fully applicable to EVs - in fact, they discuss a shortcut to kicking the Leaf into "Neutral", something we can do so much faster and easier with our iMiEV. :lol:

One of the reasons I'm bringing this up is that when trying to reconcile the disparity of results of magazine performance tests of our iMiEV, I hypothesized that both a lower state of charge (thus lower voltage) and running the heater/aircon could significantly affect the testing, especially the acceleration tests.

 

[marlon]

Dear Joe:

I see this thread hasn't been active in a while. Were you able to determine what the power guage actually measures. If it is amps, is the voltage constant. Also, is there a way from the OBD system or perhaps directly, to record the measurement. I'm hoping to find some way to measure actual energy used. If we've got power, we can integrate over time. If its amps and the voltage is constant we can multiply by the voltage and then integrate.
Or is there a better way to monitor energy used?

 

[JoeS]

Hi Marlon. Your question I assume is targeting energy used over distance (or the inverse), as we have no such readout?

The Leaf displays energy consumed over distance - just yesterday I drove with a friend in his Leaf as he was bragging showing that he was getting 5.0mi/kWh, but that is not the same as wall-to-wheels and it is unclear to me if the Leaf even includes the energy consumption of the vehicle's other powered systems in this figure.

I've seen some inkling that the information is available on the iMiEV's CAN bus, but until our CAN bus team gets the interface deciphered and a usable product for us, we can only take simple samples.

Inasmuch as, when driving, the currents are constantly changing dramatically and the voltage not only varies instantaneously in response to current draw but also decreases with SOC, I think it would be all but impossible to record any meaningful energy consumption data manually. If we could simultaneously record and store the current and voltage as we drive, that would give us the power and thus over time, the energy consumed.

To answer your question, I have not instrumented my iMiEV to measure traction pack voltage (yet), and it's somewhat low on my priority list as I'm hoping the CAN bus team comes up with something I can buy.

For myself, I had meticulously recorded my own energy consumption over 8000miles, yielding wall-to-wheels of 4.2mi/kWh
Ref: Wall-to-Wheels Consumption

As I mentioned in my previous post, I am interested in this to determine if it's peak power or peak current out of the battery that is being limited by the iMiEV's BMS - in the hope that that will explain the apparent poor acceleration in some of the magazine road tests (e.g., if they had the heater running and the battery not fully charged) - as I would expect that the iMiEV's BMS priority is to preserve battery life at the expense of degraded acceleration.

 

[peterdambier]

Just for comparison - I got a meter finally. Calculated 7.5 kilometers per kilowatt hour that is 4.6 miles but ...

From home I can go roughly two directions first is over the hill and very steep down the other side. There is one part of 17% but that part I go rarely and I have seen the i-MiEV does not like it. The other side is hills and valleys but not so steep. That is what gets me 7.5 kilometers over a distance of some 70 kilometers including return.

What messes up things is the gauge the turtle is showing me.

I have learned with 230V/16A charging 1 bar means very closely 1 kWh charged. So I can actually charge 16 kWh but that does not mean I can store 16 kWh in the battery and much less does it mean I will get 16 kWh out of the battery.

I have driven 68.1 kilometers out of a fully charged battery and I have charged 9.053 kWh afterwards. That gives me 7.5 kilometers out of every kWh or a range of 120 kilometers. Every car is different, so is every driver. I guess JoeS 4.2 miles per kWh is more reliable than my 7.5 kilometers and it depends where you go and how you drive. Avoid the final 25 kilometers in your calculation of range but you can rely on the kilometers per kWh you have calculated. The bill from Hydro Quebec will proof it. :mrgreen:

When I am charging in the wild I can trust the gauge to estimate how much and how long charging. Another lesson I learned the final bar will take an hour charging or more. So going long distance charging more often gets me further than charging long time and charging to the rim is not a good idea.

Knowing plug to wheel do I need battery to wheel?

 

[JoeS]

So going long distance charging more often gets me further than charging long time and charging to the rim is not a good idea....Knowing plug to wheel do I need battery to wheel?

peterdambier, if the car is left plugged in, the last hour or so is a decaying power draw as the battery is being balanced, so you are correct in saying that completely topping up while on the road is less efficient use of time than partial charging.

Battery-to-wheel consumption is of academic importance, IMO, as it is wall-to-wheel which we pay for. :roll: Unfortunately (and unlike an ICE), this number is terrifically influenced by our use of the heater.

 

[Zelenec]

Unfortunately (and unlike an ICE), this number is terrifically influenced by our use of the heater.

I'd say good for us it's influenced by our use of the heather. ICE drivers has no option! Even in the summer the engine produces heat and this has influence on ICE economy every day. We at least have option to decide.

 

[JoeS]

Unfortunately (and unlike an ICE), this number is terrifically influenced by our use of the heater.

I'd say good for us it's influenced by our use of the heather. ICE drivers has no option! Even in the summer the engine produces heat and this has influence on ICE economy every day. We at least have option to decide.

Zelenec, I agree with you! My choice of the word "unfortunately" was meant in this context: whenever the number "miles/kWhr" or "kWhr/100km" (or whatever other metric one chooses to use defining energy consumption over distance) is being discussed it would be "proper" to exclude the uncontrolled non-motive-related variables (primarily heater and aircon). In my own case, I stopped tracking my iMiEV's energy consumption/distance when summer ended as I realized how much the arbitrary heater use was contaminating the data (although I am still keeping track of every kWhr consumed for 'cost' purposes).