Prius Prime Plus in my hands

It was also practice with lessons learned. I need to figure out how to get the time stamps too.

Bob Wilson

 

Thanks, I have more details about this first test. FYI, anyone with a reasonable video/smart phone can run the same protocol and share their results:

• temperature ~63F, estimated right-quarter wind 6-9 mph wind
• cabin fan was on until seconds 4, no heat or A/C, just fresh air
• car was in "D" against a curb so it would not 'creep'
• parking brake was set, redundant to the curb
• duration ~18 minutes

67 MB, mp4, source.

If I had a "Buster" crash dummy in the driver seat, I could set everything up from the passenger side and take a break. Just it isn't clear how much more accuracy is needed as this gives a rule of thumb for Prime charging the traction battery to 80%:

• $2.00/gal * 0.75 gal ~= $1.50 for 80% charge
• 6.4 kWh * 80% ~= 5.12 kWh, ~ $0.56 at $0.11/kWhr residential HSV rate
• ChargePoint L2, rated 6.6 kWh @$0.85/hr in Nashville, TN

Bob Wilson

 

Perhaps inartfully posed, there is a valid question here:

What is the frugal and safe way to run a fully fueled and charged Prime tank dry:

• Use EV mode until the SOC reaches ~12% (about 3 miles) or ~25% (about 6 miles.) This is the cheapest motive power assuming Huntsville $0.11/kWh rates.
• Switch to HV mode to preserve the charge.
• If by design or accident, the charge falls below your 'safe margin' range, use 'Charge' mode to bring it up before the gas runs out. Then resume HV mode
• When the SOC % decreases because the engine is finally out of gas, use the EV safety charge to find a safe place to park and refuel.

So what sort of 1,000 mile tank challenge might this be used for?

Bob Wilson

 

When dealing with a small sample set, 17 points 0%-16%, there are not enough data points to trust a gross number like an average. In those cases, I like to graph the data because we often see patterns to determine if there might be problems:

• 0%-1% - this is an edge condition because we have very little, no control, over the initial state of the engine and specific HV part of the traction battery charge.
• 4% - noticed the fan was on and temperature set to 62F, seeking outside air flow, so I turned it off. There may be some unknown, heat-pump load up to this point.

Due to the statistically small sample set, we have to use other heuristics to decide if the data points can be trusted or used. So I tossed out the early points because we can't control the initial conditions and part of the observations overlapped my failed attempt to exit the car and continue recording metrics. By happy accident, the average I choose seems pretty close to the longest, flat segment of data points. Furthermore, the risk of 'sand bagging' with a too optimistic fuel burn per SOC% could lead to early fuel exhaustion.

Now there may be more interesting things about charge mode. Like Edison said 'the secret to invention is to have lots of ideas.' My curiosity about it is satisfied but happily, I've shown how to use a video recording to get metrics for their experiment.

Bob Wilson

 

I was not interested in the rate of charge or time but rather the fuel burned to put a charge on the traction battery. Now it is accurate to point out without moving, the engine has to burn vehicle overhead fuel, the power that operates the computers and loads simply because the car is ON. There is also the engine overhead. There is a double-accounting issue of comparing the vehicle overhead when parked vs moving ... the vehicle and engine overhead does not double just because it is running down the road in 'charge mode.'

Another approach is to use an A-B-A test with one of my benchmark loops:

• 10 miles @28 mph in HV with no SOC, ~21.43 min - measure MPG
• 10 miles @28 mph in 'charge mode', ~21.43 min - measure MPG and change in SOC%
• 10 miles @28 mph in HV, ~21.43 min - measure MPG and report ending SOC%

This is a little tricky because I need a better video recording technique than iPhone 'time lapse' that generated a 3.4GB file that had to be played back. In an ideal world, a digital camera would take a photo at the same place on the loop. I'll have to think about this.

Bob Wilson

 

Do I understand you're thinking:

• 0.40 gal - idling engine and vehicle overhead over ~80 minutes?
• 0.35 gal - charge mode cost to run SOC 0% to 80%?
• 0.75 gal - for 80% charge?

What is the basis of estimate for "0.40 gal"?

Bob Wilson

 

Part of the problem is I don't know of a way that keeps the Prime in "D" gear and "HV" mode, and running the engine. During the setup, the car was in "D" gear and "HV" mode and the engine was stopped. I suppose I could have started the windshield defrost or possibly A/C with the windows down and set to a min or max value but now we're introducing an additional load that we don't know if it is constant.

One Prius trick is to get the engine running and shift into "N" that will keep the engine running BUT disables transmission power flow. That would give an engine overhead but significantly change the vehicle overhead.

That is why I proposed the benchmark loop in an A-B-A mode. We are way out of standard day configuration today but I can still practice the method and try the ear-bud, remote, iPhone camera operation.

Bob Wilson