ScanGauge II – Prius Gen 4 XGauges – Observations on Hybrid Battery Current

The first XGauges for the 2016 Gen 4 Prius are just being published.
I have just posted here on my initial experiences with BTA. I hope to post more on SOC in the coming months.

The first few XGauges for the Gen 4 Prius are now being published. I was fortunate enough to be in a position to do some preliminary real world testing of some of these. Previously, with the Gen2 and Gen3 models, the Hybrid Battery State of Charge (SOC) and Battery Current (BTA) were two XGauges that many PriusChat members found useful.

This post focuses on my initial observations of BTA on a Gen4 and to compare them with my previous experiences with the Gen3 and Gen2, on which I have posted previously in 2011 and 2009 respectively.

The XGauge I tested works on my 2016 Gen4 in the UK. I can see no reason why it should not work elsewhere, but YMMV!:

TXD: 07DF0153
RXF: 432180000000
RXD: 1810
MTH: 000100018000
Name: BtA (a.k.a., BCA, BTA, can be anything you like)

The hybrid (a.k.a. traction) battery current can be used as a surrogate measure of instantaneous energy consumption on the Prius. By observing the current into and out of the traction battery, it is possible to gain a better understanding of how the choices we make as drivers can affect energy consumption (energy which is ultimately generated from the burning of fossil fuels).

Here are my first observations which might be of some interest. Previously, for both the Gen2 and Gen3 models, the car’s computers (ECU) had some ‘intelligence’ to save energy when holding the car stationary in D (e.g., at traffic lights). After a fraction of a second of being stationary with the footbrake applied, the ‘creep’ action applied by the electric motor is switched off. The car no longer pulls against the footbrake. This is observed as a fall in the BTA value. As you lift your foot off the footbrake, the BTA value rises as current is applied to the electric motor and the car will creep forward.

On the Gen2, the trigger to switch off the creep and conserve battery power required firm pressure on the footbrake. It was possible to hold the car stationary with only light pressure on the footbrake and, without observing BTA, the driver would have no idea that the electric motor was continuing to pull against the footbrake.

This changed in the Gen3, where the amount pressure on the footbrake when stationary did not change the current draw. In other words, being stationary appeared in itself to be all that was needed to trigger a cut to the electric motor, so long as your foot remained on the footbrake.

My preliminary observations on BTA in the Gen4 appears to show a return to the Gen2 situation, where a firm pressure on the footbrake causes a fall of battery current draw that is greater than if holding the car stationary with only light pressure on the footbrake. The development in this Generation appears to be that this firm pressure allows the current consumption to fall to a level that is equivalent to being in P or N and also to a level lower than on the Gen3.

The initial BTA values for ‘creep’ appear the same as for the Gen2 or Gen3; but once the car starts moving, if there is no further input from the gas or brake pedal, the BTA value falls to maintain a slow crawl with hardly measurable current drain (0.4 A).

There is also a significant penalty in current drain if you hold the car stationary in D with the parking brake instead of the footbrake. The car’s electric motor will pull continuously against the parking brake.

The table below summarises my findings on the three generations. The conclusion is that you will conserve some battery power by pressing firmly on the footbrake when stationary; and if remaining in D, it is better to use the footbrake than the parking brake.


Filter:
Driver action Gen 2 Gen 3 Gen 4
Stationary in D + light foot on brake
2 - 3 Amps
1.4 A
1.4 A
Stationary in D + firm on brake
1.5 A
1.4 A
0.4 A
Lift foot off brake in D (creeps forward)
2 - 3 A
2.9 A
2.9 A
Stationary in N or P + foot on brake
1.5 A
1.4 A
0.4 A
Stationary in N or P + foot off brake
0.9 - 1.1 A
1.4 A
0.4 A
Switch on LED headlights
add 0.5 A
add 0.5 A
Switch on interior fan at lowest level
add 0.1 A
add 0.5 A
Switch on rear demister
add 2 A
Maximum EV acceleration (to mid-point of HSI)
45 A
Firm braking from 25 mph (40 kph)
- 40 A
ICE charging HV battery when at 2 bars (40% SOC) 1280 RPM
- 5 to -12 A

All tests were performed in Eco mode with devices switched off to start with (to achieve a basic reading) and then each act/device was actioned in turn. My Gen4 has Touch 2 with Go and this was left on as I had the MFD on the Gen2 and the similar display on the Gen3 activated for my earlier tests.


Note: Your ScanGauge II will need to have version 4.22 firmware. I am grateful to James at Linear Logic for his assistance. He can be contacted at XGauge@Linear-Logic.com for any queries.

I will post results of other XGauges as soon as I am fairly confident of results. In the meantime, here is a link to a list of other XGauges for the 4th Gen Prius

 

Very interesting! Thanx!

What you report for the Generation 3 is mostly consistent with what I see in mine, as far as current levels while stopped.

You seem to have solved some of the frustrations I have trying to watch traction battery current, such as:

The Scan Gauge usually rounds to the nearest 0.5A, so I can't see numbers like the 1.4A you report.
Worse, battery current readings tend to be erratic when the car is moving, even under steady-state conditions, as if there's a lot of noise. (Or maybe the sampling period is so short that it doesn't catch a whole number of AC cycles ?) The readings do generally move in the logical general direction relative to conditions, but I can only assume the average reading is correct when readings are bouncing up and down.

 

So it won't work with earlier versions? I have 4.07 right now. I really hate to go without my SG to get the upgrade, it's an incredibly useful tool.

 

I think SG is very useful too, even though I'm now finding it almost impossible to improve on the ECU's decisions on these later generations!

(Any thoughts on this would be greatfully received)

I was effectively 'forced' to get version 4.22 when I upgraded my car. I have a set up of daisy-chaining two SG-IIs, so one of mine remains at 4.06 and I use the basic gauges on that one now. You might like to offer your services to Linear Logic as a beta tester. They might be able to help you out?

I have the impression this XGauge is also rounding to a resolution 0.5A but with reported values of x.4 and x.9.

 

I may have been unclear with this comment. What I meant to say was the BTA reading does jump to and from x.4 and x.9 values when switching devices on and off. However, it does display all other intermediate numeric values at the 1st decimal place location when the motors are driving or regenerating.

 

That's a peculiar way to round. I see mostly (but not exclusively) x.0 and x.5. The erratic battery current readings seem to occur mainly when the wheels (and therefore also MG2) are rotating.

 

I will keep monitoring to see if there is a pattern to account for the 'missing 0.1A'. At this, time I am still getting more displays at 0.4 and 0.9 A when stationary.

However, yesterday evening, I was testing after dark in the rain. I had my headlights and wipers set to Auto. Turning off my headlight, when stationary in D and foot on the brake showed a value of 0.5A. Shifting to P, after a moment of a higher value, the value went up to 1.0A. Shifted to N and the value stayed at 1.0A. Shifted back to D and the value dropped to 0.5A! Kept my foot on the brake all this time and cycled through P, N and D again with the same results. Always the lowest value in D!

 

Just received my two ScanGauges back from updating (now vers. 4.45) and the BTA codes are working with my US 2017 Prius 2. Discharge current readings with slight pressure on the brake is .9 amps.