Hybrid Battery Consumption Question.

[Joseph D]

I would have thought (maybe wrongly) that any Battery Management System, would prevent a harmful discharge, whatever the cause....

I agree. It should have a preservation of life logic built into it.

...and that the HV battery would allow itself to go no where near a total shutdown, resorting to pure ICE until the vehicle is back into Regen mode of some sort

I'm fairly sure the HSD cannot work with just the ICE. It needs the MG1 & 2 to be able to function.

[Aceshigh84]

As for blinding fellow motorists with my brake-lights, I have been behind other Prii, and don't find their brake-lights to be more bright than any other car (even at night), so I don't think people need to be concerned with that.

I know that the gen 2 Auris has the led side lights, and I get enough people flashing me thinking that I am driving with fog lights on. When I use the brakes, the lights light up street signs etc for quite a distance back, so I would say they are bright.

And either way, very bright or not, I personally find it really annoying when people sit on their brakes, especially at night, as it actually does affect my vision. It isn't so different to people who drive toward you with fog lights and/or main beam turned on.

In my opinion both actions are a danger to other road users.

[RunningInPleasePass]

The Highway Code has something to say about stopping with your foot on the brake:

114

You MUST NOT

• use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists and horse riders
• use front or rear fog lights unless visibility is seriously reduced. You MUST switch them off when visibility improves to avoid dazzling other road users (see Rule 226).

In stationary queues of traffic, drivers should apply the parking brake and, once the following traffic has stopped, take their foot off the footbrake to deactivate the vehicle brake lights. This will minimise glare to road users behind until the traffic moves again.
Law RVLR reg 27

I have had this conversation over on Prius Chat, and our American friends find it amazing that anybody would do anything other then hold the car on the footbrake.

The best and easiest solution is to press Park.

[Joseph D]

The Highway Code has something to say about stopping with your foot on the brake:

114

You MUST NOT

• use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists and horse riders
• use front or rear fog lights unless visibility is seriously reduced. You MUST switch them off when visibility improves to avoid dazzling other road users (see Rule 226).

In stationary queues of traffic, drivers should apply the parking brake and, once the following traffic has stopped, take their foot off the footbrake to deactivate the vehicle brake lights. This will minimise glare to road users behind until the traffic moves again.

Law RVLR reg 27

I have had this conversation over on Prius Chat, and our American friends find it amazing that anybody would do anything other then hold the car on the footbrake.

The best and easiest solution is to press Park.

Or does it? Ok, two things,

1. The MUST NOT (compulsory) section is clearly talking about headlights and fog lights aimed at on coming or following traffic; this is further reiterated by the second bullet point in the section;
2. The second paragraph is a "should" do (optional) as it may be that your brake lights do not dazzle or cause discomfort.

As I said in my previous post, I do not consider the Prius (Gen II or Gen III) - or the majority of other cars - to be so bright they dazzle or cause discomfort to other drivers. From my observation over two years driving in the UK, I would say that those who follow the suggestion are in the minority - 30% who do to 70% who do not.

I'm afraid I'm with our American friends, in that I find it amazing (amusing even) anybody would do anything other than hold the car on the footbrake.

As a complete distraction, I note rule 113 requires you to drive in a lit street with your headlights off but nobody (without exception) does. And modern thinking would say rightly so. So do we slavishly follow the rules or not?

I don't want to start a war over this - it is just my point of view and you are free to disagree. I really find it amusing that so many get so passionate about this subject (I have read previous posts). I just wonder is the real annoyance that people perceive that the rules are being broken? Or is it something else? Surely there are many more real issues to get het up about?

My tuppence worth.

[timberwolf]

One of the problems with the Highway Code, in my opinion, is that it mixes up law with general advice and courtesy to other road users. I'd agree with your interpretation, I also looked the law up online - http://www.legislation.gov.uk/uksi/1989/1796/contents/made.

I don't have a problem with brake lights either but maybe because my first experience of driving automatics was in North America, so as the saying goes "monkey see, monkey do":-)

[barrycoll]

this is really not a binary situation folks, its all about being flexible and also awareness....to come back to my role as an Observer for the IAM, the main thrust of vehicle lighting, is to see and be seen, and the role of consideration for others...

as for the HV Battery situation, a good analogy (it seems to me, anyway) is my hard drive video recorder, which will record 2 programs, but will not allow watching a separate 3rd channel, and will default to one of the recording channels

I would have thought that the Prius would do the same, that when there was a threat to the HV Battery (by too long in N position), it would default to P, or shut down completely, with lots of bells, warning whistles, and flashing lights

[Grumpy Cabbie]

Maybe it's a car designed for World markets and only the Brits have this concern of not leaving their brake lights on and that putting a car in Neutral is preferable to putting it in park? Hence why there is no warning - because nobody other than the Brits does it.

Other markets have much more experience of automatics than we have. Other markets call the handbrake a parking brake and thus something to be used when parking rather than sitting at lights.

Maybe the rules written for 'correct' driving need relooking at? When were they decided on? 1952? 1967? 1977? Do they still recommend threading the steering wheel through your hands when turning? I'd love to see that on a high powered front wheel drive car :)

I found from experience that if one doesn't sit with ones foot on the brake at lights, you're more likely to get some idiot not notice you've stopped and barrel into you at 20 mph. I now keep foot on brake until the person behind has stopped and if the lights are still red and the traffic not continually crawling up closing gaps, I will then put the car in Park.

[aCactus]

You have to keep your foot on the brake pedal so that the hill start assist feature works - also worth remembering that all cars now have a third brake light so that following drivers can see your brake lights through the car immeadiately behind you. Despite an extensive search I cannot find a handbrake in my car.....

[RunningInPleasePass]

From what I've read about Neutral it is included on hybrid cars because it's required in some countries because of legislation.

When you select Neutral the car just disconnect the two motor/generators so the car is able to free-wheel, but of course it's then unable to charge the HV Battery.

Apparently the car gives plenty of warning when the Battery is getting low, but I can't think what it could do automatically to start charging the Battery without causing further problems.

If it put itself in to Park the wheels would lock with disastrous results if you were free-wheeling down a steep hill!

If it put itself in Drive it would creep forward unexpectedly, again very dangerous!

As to brake lights, cars with their brake lights on in front of me don't particularly bother me, I wanted to point out what I had been taught, and why, sorry if I've upset anyone.

[barrycoll]

I suppose the reason that Neutral has become so ingrained into my driving, is the 3 years I spent collecting and delivering a fleet of supercars from www.autovivendi.com

nearly (or all?) of their supercar fleet had paddle shift changes, and all were dry clutch, so it was obligatory to use Neutral when stationary, or I would be given the job to take yet another Lambo out to High Wycombe, to have the body work off, and the engine out, and a new clutch fitted....£3-4K....

clutch slip could destroy their cars in very few miles, and Neutral was achieved by pulling both paddles towards you....and it was very easy to forget to do this until it became part of the drive...

and for me it still is, as my car at the time was Golf with a DSG box, which needed Neutral or would continue to creep against a dry clutch...the footbrake de-activated this, but the hand brake didn't....

so relearning my drive is taking some time, but I must thank everybody for their input with this 'slow process'

[kithmo]

I'd opt for it autiomatically putting itself in Park when the HV Battery was low, then if someone was idiotically freewheeling down a steep hill in neutral (IIRC there's something about not doing that in the highway code as well) then they would get their just desserts, either a smashed transmission or a kissed windscreen.

[RunningInPleasePass]

I think it's better to just warn the driver that the HV Battery will go flat if they continue to leave the car running in neutral, rather then lock the wheels unexpectedly.

Another example were it would not be good to automatically swap from neutral to park would be in a chain drive car wash, (the highway code has nothing to say on car washes, as far as I know!) you could then end up getting stuck mid way through, not to mention the damage it would cause.

[johalareewi]

Somewhere in the Hybrid forum, there is a post saying that while sitting in traffic in N, the HV Battery got low and the ICE started up and began charging the HV Battery. This is despite all the Toyota bumpf saying that the HV Battery cannot be charged while in N. I think the poster was Terry something with a hybrid Auris (gen1).

[Joseph D]

Somewhere in the Hybrid forum, there is a post saying that while sitting in traffic in N, the HV battery got low and the ICE started up and began charging the HV battery. This is despite all the Toyota bumpf saying that the HV battery cannot be charged while in N. I think the poster was Terry something with a hybrid Auris (gen1).

In the case of the Gen II Prius, I'm fairly sure it does not do this. When the car gets to the stage it wants to charge charge the HV, it beeps and displays an urgent request to put the car into P or D. I have a vague recollection of this when I put it into N whilst sitting when I first got my Prius and thought I won't do that again. And haven't. Maybe this was changed and updated in later systems, but then it wouldn't technically be in neutral any longer as it physically cannot charge in the neutral state.

[barrycoll]

as the original poster, the only scenario that I has prompted me to use N, is (very) stationary at traffic lights, with a delay time of 15/20 secs

.....or similar in a m-way queueing situation

with the forums welcome advice, I will use P in future....(much bowing and grovelling)

just out of interest, what indicators does the latest Gen 3 dash board give that the 2 final bars of HV Battery are under threat???

[GreenJuice]

For both Gen 2 and Gen 3 Prius, my understanding is that you get a warning beep and an instruction to put the car into Park

Here is a useful thread on what to do if it happens to you in a car wash when you have to be in Neutral

(you can shift into IG-ON and stay in Neutral)

http://priuschat.com/threads/low-traction-battery-problem-w-prius-at-my-car-wash.83862/

There is a small but interesting difference in the 'creep' behaviour between the Gen 2 and Gen 3 which provides some insight into Toyota's thinking. These observations are not possible with the standard instrumentation in either car. It is possible to use additional instrumentation like ScanGauge II to monitor the current drain (BTA) from the HV ('traction') Battery as well as its state of charge (SOC).

When stationary in Drive, foot on brake:

In the Gen2, you have to press quite firmly on the foot brake to suppress the 'creep'. If your foot is light on the brake, only just holding the car stationary, there is a detectable current of about 2 - 3 Amps, which drops to the 'baseline' current of 1.5 Amps when you press harder on the brake.

This behaviour is different on the Gen3. So long as you are holding the car stationary on the foot brake, lightly or firmly, the BTA drops to the baseline 1.4 Amps in a fraction of a second. The car's electronics therefore 'knows' that you want to be stationary and shuts off the 'creep' to save on wasting energy.

If you apply the parking brake ('handbrake') and hold stationary with your foot off the footbrake completely, the current rises to 2 -3 Amps in the Gen2 and 3.5 Amps on the Gen3; and you will feel the car just lift slightly as it strains against the parking brake. That situation is, of course, wasting energy. You can only avoid straining against the brake in Park or Neutral.

Here are some other observations on current drain using ScanGauge II on the Gen 3, to help put options into perspective:

Baseline current drain (BTA): 1.4 A

Switch on Cabin Fan at lowest level: not detectable

Switch on Radio at Volume 15 - 25: not detectable

Switch on Headlights (dipped beam): Adds 0.5 A

Switch on Headlights (high beam): Adds 1 A

Switch on AirCon: Adds 2.5 A

Switch on Heated Seats (each) Adds 0.5 A

'Creep' - foot off all pedals, from stationary: Add 3.5 A

Accelerate on EV to max before ICE starts: Adds 27 - 35 A

Current drain by the Air Con and Heated seats is actually not *that* great, and less than the energy used to creep at around 3 -5 mph

Accelerating to 20 mph from stationary on 'EV only' will drop SOC by about 3%. If I enter into heavy London stop-start traffic with the ideal 60% SOC, I can manage about 6 accelerations from stationary before the ICE is forced on at SOC 41%,

It appears that in the development of the Gen 3, the designers have optimised the 'creep' behaviour for those who hold the car stationary in Drive with the foot on the brake. On a world-wide scale, I suspect this is how most drivers actually do it.

Japanese hypermilers on the Gen2 used to get round this by performing what they called a 'dance' at stop-start situations:

Left hand - slip into neutral as your speed drops below 7 mph

Right foot - on brake till stationary

Left foot - parking brake

Right foot - off footbrake, wait till time to move

Left hand - slip into Drive

Left foot - release parking brake

Right foot - on accelerator!

[RunningInPleasePass]

Thanks for this information, this is what I wanted to know with my original questions,

[kithmo]

I think it's better to just warn the driver that the HV battery will go flat if they continue to leave the car running in neutral, rather then lock the wheels unexpectedly.

Another example were it would not be good to automatically swap from neutral to park would be in a chain drive car wash, (the highway code has nothing to say on car washes, as far as I know!) you could then end up getting stuck mid way through, not to mention the damage it would cause.

AAARRRGH, Auto car wash, NOOOOOOOOOO!

I never use auto car washes, they damage your paintwork.

[RunningInPleasePass]

Your right, it's a pain sometimes but far better to wash by hand.

[Joseph D]

Here are some other observations on current drain using ScanGauge II on the Gen 3, to help put options into perspective:

Baseline current drain (BTA): 1.4 A

Switch on Cabin Fan at lowest level: not detectable

Switch on Radio at Volume 15 - 25: not detectable

Switch on Headlights (dipped beam): Adds 0.5 A

Switch on Headlights (high beam): Adds 1 A

Switch on AirCon: Adds 2.5 A

Switch on Heated Seats (each) Adds 0.5 A

'Creep' - foot off all pedals, from stationary: Add 3.5 A

Accelerate on EV to max before ICE starts: Adds 27 - 35 A

Japanese hypermilers on the Gen2 used to get round this by performing what they called a 'dance' at stop-start situations:

Left hand - slip into neutral as your speed drops below 7 mph

Right foot - on brake till stationary

Left foot - parking brake

Right foot - off footbrake, wait till time to move

Left hand - slip into Drive

Left foot - release parking brake

Right foot - on accelerator!

My thanks for that information too. Very useful.

One metric missing that I'd interested in is the current draw whilst sitting on the footbrake with the creep off. I am picking that it would be not detectable or else certainly less than the 500 mA draw of the dipped headlights.

I've tried the "'dance' at stop" technique and it is just too much like hard work. Only a long stop would get me to do it, and then I'd rather just engage the parking brake and press P.

Apart from the obvious damage caused by shunt in the rear, why do they do the 'dance' rather than what I do?

[Cyker]

*hugs everyone that uses the hand brake*

@GreenJuice - Excellent info

The HSD neutral is an unfortunate artefact of driving laws in some countries; The law is there to allow a driver to disconnect the engine from the wheels in case something goes wrong (e.g. that Ford ECU problem that caused the engine to accelerate with no user input!).

With the HSD this is physically impossible as the whole drivetrain is locked together, so the 'neutral' just kinda fakes it by spinning MG1 against the ICE so nothing gets to the wheels. I didn't know it couldn't charge in N tho'; I had assumed it could still charge via MG1, but I suppose if MG1 is being powered to spin against the ICE that would make sense...!?

[barrycoll]

that is a brilliant precis of Prius energy usage, GreenJuice....many thanks...

oddly enough, the Japanese Dance is exactly how I treat a stationary situation, which is really no difference to driving a manual 'ordinary car', except that the Prius foot/hand brake makes the experience very simple...in the olden days, it was .footbrake/declutch/handbrake/neutral/..and then declutch/gear/handbrake/accelerator

....................but we are back to the situation of involving using this 'unfortunate artefact' of N, with its attendant "potential" problems, (although P is always an option)

I am sure that the use of just the footbrake is the Norm for most drivers, and seems to be built into the Prius's genetics as of the Gen 3, but as I don't like sitting behind someone with and endless flashing of their turn indicator, then I just assume that whoever is behind me would appreciate something similar

it would be interesting to know that actual incidence of HV Battery 'destruction' in the Gen 3 Prius worldwide, especially IF there is a

large flashing warning that ££££ Armageddon is just around the corner..

[Grumpy Cabbie]

I can't imagine being run low once or twice will do much harm to the Battery as such, but rather it gets too low for the car to actively charge it up. This would need a trip to the dealers.

There is a graph on PriusChat showing the number of charge cycles the Prius HV Battery can handle. I think it went along the lines that if you used the full capacity and ran it to empty you'd be able to do it about 1,500 times before it was dead. Expensive. If you discharged it in the 'happy' zone between 40% (2 bars) and 60% (8 bars) then it was something like 200,000 cycles or so. That's why when the Prius says it's full it isn't and when it's empty it isn't really either.

That's another reason why the Battery lasts so long compared to mobile phones and cordless drills which use the entire range from full to empty. Though if your battery costs £30 instead of £2,000, then that's not a problem.

[GreenJuice]

One metric missing that I'd interested in is the current draw whilst sitting on the footbrake with the creep off. I am picking that it would be not detectable or else certainly less than the 500 mA draw of the dipped headlights.

Not sure I quite understand your comment, so forgive me if this response is wrong.

The lowest level of current draw is 1.4 A. If you are stationary in Drive with the foot on the brake, this is what you see on the XGauge BTA.

If you go to Neutral or Park, it remains the same.

If you stay in Drive and lift your foot off, the car will creep and BTA rises to 4.9 A (it soon settles down at 3 mph to a higher or lower value depending on the road incline).

If you then brake again and come to a halt. The creep is switched off in a fraction of a second and BTA drops to 1.4 A again as soon as you are stationary (not before).

If you remain stationary and turn on the lights (or allow them to come on in the 'auto' setting) the reading on BTA is 1.9 A.

Apart from the obvious damage caused by shunt in the rear, why do they do the 'dance' rather than what I do?

The 'Dance' was for the Gen2 which did not 'switch-off' the creep as easily as in the Gen3.

Hypermilers trying to sqeeze every ounce of energy developed this method, but it could easily be argued that the added value is minimal!

Remember that one of their aims is also to minimise *all* energy conversions, both in and out of the traction Battery (as all conversions are theorectically wasteful!)

Basically, as your speed drops below 6-7 mph, you do not regenerate any more energy from deceleration and friction braking then takes over. At this point, you might as well 'electrically disconnect' MG1/MG2 by going into Neutral to minimise the chance of energy conversion. Keeping your foot off the foot brake has a further minor energy saving which is that your brake lights are off and brief brake pump action is avoided (I am not justifying this, just explaining!). Holding the car with the parking brake instead of P, saves an immeasurable amount of energy.

One other point to make is that hypermiler's actually prefer to not stop if at all possible. Therefore, they would aim to 'Glide' (I'm using this word in the specific hypermiler language; i.e., 'assisted' with foot on the accelerator keeping BTA at 1.4 A) towards the 'potential' stop situation but actually hoping they don't actually stop, flicking to Drive and taking off on their next 'Pulse' phase of a P&G cycle.

Hope that makes sense!

[GreenJuice]

If you discharged it in the 'happy' zone between 40% (2 bars) and 60% (8 bars) then it was something like 200,000 cycles or so. That's why when the Prius says it's full it isn't and when it's empty it isn't really either.

Yes, I think this is really important to emphasise to new users - not to worry by focusing on those bars.

The car's electronics will keep the HV traction Battery between 40% SOC (empty) and 80% SOC (full) and for most situations there is ample capacity to absorb occasional deviations at both ends.