Full Traction Battery - still charging?

[Mick F]

We often arrive home with a fully charged Battery.  This is because we live in a valley and there's two miles of constant downhill, some of the latter part on the brakes.  It must be possible somewhere in the world to descend a hill that is far longer than ours.

If the Battery is full, where does the "excess" charging current go?

Mick.

[Mike J.]

3 hours ago, Mick F said:

We often arrive home with a fully charged battery.  This is because we live in a valley and there's two miles of constant downhill, some of the latter part on the brakes.  It must be possible somewhere in the world to descend a hill that is far longer than ours.

If the battery is full, where does the "excess" charging current go?

Heat, like any non-hybrid.

[Catlover]

I noticed driving my Prius Gen3,  that when driving along a M-Way the Battery charge tops. The graphic display in the Prius (dont know if same in a Yaris) that shows the engine, motor/generators, hybrid batt and the wheels show when the Battery is tops that apart from the engine turning the wheels but also the hyb batt shows it sending power to wheels as well. This thus helps with mpg, as the engine is getting a boost from the Battery thus not needed as much.  Thats how I interpret it anyway, will stand corrected. 

[Mick F]

Thanks for the replies.

The car coming down a hill - providing the system is warm and the heater not doing much - the engine is completely stopped so it can't absorb the energy.

Heat?  I can understand that with engines and brakes - but the excess current being converted into heat with no brakes on and engine stopped?

The Battery can't continue to heat up coming down Alpe d'Huez for instance.

Mick.

[Mike J.]

There is no excess current as the regen system is off. With no regen, you use brakes and you can also go into B mode to join the engine to the wheels to get a bit of engine braking.

[Mick F]

26 minutes ago, Mike J. said:

There is no excess current as the regen system is off.

Not according to the display on the screen as it still shows a green power flow back to the Battery even with the Battery shown as full.  Also, the Power gauge on the dash shows that it's charging.

If the regen system is off, how is the car being held back?  Surely it would freewheel as if in Neutral .......... which it doesn't.

Rarely use the B mode.

Mick.

[Anthony Poli]

There is power being used, the hybrid system uses a smaller but consistent amount.
B mode is recommended for a long decent, that limits the amount of power regeneration.


Toyota wouldn't create a situation that would damage the just by going downhill.


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[Mick F]

2 minutes ago, Anthony Poli said:

There is power being used, the hybrid system uses a smaller but consistent amount.

Toyota wouldn't create a situation that would damage the just by going downhill.

Yes I'm well aware that Toyota know what they're doing! 

Just that Im curious about how it still shows charging despite a full Battery indication.  It must be like you say, the system still using it.

Mick.

[Bomber209]

Hi, It's just the same as a normal 12v Battery. The Alternator continues to pump out power even though the Battery is fully charged. A voltage regulation circuit kicks in and creates (in theory) an open circuit.

[Mike J.]

2 hours ago, Mick F said:

Just that I'm curious about how it still shows charging despite a full battery indication.

It doesn't on mine. If Battery is full and engine is running (for heating) there is no flow to Battery.

3 hours ago, Mick F said:

Not according to the display on the screen as it still shows a green power flow back to the battery even with the battery shown as full.  Also, the Power gauge on the dash shows that it's charging.

The Battery is not full then. I suggest you use the hybrid app to find out exactly what is going on.

[Anthony Poli]

The battery is not full then. I suggest you use the hybrid app to find out exactly what is going on.

Wonderful app, much easier than using torque and the the information is in a more readable format.

I have also used dr Prius, which is just a tool for checking the condition of the hybrid Battery.


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[Bob110023]

Hi. As we all know a Battery is also a power storage device. Even when fully charged and not doing anything there will be natural drainage from the Battery. When fully charged the Toyota system might show that it is still charging the hybrid system. This of course is correct but the input would be greatly reduced to a trickle charge until a larger input is required.cheers

[Mick F]

That sounds correct to me.

Our power meter definitely shows a charge when fully charged, and the green flow diagram is still there too.

Can't say I'm fussed about having an app to check on stuff.  The info on here is enough.  It was just a query on how it all works.

Thanks, Mick.

[Mike J.]

2 hours ago, Mick F said:

Our power meter definitely shows a charge when fully charged, and the green flow diagram is still there too.

It doesn't for me, so back to first principles - what is your definition of fully charged via the display? On mine, nominal (let's treat the Battery nicely for longevity) fully charged has 2 clear segments, lots of regen. or engine running for heat rather than charging, but may as well do it any way, has one clear segment. "Oh my god it is cold and I was left overnight fully charged" - no clear segments. So, if you are in regen mode with 2 clear segments, you are not fully charged until you have been in the one clear segment for a while - you won't go into no clear segments when driving. This info seen in the first gen. Yaris hybrid.

[Mick F]

All segments full.

Generally, when driving on normal A roads, there's often two segments clear, but when descending a decent hill - a mile or two - the two segments fill and all are green.  Every one of them.  Loads of long hills hereabouts so it happens often.  Maybe not on faster roads, but 30mph limit ones it does, and also on long winding descents were you go for ages dabbing the brakes occasionally.

I tend not to have anything showing on the display, but when I look as we arrive home, all are full.  I've watched the power meter and the green charging flow well after all the segments are full whilst on our way home.  It was only the other day that it occurred to me that something is going on that I didn't expect or understand.

I see you live in Suffolk.  Not known for it's hills if my memory serves me correctly.  Try living in Devon or Cornwall, and you'll often see all segments full.  If you live in the bottom of a deep valley like we do, the car comes home fully charged with all segments green.

Mick.

[Mike J.]

On my car it never has all segments green - one exception mentioned. Normal driving - 2 (or more) clear. Parked up with heater on the Battery reaches its max. of one clear segment. I know it is the max because no energy flows from the engine to the Battery as shown by the display.

Your car may have different display software. You could park up with a full Battery and run the engine for heat to see if it ever stops charging - it must.

As mentioned, use the hybrid app to see if you are overcharging (above 80%) as this will cause battery longevity problems.

[Mick F]

I'll experiment later today, but I think it will prove nothing.  I'll try the running when stationary in Park with heater on and a full Battery to see what happens.  I still say that it'll show green, but I'll experiment and report back and hopefully with photos.  Can't photograph when driving though as I'm home alone this weekend as Mrs Mick F is away.

The car had a full service with Toyota Plymouth only a few short months ago.  The car and the Battery hybrid system was given a clean bill of health.

As I say, unless you live at the bottom of a deep valley, you won't see a full Battery regularly like what we do.  Toyota in their wisdom, must have allowed for this.

Mick.

[Mike J.]

I do see a full Battery (one clear segment for me) and this is via the (now regular) heating scenario.

[Mick F]

Tested yesterday afternoon.

Two photographs.  One at the top of the hill and one at home a couple of miles later.  Both times parked with handbrake on and Park selected, and both with heater turned to maximum and engine running.

During the latter stages of the descent, as normal, the green power flow was showing into the Battery even though the Battery was full.  As I say, I was by myself so couldn't photograph whilst moving, but you'll have to take my word for it that it's like that.  You'll see from the photographs that with Battery only partly full when parked, the flow is to the battery, but when full it's blank.

Mick.

[PeteB]

On 12/14/2018 at 9:38 PM, Mick F said:

...Try living in Devon or Cornwall, and you'll often see all segments full.  If you live in the bottom of a deep valley like we do, the car comes home fully charged with all segments green.

... or Scotland!

"Maxed out" doesn't just mean all the bars are lit - it takes quite a lot of extra regeneration after the eighth bar lights up before the system truly maxes out (like the fuel gauge, each bar covered a range of quantities).  The car's behaviour changes when this happens, and you're likely to be very aware of it because the sound changes, but mostly the braking changes.  It's still well power assisted, so won't be onerous, but B mode certainly seems to make it a bit less of a chore.

I'd covered getting on for 100,000 miles in 4 years in my first Prius Gen 1s before I experienced my first HV Battery "max out", but a holiday in Scotland made it a daily occurrence.  When reaching the bottom of a 5-6 mile 20% (1 in 5) hill, you got a good idea what an EV would feel like as the Hybrid System tried like mad to use up some of the excess electricity so there'd be room for more free energy when braking or going down the next hill.  The Gen 1 had no EV button, but while maxed out modest pressure on the accelerator would see electric only driving up to at least 60 mph!

I never experienced a single max out in a Gen 2.  I never owned one, but did about 50,000 miles in cars owned by my firm.  This was mostly in or around London, so no hills big enough to manage 8 bars lit, never mind maxed out.

I owned a Gen 3 Prius for 4 years (60,000 miles) before my current Gen 4 and only got maxed out a few times during a break in Devon in 2016.  I did, however, notice it was easier to get 7 bars lit in normal driving using my normal careful economic braking.

I've had my Gen 4 since June 2016 and covered 33,500 miles so far.  Again, not a single max out.  It seems even easier than the Gen 3 to light 7 bars, and on very rare occasions 8 bars (but nowhere near maxed) particularly on a series of roundabouts with 70 mph limits in between.

[Mick F]

Thanks for that interesting and informative post.

I have noticed the car behaving differently when fully charged, though I'm not aware of it being "maxed out" or not, but it does sound and feel different.  I'll pay particular attention to the braking feel next time I'm out in the hills!

Mick.

 

[Mike J.]

We do have different software - I guess Toyota thought it wrong to have it showing one clear segment when normally maxed out even though it more closely followed reality - batteries last longer if the max charge is 80% and are never fully discharged.

Good to see that your car does stop charging when the Battery is full.

[Anthony Poli]

We do have different software - I guess Toyota thought it wrong to have it showing one clear segment when normally maxed out even though it more closely followed reality - batteries last longer if the max charge is 80% and are never fully discharged.
Good to see that your car does stop charging when the battery is full.

I agree.
From my own observations the lowest for my previous 2010 Auris is 37% with a little bit showing on the Battery icon. With almost a full icon it was 79%.
During normal flat level driving the Battery would swing between 37 to 60%.

With the 2013 Yaris, it was about the same. It rarely had all bars filled.

It isn’t just hills that would pose a problem, motorway cruising is another situation where the charge needs to be stopped.





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[Mick F]

18 hours ago, Mike J. said:

Good to see that your car does stop charging when the battery is full.

The point of my OP is that when descending with a fully green Battery, it IS charging.  It stops when the car stops, but regen continues when descending.

Next time I'm in the car with Mrs Mick F in this situation, I'll get her to take a photo.

Mick.

[Anthony Poli]

Maybe another way to prove your point, would be to switch the display the trip minute by minute and display how many 30Wh blocks are displayed for the descent. In theory that should show how much power has been generated by the regenerative braking alone.

The problem with the energy monitor is that, it isn’t telling you what’s happening in reality. It maybe showing a full Battery while it’s continuing to charge. It doesn’t now show the charge current or the voltage that the motor is generating.

As the Battery voltage rises, either the charging voltage has to increase or the charging current to the Battery falls.


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