Unexpected lack of regen braking

[ChrisMiller]

Usually I charge my PHEV at home and it's usually completed its charge before I take it out again. I fully understand that when at (or close to) full charge, only limited regen braking is available and I'm used to the effectiveness to expect in these circumstances. Yesterday, I needed to interrupt mid-charge for an 'emergency' dash to the shops, so I needed to press the 'stop' button on the charging unit; the battery meter showed full, with the corresponding range on the guessometer. I was surprised to find that rather than limited braking, there was none at all, just as though I was in B0 rather than B5. This continued to the shops (just over a mile away*) and on the way back I got the normal (reduced) amount of braking available with a fully charged battery.

I posted this, because it's capable of catching you out if you're expecting 'electric' braking which isn't there. My guess (based on no information whatever) is that the battery gets warm during charging, and in normal circumstances it has had a chance to cool down. Possibly with a warm battery, the regenerative charging is further restricted (or prohibited altogether). But I'm sure there are readers of this forum with greater expertise than mine .

* I usually walk, but in my defence it was pouring with rain

 

[Claymore]

Life with the PHEV seems to be always full of surprises but for me this isn't one of them.

When I go to the local shop (downhill) each morning, for the morning paper after the usual overnight charge I never get any regen braking, or at least not enough to register with me, until I've actually used some drive battery.

I don't think it's anything to do with the battery's temperature, just that if it's fully charged there is nowhere for any regenerated power to go so the car doesn't generate any and therefore you get no 'leccy' braking.

If you've used preheat or pre aircon you will get some braking as the battery will not be quite fully charged.

JimB

 

[ChrisMiller]

There definitely is (a small amount of) regen braking when fully charged*. Get going, put the PHEV into B5 and lift your foot off - the car will slow down; set it to B0, it won't (other than by rolling resistance). Of course it's far less than the B5 braking effect once the charge level has dropped by 5-10%.

The dash will show charge flowing from the wheels to the battery - it didn't when I encountered the unusual situation I described above. I thought at first that something might have broken, but the (reduced) braking effect returned after a mile or so.

*By which I mean letting the car charge until it reaches 'charging completed' and then taking it out on the road a few hours or a day later.

 

[user 816]

There is a stop button?

my charger is permanently on, plugged in inside the garage with the charge cable through a slot in the door frame, car connector sits on a wall mounted holder. I just shove it in the car when parking and yank it out when I need to go, never pressed a button.

will go investigate in the morning :lol:

 

[anko]

In the last four years, I have departed with a partially charged battery often: abort charging before battery is full and take off. Never have I experienced reduced regen braking in these situations.

 

[greendwarf]

This is an interesting dialogue. Perhaps there is more going on in the last hour or so of charging than we are aware. I recently had to plug in during the day when there was only 1 mile showing on guessometer. When I stopped the charging about 3.5 hours later I had apparently a full battery and 24 miles predicted, much to my surprise. This was with the standard brick into a 13amp socket at home. Normally I charge overnight so have always assumed I need the full 5.5 hours to get this sort of result.

 

[ChrisMiller]

There is a stop button?

I use the standard 13A domestic 3-pin charger supplied with the car, which has a stop button. (I assume this didn't change with the facelift?)

This is an interesting dialogue. Perhaps there is more going on in the last hour or so of charging than we are aware. I recently had to plug in during the day when there was only 1 mile showing on guessometer. When I stopped the charging about 3.5 hours later I had apparently a full battery and 24 miles predicted, much to my surprise. This was with the standard brick into a 13amp socket at home. Normally I charge overnight so have always assumed I need the full 5.5 hours to get this sort of result.

I monitor charging using the phone app, which shows the battery reaching 100% (as displayed) charge about an hour before the charging 'officially' completes. My guess (based on 50-year-old school physics) is that charging generates heat (as it can't be 100% efficient). As the battery gets close to fully charged the internal resistance, and hence the heat generated, increases. So for the last few(?) percent the car/charging system reduces the power and creeps up to the 100% mark (which isn't really 100%, but let's not go there ).

I think that's why the public high-power chargers stop at the ~80% mark. But I'm sure there are electrical/electronic engineers on this forum who can provide a much better account.

Speaking of which: @anko - I'm sure I haven't seen this when I've aborted charging with the battery significantly less than fully charged. By a fluke, when I needed the car it had reached full charge, but was (or had been quite recently) charging at close to the maximum rate (the 3-pin plug was slightly warm).

 

[MikkB]

I have found that I have an apparently full battery (all bars full on display) with full range quite a long time before the charging process cuts out itself (as much as one hour according to the remote app, ie, battery appears full but time to completion estimated as one hour).

In these circumstances I find I have no regen braking until some of the charge has been used up. Makes me wonder why the charging process doesn't shut down earlier?

Mikk

 

[anko]

Makes me wonder why the charging process doesn't shut down earlier?

Because you will have less range on a full charge?

 

[MikkB]

Makes me wonder why the charging process doesn't shut down earlier?

Because you will have less range on a full charge?

"I have found that I have an apparently full battery (all bars full on display) with full range quite a long time before the charging process cuts out itself "

 

[anko]

Makes me wonder why the charging process doesn't shut down earlier?

Because you will have less range on a full charge?

"I have found that I have an apparently full battery (all bars full on display) with full range quite a long time before the charging process cuts out itself "

You are talking about an apparently full battery. I am talking about a full battery. You may think you have full range on an apparently full battery, but how could you ever know?

Even in that last half our of charging, although less then before, energy is still added to the battery. Also, with the right tools, you can see %SOC increase.

 

[MikkB]

Even in that last half our of charging, although less then before, energy is still added to the battery. Also, with the right tools, you can see %SOC increase.

I see, so that last hour of charging is for a very small gain in charge and range? Must be very small if the displayed charge and range does not increase visibly, but I take your point. The good news is that I'm pretty much fully charged after just 2.5 hours on the charger, which is great.

 

[anko]

See how much you may be missing ;-)
(Y-axis is kW)

BTW: Don't be misguided by the duration of my charge cycle. It is relatively short because my battery health is down to 72% or so.

 

[Kesto]

You only get B5 effect after you have dropped about below 80% of battery charge . The 20% is a fine balancing act. Hence rapids get cut off at 80% charge. Its a slow trickle after that hence regen B5 will behave as B0 or somewhat nearby. Thats my understanding.

 

[ChrisMiller]

You only get B5 effect after you have dropped about below 80% of battery charge . The 20% is a fine balancing act. Hence rapids get cut off at 80% charge. Its a slow trickle after that hence regen B5 will behave as B0 or somewhat nearby. Thats my understanding.

B5 on a full battery produces an effect that's directly noticeable (and I certainly noticed when it wasn't there!) and also shows on the instrument panel, both on the power meter and the displays showing the direction of energy flow. I would say that B5 in these conditions is similar to the effect of B2 (or D if you prefer) once the battery has partially discharged - but that's just based on my 'feelz', nothing scientific .

 

[NightPHEVer]

There is a stop button?

my charger is permanently on, plugged in inside the garage with the charge cable through a slot in the door frame, car connector sits on a wall mounted holder. I just shove it in the car when parking and yank it out when I need to go, never pressed a button.

will go investigate in the morning :lol:

There's definitely a 'stop' button on the Mitsubishi supplied 3-pin plug 10amp charge cable which is to be pressed if the charge has not completed. If the charge has completed there's a red flashing light that indicates this. As far as I can remember 'stop' then doesn't have to be pressed, just switch off at the wall and disconnect from the PHEV. I couldn't say what might result from just pulling the charge plug out from the PHEV with it all still live. Presumably you've not suffered any catastrophic outcome so far though?

No 'stop' button on my Rolec 32amp wall charge point though - pressing the clicky latch that connects or disconnects the plug-in end to the PHEV switches the Rolec on or off.

 

[HHL]

There is a stop button?

my charger is permanently on, plugged in inside the garage with the charge cable through a slot in the door frame, car connector sits on a wall mounted holder. I just shove it in the car when parking and yank it out when I need to go, never pressed a button.

will go investigate in the morning :lol:

There's definitely a 'stop' button on the Mitsubishi supplied 3-pin plug 10amp charge cable which is to be pressed if the charge has not completed. If the charge has completed there's a red flashing light that indicates this. As far as I can remember 'stop' then doesn't have to be pressed, just switch off at the wall and disconnect from the PHEV. I couldn't say what might result from just pulling the charge plug out from the PHEV with it all still live. Presumably you've not suffered any catastrophic outcome so far though?

No 'stop' button on my Rolec 32amp wall charge point though - pressing the clicky latch that connects or disconnects the plug-in end to the PHEV switches the Rolec on or off.

Correct... you cannot unlatch the connector on the car without also terminating the charging process. As soon as you press the latch, this happens....that's the way it is designed. There is also a stop button on the "brick", but it really isn't needed.

As for the charging, the normal sequence for Li-Ion is an initial constant current charge and then, as the battery approaches full charge, it changes to constant voltage (4.1 in the PHEV). The initial current limit is determined by type of "brick" which communicates the maximum allowed from that particular mains supply. In Australia either 8A or 10A. We don't have the fast charge capability, which works differently (I think the new model has). Also, regenerative braking can put vastly more current into the battery than either charging method, so it must be limited severely when the battery is full or nearly full in order to protect it.

 

[Harald]

The topic has an aspect clearly beyond some recovery potential that will be lost.
Worst case would be a complete loss of braking capacity on longer downhill distances. (Not probable, but possible...)

It is a pretty bad idea having a fully charged battery before driving down a steep mountain road:

• - The regen system cannot brake as the battery is full.
  - The ICE will have no relevant braking capacity due to the lack of a low gear.
  - The only remaining braking system? 4 disk brakes that will overheat after a while...

I do not feel comfortable in a car with > 2 tons (or > 3.5 tons with a trailer) total weight with limited braking capacity...
... and will therefore pay attention to avoid having a fully loaded battery on top of a hill.

Best regards from Austria, Harald

PS:
If anybody should be in such a situation, setting aircon on maximum could be used for emptying the battery.

 

[anko]

You would have to live (or at least charge) on top of a hill. Otherwise, how would you ever achieve 100% soc at the summit?

For those that do, some cars (not ours) offer a Hill Top Reserve setting. It prevents the car from charging to 100%.

(Some say the setting is realy designed to allow you to prolongue battery life but that, for obvious reasons, it cannot be marketed this way :? )

 

[ChrisMiller]

I do live near the top of a hill - but we're not talking Zugspitz, it's about 1.5 km at 15% gradient, with the same again up the opposite side of the valley. When the car is (normally) fully charged, even B5 can't prevent it accelerating down the hill. But returning home with a depleted battery, B5 is more than sufficient to hold the speed (there's a 50 mph limit, so I can play with the regen settings to maintain the appropriate speed, and gain a mile or two of charge as well).