How does a full battery accept regen braking energy?

[Nathan Steele]

My commute starts out going down hill immediately for two miles and the regen circle twirls the whole time even though my battery is full. Where is that juice going? I make a point of not using any accessories so I don't think I'm using up all that juice as it's being generated. Is the battery underutilized when new (e.g. 80% capacity) and gradually used more over the life of the vehicle (eventually 100%) to maintain a constant range on an aging battery like the Chevy Volt does? If so it would be a tempting hack target.

[Gigi]

I'm interested in hearing from an expert on this.

 

My experience of "Where is that juice going?" is that it doesn't seem to be going anywhere. 

 

Less than a quarter mile into my drive out of my neighborhood is a steep hill going down to a creek and then steep back up the other side.  Driving our Focus Electric, if I put the shift lever in L going down the hill, it will hold the car's speed for a short distance and then it is as if the car goes into "free fall" and I need to press the brake pedal to keep the speed down.  In the Fusion Energi, putting the lever in L going down the same hill, I have had the ICE come on to brake the car.  This suggests to me that when the battery is up to a certain state of charge, it will no longer accept incoming current and regenerative braking is turned off.

[murphy]

That is correct.  If the battery is full the ICE will run in air compressor mode to hold back the car.  It is not actually running and uses no gasoline when doing this.

[Gigi]

That is correct.  If the battery is full the ICE will run in air compressor mode to hold back the car.  It is not actually running and uses no gasoline when doing this.

Thanks, murphy.  That's what I thought.

 

What happens next in my experience is that once the ICE is on, it stays on for a couple of miles, perhaps to warm up and cycle the oil to keep it fresh.  I have taken to just using the brakes going down that hill when the Energi is fully charged so that the ICE stays off altogether.

[frbill]

What happens next in my experience is that once the ICE is on, it stays on for a couple of miles, perhaps to warm up and cycle the oil to keep it fresh.  I have taken to just using the brakes going down that hill when the Energi is fully charged so that the ICE stays off altogether.

 

I sometimes forget that the ICE will come on and at the bottom of the hill shift to L. Then I go DOH and suffer the EV% penalty while the ICE warms up.

[Neil]

I have wondered the same thing - another question I have is when the EV battery is expended and the Hybrid system comes on, if the regen system generates more power then the Hybrid battery can hold (already at 100%) will it go to the EV battery?  For example, my route home from work has a mile long section of a fairly steep downhill grade.  It just so happens that downhill grade starts right at the normal limits of the EV battery. If i drive carefully I can sometimes make the grade before the Hybrid system comes on (the EV battery range showing 1 or 0 miles) and using the regen system I can up the EV battery range by a mile or two.  For example, I hit the grade with 1 mile showing on the EV battery, and by the time I get to the bottom the EV range shows 2 or 3 miles. 

 

My question is, if the Hybrid mode kicks in right as I reach the grade, will the power generated by the regen system go to the EV battery since the Hybrid battery is at 100% or is it simply lost. Which brings up another question - The first law of thermodynamics states that energy is neither created or destroyed - so where would the energy from the regen go if the battery can't store it?  Heat? 

[murphy]

It will go to the EV battery.  There is only ony battery.  The hybrid battery is a reserved portion of the whole battery.  There is a thread on the forum describing a complete recharge of the EV battery coming down from the top of Pikes Peak in CO.

[Neil]

It will go to the EV battery.  There is only ony battery.  The hybrid battery is a reserved portion of the whole battery.  There is a thread on the forum describing a complete recharge of the EV battery coming down from the top of Pikes Peak in CO.

Cool!  I wondered if it was just one battery.  That makes sense.  

[jeff_h]

Note from my trip where it went from hybrid mode up to 9 miles... and yes I remember that someone got theirs back up to full, don't remember which person it was...

 

http://www.fordfusionenergiforum.com/topic/1179-once-the-charged-hvb-is-drained-its-stuck-in-hybrid-mode-not-really/

[viajero]

Which brings up another question - The first law of thermodynamics states that energy is neither created or destroyed - so where would the energy from the regen go if the battery can't store it?  Heat? 

 

Yes, heat.  All the potential energy lost to going downhill, or kinetic energy lost to slowing down, ends up as heat if the battery can't store it.  If using engine braking, the compression of the air in the cylinders heats up the engine block and the heat is dissipated through the radiator just like the heat from burning gas when driving.  If using friction brakes, the brake discs and pads heat up and dissipate that heat into the air.

[Gigi]

My experience of going downhill in my Focus Electric in L with a full battery and feeling the car go into "free fall" suggests to me that the electrical resistance of the motor/generator was turned off when the battery was back up to capacity.  The brake pads would have clamped the rotors then to slow the car making heat and creating brake dust.  Yep, energy always goes somewhere.

[gerdia]

It will go to the EV battery.  There is only ony battery.  The hybrid battery is a reserved portion of the whole battery.  There is a thread on the forum describing a complete recharge of the EV battery coming down from the top of Pikes Peak in CO.

One?! I was told at the dealer it had two, is this the reason why,  that when I go into hybrid mode the battery level (hybrid) is at half? i can never seem to bring that up to full, again, while driving in hybrid. the battery display does change from EV to basic.

Great forum, learning some stuff here, thanks everyone for all your inputs.

 

Gerry

[Gigi]

One?! I was told at the dealer it had two. . .

Typical.  Often, you will find better information here than at your dealer.

 

As I understand it, there is one battery and the vehicle merely switches from EV to hybrid mode when the battery reaches a certain state of charge.  I don't think it is like a hard drive on a computer that is partitioned into different "drives" that are actual physical sections of the disc.  Somebody correct me if I am wrong about this, please.

 

With enough downhill driving, I have seen my battery indicator reach the top when driving in hybrid mode.  Others here have seen the indicator switch back to EV mode and seen miles increase on the indicator with very long downhill drives in the mountains.

[SteveEnergi]

It is only one battery and I'd say you could consider the battery "partitioned".  n number of cells are probably reserved for hybrid driving, unless they're reserving a percentage of the battery for hybrid driving.  Either way, it probably doesn't matter as it is just one high-voltage battery for EV driving.  The only "other" battery is the 12volt, and that battery isn't used for propelling the vehile.

[seadiel]

From my personal experience, when the car switches to hybrid mode and then you go down a long steep hill. I have noted it will display a full blue bar and then if enough is captured it will switch to where it displays the # of miles left. If you captured enough energy it will only switch over when you have captured at least 1 mile worth of energy.

[Apogee1]

Trust me the on-board systems of the car is consuming more energy than the regen braking system is returning to the system.  While it may seem as though that energy has no place to go, it is going back into the battery pack.  This is very evident in my Leaf, which is 100% EV, and I can tell you from experience that when you car is on, it uses more energy than the regen system can put back even going down hill, and the Leaf has regen coasting plus regen braking adding to the battery. Something I wished the Energi had.  

[murphy]

The Energi has regen coasting if you drive in L.

[Russael]

The Fusion Energi does have regen coasting.  I drive with the energy flow arrows on the top/bottom of the battery level indicator.  If I'm not using climate, or if the climate is only maintaining temperature, when I take my foot off of the accelerator, it shows that power is flowing back in to the battery.  This is just in D mode.  L mode is significantly more aggressive.

 

However, if you start off with a fully charged pack, put it in L, and then drive down a steep hill, the ICE will come in in 'air compressor mode' to provide engine braking.  If the battery pack is fully charged, regen just stops working in certain driving modes.  it doesn't have a waste mode like a railroad locomotive when it uses the traction motors for braking.

 

The Fusion Energi's regen system is VERY good and people have said that they've fully recharged their packs going down a tall mountain. 

[Apogee1]

The Energi has regen coasting if you drive in L.

 

Well if this is the case, I'm a bit happier now.  most of the information I read about it said it didn't have it, and the sales rep also indicated it didn't have it, and he was a certified Engeri sales rep. For me this is good news!

[murphy]

When driving in L the car decelerates rapidly when you take your foot off of the accelerator pedal.

The downside is you are slowing down without the brake lights being on to warn the driver behind you.

At least I don't think they are on.  Has anyone tested this?

[Apogee1]

The downside is you are slowing down without the brake lights being on to warn the driver behind you.

 

 

This isn't an issue, been driving like this with my Leaf for over a year, and the lack of no brake lights has never once been a problem. 

[Apogee1]

Ok, just did a full range of testing, and read the manual just to make sure, and I was right all along.  There is no always on coasting regen on this car.  Driving in L only does engine compression braking, but no Regen.  Having the grade assist option turned on does allow for regen, but ONLY if "the vehicle determines the amount of engine motoring and high-voltage battery charging".Ref., Page 166. This means that unless you are going down a grade of less that 5%, there will be no Regen coasting unless the car determines that there will be.  On level grade no Regen at all.  I just tested my car on all the conditions except for steep downhill (in the Dallas are we have none of that). 

 

L - Engine compression braking.  No Regen arrows or of energy into battery.

D with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.  

L with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.

 

For reference, please see Page 166 of the owners manual for this.  Disappointed again.   :(

[Russael]

Ok, just did a full range of testing, and read the manual just to make sure, and I was right all along.  There is no always on coasting regen on this car.  Driving in L only does engine compression braking, but no Regen.  Having the grade assist option turned on does allow for regen, but ONLY if "the vehicle determines the amount of engine motoring and high-voltage battery charging".Ref., Page 166. This means that unless you are going down a grade of less that 5%, there will be no Regen coasting unless the car determines that there will be.  On level grade no Regen at all.  I just tested my car on all the conditions except for steep downhill (in the Dallas are we have none of that). 

 

L - Engine compression braking.  No Regen arrows or of energy into battery.

D with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.  

L with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.

 

For reference, please see Page 166 of the owners manual for this.  Disappointed again.   :(

 

You need to turn the charge assist arrows on if you want to see it in action.  Page 85 of the manual (My page numbers are from the 2013 manual):

 

Display -> [Your Display mode: IE Inform, Enlighten, etc] -> Battery Display -> Charge Assist -> Yes/No

 

[Page 78] Charge Assist — An arrow above the battery indicates the battery is being charged;

an arrow below the battery indicates that battery power is being used for propulsion

or to power the vehicle accessories.

 

Page 178 describes the regenerative braking system as well.

 

Even if the arrows aren't enabled, the car continues to capture coasting energy and braking energy and stores it in the battery.

Edited March 22, 2014 at 11:51 PM by Russael

[JATR4]

Ok, just did a full range of testing, and read the manual just to make sure, and I was right all along.  There is no always on coasting regen on this car.  Driving in L only does engine compression braking, but no Regen.  Having the grade assist option turned on does allow for regen, but ONLY if "the vehicle determines the amount of engine motoring and high-voltage battery charging".Ref., Page 166. This means that unless you are going down a grade of less that 5%, there will be no Regen coasting unless the car determines that there will be.  On level grade no Regen at all.  I just tested my car on all the conditions except for steep downhill (in the Dallas are we have none of that). 

 

L - Engine compression braking.  No Regen arrows or of energy into battery.

D with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.  

L with Grade Assist - Level and downhill test produced no Regen arrows or energy back into the battery.

 

For reference, please see Page 166 of the owners manual for this.  Disappointed again.   :(

 

We must be reading a different manual.  Here is what I found on pp 172-173.  I read it to say that there is regenerative braking--if needed--whenever the accelerator pedal is released.

 

Brakes

 

When you release the accelerator pedal or press the brake pedal, the brake controller automatically detects the amount of deceleration requested and optimizes how much of the deceleration will be produced by regenerative braking. The remaining portion is generated by standard friction braking. When the battery is almost fully charged, the amount of regenerative braking is limited to avoid overcharging, and the requested deceleration is produced by standard friction braking alone.  Regenerative braking does not take the place of the standard friction brakes: it only assists them. Regenerative braking has also been designed to interact with the anti-lock brake system. Regenerative braking is disabled when the anti-lock brake system is activated or the battery is fully charged.

 

Regenerative Braking System

 

This feature is used to simulate the engine braking of an internal combustion engine and assist the standard brake system while recovering some of the energy of motion and storing it in the battery to improve fuel economy. The standard brake system is designed to fully stop the car if regenerative braking is not available.  During regenerative braking, the motor is spun as a generator to create electrical current This recharges the battery and slows the vehicle. In effect, once the accelerator pedal is released, the motor changes from an energy user to an energy

producer.

Edited March 23, 2014 at 12:12 AM by JATR4

[murphy]

Why is the engine on?

Set the car to EV only mode.

Get up to 35 mph.

Take your foot off of the accelerator and shift to L.

Does your car not slow down in a hurry?

The battery can not be completely full or there is no regen braking.