I'm curious about how the IMA battery charges. Is regenerative braking the only way? i.e. if the battery is low, must you be in motion to charge it? If that is the case, then it's better to be going highway speeds, right?

I've only had forced regen kick in twice, and both times I was on the highway, so I got about 4 bars of charge.

Thanks!

 

has anybody ever have the battery fully charged...all light lit up?

 

Yes, on highways.

 

All my lights have been lit up before but after a lot of freeway driving. It has not been fully lit when I do mainly city driving, its usually half way full.

 

All eight of my bars were lit this morning. I took special note of this, because it seems my car always does a forced regen on my ride home in the afternoon. If the battery is FULLY charged now, there shouldn't be a need for the regen in the afternoon... unless something is draining the battery during the day.

By the way, during the forced regen on the highway, it usually appears as only one green bar... but it's still a significant load. Once it goes away, you can feel a noticeable surge, and the MPG goes up by approx. 5.

 

I had all eight of my bars lit up after driving several miles down a canyon. I was still getting regen for a while after all eight bars, but, at some point, this completely stopped and I was getting no regen at all.

 

Yes, every day. As we drive down the hill from our house (800 ft elevation) the battery gets to a full charge before we get all the way down the hill. It gradually goes down from 4 bars of regen to 3, 2, 1 and then none, and we have to brake the rest of the way down.

 

Like Anahymbrid, I see forced charging on the way up, and a full pack on the way down. Translation: If I could only tell the dumb system not to charge on the way up and waste engine power when I need it most, then it would be able to replenish more on the way down. Driving with so many hills also puts me in a fairly precarious situation, my car's mileage is very sensitive to battery state of charge. If I deplete my battery earlier in the day by driving in traffic or around parking lots (where I should be able to run with IMA disabled if I wish), then I see large drops in efficiency due to the additional load for a long time thereafter. This is why I speculate a few switches, even a basic IMA on/off (trick the BCM into thinking I'm in neutral?), would allow me to improve my efficiency 5%+ on every tank.

If the battery is near zero capacity, it will actually fast-idle to charge the battery when you're stopped. I once ran out my 12v battery accidentally and the computer had to do this to calibrate the state of charge on the 144v pack. (Odddly enough that impoved my MPGs a lot -- I suspect the real battery capacity and the computer had been out of sync for a while)

 

No. You also have hidden charging.
If the SOC is less than "normal" full- then the ICE works to recharge the battery, although no bars are visible. The charging is "hidden"
No. As long as the ICE is running it will recharge, even if not moving.
Better compared to what?
While idleing charge happens more slowly.
I haven't noticed any increase in the charge rate from about 40 to 60, given the distance traveled.
I believe charge rate also depends on temperature data from the battery.

 

re: is it better to have regen at hwy speeds...

Like using AC, the hit to FE as a % is lower when at high speed because the fraction of 'more power' needed is a smaller percentage of what it can/is already making.

The absolute increase in fuel usage is the same either way; its just that your instant FE number will look harsher at low speed than at high speed when the regen hit occurs.