battery fully charged...regen overcharge?

Sorry if this has been answered before...I searched but did not find a clear answer. Two weeks into i3 ownership and I'm scratching my head about something.

I live at the top of a long hill. I leave my house at 100% charge and proceed down for about 1mi/2km and lose 1000 ft/300 m of altitude.

What is happening with the regen energy? Am I filling reserve capacity in the battery? Is it getting bled off into some resistor? Is the motor actually running and the car is automagically using brakes to simulate regen?

Obviously, I'm worried about either damaging the battery or wearing out brakes.

Thanks!

When your fully charged, regen is disabled/reduced, friction break is used to make up the difference.

I don't think so.

The i3 has reserve capacity in the battery. If you charge on top of a hill and run down the hill you will notice your range increases. I live on top of a 300m hill and I see this every charge. This is one of the reasons the i3 battery is limited to 18.8kWh capacity when the actual battery capacity is closer to 22kWh.

When you are close the maximum available capacity, regen is reduced and friction break is used. The battery never gets anywhere above 19.4kwh (I have observed this going to down a fairly steep incline, using the service menu max capacity read-out)

You can also hear the friction brakes being used, in those sort of conditions

I33t said:

I don't think so.

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You may not think so, but the fact is that i3 uses friction brakes instead of regen when the battery is full. I experience this every morning when I leave home for work. First few stops and you can clearly hear how pads are grabbing disks up front.

Two good things going on though:
a) this behavior is transparent. untrained driver will have no idea whether regen or brakes are used, the deceleration is the same. Which is huge safety plus in my mind (compare that to leaf where with full battery it just coasts)
b) as soon as there is any space for fresh electrons the car returns to regen. Again huge improvement vs. Leaf where you need to drive several miles to regain any useable regen.

Either way - if you live on top of a hill it would be best not to charge it to 100%. Otherwise you're wasting energy using friction brakes going down.

I live on a hill and I have always wondered why often the first stop or two felt different. The brake Regen has a coarser feel than the smooth effect you get from the electric Regen on those first stops. I can go either uphill or down to leave my neighborhood and if I start out uphill the Regen acts as normal since I have lowered the SOC by climbing the hill to the first stop. Going downhill the first stop is noticeably different perhaps due to the brakes having a layer of rust since they rarely get used.

I would be nice if this emulation of Regen could be also be used when the traction control cuts the electric Regen out when slowing over bumpy pavement. I am assuming that the emulation is using all 4 brakes instead of just the rear wheels like the electric version although it could be limited to the back brakes only. Anyone know?

I would think the battery charge indicator would be the final word as to whether all or some part of braking is regen vs pad to metal

I always thought that part of the battery above the 18.8 usable was off limits to any form of charging. What would happen if you drove down Pikes Peak every day with a full battery in regen mode? It could charge well beyond the 18.8 and wreck the battery

Ron

Anecdotally my i3 charges to 19.4 max kappa according to service menu, when preconditioning. But supposedly the usable capacity is 18.8kwh - I tend to see this when not preconditioning.

I think its fair to say the software is designed to manage the pack to around 18.8kwh, whether thats charging or regen.

Tomasz said:

I33t said:

I don't think so.

Click to expand...

You may not think so, but the fact is that i3 uses friction brakes instead of regen when the battery is full. I experience this every morning when I leave home for work. First few stops and you can clearly hear how pads are grabbing disks up front.

Two good things going on though:
a) this behavior is transparent. untrained driver will have no idea whether regen or brakes are used, the deceleration is the same. Which is huge safety plus in my mind (compare that to leaf where with full battery it just coasts)
b) as soon as there is any space for fresh electrons the car returns to regen. Again huge improvement vs. Leaf where you need to drive several miles to regain any useable regen.

Either way - if you live on top of a hill it would be best not to charge it to 100%. Otherwise you're wasting energy using friction brakes going down.

Click to expand...

I can hear the brakes because the discs have surface rust, I hardly ever use them. The car gains pretty close to the same amount of extra range going down the hill whether I leave with a full charge or a half charge. You may be correct, but the evidence in front of me does not seem to support your suggestion.

How do we get into the service menu to display the SOC?

I33t said:

How do we get into the service menu to display the SOC?

Click to expand...

Don't answer that, I found it.

13.08 Batt.Kappa.max: 19.2 kWh
13.09 Batt.Ladung: 60%
13.10 Batt.Ladung: 10.5 kWh

Hopefully get a chance to drive to a certain spot and measure the regen, then repeat with a full charge. Will report back when completed.

Assuming the i3 regen is similar, the vw e-golf owners manual states there's no regen if the battery is fully charged and reduced regen if it's above 85%.

Can the i3 regen be turned off, as with the e-golf? I've concluded if maximum range is crucial, one should drive with no regen, coast as much as possible, only using the brake regen for the last 10-20% if that. This makes sense by thinking the extreme case of never using the brake. If you never use the brake, it means you never had to accelerate more than necessary in the first place. Thus total energy is minimized, since regen can only recapture a fraction of the energy expended to accelerate, although more time may be required

It would be interesting to know how much additional range one could squeeze out driving this way. Is it enough to make it worthwhile? It seems like it would be highly dependent on the regen efficiency number

Ron

cove3 said:

Can the i3 regen be turned off, … ?

Click to expand...

Not by the driver.

It is easy to coast in the i3...the go pedal has a range of functions from max power through coasting to max regeneration...all you have to do is manage your foot to coast. So, the choice is yours - the range is linear through all functions from max go to max regen and coasting at one point somewhere in the middle of the pedal movement - just watch the dash display, and once you see that and feel what it's like, you can hit it without looking.

+1

Turning off regen seems a strange idea to me, I don't think I have driven any car anywhere that has not required me to actively slow down at some point. If you turn off regen then the energy is transferred to heat in the brakes instead of energy in the battery. How are you going to get more range doing that?

In the e-golf driving in D mode with no regen, when you hit the brake, it regens. You can see the energy gauge go into the red zone showing the battery being charged during braking. The brake pads actually hitting metal only occurs during emergency stops or if the battery is already fully charged.

Using one of the 4 regen settings is more for the convenience of not having to constantly move your foot from the gas pedal to the brake and back, but you will lose some range as you give up coasting to slow down. The most efficient driving mode which will get you the most range and mpg is anticipating and coasting and with minimal regen via braking only near the end, But it's not the most fun or time saving method

Ron

REgen only when using the brake pedal would make the transition between an ICE and a BEV maybe cleaner, but I have had no issues after the first day or so going between my ICE and my i3. I rarely use the brake pedal on the i3. And, the car is smart enough to use the brakes when required to avoid overcharging the battery during the process.