REX road test

[gaz26]

http://www.autoexpress.co.uk/bmw/i3/66751/bmw-i3-range-extender

A bit disappointing re noise

 

[Plug]

"It is just about possible to hear it running – the sound is of a very distant thrum"

http://www.autocar.co.uk/car-review/bmw/i3/first-drives/bmw-i3-range-extender-first-drive-review

 

[gaz26]

Autocar review more encouraging. If Auto Express comments of sounding like a lawnmower are true then may force people to think the BEv is the way to go or if you need the safety of the extra range buy a conventional car ?

 

[AndrewDebbie]

http://www.autoexpress.co.uk/bmw/i3/66751/bmw-i3-range-extender

A bit disappointing re noise

Instead, it churns into life to replenish the battery when charge drops to 3.5 per cent, which equates to a range of around three miles,

That is new. Either they got it wrong or BMW made a change.

Leaves you in an odd position -- No battery left at all when the REx starts up on automatic.

 

[Jeremy]

I think the Auto Express review is deeply stupid.

Whether or not people need the REx option depends entirely on the use they want to make of the car. I use my car every day in the city and make a few 200/300 mile trips per year - it's perfect for that use.

Saying "hold your nerve and go all electric" in my case would mean sitting on a hard shoulder somewhere for 3/4 years until BMW get their UK fast charge network established.

I also think it's odd that they commented on the noise while the car was stationary. Under normal conditions the REx motor will never run when stationary. A BMW rep who's driven one told me the noise is almost inaudible when driving - but quite noticeable standing outside a stationary vehicle. Since I'll only engage it on the motorway - I'm happy.

 

[MarkN]

Another review mentioning the range extender: http://www.whatcar.com/car-news/bmw/i3/2014-bmw-i3-first-drive-review/1216668

This one is also devoid of almost any useful information about the REx. Is BMW forbidding the press from testing REx performance?

 

[AndrewDebbie]

I wonder if this is one of those cases where the journalist just made things up. It does happen.

The autostart at 3.5 % SOC disagrees with everything else I've read about the REx.

Ditto on the noise levels.

 

[TomMoloughney]

I wonder if this is one of those cases where the journalist just made things up. It does happen.

The autostart at 3.5 % SOC disagrees with everything else I've read about the REx.

Ditto on the noise levels.

Andrew: BMW has been playing with different levels of autostart for the REx. I've talked to people that have driven then when it turns on once it dips below 5% so the 3.5% isn't much different. I know the word had been that the REx will turn on once the SOC dips below 20%, but I do believe that was not correct and that it will be much lower, like around 5%. The REx is proving to be powerful enough to drive the car and even increase the SOC up to a higher level so why not let it dip as low as possible before turning it on - more all electric miles for the driver!

 

[Jeremy]

Tom

I spoke to my local dealer rep yesterday who had just come back from a Leipzig factory visit.

He had been told there that the REx will maintain the SOC at the level when it's engaged - but not improve it.

He said this was to stop people using the REx motor as a charger.

Have you heard of this?

 

[ChrisC]

Yes, that is typical of REx drivetrains, since the Volt came out over three years ago. You just want to generate enough power to move the car down the road to your final destination, where you can plug in again. Get the electricity from the grid is FAR more efficient than from that little portable gas engine -- both in emissions and in cost. And by "far more" I mean like three TIMES more efficient, 300%.

 

[ultraturtle]

BMW has been playing with different levels of autostart for the REx. I've talked to people that have driven then when it turns on once it dips below 5% so the 3.5% isn't much different. I know the word had been that the REx will turn on once the SOC dips below 20%, but I do believe that was not correct and that it will be much lower, like around 5%. The REx is proving to be powerful enough to drive the car and even increase the SOC up to a higher level so why not let it dip as low as possible before turning it on - more all electric miles for the driver!

It is likely that we have a misunderstanding of terminology here between State of Charge (SOC) and useable State of Charge. A lithium ion battery pack can be cycled only so many times before it dies. Cycling it to near zero State of Charge drastically diminishes its useful life, and charging to near 100% does somewhat as well (although to a lesser extent.) Different EV manufacturers address this limitation in different ways. My current plug-in EV does not allow the SOC to deplete below 20%, nor charge above approximately 85% in an effort to make the battery pack last approximately forever, but taps only 65% of its useable capacity. Other manufacturers are far more aggressive, including BMW, which taps 85% of of the battery pack's 22 kwh capacity (18.8 kwh). My guess is that both the 5% and 20% numbers are accurate, and that BMW will allow (although probably not recommend) a full charge to 100% SOC and allow depletion to 15% SOC in order to protect the battery. For REx operation, it makes perfect sense for the gasoline powered generator to kick on at 20% total SOC in order to provide a 5% cushion for hill climbs that tax the electrical generation capacity greater than it's output and allow for recharging to that 20% mark. 15% minimum total SOC plus 5% trigger SOC equals the oft quoted 20%. Interestingly, that 5% of total SOC is pretty close to 4% of useable SOC, making all 3 numbers (20%, 5%, 3.5%) look about right to me.

 

[stef007]

Found some interesting youtube videos regarding the rex and its noise (German speech, no English)

Rex running while car stopped and SOC probably less than 3.5%:
http://www.youtube.com/watch?v=fco8eRC4PKc

dB Noise measurement:
http://www.youtube.com/watch?v=yUshzxIvel0

Running on Rex alone (low battery) and up-hill:
http://www.youtube.com/watch?v=ohZ0M5-UJfw

You can check also his other videos:
http://www.youtube.com/user/MrElectricVehicle?feature=watch

Greets