How REX works?

[smoger]

I saw the article that REX was turned on even there's 30~40% battery capacity.
But i also saw in this forum that REX turned on at 6% of capacity. Which one is true??
If the REX engages at low SOC(state of charge) level, such as 6%, it is somewhat dangerous.
Theres amounts of heat increases in battery and it reduce the life.
I'm wondering that if the SOC starts from 6%, the SOC at end of driving is also 6%? or more higher?


and, Anyone know how the REX works? one thread insist that theres only 3 different output power level.
Is this a official? or just the owner's opnion.

 

[i3burlington]

I was interested in the Rex but am now probably going bev due to the battery strain that the deep cycles would cause

In USA and canada, we can't manually turn on the Rex
In Europe it can be engaged anywhere after 70% charge remaining

Deep cycles drastically reduce the battery life
It will be interesting to see in a few years what effect the deep cycles of the Rex cause in real life

 

[TomMoloughney]

The 6% threshold is of the usable capacity, not the packs overall capacity. There is a buffer already there for safety purposes and to prevent deep discharge damage. So when the REx turns on the battery is probably really at around 12% to 15% capacity.

I've driven over 140,000 electric miles in BMW's e-mobility pilot program and purposely ran my cars till they just about stopped moving dozens of times and probably plugged in with the usable SOC less than 5% sixty or seventy times. The capacity loss I experienced was about what I would expect it would be even with being cautious about deep discharges, which was about 3% to 3.5% every 15,000 miles.

Personally I wouldn't even consider worrying about the 6% SOC activation point of the i3 REx unless perhaps you would be driving so many miles that you'd be activating it every single day. Even then unless you lived in a very hot region where the battery temperatures would always be at elevated levels you probably would have very little noticeable advanced degradation compared to another car that didn't get driven to the 6% low limit often.

It's actually much worse if you fully charge the car to 100% and let it sit for long periods of time without use (weeks).

 

[fdl1409]

True, 6.5% SOC is far away from deep discharge. The car doesn´t permit deep discharge at all and will shut down much earlier. With my Mitsubishi i-MiEV, I have run the battery down close to zero many times. After 15 months and 11.000 miles, I could not detect any reduction in range, rather felt the opposite.
I have more faith in my i3 batteries now, don`t believe range reduction will ever be a problem to me.

Even more, the REx will keep the SOC at 6.5% whereas a BEV can be discharged to 0% SOC. And if you are a long distance driver, the REx will supply a decent percentage of your mileage, thus reducing the amount of power burdened on the battery. Fewer cycles, longer life. What will you do with a BEV instead? Frequent rapid charges are probably worse for the battery. Worst of all is heat, and the i3 battery is protected against that by active cooling.

I also believe that it is no problem at all that the REx starts no earlier than 6.5% SOC. As far as we know you can drive almost without limit as long as you fill it up and don´t let the REx run dry. In normal speed and driving conditions the SOC will stay close to 6.5%. If you want to deplete the rest you really have to drive very fast - more than 80 mph for a significant distance - or go up a very long and very steep mountain. Even then nothing will happen, only speed can be reduced.

Did we read any reports about problems with the REx yet? Don´t expect any.

Frank