Charge/ePower display with Rex running, and Rex not stopping

[MarkN]

When the Rex is running, does the current coming from the Rex affect the indicator on the Charge/ePower display directly in front of the driver? We had an i3 Rex for 24 hours for an extended test drive and I intentionally ran the battery down so that the Rex was engaged while I drove on I-25. I was hoping to find out how fast I could drive on a level section of the interstate without exceeding the Rex' power by modulating the accelerator so that the indicator on the Charge/ePower display was exactly in the center. But I slowed down almost to 60 (the speed limit is 75 and 60 seemed dangerously slow) and the indicator remained to the right of center in the ePower region. So either the Rex power is worse than I thought or the indicator doesn't take the power from the Rex into account. I certainly hope it is the latter.

Earlier in the test drive the Rex came on for the first time about a minute before I got home. I pulled into my garage and pressed the Stop button to turn off the car, but the Rex kept running. I tried pressing the Stop button a few more times, and then got out of the car, but the Rex stayed on. Finally several minutes later it shut off. Was this because the Rex was in its six minute warm up cycle? This seems dangerous--I wasn't in a hurry so I could leave the garage door open until the Rex stopped, but what if I had to close the door? Is there some way to force the Rex to shut off, short of pulling spark plug wires?

 

[WoodlandHills]

The only way to get the indicator to stay in the middle is to coast, that is, to emulate a conventional car in neutral. Unless you are descending a hill, the car will slowly decelerate with the acellerator pedal in that position.
I do not know of any reasonable method of shutting the REx down before it is ready to do so on its own. I suppose one could start pulling wires, but it would probably shut down by itself by the time you got access to the REx.

 

[Tomasz]

Are you 100% sure that the REx stayed on? There is a fan that stays on for about 5 minutes after you shut it down, but it never happened to me that the REX itself stayed on when the car was off no matter when it came on.

 

[jadnashuanh]

The REx has more than one programmed speed (and therefore current output capability), and will adjust itself to try to maintain the current SOC, if it can. IOW, your test probably didn't tell you much of anything. You'd have to be watching the battery SOC, which, on the REx (available on the BEV probably in the next s/w update) is available to be shown as a number, verses just the bar graph to see what is going on.

There is also a graphic you can call up that shows how power is being used. I dont' have a REx, but have heard it can show you the power flow including the REx. That, if it is implemented as I think it is, would show whether there was power coming out of or going into the batteries.

As I understand it, it won't go to max output unless you are above 56mph or so, but may not, if it is not needed based on current conditions (say you're coasting down a hill).

Think of it this way...when your batteries are nearly down to SOC 0, you are running a car with a max of 34Hp, smaller than many motorcycles out there and pretty much any car sold in the USA...there are limits on what you can ask the vehicle to do once you get to that point. Your goal should be to avoid getting into that situation, easier as implemented outside of the USA. Cruising at rational speeds on the level, the REx can keep up and probably recharge the batteries some in the process; power required goes up radically with increases in speed from drag and creature comfort.

 

[MarkN]

Are you 100% sure that the REx stayed on? There is a fan that stays on for about 5 minutes after you shut it down, but it never happened to me that the REX itself stayed on when the car was off no matter when it came on.

At least 95% sure. There was no change in the sound when I pressed the start/stop button. I got out and walked to the rear of the car and it definitely sounded like an engine.

 

[Tomasz]

At least 95% sure. There was no change in the sound when I pressed the start/stop button.

That doesn't mean a thing, the fan works steady, no change in RPMs either.

I got out and walked to the rear of the car and it definitely sounded like an engine.

In that case make an appointment with BMW asap. The only case I can see the engine running that long if the SOC was in the very low range (below 1.9%) but you've said it turned on mere minute before you arrived. Even with strong uphill it shouldn't drop below 4-5% within a minute after it kicked in at 6.5%.

 

[MarkN]

At least 95% sure. There was no change in the sound when I pressed the start/stop button.

That doesn't mean a thing, the fan works steady, no change in RPMs either.

I got out and walked to the rear of the car and it definitely sounded like an engine.

In that case make an appointment with BMW asap. The only case I can see the engine running that long if the SOC was in the very low range (below 1.9%) but you've said it turned on mere minute before you arrived. Even with strong uphill it shouldn't drop below 4-5% within a minute after it kicked in at 6.5%.

This was on a test drive, so it isn't my car. I'm not likely to buy the particular one I drove since it lacks two of the options I want.

 

[jadnashuanh]

The REx is a 34-HP engine. Depending on how you are driving the car: the speed, headwind, slope, options running, the load; you could exceed the power draw from the thing and be drawing down the batteries. Consider that the electric drive motor is a 170-Hp device...a 34-Hp engine could never produce 170Hp, and something has to give (and it's the batteries). This is why, if your batteries are drawn down too far and you ask the car for more than you can be putting into it, the battery management logic will prevent drawing down the power from them, and you're essentially then running with a 34-Hp (well, less, since there's a conversion loss going from torque into the generator verses power out) motor...When was the last time you drove a car with a 34-Hp engine? Probably a very long time, if ever (think original VW Bug, or maybe a 2CV). The REx can keep up, but not at high speed, especially if charging up a grade - it may even be able to bring the battery SOC up some, but it all depends on how much you're using. It's a tradeoff...bigger engine, more weight, lower efficiency, probably needing bigger gas tank, bigger brakes, heavier suspension, etc., which again, means more weight to pull around. It's a fine balance, and the optimization was to treat the car best for running around town, and that doesn't require enough engine to do that at 70mph going uphill with all of the creature comforts running for extended periods...short term, okay, but not extended.

 

[Tomasz]

The REx is a 34-HP engine. [...] short term, okay, but not extended.

And what does all of the above have to do with the REx not turning off in the garage?

 

[BrianStanier]

I would say it was the fan. It is quite load, especially in a confined space.

 

[roofless]

I had the same experience with REX fan staying on while the car was charging, and I agree it was pretty loud and I was reluctant to close the garage door. I went back to check after 10 minutes or so, and the fan was off.

However, the next morning, the car was still charging (L1 occasional use charger), and the fan was on again, but not as loud as the evening before. Has anyone else had this happen? I disconnected the charger and the fan stopped.

 

[justanotherdrunk]

im purposely driving the batteries down so that the rex will burn the gas down to near zero


and then put fresh gas in

dont know how long the gas was sitting there on the lot before i got it


havent noticed the rex coming on while stopped

 

[justanotherdrunk]

Verified today:

The REX engine running sound

vs

The REX engine stopped and fan running sound



are completely different and would never be confused