REX driving issues

[gaz26]

http://transportevolved.com/2013/11/27/bad-news-as-bmw-i3-gets-only-4-star-crash-test-rating-poor-drive-report/

 

[Stevei3]

Hi Gaz,

I guess you are not too pleased @ the moment. But do bear in mind the that the journalist in the original Telegraph article tried his hardest to run down the battery beyond its power reserve. For the right journalistic purposes one has to agree (although I don't like the 'tone' of the article), but isolating the 'run-flat' experience from its context, like in the article you linked, is a highly tendentious way of making headlines IMHO.

Steven

 

[kentheteaman]

but isolating the 'run-flat' experience from its context, like in the article you linked, is a highly tendentious way of making headlines IMHO.

Steven

Hi Steven,

I agree.
When the journalist started to his destination 70miles away - he only had 49miles charge remaining. Then he used all the electrical things like windsheild wiper and heating etc which brought down the charging even further.

So he only managed 45miles when his batter ran out to 5kwh charge. Then the Rex kicked in to the rest of his journey.

So he was driving back with 5kwh charge in his battery and Rex running, when he encountered a sudden loss of power and the car slowed down for few mintues(Probably when the charge felldown even low below 5kwh). We need to remember that the Rex only maintains the state of charge and it DOES NOT charge the battery.

So the car slowed down and recovered with in few minutes and he was able to regain his speed.

Having sais all that, his review of the i3 was still very possitive and he was very happy with its quality of drive. He was only pointing out the restricted range of all the EVs provide that inculdes i3.

Realisticaly speaking if we get 70miles on battery and another 60miles on Rex which will be 130miles range which is far enough for most of our regular driving needs.

 

[TomMoloughney]

If you understand how it works and are reasonable with how you drive it while in range extender mode, you won't have any issues getting wherever you need to go. The REx isn't a "go anywhere, under any condition" driving option. It's an auxiliary power unit who's primary purpose is to extend your electric range a bit to get to the next destination so you can plug in and recharge. You can of course by driving carefully, continue to drive hundreds of miles without an issue if you need to, but that's really not the primary function.

That being said, you can intentionally overwhelm the range extender if that is what you purposefully try to do, which is what I believe what was this journalists goal. I'm not saying he was doing so to discredit the i3, perhaps he just wanted to see what would happen if he continued to drive faster than the recommended speed while the state of charge was obviously declining. This will probably never happen in real life, as long as the driver understands how the REx works and how to prevent overwhelming it. You simply slow down to 60 or 65mph for a couple minutes if you see the SOC dropping down near zero and the REx will then be able to get the SOC back up to a safer level.

 

[Jeremy]

Ken

I've read the Telegraph piece twice - but I can't find where he said he only had 49miles range left at the start of his journey.

I thought he said he started with a full charge.

Obviously this makes a huge difference to the outcome - can you point me to the "49 mile" reference?

 

[Stevei3]

Hi Jeremy,

the 49 miles is a quote from the accompanying video. You can also watch the video on Youtube:

http://www.youtube.com/watch?v=fmfb8Mt5qvE

Steven

 

[Bunter]

Speaking of Telegraph reviews, in the earlier one on the electric only i3 Andrew English says you can buy a Nissan Leaf for £11k. Is that right? He must be comparing new prices with second hand prices.

Bill

http://www.telegraph.co.uk/motoring/car-manufacturers/bmw/10409074/BMW-i3-review.html

 

[kentheteaman]

Ken
Obviously this makes a huge difference to the outcome - can you point me to the "49 mile" reference?

Hi Jeremy,

As steven pointed out, it is in the video part of the review
http://www.youtube.com/watch?v=fmfb8Mt5qvE

At 0:47 - 0:51 he says that.

regards,
ken

 

[Jeremy]

Thanks Ken & Steven for the 49 mile reference.

Why did he say "fully charged" in the written piece I wonder.

Sound like he was planning for a range problem doesn't it?

 

[kentheteaman]

You simply slow down to 60 or 65mph for a couple minutes if you see the SOC dropping down near zero and the REx will then be able to get the SOC back up to a safer level.

Hello Tom,

Would have all the specifications of Rex engine - how to use, when to switch it, when not to use it ect.... That will be helpful.

regards,
ken

 

[TomMoloughney]

You simply slow down to 60 or 65mph for a couple minutes if you see the SOC dropping down near zero and the REx will then be able to get the SOC back up to a safer level.

Hello Tom,

Would have all the specifications of Rex engine - how to use, when to switch it, when not to use it ect.... That will be helpful.

regards,
ken

Hi Ken,

The range extender is a 650cc two-cylinder gasoline engine developing 34 hp (25 kW). It will automatically turn on when the state of charge dips below approximately 5% and it will hold the charge at that level (it doesn't increase the state of charge so you can't use it to actually charge the car). On European models you can manually turn it on once the state of charge dips below 75%. The reason you may want to do that is to hold the state of charge at a level higher than 5% if you know you'll need a lot of power later to say, climb a mountain or if you are going to be driving in a zero emission zone and want to keep from depleting your charge before you get there.

In the US however, we can't manually turn on the range extender unfortunately due to regulatory compliance. Basically the government wants to make certain the i3 is driven in all electric mode as much as possible, so it restricts the ability of the owner to be able to turn it on early. BMW can ignore this rule of course, but then the car may lose privileges like carpool lane access and tax exemptions in some states and BMW won't get as many Zero Emission Credits per vehicle sold as they would by restricting the range extender.

 

[Jeremy]

Sounds like an opportunity for a freelance software hack.

In the consumer electronics industry it's common for products with identical hardware to offer different capabilities in different countries for marketing reasons.

I remember a Sony video camera that hard certain input/output facilities disabled in European markets - although they could be restored by a "illegal" software download from a US source.

Similarly, my Lexus has a stupid safety feature that prevents the satnav being reprogrammed, or the main phonebook accessed, on the move - even for a passenger.

I believe there's a published hack for defeating this - although I haven't risked it.

Time (and human ingenuity) will tell!

 

[kentheteaman]

Hi Ken,

The range extender is a 650cc two-cylinder gasoline engine developing 34 hp (25 kW).......... quote]

Thank you, Tom.
Very useful as always.

regards,
ken

 

[Sranger]

Sounds like an opportunity for a freelance software hack.

In the consumer electronics industry it's common for products with identical hardware to offer different capabilities in different countries for marketing reasons.

I remember a Sony video camera that hard certain input/output facilities disabled in European markets - although they could be restored by a "illegal" software download from a US source.

Similarly, my Lexus has a stupid safety feature that prevents the satnav being reprogrammed, or the main phonebook accessed, on the move - even for a passenger.

I believe there's a published hack for defeating this - although I haven't risked it.

Time (and human ingenuity) will tell!

If BMW is smart, this info might fall off of a truck some where....

I think it is 100% silly to not allow us to engage the REx early. The reason is simple. NO ONE is going to buy a $40-$50K electric car and NOT use the EV mode as much as is possible. That is the ENTIRE POINT of the vehicle...

Heck the #1 discussion of most VOLT forms is how to NOT use any gasoline. It has become and game/obsession for most owners....

 

[GPVG33]

Sounds like an opportunity for a freelance software hack.

In the consumer electronics industry it's common for products with identical hardware to offer different capabilities in different countries for marketing reasons.

I remember a Sony video camera that hard certain input/output facilities disabled in European markets - although they could be restored by a "illegal" software download from a US source.

Similarly, my Lexus has a stupid safety feature that prevents the satnav being reprogrammed, or the main phonebook accessed, on the move - even for a passenger.

I believe there's a published hack for defeating this - although I haven't risked it.

Time (and human ingenuity) will tell!

If BMW is smart, this info might fall off of a truck some where....

I think it is 100% silly to not allow us to engage the REx early. The reason is simple. NO ONE is going to buy a $40-$50K electric car and NOT use the EV mode as much as is possible. That is the ENTIRE POINT of the vehicle...

Heck the #1 discussion of most VOLT forms is how to NOT use any gasoline. It has become and game/obsession for most owners....

+1....... Finally someone in the same page.

 

[Mike74jcw]

+2........the REx won't provide much benefit if you can't turn it on above 5% (at which point performance will be quite limited, I assume) unless you're driving in low speed stop and go.

 

[ecoangel]

Interesting reading about use of REX and battery depletion uphill.

LE Mobile did an EV conversion for the lightweight Audi A2 mk1:

http://www.le-mobile.de/index.php?lang=en&page=25

Click on their charts for KW requirements.

The car weighs in around 1100kg similar to i3 - maybe slightly smaller frontal area and Cd of 0.28 (1.2 version has 0.25 Cd) :

To drive the A2 EV at 80 mph on the level they estimate 22 KW whereas for a 5% climb in order to maintain that speed they'd need 41.5 kW !

So it looks like 22kW car would have to slow to 55 mph from 80 mph on a 5% climb.

In terms of range, for a 20kW battery (fully charged) they estimate 150km (93 miles) on the level at 90km/h (55mph) but just 63km ( 39 miles) if that were 5% uphill.

 

[rclams]

The range extender is a 650cc two-cylinder gasoline engine developing 34 hp (25 kW). It will automatically turn on when the state of charge dips below approximately 5% and it will hold the charge at that level (it doesn't increase the state of charge so you can't use it to actually charge the car). On European models you can manually turn it on once the state of charge dips below 75%. The reason you may want to do that is to hold the state of charge at a level higher than 5% if you know you'll need a lot of power later to say, climb a mountain or if you are going to be driving in a zero emission zone and want to keep from depleting your charge before you get there.

Tom:

Is it correct to assume that the in US Rex mode, the 5% remaining charge will help support temporary, high kW needs, such as acceleration away from a light, pulling out to pass or a short, steep incline and that the Rex engine/generator would then recharge the battery back to the 5% level?

But, wouldn't this high current cycling near the bottom of the voltage range of the battery cause accelerated wear and tear on the battery?

Or is this last 5% of "usable" storage sufficiently buffered by the "hidden/unusable" capacity of the battery?

:idea: Sounds like an excellent application for a "super-capacitor" and/or KERS system!

 

[surfingslovak]

Is it correct to assume that the in US Rex mode, the 5% remaining charge will help support temporary, high kW needs, such as acceleration away from a light, pulling out to pass or a short, steep incline and that the Rex engine/generator would then recharge the battery back to the 5% level?

I realize that you addressed this question to Tom, but perhaps I can help answer some of this. While I don't have any specifics, I can offer up some general information, which pertains to the overall design. The REx is limited to a maximum of about 25 kW of output power. Since this would not result in a satisfying driving experience, it has been long assumed that the REx will be augmented with battery power for the use cases you mentioned above. Unfortunately, if the battery reserve is limited to 5%, this only translates to about 0.6 kWh of usable capacity. Enough to climb 500 feet or drive about 3 minutes at the top speed of 95 mph instead of 75 mph, which is what the REx can sustain indefinitely on flat terrain.

But, wouldn't this high current cycling near the bottom of the voltage range of the battery cause accelerated wear and tear on the battery?

Yes, it's not recommended to dip that low. Having said that, the drivers of other lithium-ion powered vehicles have not been able to see much of a difference in practice. Also, manufacturers typically test the batteries with a very aggressive test cycle, and discharge them completely on each run. We know that these batteries can sustain many hundreds, if not thousands, of deep cycles. While shallow cycling is recommended for improved longevity, it's difficult to discern much difference from occassional deep discharges in the field.

Or is this last 5% of "usable" storage sufficiently buffered by the "hidden/unusable" capacity of the battery?

While I don't have any specifics, this has been the case with other commercial EVs. There typically is about 2% charge left, when the vehicle stops dead after turtle mode. This charge is not accessible to the driver, and it's supposed to prevent bricking of the battery in the event that it's not recharged soon after the car stopped.

 

[Boxster1971]

From the UK BMW i3 web site:

"The range extender is a small, smooth-running combustion engine that runs on unleaded petrol. This acts as a generator, which maintains the charge of the high-voltage battery so that the vehicle can continue to drive electrically. It will cut in automatically when your battery state of charge falls below 20%, but you can choose to use it earlier should that better suit your journey."

I doubt that the i3's in USA will limit REX to start at 5% SOC. If it is limited it would likely be at 20% like other markets to optimize battery life.

- - Mike