Differences in range; Nissan Leaf versus Renault Fluence.

Hi Guys.

I'm in the UK and have a Renault Fluence ZE.

I've been lurking for a while, seeing what the 'Leaf' experience is like. I signed up mainly to access the 'search' function here (... can't search unless logged in, it appears!).

OK, well, I'll dive straight into what I was looking for here today - I was wondering if field weakening has ever been discussed?

Reason I'm asking is because the Fluence is a bigger, heavier car with a smaller battery, but it seems to have a better range? This isn't just the NEDC test talking (it reckons on Fluence at 115 miles, cf. Leaf at 109 miles). It's also me in dialogue with the one other private owner of a Fluence here in the UK I'm aware of. We get 100 miles range out of ours as a matter of routine. Well, in my case I've only done 300 miles in it in the week I've had it so far (so, not quite 'routine', perhaps). But my experience so far is consistent with the other guy who has put 2,000 miles on his.

Anyhow, I was wondering whether it comes down to the different motor technologies. The Leaf has a permanent magnet motor, and it'll have a design speed of around 3,000 rpm in the constant V/Hz region of operation. Above that, I presume it'll have to do some sort of field weakening scheme, which'll make it less efficient for fast, light load conditions. Usually, field weakening is done by injecting Q-axis current, which, in effect, opposes the magnetic fields of the PMs (in fact, in extremis, field weakening can begin to demagnetise PMs!).

The Renault ZE cars have Continental's coil rotor motors, which therefore don't need to perform any field weakening, and would therefore likely simply alter the field/phasing to pick [presumably] whatever V/Hz characteristic is demanded. I started out driving very cautiously so as to judge how much range I might get (I used the 'Leaf Range Chart' initially), but soon realised after covering nearly 30 miles on less than a quarter of indicated charge I was doing better than that chart. So I simply started picking the speed up and up. I now aim for 60~65 on the motorways, and aim to stay under ~15kW power up and down hills (I slow down to ~50 on the uphills I take, but would hit 80 on the downhills if I keep feeding in 15kW so I usually back off then). With that sort of driving, I get 4.7~5.2 M/kWh.

So, what do you guys think? Is field weakening sucking up some of the Leaf's range, or maybe we cruise more gently because we have less power at our toe-tips? Or is there some miscalculation of energy/distance afoot, or ... ?

We don't have Renault in the USA at all. "The last new Renaults — 475 of them — were sold in the USA in 1990, according to sales-tracker Autodata. The French automaker's biggest year in the USA recently was 1988, when it sold 14,712. Toyota sells more Corollas than that in a single month in the USA." (USA TODAY)

So, I can't compare. I also can't comment on "field weakening"... it's never come up here and I seriously doubt there is an issue.

I'm interested in how you "beat the Range Chart". Does that mean that at your "4.7~5.2 M/kWh" you aren't able to drive 5 * 21kWh useable when new and at 70F/20C and above = 105 miles?

Remember, this has NOTHING to do with the dash instrument the forecasts range. Also, are you resetting your economy meter with each "tank full" of electrons?

TonyWilliams said:

I also can't comment on "field weakening"... it's never come up here and I seriously doubt there is an issue.

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I'm not saying it's an 'issue'. The Leaf's a great car, but it does have a permanent magnet motor. These are much more efficient at lower speeds, than externally excited rotors, within their V/Hz operating range, but to get high power/weight from the motor they are run faster than V/Hz, which then is potentially less efficient than coil rotors. There's no 'issue' if you have a PM drive, because it is what it is! However, it's not inconceivable that Leafs of the future might end up with the same rotor coil technology, as Renault are now starting to take over manufacture themselves (early models were supplied by Continental). With price of magnets as they are, I think rotor coils will be the EV tech of the future, if only on cost but especially if the rotor coil motors turn out to be more efficient as well, in 'real' use. I don't know if they are, I'm no motor designer, I was just asking if anyone had considered it before.

I'm interested in how you "beat the Range Chart". Does that mean that at your "4.7~5.2 M/kWh" you aren't able to drive 5 * 21kWh useable when new and at 70F/20C and above = 105 miles?

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I'm not sure what you mean, exactly, but I can tell you this is based on real miles covered, not on what the gauges say. I'm definitely getting better than 4.3M/kWh on my commute, whilst staying above 55 mph for 18 miles of my 23 mile journey. I can get there and back twice (actually, total = 90 miles) on one charge by which time it's just lit the low battery warning, having dipped into the last of the 8 segments of the SOC gauge. (This is in ambient, no-accessory load, conditions. I'm not expecting to be able to do the run twice on one charge with accessories running.)

TonyWilliams said:

We don't have Renault in the USA at all.

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Sure. I'm aware that US doesn't 'do Renault' anymore, but I reckon you guys would love this car. It's a very wide, relaxed saloon-cruiser, much more in keeping with traditional 3 box cars. When you're up-close at the rear of the vehicle, it looks far more like a Jaguar saloon than you'd ever expect a Renault to look like! It's really quite a big car, and, IMHO, actually too big for typical UK car parks!

I'd not put it past Renault Nissan that they might try re-badging it Nissan at some stage, because with Better Place's 500k unit order folding up then they'll have to re-evaluate what markets are likely to buy it (it's barely selling in the EU), or drop the model altogether.

donald said:

Sure. I'm aware that US doesn't 'do Renault' anymore, but I reckon you guys would love this car. It's a very wide, relaxed saloon-cruiser, much more in keeping with traditional 3 box cars. When you're up-close at the rear of the vehicle, it looks far more like a Jaguar saloon than you'd ever expect a Renault to look like! It's really quite a big car, and, IMHO, actually too big for typical UK car parks!

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Interesting, thanks for sharing. I owned a Renault Alliance, manufactured in mid 80s by AMC. There was also Renault LeCar, which was based on Renault 5. I believe those were the last two vehicles with the Renault badge sold in the US.

TonyWilliams said:

I'm interested in how you "beat the Range Chart".

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I'm pretty sure OP was using your LEAF range chart while driving the Renault since he had nothing similar available for the Renault.

donald said:

I'm not saying it's an 'issue'. The Leaf's a great car, but it does have a permanent magnet motor. These are much more efficient at lower speeds, than externally excited rotors, within their V/Hz operating range, but to get high power/weight from the motor they are run faster than V/Hz, which then is potentially less efficient than coil rotors.

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It's no secret that the LEAF's efficiency drops significantly at highway speeds. Obviously aerodynamics are part of the reason for this, but the drivetrain does seem to be part of the equation, as well. Perhaps you are onto something!

donald said:

There's no 'issue' if you have a PM drive, because it is what it is! However, it's not inconceivable that Leafs of the future might end up with the same rotor coil technology, as Renault are now starting to take over manufacture themselves (early models were supplied by Continental). With price of magnets as they are, I think rotor coils will be the EV tech of the future, if only on cost but especially if the rotor coil motors turn out to be more efficient as well, in 'real' use. I don't know if they are, I'm no motor designer, I was just asking if anyone had considered it before.

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Tesla also uses induction machines in their EVs. You may be interested in a discussion we had on this topic in the Chevy Spark EV thread. In there you will find some plots of efficiency curves as well as a link to an article comparing the two technologies. If you have any similar data for the Renault that we could use for comparison purposes, it would be very interesting!

RegGuheert said:

TonyWilliams said:

I'm interested in how you "beat the Range Chart".

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I'm pretty sure OP was using your LEAF range chart while driving the Renault since he had nothing similar available for the Renault.

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Of course. Thanks.

RegGuheert said:

TonyWilliams said:

I'm interested in how you "beat the Range Chart".

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I'm pretty sure OP was using your LEAF range chart while driving the Renault since he had nothing similar available for the Renault.

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The Fluence displays a number of interesting things on its dash, including the remaining usable kWh figure. I asked one of the drivers to post a few photos, and he graciously agreed. The navigation system supposedly does a decent job predicting how far the car will go. I doubt that it takes all the factors into consideration, but still. Given that the OP knows the remaining usable capacity, all that's needed is the energy economy figure at different speeds, which is what he might have gleaned from Tony's chart. I think the better than anticipated range at higher speeds is due to better aerodynamics. I observed something similar with the ActiveE as well.

What is your average speed over there? One likely suspect is our long drives at high freeway speeds in the US. I know the the UK and EU tend to have more low to medium speed roads, and, Germany excepted, fewer long drives at 100+ KPH. The Leaf will do 160+ kilometers if driven at low enough speeds.

LeftieBiker said:

What is your average speed over there? One likely suspect is our long drives at high freeway speeds in the US. I know the the UK and EU tend to have more low to medium speed roads, and, Germany excepted, fewer long drives at 100+ KPH. The Leaf will do 160+ kilometers if driven at low enough speeds.

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Well, the speeds I have been aiming for on my commute so far have been around the 55~60 mph mark, but am slowly picking up the speed as I gain more confidence in its range. Basically, I have been aiming to keep just ahead of the HGVs (90kph) in the 'slow lane' until I am familiar with the range I am actually getting, and to gain trust the SOC meter.

My basic MO is to build up speed when a grade is coming up by applying a steady ~15kW power (thus, trying to minimise peak discharge rates), and this usually gets me up to 65~70 on the flat. Then the grade slows me down, steady 15kW, but then keep 15kW on the other side of the hill and build up speed again until I hit 70~75 (which usually sees me flying off into the outside lane), then I'll back off at max V but avoid going into regen. The way I see it, optimum range from a given battery charge is achieved by the lowest gross discharge/recharge rates. But, yeah, in summary I aim for 60ish, and sometimes hit 80 on the downhills to avoid going into regen.

I also go through several miles of 'variable speed limits' along the motorway route, which are often active and usually showing 50 or 60.

Typical UK motorway speeds; 1st lane - 55~65, 2nd lane - 65 to 75, 3rd lane - 75 to 85.

I don't appear to have the readout of battery charge, shown in the photo above. I'll go check it out again, maybe there is a button I'm not pressing. I think the Fluence has already been through several subtle iterations since pre-launch and it would not surprise me at all that there are differences between the models/countries. (The analogue SOC gauge shows 8 sectors, which I mentally divide each into thirds, giving me a visual feel for 24ths of the capacity. I assume each third of a sector gives me ~4 miles, and so far it has proved very accurate to presume this, all the way down into the final 'red' sector. It seems quite 'linear', each sector giving around 12 miles worth. I've already gained enough confidence in the SOC accuracy that I'll happily plan to dip into the final sector.)

donald said:

I don't appear to have the readout of battery charge, shown in the photo above. I'll go check it out again, maybe there is a button I'm not pressing. I think the Fluence has already been through several subtle iterations since pre-launch and it would not surprise me at all that there are differences between the models/countries.

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Interesting! The kWh display definitely got my attention, since it's a worthwhile improvement. It would be disappointing if it was subsequently removed. The photos referenced upthread were taken in a Fluence supplied by Renault to Better Place in Israel.