Real World Driving - Renault Z.E. Forum
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post #1 of 64 (permalink) Old 10-21-2013, 04:32 AM Thread Starter
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Real World Driving

I wanted to start a thread on 'real world' driving. The 'how far in a Fluence' thread has been useful especially when I had to deliver my car home on an epic journey.

My wife is now driving the Fluence on her daily commute of 30 miles (20 miles motorway speeds and 10 miles urban) using the pre-heating (which works great by the way) and the cabin temperature on AUTO at a constant 21C setpoint. Outside temps approximating 10C just now. Range wise I would concur with Donald that I can get 60 miles using the car 'normally'

Now that I have my chargemaster homecharge station up and running I can log into the portal and see how much kWh EACH charge session consumes (inclusive of the pre-heat)

My early findings indicate that the car is covering approx 2 miles for every kWh of CHARGE. My findings also indicate that there must be some inefficiency in charging. I covered 42 miles yesterday (which took me down to 3/8 charge). Charging that up overnight with pre-heat took 21.26 kWh. I now it can be worse that that if the battery cooling fan kicks in but that only seems to happen if the battery charge is below 1/8th when you commence charging?

I am currently paying 10p/kWh so the Fluence is costing me 5p a mile to run. My fixed deal is ending in December so I fully expect to be paying 13p/kWh come January.
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post #2 of 64 (permalink) Old 10-21-2013, 04:56 AM
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RE: Real World Driving

Electricdream, very intersting figures you have produced. I cannot provide similar figures from my experience as I am currently using the 10A cable, not my wall charger. I also do not use pre-heating.

However, as a rough guide:
My last charge to replenish 65m of use took, if I remember correctly, almost exactly 8 hours to charge at 10A. That, by my maths, works out at 65 miles consuming 2.3kw/hour, or 18.4kwh. That means a figure of 3.53 miles per kwh.

Your figure of approx 2 miles per kw seems very low in comparison, even allowing for the pre-heating. Surely pre-heating cannot be using 43% of your charge?

I will check more accurately at the next charge - the time taken is the one figure I have not been recording, but on an earlier charge to replace 57 miles of use it fitted within the 7 hour offpeak charge time so that works out at a very similar 3.54 miles per kwh.

These figures of mine assume the cable DOES charge at 10A. If not, what did I pay hundreds of pounds for?

Anyone else got any figures?

Oh, and my offpeak electricity costs 6.54p per unit, rising to 7.3p for the coming year on a fixed tariff.

Incidentally Donald has mentioned yet again his motorway journey where he achieved a range of 120 miles. Try as hard as I can I have never exceeded 107, quite a discrepancy unless with 4600 miles on the clock my battery is already suffering. I hope not!!!
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post #3 of 64 (permalink) Old 10-21-2013, 05:16 AM Thread Starter
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RE: Real World Driving

Quote:
Originally Posted by pauledg
Electricdream, very intersting figures you have produced. I cannot provide similar figures from my experience as I am currently using the 10A cable, not my wall charger. I also do not use pre-heating.

However, as a rough guide:
My last charge to replenish 65m of use took, if I remember correctly, almost exactly 8 hours to charge at 10A. That, by my maths, works out at 65 miles consuming 2.3kw/hour, or 18.4kwh. That means a figure of 3.53 miles per kwh.

Your figure of approx 2 miles per kw seems very low in comparison, even allowing for the pre-heating. Surely pre-heating cannot be using 43% of your charge?

I will check more accurately at the next charge - the time taken is the one figure I have not been recording, but on an earlier charge to replace 57 miles of use it fitted within the 7 hour offpeak charge time so that works out at a very similar 3.54 miles per kwh.

These figures of mine assume the cable DOES charge at 10A. If not, what did I pay hundreds of pounds for?

Anyone else got any figures?

Oh, and my offpeak electricity costs 6.54p per unit, rising to 7.3p for the coming year on a fixed tariff.

Incidentally Donald has mentioned yet again his motorway journey where he achieved a range of 120 miles. Try as hard as I can I have never exceeded 107, quite a discrepancy unless with 4600 miles on the clock my battery is already suffering. I hope not!!!
Yes I agree the 2 miles per kwh is low, but the data from the chargemaster portal seems to be accurate. I have smartmeters in my house so I c get half hourly data which seems to back it up.

That's why I believe there is some inefficiency in the charging, ie I used 21.26kWh to charge a 22kWh battery by 5/8ths.

I know you are using the 10A charger maybe the only way to really tell is to get one of those plug-in energy monitors. Remember my wife is driving at motorway speeds for the majority of the commute and that means AT LEAST 70mph. It is not really an issue for me, just the reality of 'real-world' driving.

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post #4 of 64 (permalink) Old 10-21-2013, 05:19 AM
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RE: Real World Driving

Quote:
Originally Posted by pauledg
Incidentally Donald has mentioned yet again his motorway journey where he achieved a range of 120 miles. Try as hard as I can I have never exceeded 107, quite a discrepancy unless with 4600 miles on the clock my battery is already suffering. I hope not!!!
If I remember correctly he didn't do a 120 miles on one charge, but a 120 mile journey where he topped up half way back. The total of the top up and what was remaining would have allowed the journey under one charge but only just - down to a mile.

Still, 107 miles is amazing when you read what Leaf owners are getting.

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post #5 of 64 (permalink) Old 10-21-2013, 05:44 AM Thread Starter
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RE: Real World Driving

Quote:
Originally Posted by GrumpyCabbie
Quote:
Originally Posted by pauledg
Incidentally Donald has mentioned yet again his motorway journey where he achieved a range of 120 miles. Try as hard as I can I have never exceeded 107, quite a discrepancy unless with 4600 miles on the clock my battery is already suffering. I hope not!!!
If I remember correctly he didn't do a 120 miles on one charge, but a 120 mile journey where he topped up half way back. The total of the top up and what was remaining would have allowed the journey under one charge but only just - down to a mile.

Still, 107 miles is amazing when you read what Leaf owners are getting.

Yes that is the same Leaf owners who sit with a blanket on so they can switch the heater off. Now that is hardcore. That's why it is important to really work on 'real' driving. If you want to go no more than 60 miles a day then buy a Fluence. If you want to do more than 60 miles then don't. I can get 100 miles from the Fluence. Heating off, 50 mph, but do I want to really live my life like that? I want to drive at the legal limit for the road I am on, speed away from the lights when I am in a hurry and sit in a nice air-conditioned cabin at 21C constant. The Fluence it seems will do that all day long as long as you only want to travel 60 miles on one charge. The only unknowns just now are the approaching winter and possible performance degradation of the battery. Lets see how it handles -5C outside.

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post #6 of 64 (permalink) Old 10-21-2013, 08:35 AM
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RE: Real World Driving

I did a drive a month or so ago that I knew would be 52 miles one way - Warks to Lincs - actually turned out to be ~55.

Got there with well over half a battery, sufficient that I put the a/c on, on the way back. I'm quite confident it would've done 120 miles again.

But it does come down to driving style - there is simply no way you get that unless you are tuned into the economies of the vehicle - the basic message is try to pull less than 12 kW at all times. Sometime you might need to chug it up a slope, but you just can't go pulling 20 kW out of the battery and expect that sort of mileage. It can be tough to drive like that and you have to be prepared to drive slowly.

The heater energy consumption is pretty hard on the battery. When the winter sets in real hard, I am seriously wondering whether we're looking at some seriously short ranges. We'll find out ....

The pre-heater is good for making significant savings - by heating up the coolant fluids before the battery does, you save a couple of kWh on the range. Once it is warmed up, the heater doesn't use a terrible amount of power, it's the initial heat-up that costs dear.

Your wall-to-wheel consumption sucks. However, this may pass. When I did my first ever full charge, it kept on drawing power for hours after the charging had reach 100%. So much so that I actually went out and depowered the charger thinking something was wrong. I think if it has been used erratically in the recent past (read - parked in a dealer compound for months) the battery needs to do some management stuff to level out the cells. It's just my hunch, and if so then your early figures will look rubbish and you should discard those and start again from 'zero' after a couple of full charges.

My wall-to-wheel consumption has been around the 4.15 miles/kWh mark for the first 1,500 miles. The dash-indicated mileage for the same distance has been ~4.6 miles/kWh, so I appear to be looking at 9% charge losses. Most of my mileage is pottering along the motorway at mid-50s, so I am around the minimum energy consumption.

I'm pretty sure the losses are higher using the 10A lead.

My original reason for logging the drawn energy with my own instruments was to test the Chargemaster logging data. However, my unit doesn't log any data onto the website. Something's not working properly, so I can't say if the Chargemaster monitors drawn energy accurately or not.[hr]
Quote:
Originally Posted by electricdream
The Fluence it seems will do that all day long as long as you only want to travel 60 mile


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post #7 of 64 (permalink) Old 10-21-2013, 09:06 AM Thread Starter
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RE: Real World Driving

"My original reason for logging the drawn energy with my own instruments was to test the Chargemaster logging data. However, my unit doesn't log any data onto the website. Something's not working properly, so I can't say if the Chargemaster monitors drawn energy accurately or not"

Have chargemaster got the serial number of the unit linked to your address? I just had to phone them up and they sorted it that day. I am confident of the consumption data from the chargemaster unit as I can back it up with my half-hourly data from the smartmeter. Also it would be pretty pointless if the chargemaster was inaccurate as that is the whole point of getting the unit free so the government can collect consumption data. Imagine 20 million electric car users charging up overnight, that is a serious amount of baseload for the new Chinese nuclear power station!!

50mph is as far as we now the best speed for maximising consumption but try telling that to my wife when she is late for work (as I say real world driving)
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post #8 of 64 (permalink) Old 10-21-2013, 09:38 AM Thread Starter
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RE: Real World Driving

Another point has just come to my mind.

As I am using the pre-heat I charge the car up every night irrespective of charge in the battery. I know you guys usually let the battery drain down. I am usually charging from half to full EVERY night after the commute. But at weekends the car could be nearly fully charged and I still stick it on charge.

In terms of long term test I am going to post every month my miles driven against my charge consumption (as supplied by the chargemaster portal).

That will factor out any possible battery conditioning issues identified by Donald.

So from October through to March I would expect the consumption to go up as it gets colder. Watch this space!!
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post #9 of 64 (permalink) Old 10-21-2013, 02:44 PM
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RE: Real World Driving

Even if you are aiming to drive fast, there are still ways of doing it efficiently. Don't go for big accels only to ease off again, just keep a steady power input. If you apply a steady 20kW on the flat, you'll be doing 70 mph only a few seconds behind someone who's nailed the pedal and backed off at 70.

Also once moving, don't go for big pedal inputs. Just make very gentle adjustments to your speed, and if you see the traffic just slowing down a little ahead, ease back before you need to slow down. You can go a surprisingly long way at almost no noticeable deceleration from 70 mph by applying just 5 kW. The mph fall away very slowly from high speed, even with only a very small input of power. The fundamental difference with ICE cars is that there are no 'zero load pumping losses' which means that cars run pretty inefficiently at low power output and high rotational speeds. An EV loses almost nothing by adjusting the pedal input to give you around the zero kW.

If you are going uphill then avoid pressing the pedal down. Just let the car slow down a little whilst maintaining a reasonable power input. You won't slow down that much if you keep 20kW dialled in and once over the hill just keep 20kW on and before you know it you'll be over 70. Try keeping it at 15kW if you can, if it is only a gentle slope.

And, of course, going down hill if you keep the power on at 15kW or so, you'll be hitting the car's max speed in no time. You don't need much power to go down hill!! An ICE needs to be generating power just to overcome the internal losses in the engine.

Just keep it under 20kW and go for long, steady acceleration, nothing short and fast. You'll get where you're going just as quick, but a lot more efficiently.

The reasons are due to internal resistance of the battery. For ICE cars, more power is, relatively speaking, generated more efficiently. But it is the reverse for EVs. More power you get the double whammy of mechanical and electrical losses. Draw as little power from the battery as you can to keep the drawn current low. It is also true for regeneration too - where appropriate it is better to keep a little pedal pressure on to keep the regen around the 10kW level. Try not to zoom up to a stopping point relying on 30kW max regen, as the battery will recover less of that energy if it is delivered at a higher current.[hr]
Oh, and on the subject of charging 'theory': For long battery life, it is best to avoid leaving the battery charged to a high level. Preferably, you should avoid running up to full charge and leaving it like that for any length of time, it is best that you drive away promptly after a 100% charge.

The reasons are that lithium cells suffer voltage stress when the cells sit at the full 4.2V. I suspect, given that Renault lease these battery packs, that they are larger than they need to be and probably only charge them up to 4.1, or maybe even only 4.05V per cell, because they don't seem to be concerned about repetitive 100% charges.

However, voltage stress is a spectrum of degradation processes and it is best to leave Li cells around their middle voltage for as long as possible.

Overnight, of course it has no timer so we all have to just plug it in and wait for a full charge. What I tend to do is charge up to 6 or 7 octals in the evening when I get home and manually unplug the car.

I think what I might end up doing in the future when it gets cold is charging up to 7 octals the night before then unplugging, and deciding in the morning if I need to plug it back in for a pre-heat. It seems that you don't have to be completely full for the pre-heat to get going, but I've not experimented enough to know exactly when it does this. What I have found is that it has to be in a state to begin preheating one hour before the programmed time, else the whole preheater thing doesn't start. It's really stupid, I mean if I want the car to warm up I should have the option simply to plug it in and demand the temperature *I* want the car to heat up to. But we don't even have that level of functionality to demand a particular temperature, let alone simply plug it in to warm it up?!?! It's pretty daft. 'Work in progress' as Paul suggests!
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post #10 of 64 (permalink) Old 10-21-2013, 06:21 PM
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RE: Real World Driving

I'll keep data on how my car performs and post updates. I'd describe my driving style as relaxed, commute is half country roads(40-50mph) and half dual carriageway (60-70mph).

Very early days but reading economy 7 meter before and after a full charge having gone 44 miles consumed 12kwh . The car I bought had got 8,900 miles on the clock. Slightly concerned that the on board instrumentation indicated a consumption of 10kwh for 44 miles today but charge level needle had fallen below half level suggesting a full charge capacity of perhaps only 18kwh. Hopefully this gauge is as inaccurate as on ICE vehicles!
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