Pre heating and cooling - Renault Z.E. Forum
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post #1 of 43 (permalink) Old 08-30-2013, 10:58 AM Thread Starter
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Pre heating and cooling

Hi guys.

I am seriously considering a Fluence now that they have become 'affordable' second hand. I was interested to hear how the pre-heating and cooling works in practice. I really like the idea of getting in the car on a winters day with all the windows clear and the interior nice and toasty.

Is is an easy thing to set up or does it have to be done via the app on your phone (which I believe may not be working all that well)

Regards.
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post #2 of 43 (permalink) Old 08-30-2013, 01:24 PM
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RE: Pre heating and cooling

Ah! If only they actually set it up to do that!

No. Unfortunately, it is a good idea, which they have promptly balls up. The pre-conditioning only works once the car has reached 100% charge, the lead is still plugged in, and a manual button on the climate control panel has been pressed before you exit and lock the car.

There are a number of annoying reasons why that method is not such a good idea. Firstly, as you probably know, using the middle-range of state of charge is optimum to the battery. Running higher SOC all the time ages the battery, but you have to push the battery there if you want the pre-conditioning function. My commute is perfectly suited to a daily 25 to 75% recharge. I don't want to charge it up to 100%.

It makes no sense at all not to be able to manually interrupt the charging to force the heating of the cabin off the mains if the charging has not yet reached 100%, because otherwise it obliges you to, inefficiently, charge the battery up and then use the battery to heat the car if you want to get going in it before a full charge. That's daft.

Secondly, when it is cold it is a good idea to be giving the battery a gentle charge so as to warm it up before use. This is also an argument for why there should be a charge timer (either on the car, and/or on the charging unit). But you have to wait until the charging stops before heating the car up. You should be able to demand a little of both, as the moment of your departure looms.

And thirdly, you cannot set the timer on the car when it is not plugged in, which means that you can't set the car to warm up in the car park before you go out to it. You have to get into the car, then wait with it to warm up/cool down. How absolutely tedious, when the technology exists to give you exactly what you want.

*I* am the boss of the car. *I* am its God! If I demand heating to crank up on a timer, I should be able to make the car do that, not have some nanny committee in Renault decide that I might run the battery flat if the car is unattended. So what. If *I* set the car to do that, that should be up to me.

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post #3 of 43 (permalink) Old 08-31-2013, 04:04 AM
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RE: Pre heating and cooling

Quote:
Originally Posted by donald
Ah! If only they actually set it up to do that!

A masterpiece of clarity. If only someone would listen. But then it's too late, their brains were not in gear when they designed the thing. Still, if everything worked ok we'd have nothing to talk about......
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post #4 of 43 (permalink) Old 08-31-2013, 04:09 AM Thread Starter
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RE: Pre heating and cooling

Quote:
Originally Posted by donald
Ah! If only they actually set it up to do that!

No. Unfortunately, it is a good idea, which they have promptly balls up. The pre-conditioning only works once the car has reached 100% charge, the lead is still plugged in, and a manual button on the climate control panel has been pressed before you exit and lock the car.

There are a number of annoying reasons why that method is not such a good idea. Firstly, as you probably know, using the middle-range of state of charge is optimum to the battery. Running higher SOC all the time ages the battery, but you have to push the battery there if you want the pre-conditioning function. My commute is perfectly suited to a daily 25 to 75% recharge. I don't want to charge it up to 100%.

It makes no sense at all not to be able to manually interrupt the charging to force the heating of the cabin off the mains if the charging has not yet reached 100%, because otherwise it obliges you to, inefficiently, charge the battery up and then use the battery to heat the car if you want to get going in it before a full charge. That's daft.

Secondly, when it is cold it is a good idea to be giving the battery a gentle charge so as to warm it up before use. This is also an argument for why there should be a charge timer (either on the car, and/or on the charging unit). But you have to wait until the charging stops before heating the car up. You should be able to demand a little of both, as the moment of your departure looms.

And thirdly, you cannot set the timer on the car when it is not plugged in, which means that you can't set the car to warm up in the car park before you go out to it. You have to get into the car, then wait with it to warm up/cool down. How absolutely tedious, when the technology exists to give you exactly what you want.

*I* am the boss of the car. *I* am its God! If I demand heating to crank up on a timer, I should be able to make the car do that, not have some nanny committee in Renault decide that I might run the battery flat if the car is unattended. So what. If *I* set the car to do that, that should be up to me.

Donald

Thanks for the detailed reply.

Although I agree Renault could have done things better with regard to this from my own selfish point of view I would be happy enough. The important thing for me would be to get the car up to temperature for the school run in the morning where every precious second counts!!

Two points you could clarify for me though. The manual pushing of a button before you lock the car, does that set the time you want the heater to come on at or is it as basic as when the battery gets to 100 per cent then the heater kicks in (seems a bit wasteful if it reaches 100 per cent by midnight and you are only setting off at 8am)

Second point is you say the battery has to get to 100 per cent charged how is that measured. Is it every bar full on the charge gauge. I was concerned that a few years down the line when the battery is incapable of reaching 100 per cent and only gets to the 75 per cent capacity that Renault guarantee then the pre-conditioning will never kick in (surely not?)

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post #5 of 43 (permalink) Old 08-31-2013, 06:39 AM
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RE: Pre heating and cooling

So, [as I understand it - not yet tried out in anger] you can manually set two timer programmes into the climate control (e.g. morning commute, and evening commute). They stay set. Then when you want them to operate, you press the button as many times as necessary to activate prog 1, or prog 2, or both, or none.

If one or both of those progs are set to be active (and the dash warns you if they are, or are not, set on exiting the car), then, as far as the handbook says, one hour* before the set time, if the car is '100%' ** charged and has mains available, it'll fix the interior temp so it is comfortable by the set time.

*Why an hour I don't know - seems wasteful, 30 mins would do. Maybe the idea is that you deliberately set it slightly later than you actually need it, in case you get delayed, so the 'hour' is, rather to cover the period around your due departure time. You'd figure that out when you come to use the system, I am sure, but ultimately it will come on before the due time set.

**Good question - so, Li-ion charging goes through a constant current period, then enters a 'saturation' period, which is when the cell voltage has reached its set peak (probably 4.2V) and then the current is gradually ramped down so as to sustain 4.2V cell voltage. The charging rate is low enough on the Fluence that it might not really enter the saturation period. In any case, I'd guess that the system triggers when the cells reach 4.2V, and there is probably an ongoing charge current whilst heating the cabin that is still applied to the batteries to take them to their full saturation charge. In other words, if I was engineering the system, I'd be making use of the 'spare' current capacity of the charging circuit once the charging current begins to ramp down, rather than simply wait until the full charge cycle has ended.
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post #6 of 43 (permalink) Old 08-31-2013, 06:53 AM
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RE: Pre heating and cooling

Quote:
Originally Posted by donald

Li-ion charging goes through a constant current period, then enters a 'saturation' period, which is when the cell voltage has reached its set peak (probably 4.2V) and then the current is gradually ramped down so as to sustain 4.2V cell voltage. The charging rate is low enough on the Fluence that it might not really enter the saturation period. In any case, I'd guess that the system triggers when the cells reach 4.2V, and there is probably an ongoing charge current whilst heating the cabin that is still applied to the batteries to take them to their full saturation charge. In other words, if I was engineering the system, I'd be making use of the 'spare' current capacity of the charging circuit once the charging current begins to ramp down, rather than simply wait until the full charge cycle has ended.
Very interesting, Donald. I have just completed an overnight charge. At the end of the 7 hour offpeak period I checked using the app and it reported 100% charge, 101m range - the charge having taken 7h 05m.

Now as the car was at 25% charge (or just under) when charging started the car whould have required 16.5KWh of charge. The 10A cable had only theoretically provided only 14KWh, hence not a charge tp 100%..

However the car continued to charge for the next 3/4 hour, gaining another 4 miles of range before the car shut off the charger. Was this extra period your saturation period, does the app show 100% when the battery is actually less than brim full, or what?

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post #7 of 43 (permalink) Old 08-31-2013, 08:41 AM
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RE: Pre heating and cooling

I don't know. Yet. I have bought a current/energy monitor and I asked the installer to leave a loop of the live wire inside a junction box when he fitted it. [Stupidly, I did not ask if he could fit a 3 pin outlet on the same circuit, so I'll not be able to repeat that with the 10A lead.)

So at some stage, I will set it up to monitor input power/energy. I'll familiarise myself with the characteristics of the Fluence's charging behaviour, then I'll have a better idea what is going on.

With the 10A lead, it'd be charging less that the '0.15C' rate, which would ordinarily be considered to be sufficiently slow that there would not be a saturation charge. But I expect there will always be 'a little' saturation charge, and I expect that is, indeed, what you are seeing.

As an Li-ion battery is charged, the 'actual' open-circuit voltage at rest for a fully 100% charged cell should be 4.2V for 100%. So the charger will get the cells up to 4.2V. An 'instantaneous' evaluation of the cells might then determine that they are at 100%, but actually the cell voltage will drop when the charging current is discontinued.

Or alternatively the current is ramped down once the cells are at 4.2V, until the current drops below some pre-set value, rather than simply shutting of the charge current. This is the start of the 'saturation' charge. However, once the battery is 'rested' by the monitoring electronics, the cell voltage will drop again, and applied charge may, again, exceed the pre-set minimum current for charging. It will keep iterating this, until both a) the cell voltage is 4.2V, and b) an applied charge current does not exceed the pre-set minimum.

If charging were to continue above this, the cell voltage would become dangerously elevated. Above 4.3V the cell electrodes begin to become plated in lithium, permanently damaging capacity, and if it continues too long then it may produce a short, through which the other cells in parallel with it may discharge and cause a 'thermal event'. So it is essential not to apply too high a current that might lead to the cells exceeding 4.2V.

It is quite possible that Renault have designed the system not to even get to 4.2V, but instead to regard a lower cell voltage as max, such that you only see 22kWh of what might actually be a 25kWh battery. In fact, the Leaf battery is a 24kWh battery for which only 21.5kWh is made available. Consider the actual battery pack of the Leaf is 200kg and the Fluence is 250kg, I would have guessed that Renault have built in quite a big overhead in the unused battery capacity. GM claim the Chevy Volt only uses 64% of its full battery capacity, missing 20% at low SOC and 16% at high SOC. This keeps the cells well within their optimum range for maximum longevity.

I might guess that Renault do likewise as their batteries are leased, and they want to maximise their survival. It may also be that as the battery ages, the software is set to make use of some of that overhead capacity, so the battery does not appear to age quite as badly as it might be - I don't know if that is true, but it is possible they might have done it this way.

For example, equipment that is routinely held on charge, such as emergency equipment with Li cells, will cycle between, say, 4.0V and 4.05V, such that 4.05V is considered the cell max voltage. This reduces voltage stress considerably and extends life when held at that voltage. It is always best to avoid high cell voltages altogether if the battery is to be left for any length of time. If you charge to 100%, try to do so only just before you set off, so the battery spends the least time to those high voltage stress levels.

For fast charging - not that this applies to our current model Fluences - the reason the charging only goes up to 80% is because fast charging does not enter the saturation charging regime. In other words, it applies a constant maximal charging current, and as soon as the cells hit 4.2V then the charging stops, so there is no ramp-down of the charging current.

(All of the above is to the best of my understanding of Li-ion tech, and if I have any of the specifics in error, then I'm happy to be corrected and educated further!)

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post #8 of 43 (permalink) Old 09-01-2013, 03:49 AM
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RE: Pre heating and cooling

Thanks, Donald. The ageing scientist lurking inside me appreciates the lesson on battery technology. My knowledge stops at remembering that the placing of accumulators on the seats of local buses was expressly prohibited! Those were the days....
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post #9 of 43 (permalink) Old 09-02-2013, 03:03 AM Thread Starter
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RE: Pre heating and cooling

OK guys. I also appreciate the lesson on battery charging, interesting post.

Further to my original post and irrespective of the nonsense engineered in by Renault that you have to get to 100% charge before the pre-conditioing can cut in, can anyone report on how it performs in practice. i.e is the car up to a comfortable temperature and windows defrosted on a winters day when leaving the house. I read that the heaters were a bit underpowered on the earlier Nissan Leafs. Any such issues with the Fluence when it is minus 5 outside?

Regards.

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post #10 of 43 (permalink) Old 09-02-2013, 03:28 AM
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RE: Pre heating and cooling

Electricdream, I think you're going to have to be patient and wait for an answer, I don't think any of us have run our Fluence through the winter. I did buy mine as a New Year present to myself but it took a month to get delivered, missing the cold weather. I will hazard a guess that a battery that has lost capacity will not prove a problem, I suspect the "end of charge notification" is what will trigger the preconditioning routine. But time will tell.
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