How much power does your EV draw AFTER 100% charge?

[donald]

I put this in this forum because this is to do with wall-to-wheel efficiencies.

OK, so I have had my EV (a Renault Fluence*) for a few weeks now but only tried charging to 100% over night, last night. Previously, I just put in as much as I needed for my next trip.

One might casually presume 'ah, it turns off!', but mine kept on consuming 600W long after it reached full charge. The battery cooling fan was running, which might be most of that 600W. But why was it running? Cell equalisation? Is it because the dumb TMS just runs the fan after a charge if it has mains power because it has no clue of the cell temps? Overcharging!? :shock:

Whatever it is for, it consumed an additional 30% energy over what it needed to, as far as I can see, and I turned it on late at night, and off within a few hours of it finishing its charge.

Very disappointed! Is it doing something useful or am I now bound to manually intervening in the charging process?

So, question for the Leaf: If you leave it plugged in to let it hit full charge, what happens next? Does it keep on consuming power, and if so; how much and why?


*(I'll add that I'm not asking simply as a 'comparison' on a Leaf site, but because my Fluence is on a lease and at the end of that I am more likely to buy a Leaf outright, than a Fluence and its battery lease scheme. So I want to understand all the foibles of all and any EVs I might be considering.)

 

[adric22]

I can't tell you exactly how much the Leaf consumes after a full charge, but I know it consumes something. The Volt consumes even more because it runs a coolant loop using the A/C compressor to actively cool the battery down (or heat it up, if needed) The Leaf does have a battery heater, but I doubt you'd be seeing that operating during the Summertime right now. Then again, if you have a Fluence you are probably in Europe.. Are you in Norway or Sweden?

 

[smkettner]

afaik my LEAF draws absolutely zero before or after charging.
The contactors on the wall unit are open (power off) after charging.

 

[dgpcolorado]

^ Yes, the LEAF draws nothing from the wall once charging is completed, from what I can measure. The EVSE draws a watt or two on standby. The car itself has a drain from running the electronics off of the 12 Volt battery, but it seems to be fairly small and isn't coming from the wall.

Of course, the lack of a battery cooling system has its disadvantages, as has been much discussed in the various battery degradation threads.

 

[vegastar]

The Fluence has a cooling fan for the battery? Any reference of that?

 

[TomT]

There is no external battery cooling system of any kind on the Leaf (unfortunately)...

The Fluence has a cooling fan for the battery? Any reference of that?

 

[donald]

The Fluence has a cooling fan for the battery? Any reference of that?

Yes - the whistling sound from the back of it, which 'speaks' for itself!!!

AFAI understand - it is a closed system that aims to recirculate air within the battery and amongst the heat sinks to the batteries, and in this way maintains an even, rather than a specifically lower, temperature. I guess that might be particularly necessary for the Fluence battery pack because it is a block, cuboid structure and the centre cells would not otherwise get good ambient-external cooling. I believe the cooling itself is still by natural convection/radiation to ambient.

I could be wrong about that - there is a 2 yearly service item to 'replace battery cooling fan filter', so whether it might draw air from the cabin space, I don't really know for sure.

In fact, given the battery pack is 'in the boot', I am suspecting that the act of charging the batteries will help towards keeping the cabin warm, as a direct (and beneficial) result in Winter (at least, I'm expecting it to resist icing up around zero C). I've yet to find that out!..

I thought the Leaf had, likewise, a closed system so as to maintain an even cell temperature? Are you sure it has nothing at all like this?

 

[donald]

Are you in Norway or Sweden?

UK. To be fair, it was a hot day yesterday, 28C, and quite a hot night last night - 22C at midnight. Very unusual for this time of year. Maybe it does take that long for the block of batteries to cool down on a hot night, in a closed unventilated cabin space?

It's a good point, actually. I will bear it in mind and maybe explore this phenomena again sometime. I guess the flip-side of that is to wonder whether it is better to run the batteries to full charge and let this cooling fan run, than let the cells 'stew' in their heat inertia? hmmm..... That's really down to the TMS, whatever it does (I expect it'd only be a very simple, 'one-order' control system on a thermal switch that appears to run only when it is plugged to the mains). I think I am going to have to presume I just do what I want to do (i.e., cut the charging short and not waste money by letting the battery consume power after full charge) and the battery will have to protect itself as it might need to.

 

[stjohnh]

One might casually presume 'ah, it turns off!', but mine kept on consuming 600W long after it reached full charge. The battery cooling fan was running, which might be most of that 600W.

Something else must be happening. I have several fans I use in my house on warm days, even the smallest blows a lot more air than I can imagine a battery pack cooling fan would need, and it draws 60 watts on max speed. Very hard to believe the 600 watts is only a cooling fan.

 

[smkettner]

600w would seem to be a compressor type cooling system.
LEAF has no cooling system. The battery will just sit and roast.

 

[donald]

OK, so I trust the SOC meter, it has given me no cause to doubt it at all so far.

I have just added 7/16th onto the indicted charge meter (= ~44% of 22kWh = ~9.6kWh of charge), over a 3 hour charge that used 10.6kWh from the wall. That sounds consistent to me. If the fan was consuming 600W itself, then that'd have been 8.8kWh to the battery and 9.6 gained, which makes no sense at all.

If I was a betting man, I'd say the fan sounded like it was in the 50-100W range.

Here's a curious thing - so I just unplugged it from charging, and this fan had been running throughout this particular charge cycle (doesn't always run). But before I did, I sat in the cabin (which did seem quite warm), wound a window down a crack and held a piece of paper to it, whilst the fan was loud and clear in the battery pack. There was a slight pressure build up in the cabin which tended to cause the paper to be sucked outwards. I turned the charge station off, fan went off, and then repeated. No pressure in the cabin. So it seems the fan is pushing air into the cabin from the battery!? The particularly curious thing is that I have previously looked to see if I could tell whether there was air being sucked in or out by the battery and I can see no ventilation ducts to the battery underneath/outside. I guess there must be a hidden one, well screened from road dirt, somewhere?

 

[TomT]

Nope.

I thought the Leaf had, likewise, a closed system so as to maintain an even cell temperature?

 

[johnrhansen]

I've noticed with my leaf on the few occasions I've charged to 100 percent that the charge indicator shows 100 percent about 45 minutes before the charger turns off and the last blue light stops blinking. The meter is spinning at about the rate a 600 watt draw would make it spin. Everything stops though after the blue light stops blinking.

 

[gbarry42]

Well, the LEAF has a cooling system, all right, but it is used to cool the charger, not the battery. When the LEAF is charged, (whether at 80% or 100%), it tells the EVSE to disconnect, which is equivalent to pulling the plug.

With the LEAF going to 100%, though, as it nears full charge, the charge current tapers off to a very low level, while the battery balance circuits do their thing. Even so, any overhead in the charger and cooling system is still active, so at this endpoint things are not very efficient.

Many LEAF owners have reported that the charging system may turn on again after a few hours, to do another balancing cycle. It has never happened here, and I would know, because the Blink EVSE goes "THUMP!" when it connects.

About that "maybe overcharging the battery" proposition: I've realized that you can't put extra current into a lithium-ion cell and get away with it like you could on other chemistries. The voltage would continue to go up until the battery eventually destroyed itself. So, this is one time you can be (almost) sure the battery isn't being overcharged. "Almost" means check the newspapers for sensational stories of EV fires, and if you don't find any, then this isn't happening.

 

[planet4ever]

I have just added 7/16th onto the indicted charge meter (= ~44% of 22kWh = ~9.6kWh of charge), over a 3 hour charge that used 10.6kWh from the wall. That sounds consistent to me. If the fan was consuming 600W itself, then that'd have been 8.8kWh to the battery and 9.6 gained, which makes no sense at all. If I was a betting man, I'd say the fan sounded like it was in the 50-100W range.

We can only make guesses about the behavior of the Fluence based on our knowledge of the LEAF, but I agree that 600W for a fan alone sounds quite high. I would expect the fan to run off 12v, not 400v, so there is probably a DC/DC converter involved in the process. Perhaps the 12v battery dropped well below its fully charged level while the traction battery was being charged, and the 600W is mostly going to recharge it. Or, as smkettner suggested, the 600w might be a compressor type cooling system. In that case the numbers would make more sense if you assumed something less than 22kWh usable battery capacity.

Here's a curious thing - so I just unplugged it from charging, and this fan had been running throughout this particular charge cycle (doesn't always run). But before I did, I sat in the cabin (which did seem quite warm), wound a window down a crack and held a piece of paper to it, whilst the fan was loud and clear in the battery pack. There was a slight pressure build up in the cabin which tended to cause the paper to be sucked outwards. I turned the charge station off, fan went off, and then repeated. No pressure in the cabin. So it seems the fan is pushing air into the cabin from the battery!?

That behavior sounds designed to me, not curious. As you said earlier, the Fluence may use battery heat to warm the cabin. To repeat what others have said, The LEAF has no battery fan. None. There is no battery fan filter to replace. The closest would be airflow under, and perhaps over, the sealed battery unit while driving.

Ray

 

[DaveEV]

I've noticed with my leaf on the few occasions I've charged to 100 percent that the charge indicator shows 100 percent about 45 minutes before the charger turns off and the last blue light stops blinking. The meter is spinning at about the rate a 600 watt draw would make it spin. Everything stops though after the blue light stops blinking.

That's the '13 LEAF just topping off and balancing the battery as best as it can...

 

[donald]

With the LEAF going to 100%, though, as it nears full charge, the charge current tapers off to a very low level, while the battery balance circuits do their thing. Even so, any overhead in the charger and cooling system is still active, so at this endpoint things are not very efficient.

Well, I will run it again and let it stew a bit longer, in case it does need to do a full battery balance once in a while, or whatever it does.

I did see the current ramp off, and presumed that was entering the saturation charge at that point and approaching 100%.

Still not happy losing high %age of wall-wheel efficiency in apparently wasted kWh, but will try it out a couple of times first to see if it is just an occasional bit of self-maintenance it does.

 

[donald]

Well, I have run two further cycles to 100% and these have hit 100% charge indicated on the dash, thereafter charging continued for a further 30 minutes, and then it tapered off gradually over a further 30 mins, at which point the battery isolator opened and ended the charging. This is quite a different behaviour to the one I reported above.

So I think this behaviour might well be an occasional battery management activity and not the usual charging process.

 

[Stanton]

^ Yes, the LEAF draws nothing from the wall once charging is completed, from what I can measure. The EVSE draws a watt or two on standby. The car itself has a drain from running the electronics off of the 12 Volt battery, but it seems to be fairly small and isn't coming from the wall.

I can confirm that ~1 Watt (or so): I constantly monitor the energy consumed at that 220v socket (via a "modlet").

 

[donald]

Ah ha....

Item 4 'Internal cooling system'
Item 9 'Peltier effect external cooling system'

I guess a Peltier system might well have accounted for a 600W drawn power - it looks like it was active cooling to cool the charged battery - I guess I should've left it running, then, to do its job, but there again I'm sure if it was critical it'd use battery power for that task if it was not plugged in......

Anyone fancy suggesting an active Peltier cooling system to Nissan?