Running out of (HV) battery in an EV

[awbugritt]

I once started running out of petrol in my company car(a big no no as I didn't pay for fuel!) up an incline. However, using the choke(remember those???) I crested the rise, descended at a considerable rate of knots downhill in neutral with enough momentum to ascend the next hill and freewheeled to the solitary petrol pump next to a pub, which was fortunate as I was out in the sticks and about 10 miles in any direction from a petrol station!

Lastly (honest!) I conked out on my bike many years ago having forgotten to turn the reserve switch on the last fill-up. A fellow biker travelling in the opposite direction with his wife on the pillion, turned round, left his missus with the bike (which was being paid for on finance) ran me back to his house about 5 miles away as the nearest garage didn't sell petrol cans would you believe, fueled up the bike, then shot off saying drop the can off sometime as we're off to Wales! That would never happen now!

 

[Rolfe]

That's the great thing with ICE cars. If you run out, all you need is a lift to a petrol station and a can. When I conked out (because I'd forgotten that I'd put half the petrol in the emergency can into the snow clearing maching months previously) a passing driver ran me seven miles to the nearest petrol station to fill it up, and back.

When I did the same outside my music teacher's house (long story, I think a garage had drained the tank and then replaced "some" petrol when they realised I was coming to get the car) I got a bus home, with my fellow-pupil, we went to her house, picked up her car and my petrol can (which I had left behind because the car had been emptied to go to the garage), and she drove me back to my car.

(About a month later she had a catastrophic puncture in the same situation, and I had to mount a rescue attempt of a mutual friend she was supposed to be picking up, then take her home, then later take her back to her car when the RAC man messaged to say he was there. Bottles of wine were flying around from one to the other on account of all this.)

With EVs you know you're likely to be in a world of hurt if you run out. You can't rescue yourself. At best maybe the rescue van will have a generator, but you might be in for the Low Loader of Shame. I still don't think these portable battery packs you can carry in the boot will catch on, they're too big and heavy and (probably) expensive, and most cars have a bit of a reserve charge anyway (apart, apparently, from the e-Niro).

I did hear something interesting on one of the podcasts I watched. Why shouldn't EVs be equipped with VtV capabilities as well as VtL (and maybe VtH)? If that was standard, any passing EV with sufficient charge and sufficient time to spare (don't know how long it would take) could rescue another. Rescue services could simply drive EVs, and use their own vehicle to top up a stranded client.

 

[Roldorf]

Here is one where the idiot used his GOM thinking it was a linear indication of range.

 

[Rolfe]

He WHAT?

I watched it, but my German isn't good enough to follow all that explanation. The film just showed him driving along merrily, and the next minute he was being rescued by the Low Loader of Shame. He got into a parking place at a rest stop, but not to a charger?

 

[Roldorf]

As he was returning home from his trip and just after Augsburg he had 14% and had to go up a hill on the Autobahn. The battery percentage dropped very quickly to only 2% then rapidly to 1% then 0% then turtle mode. Luckily there was a parking place where he managed to pull off on the Autobahn where it promptly shut down. Germanys motorways have lots of parking places where the only facilities are some benches and a toilet block, which you can see in the background where he was stranded (9,37 in the video).
Luckily he was an ADAC member and they came and towed him to the next charging station.

 

[Rolfe]

I have been on the German autobahns, so I recognise what happened. At first I was surprised he had only managed to get to a Rastplaz and not to somewhere with a charger, but then I remembered a drive between (I think) Frankfurt and Würzburg, where I got very nervous in a Golf with a 50-litre petrol tank!

This is quite similar to what happened to the guy in the other videos, who thought he had enough range but was then caught out by a precipitate drop being reported by the car. A long hill could be an explanation, of course, but this seems to have been a very sudden drop.

As far as I can see, the MG4 doesn't behave like this. I regularly drive from my home to Glasgow, which involves a drop of 230 metres. I use 25% of battery to get there. I use about 28% of battery to get back. The situation is similar when I return from Edinburgh, which is a similar change in elevation but over a smaller distance. I am aware that my miles/KWh is a poorer on the way back than on the way there, but I have never experienced a sudden drop in range like that, even going up from near sea level to 300 metres in a few km.

Speed will also run the battery down more quickly of course. When my battery was on 5% I accelerated to overtake another car and went up to 80 mph (130 km/h), but the battery % didn't do anything alarming at all. (I was also going uphill when I did that, from 220 to 270 metres.)

It may be that the gradients in Germany are more pronounced and/or more prolonged, but on a motorway I wouldn't expect the gradient you'd get on a mountain road. The behavior of the car that you describe in the video, and indeed the similar behaviour of the Kia in the other videos, is quite deceptive. I have some sympathy for a driver who is caught out by this. It's quite different from the buffer of 8-15 miles (albeit sometimes at turtle speed) that's being shown for other cars (including the MG4) in other videos. (Although I think I saw a reference to a different MG model stopping not long after it got to zero range, so they may not all be the same.)

I had another look at the first Mr EV video, and he says that the battery percentage was at 20%, then it suddenly went down to 4%. I don't know how sudden that was, as I don't think the % charge is on the main screen of that car, you have to call it up specifically, so he probably wasn't watching it continuously. Nevertheless that is a very sudden drop by any standards.

He was on the motorway, but he said nothing about hills, and it would take one hell of a hill in the English midlands to drop a battery that fast. Something not right there.

Something I did think about was balancing the battery. I'm having trouble finding out for sure if that Kia has an LFP battery, but I think it does. One of the reasons (perhaps the main reason?) they tell us to charge the LFP battery to 100% and let it balance every time is that if you don't, the GOM is unreliable. The battery has a very level charging profile, or something like that, and the BMS can't really tell how much is left in a partially charged battery. It relies on knowing where it was when it was 100% charged.

I read somewhere else that it was possible for a battery that hasn't been allowed to balance to be quite hazy about how much charge it still has as it gradually gets lower, then suddenly as the end approaches it gets a real sense of where it's at and reports the truth. Hence the GOM may seem to drop very suddenly at that point.

I also have the LFP battery, but mine behaved fine when I ran it down to 4%. The projected range stayed reasonable, within kicking distance of 2 miles for every 1% charge, and there were no nasty surprises on the final leg, even when I gunned it a bit. At Abington it told me (I think) that I had 28 miles range, at 15% charge, and the distance home is 23 miles. That's where I turn off the motorway, so it's not unexpected that I got better economy after that - I was on an A road driving 40-60 mph most of the time. I saw both the range and the % charge drop evenly and predictably, and got home on 4% charge with 8 miles on the GOM.

I always take the battery to 100% and let it balance. I wonder if Mr EV had been doing a lot of partial charges on his Niro? That might explain the problem.

 

[Gadget Geek]

Part of the explanation of sudden drop off in range is due to the discharge characteristics of batteries.

 

[Lovemyev]

One of the reasons (perhaps the main reason?) they tell us to charge the LFP battery to 100% and let it balance every time is that if you don't, the GOM is unreliable.

This has been duly spotted and reported by Tesla Bjorn on one of this long distance challenge’s.
He states that one of the slight variations in the LFP battery chemistry, is it CAN struggle to accurately report the remaining predicted range on the GOM.
Charging to 100% is therefore recommended to help avoid incorrect reporting.
The older more dense NMC battery chemistry is regarded as being a little more sable in its reporting when charging to a lower SOC on a regular basis apparently.

 

[johnb80]

Part of the explanation of sudden drop off in range is due to the discharge characteristics of batteries.

View attachment 19425

But that should be programmed into the BMS, it definitely is in my house LifeP04's.

 

[Gadget Geek]

But that should be programmed into the BMS, it definitely is in my house LifeP04's.

Agreed, but domestic loads tend to be less severe than an EV's and that "drop off the cliff" when the cell voltages drop below a certain level must have quite a wide margin of error.

 

[tsedge]

Agreed, but domestic loads tend to be less severe than an EV's and that "drop off the cliff" when the cell voltages drop below a certain level must have quite a wide margin of error.

Yes, it is far from a perfect calibration / compensation as far as I can see.

And it may depend on what you pay for (more expensive solutions are more linear or more linearly calibrated at any rate).

 

[Rolfe]

This has been duly spotted and reported by Tesla Bjorn on one of this long distance challenge’s.
He states that one of the slight variations in the LFP battery chemistry, is it CAN struggle to accurately report the remaining predicted range on the GOM.
Charging to 100% is therefore recommended to help avoid incorrect reporting.
The older more dense NMC battery chemistry is regarded as being a little more sable in its reporting when charging to a lower SOC on a regular basis apparently.

That's interesting, I don't think I saw that video. It's something I think I worked out while I was typing that previous post. When I first got my car I was hearing a barrage of "it's bad for the battery to charge above 80%" from all quarters, and even though I was aware that was a recommendation for the NMC, I was also hearing people say that LFPs should be treated that way too. And yet, MG deliberately removed the feature in the app to stop the charge at 80% for the SR. I used to feel guilty about taking the battery to 100% every time, even though that was what MG recommended.

Then I saw some more videos that were a lot more reassuring about the LFP, just bang it up to 100% and leave it, it won't care, say the experts. (Although I don't think I'd leave it at 100% if I wasn't going to be using it at all for a while.) And other videos explained what's in Gadget Geek's graph, and said the GOM and the SoC might not be accurate in a battery that hadn't been allowed to balance.

It kind of clicked when I listened to Mr EV say that one minute his battery was reporting 20% and the next it was on 4%. I googled the Kia e-Niro and I think it's LFP. I don't know if the car in Roldorf's video was also an LFP, but it seems likely.

Of course if you aren't driving your LFP car down low, if you always charge above 20%, then you're never going to run into this. But if you've been swayed by the "100% is bad" propaganda and haven't been letting your LFP balance at 100% often enough, then you take it right down, that could be where you suddenly find yourself without the range you imagined you had.

 

[Rolfe]

Yes, it is far from a perfect calibration / compensation as far as I can see.

And it may depend on what you pay for (more expensive solutions are more linear or more linearly calibrated at any rate).

I don't know whether the problem is susceptible to having money thrown at it or not. What I have read seemed to suggest that it was an inherent property of the LFP to have such a flat curve, and that the BMS has to rely quite heavily on knowing where it was when it started at 100% with the cells balanced. If it's subjected to a lot of partial charges without being able to balance then this information is lost.

Are your house batteries often cycled up and down mid-charge without being able to balance at 100%?

 

[Lovemyev]

That's interesting, I don't think I saw that video.

I think it was one of the videos he did while over in Thailand ?.
When he was testing one of cars by doing the long climb up the mountain .
It could have been the Ora Cat ?????.
He was trying to load the motor and raise the heat, as some other owners had complained about the car loosing power and then shutting down due to the motor over heating.
As he was driving towards the mountain, he commenced the conversation over the different types of battery chemistry and it’s affects on GOM range.
His knowledge on EV testing etc is pretty much unrivalled TBH.

 

[Rolfe]

I may have watched the start of that, not sure if I watched it all. It could have been a partial memory of that which caused me to think about this as a possible cause of what happened to Mr EV, though.

 

[siteguru]

There is the flipside of GOM inaccuracies ... last winter I had a situation where I got home with the GOM showing 6% SoC; when I recharged (on my wall box) to 100%, the kWh actually stored equated more to a starting SoC of 20%.

 

[Rolfe]

I suppose the error can go in either direction, but you're unlikely to notice if it's under-reading unless you do what you just described. Had you been charging to 100% and balancing at the time it happened, or had you been doing partial charges? Did your actual miles travelled suggest you had more in the tank than the car was admitting to?

This is part of the reason I just bought the extension lead you found online. Mainly I want to be equipped to charge at a friend's house when I'm staying there, if necessary. However it occurred to me that that and the granny charger could just possibly be a lifesaver on a long journey if that sudden recalibration from 20% to 4% that Mr EV experienced happened.

It's as well to have a plan if you suddenly, unexpectedly find yourself crawling in turtle mode with the nearest charge point too far away. Of course we don't know if the SR will crawl as far as the LR crawled for Bjorn, but my first thought would be, does anyone near here have a wall box? Failing that, my second thought would be, is anyone here IN, and can I get the car close enough to plug in the granny?

I've been thinking, how long would it take to get useable mileage from a granny charger in that situation? Mine usually charges at about 1.85 Kw. So an hour at that rate, and assume 4 miles/KWh because you would be driving economically to get the a charger, is about 7.4 miles. And would take about 55p worth of electricity. It would depend on how far your nearest charger was, but considering how long the rescue services take to get out to stranded cars, it could be a lot quicker than waiting. Even if you could get to a type 2, you could get enough there at a faster speed to get further on to a rapid.

 

[maskull]

I pulled up at a rapid today to top my car up . There was an E Tron pulled in just before me with 1% on his car . Not run flat , but if that charger wasn't working ( which it is a fairly common at that charger ) he would have soon met the criteria for running out .The nearest rapid charger from that is about 15 miles away

 

[Rolfe]

He'd have had to be extraordinarily lucky to have made that, for sure. Though was there a type 2 nearer? He could have got enough on that to get on to another rapid, if so.

My own plan if I ever managed to do anything that unwise and the charger was broken, is to phone the number on the charger and cry a bit and tell them I'm a poor elderly lady driver all alone, and if they can't reboot the charger remotely, can they send a repairman? And if that doesn't work, start figuring out where is the nearest housing development where the residents are likely to have wall boxes, and go begging (same schtick).

 

[maskull]

He'd have had to be extraordinarily lucky to have made that, for sure. Though was there a type 2 nearer? He could have got enough on that to get on to another rapid, if so.

My own plan if I ever managed to do anything that unwise and the charger was broken, is to phone the number on the charger and cry a bit and tell them I'm a poor elderly lady driver all alone, and if they can't reboot the charger remotely, can they send a repairman? And if that doesn't work, start figuring out where is the nearest housing development where the residents are likely to have wall boxes, and go begging (same schtick).

There were 8 7kw within about half a mile from the rapid he was using . He told me his GOM was giving him 5 mile range left . He only charged to 20% ( luckily for me ) so that he could get home to his home charger . Personally I think it was a bit foolhardy to run the battery that low , especially with a baby on board . I've never let mine go below 40% , hopefully to avoid such situations .