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Estimated Battery Degradation - Model 3
- Thread starter pdk42
- Start date
I am slowly learning not to be paranoid about teslafi "degradation figures" I used to check them every other day to see how much range as I had lost.
Then it occurred to me that when I had an ICE car I didn't care a bit if my range was 5 miles less on a full tank than it was at the last fill up, or that if I had fun rather than being staid i'd lose about 20 miles of range. My last couple of cars all needed super unleaded and I really didn't mind checking along the route to make sure I knew where a garage selling Shell V power etc was. So it really is no different to that, except my inexperience in EV's is showing.
I am sure in six months I wont care. Sure i'll keep track of efficiency, and I love a nice graph as much as anyone. But for those reasons I am slowly not worrying about "Degradation reports" and getting on with enjoying my nice M3P
Then it occurred to me that when I had an ICE car I didn't care a bit if my range was 5 miles less on a full tank than it was at the last fill up, or that if I had fun rather than being staid i'd lose about 20 miles of range. My last couple of cars all needed super unleaded and I really didn't mind checking along the route to make sure I knew where a garage selling Shell V power etc was. So it really is no different to that, except my inexperience in EV's is showing.
I am sure in six months I wont care. Sure i'll keep track of efficiency, and I love a nice graph as much as anyone. But for those reasons I am slowly not worrying about "Degradation reports" and getting on with enjoying my nice M3P
it is an understanding concern. It's an expensive car with a battery that essentially needs to last the life of the car. Even if it is replaceable, the costs involved are probably ridiculous. It's basically a giant iPhone lol.
That being said you can go mad looking at these stats, I think. My iPhone battery is down to 93% "health" and my MacBook Pro (also essentially irreplaceable battery) is at 94%. Neither has got to a point where I actually feel like I'm losing precious minutes of runtime.
Unless people are actually driving their Model 3s from 100% to 0% on a regular basis, and every mile counts (you would be pretty mad to set out to drive the estimated range, given it could go up and down based on different variables), then the reality is that the drop in range, if it is even real, is a psychosomatic problem rather than a practical one.
The data is flawed anyway. People are assuming that a) TeslaFi is right and b) the "fleet" data is accurate. There's no allowances made for weather, battery temperature, etc. So, people are comparing their own idiosyncratic data with other peoples idiosyncratic data, and coming up with what they think are objective numbers and trends. That way madness lies.
That being said you can go mad looking at these stats, I think. My iPhone battery is down to 93% "health" and my MacBook Pro (also essentially irreplaceable battery) is at 94%. Neither has got to a point where I actually feel like I'm losing precious minutes of runtime.
Unless people are actually driving their Model 3s from 100% to 0% on a regular basis, and every mile counts (you would be pretty mad to set out to drive the estimated range, given it could go up and down based on different variables), then the reality is that the drop in range, if it is even real, is a psychosomatic problem rather than a practical one.
The data is flawed anyway. People are assuming that a) TeslaFi is right and b) the "fleet" data is accurate. There's no allowances made for weather, battery temperature, etc. So, people are comparing their own idiosyncratic data with other peoples idiosyncratic data, and coming up with what they think are objective numbers and trends. That way madness lies.
LongRanger
Active Member
Right from picking the car up I stuck it on Energy % instead of Miles for battery indicator and have decided not to bother with the various apps. Living in an area with such unpredictable weather, loads of hilly roads and my long trips being 200+ miles, on a lease car it matters not to me if the battery degrades 10% over 3 years. If it suddenly started losing range like a leaky tap then it would just go back for repair.
I can understand if you have the time to monitor such things and have sunk your own money into the car, it makes sense to look after what your hard work has bought - same as you would with extra oil changes, regular maintenance etc on a petrol or diesel if you really cared about it.
I can understand if you have the time to monitor such things and have sunk your own money into the car, it makes sense to look after what your hard work has bought - same as you would with extra oil changes, regular maintenance etc on a petrol or diesel if you really cared about it.
Jason71
Well-Known Member
I've been wondering if doing a lot of regen is bad for the battery. I have seen an estimate of the M3s regen ability at the equivalent of 75kw/h!. In which case it would be like the equivalent of constant DC charging which would make cars doing a lot of round town driving using regen more prone to degradation than motorway cruisers over the same mileage. i.e. just like ICE cars
Glan gluaisne
Active Member
Looking at the data from Teslamate, it looks as if regen rarely exceeds about 60 kW to 70kw, and then only for a few seconds at a time. Regen recovers around 8% or so of the energy used, roughly, so that would only be about 6 kWh or so for a complete battery discharge, so not really a lot in the overall scheme of things.
Jason71
Well-Known Member
8% Where does that figure come from? Teslamate? How is it determining that? I'm not sure what there is in the Tesla API data that would allow an accurate determination of that?
Glan gluaisne
Active Member
Years of driving cars with regen and looking at data, and not Tesla specific, but regen is regen and will be broadly similar in terms of recovered energy for any car with it, or at least any car that doesn't apply the friction brakes until a very low speed, normally.
Back when I was into amateur race events we used to work on the basis that the brakes might have to deal with about 20% of the energy delivered by the engine in a race on a fast circuit, but much less when driving on the road. This data was used to determine how much heat might build up in the brakes, how much brake cooling might be needed and basic stuff like the best brake pads to use for a given set of conditions (too hard meant poor effectiveness at low speed, too soft meant too much fade at high speed). Not hard to use the data from the brakes to estimate how much energy they were having to deal with.
That could be a loss of 20 miles per gallon rather than on a whole tank! Some years ago I had occasion to have to "wring the neck" of a tiny (and truly dreadful) Matiz that was owned by my stepfather ... I got 26mpg on a long journey... you could get in excess of 50mpg driving normally!
Jason71
Well-Known Member
Not sure about the total. 8% does not sound crazy though I would like a little more to base it on than just your experience. I'm not sure that would pass peer review
But actually thinking about it, Given that dropping from 75mph to 70mph would recover a similar amount of energy to going from 30mph to 0mph maybe motorway driving and town driving are not actually so different anyway whatever the actual figure?
Glan gluaisne
Active Member
Not sure about the total. 8% does not sound crazy though I would like a little more to base it on than just your experience. I'm not sure that would pass peer review
But actually thinking about it, Given that dropping from 75mph to 70mph would recover a similar amount of energy to going from 30mph to 0mph maybe motorway driving and town driving are not actually so different anyway whatever the actual figure?
It's a really hard thing to measure, but about ten years ago some of the more fanatical Prius crowd set about trying to measure it, by semi-hacking into the car and recording live data (can be done is a similar way to the Tesla, I think) they concluded that 8% was about the best the car could ever achieve. Like the Tesla, the Prius doesn't normally use the friction brakes until the speed drops below 5mph, or unless there is a rapid application of the brakes (emergency stop type application), so the read across to any other car with full regen braking is probably reasonable.
Back when I was into amateur racing the cars were instrumented, so we knew how hot various parts of the braking system were getting and also how much cooling air was coming through the ducts. For drag reduction reasons these ducts needed to be as small as possible, whilst still preventing the brakes from getting too hot. As already mentioned, the highest figure we ever saw, for a fast circuit, was about 20% of the total energy in used in any lap being absorbed by the brakes, so that sets an upper bound on regen, one that's way higher than would be seen in road use.
The lions share of the energy goes into pushing the car through the air and overcoming normal rolling resistance, with the former increasing in proportion to the cube of speed through the air. Not hard to work this out, knowing some basic parameters. IIRC, the projected frontal area of the Model 3 is around 2.2m² and it has a published Cd of 0.23, I believe. At 50mph (22.352m/s) the drag force (ignoring rolling resistance) would be 0.5 x 1.225 x 0.23 x 2.2 x 22.352² = ~155 N. The power needed to overcome this aerodynamic drag is going to be 155 x 22.352 = ~3.46 kW. On top of that, energy will be needed to accelerate the mass of the car to that speed, plus there will be power needed to overcome the rolling resistance of the tyres (less than the aerodynamic drag by a lot, and dependent on load, tyre pressure, temperature, surface roughness, surface friction coefficient, etc, so not easy to calculate).
The kinetic energy the car has from travelling at any given speed is the only recoverable element that regen can make use of, as the energy used to overcome rolling resistance and that used to overcome aerodynamic drag is lost, by heating up the air and the road surface. Assuming the same speed of 50mph (22.352m/s) and a car mass of 2,000kg, the kinetic energy will be ~500 kJ, or ~139 Wh, so not a lot, and some of that will be lost as heat to aerodynamic drag and rolling resistance throughout the slowing down period, plus some will be lost due to the loses in the regen system.
If we take a hypothetical and very simplistic journey, where a 2,000kg mass Model 3 accelerates on level ground from a standstill to 50mph, and we ignore rolling resistance, and the drag during acceleration and deceleration (just to over-simplify things), with the car driving for half an hour at 50mph, then it will use about 1,730 Wh from the battery, and could theoretically recover a maximum of about 139 Wh if it could possibly recover all of its kinetic energy during regen braking. That gives a maximum regen of ~ 8.03%.
The number would change a great deal with different circumstances, like terrain, acceleration/deceleration profile, vehicle mass, temperature, etc, but it's not hard to work through a range of different scenarios and come up with the maximum that regen could recover.
Jason71
Well-Known Member
I don't disagree with the basic maths though 2000Kg is a little on the high side unless you have the whole family on board.
The thing I find hard is that no one travels at a constant 50mph or any other speed for any period of time. you are constantly adjusting for bends other traffic etc and every time you lift off you will get a bit of regen which I guess all adds up + the 50-0 at the end. in many of those lift off cases just coasting more and letting friction slow you down might actually be more efficient?? but I think I am probably over thinking this now.
At the end of the day though it is what it is.
Glan gluaisne
Active Member
I agree, that was a very overly simplistic example, and, FWIW, I absolutely did not frig it to give 8%, even though it looked as if I did! I choce half an hour and 50mph as they seemed reasonable numbers, and did think of changing them when I realised that 50mph, half an hour and 2,000kg gave the answer as being ~8%.
You could work through a large number of profiles, and accumulate the KE for every bit of acceleration. Not too hard, and the KE will be the absolute maximum of regen energy that could ever be recovered. I'm pretty confident that the Prius guys who were really into hypermiling, and monitoring all this stuff very closely, will have gathered a lot of data when coming up with the 8% regen figure, though, and I'm happy to just accept that as a pretty reasonable number, although it's not a figure that's easily attainable.
The Prius has a regen display, that shows the kWh used in short sample periods and the regen in those same sample periods, both displayed on a bar graph in the central display. For the 12 years I drove various models of Prius I think I only ever saw the regen as high as 8% a couple of times, most of the time it was down around 4% to 5%.
Given that Teslamate records the power used, the power regenerated and time, it should be possible to produce a Grafana plot rather like the Prius built-in energy display. Might be useful, although having such a display in the car would be better. I used to have that bar graph set to display in my Prius all the time, as it was fun trying to minimise the energy for each sample period (relieved the boredom when I was commuting an hour and half each way to and from work).
Rustybkts
Member
Regarding the regen discussion, I entered home built/converted cars in the RAC's Future Car Challenge in 2010, 2011 and 2012 which was from Brighton to London. A distance of around 60 miles.
All the cars were fitted with continuous data logging and my Lotus Elise EV was logged as regenerating 10% of energy used.
I will say that brakes were only for pussy's as the idea was to use as little energy as possible. I rested a feather on the accelerator to increase speed and traffic lights were monitored well in advance.
All great fun and a pity that they pulled the event after three years after supposedly losing sponsorship.
It was a great proving ground and the hobbyist could produce cars at that time as good if not better than the OEM's who entered their early pre-production models.
All the cars were fitted with continuous data logging and my Lotus Elise EV was logged as regenerating 10% of energy used.
I will say that brakes were only for pussy's as the idea was to use as little energy as possible. I rested a feather on the accelerator to increase speed and traffic lights were monitored well in advance.
All great fun and a pity that they pulled the event after three years after supposedly losing sponsorship.
It was a great proving ground and the hobbyist could produce cars at that time as good if not better than the OEM's who entered their early pre-production models.
MrBadger
Badger out
I heard $15k when someone in another thread hit an object in the road that severed a cooling line. Can't remember if it was SR, MR or LR.
At one point, it was mooted that we might get battery swaps instead of some charging but I think that was just BS. It was probably this video.
In practice when you are going downhill you feather the accelerator the amount to keep the car rolling at the speed you need so it's pretty close to coasting ... obviously real coasting would mean in that scenario that the car picked up speed which you would then have to reduce with sudden regen or actual brakes... probably wasteful too. It's interesting to look at the power/regen line on the screen to see when you are balanced between the two i.e. coasting.
Glan gluaisne
Active Member
Back when the Prius first came out there were a group of fanatical hypermilers who had this technique down to a fine art, balancing the throttle so as to keep the car coasting for as long as possible, using the power display to make sure they stayed as close to zero as possible. There were often fierce arguments between two different clans of hypermilers, those that believed that maintaining the coasting condition for as long as possible was the optimum and those that believed that the "pulse and glide" technique was the optimum. I tended to avoid getting involved, but was personally convinced that maintaining a near-constant speed and maximising coasting was the most sensible option. "Pulse and glide" seemed to me to be a bit antisocial with regard to other road users.
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