Is Tesla cheating with numbers?

3708 Views 54 Replies 20 Participants Last post by Splendid Systems, 3 d ago

Splendid Systems

Discussion Starter · 7 d ago

Tesla has historically been very secretive about the true capacity of its battery packs.

Their efficiency seems o be out of this world and their battery packs seem to last forever with barely any degradation.

A Tesla 85kWh pack that has a usable capacity of 77kWh is made of 7106 Panasonic 3.6V 18650 3600mAh batteries.

Only if you do the math, 7106 x 3600mAh x 3.6V is actually 92kWh.

When you charge them AC or DC, the charging losses seem to be larger on Tesla packs than other makes of EV's.

Could Tesla be hiding kWh through their BMS to make efficiency and battery degradation look better than it really is?

If so, is a scandal brewing?

Reactions: 4

1 - 20 of 55 Posts

kcrane

· #2 · 7 d ago (Edited)

No, unless of course you are the first person to do the calculation and reach that conclusion since those packs were launched. So for eg Munro or TeslaBjorn and dozens of Tesla fan boys and/or Tesla sceptics have missed it. That seems unlikely.

You are right about efficiency, on a 250 mile journey at motorway speeds yesterday (warm, light wind, dry) my Model Y did 4.5 miles kWh, for a range overall of 340 miles.

I think efficiency is a reasonable proxy for the level of excellence specifically in EV engineering the manufacturer has achieved, as I think Mr Farley of Ford has recently come to accept.

Appropo of nothing my other two *** packet measures of EV manufacturers are number of EVs built per year and the amount of profit made per vehicle.

Reactions: 2

Splendid Systems

Discussion Starter · #3 · 7 d ago

Bjorn actually couldn't make sense of it, his charging losses were all over the place and depended more on SOC of the car than any other parameter.

Also his tests were never empty to full and the Tesla's conveniently take forever to charge from 90% to 100% on DC.

Reactions: 1

kcrane

· #4 · 7 d ago

😮 the forum software doesn't like F. A. G.

kcrane

· #5 · 7 d ago

Splendid Systems said:
Also his tests were never empty to full and the Tesla's conveniently take forever to charge from 90% to 100% on DC.

This is true.

I often set the target charge to 100% when I stop for coffee so that the charger doesn't ping me to rush back to the car. Up to 80% is quick, 80-90% much slower, over 90% is pedestrian.

😱 is that because it is actually adding 14 kWh not the 7kWh you'd think 10% represents?

Reactions: 2

4EV-ER

· #6 · 7 d ago

TBH you cannot reverse-excel the workings of BMS so more or less it is masked somehow.

You can get a vague approximation, but there are too many variables so trying to interpret it from the cars own approximations will only get you so far...

GenerationGav

· #7 · 7 d ago

kcrane said:
😱 is that because it is actually adding 14 kWh not the 7kWh you'd think 10% represents?

That would be very easy to tell by allowing it to charge to 100% and then seeing what the charger has put into it.

Reactions: 1

Aleras

· #8 · 7 d ago (Edited)

Splendid Systems said:
Tesla has historically been very secretive about the true capacity of its battery packs.

Their efficiency seems o be out of this world and their battery packs seem to last forever with barely any degradation.

A Tesla 85kWh pack that has a usable capacity of 77kWh is made of 7106 Panasonic 3.6V 18650 3600mAh batteries.

Only if you do the math, 7106 x 3600mAh x 3.6V is actually 92kWh.

When you charge them AC or DC, the charging losses seem to be larger on Tesla packs than other makes of EV's.

Could Tesla be hiding kWh through their BMS to make efficiency and battery degradation look better than it really is?

If so, is a scandal brewing?

I actually have some real world experience of this. I am looking at buying a Tesla model s 2018 so cars i have been looking at are going 5 years old.

I have looked at several personally. Test driven three of them . I have also got detailed information on three more including the information required to calculate battery health.

There is a detailed article on Tesla info on how this can be done with information from the energy usage page and the % charge remaining its pretty accurate. Its based on usable capacity when pack was new ie 100kwh pack had 102kwh and 98kwh usable when new.

Teslafi harvests this information at fleet level. So its incredibly accurate. More so than for any other Ev manufacturer.

My personal findings. Well pretty amazing tbh. The best was 5% degredatoon. The worst 8%. Most of this is front loaded by all accounts. Teslafi confirms this over many tens of thousands of cars. This is on 5 year old cars. The ones I have looked at had between 28k and 49k miles. My take from this. I really am not that worried about battery degredation on the cars i am looking at.

Even 14 / 15 plate cars with 100k miles have been found to have only 10% degredation.

Honestly I checked myself on half a dozen cars three of which i have personally laid hands on myself. Impressive stuff.

Yes some packs failed particularly on early cars 85kwh mainly. Even these were still working with decent life at 140k when they were replaced.

See less See more

Reactions: 4

Padrino

· #9 · 7 d ago

Splendid Systems said:
A Tesla 85kWh pack that has a usable capacity of 77kWh is made of 7106 Panasonic 3.6V 18650 3600mAh batteries.

Only if you do the math, 7106 x 3600mAh x 3.6V is actually 92kWh.

Another one of your highly controversial posts.... Perhaps this will be a HUGE revelation to you but ALL car makers have built in protectiv layer. Every single one of them have at least 4kWh buffer.
If you don't know what buffer mean, I suggest you can use Google and educate yourself 😁

kcrane

· #10 · 7 d ago

If the 92kWh pack size is right then 77 kWh usable would be a very generous buffer?

Reactions: 1

simcity

· #11 · 7 d ago

Aleras said:
My personal findings. Well pretty amazing tbh. The best was 5% degredatoon. The worst 8%. Most of this is front loaded by all accounts. Teslafi confirms this over many tens of thousands of cars. This is on 5 year old cars. The ones I have looked at had between 28k and 49k miles. My take from this. I really am not that worried about battery degredation on the cars i am looking at.

Even 14 / 15 plate cars with 100k miles have been found to have only 10% degredation.

Sounds about right. My car is a 67 plate with 87K miles. Pack degradation is 7.4% according to the Tessie app.

Naturetech

· #12 · 7 d ago

I'm somewhat ambivalent about the OP's proposition. It may be true, but it wouldn't matter to me. The reason is this: most of us EV buyers worry about depleted range over time. If the buffer keeps adding more available capacity through BMS settings to prevent apparent depletion, it's fine by me.
I must say that I too am intrigued by Tesla's slow depletion; it's not like they were using secret cell chemistry 5-10 years ago. I put it down to superior cooling, but who knows?

Reactions: 2

simcity

· #13 · 7 d ago

Splendid Systems said:
Tesla's conveniently take forever to charge from 90% to 100% on DC

....errr on balance so do the vast majority of BEV's when rapid charging on DC. That's characteristic of the charge curve and nothing more sinister.

Reactions: 3

Electrickery

· #14 · 7 d ago

I would hazard a guess that the variable efficiencies seen at rapid chargers are mostly due to Tesla's method of battery heating, it's quite a lot more aggressive than other makes isn't it, to enable more rapid charging at superchargers?
Would also make it far more noticeable at a high SOC as the battery heating constitutes a far higher proportion of the overall charge put in.

Reactions: 1

kcrane

· #15 · 7 d ago

Electrickery said:
I would hazard a guess that the variable efficiencies seen at rapid chargers are mostly due to Tesla's method of battery heating, it's quite a lot more aggressive than other makes isn't it, to enable more rapid charging at superchargers?
Would also make it far more noticeable at a high SOC as the battery heating constitutes a far higher proportion of the overall charge put in.

I know it sounds like I do little but sip coffee at motorway services Superchargers, but I deliberately avoid the aggressive battery heating so that a) I don't waste the expensive leccy I've already got in the battery and b) so that it takes longer to charge and gives me more time for the flat white and cheese toastie.

Did I mention I'm retired?

🙂

Reactions: 5

CoalPorter

· #16 · 7 d ago

Splendid Systems said:
Only if you do the math, 7106 x 3600mAh x 3.6V is actually 92kWh.

Or maybe those numbers are not very precise.

4EV-ER

· #17 · 7 d ago

Electrickery said:
I would hazard a guess that the variable efficiencies seen at rapid chargers are mostly due to Tesla's method of battery heating, it's quite a lot more aggressive than other makes isn't it, to enable more rapid charging at superchargers?
Would also make it far more noticeable at a high SOC as the battery heating constitutes a far higher proportion of the overall charge put in.

Not just Tesla. Heating and cooling is used during charging to make it more effective, but it will affect efficiency. I keep track of my charges and I can see the difference depending on situation.

Either you use more leccy for heating when arriving at the charger or then you use more while charging.

You can decide which way is better, but you can't really turn it off. BMS manages the heating either way.

Reactions: 2

Electrickery

· #18 · 7 d ago

4EV-ER said:
Not just Tesla. Heating and cooling is used during charging to make it more effective, but it will affect efficiency. I keep track of my charges and I can see the difference depending on situation.

Either you use more leccy for heating when arriving at the charger or then you use more while charging.

You can decide which way is better, but you can't really turn it off. BMS manages the heating either way.

Yes I know most cars do it, I wonder if Tesla's heat it higher or have a more powerful heater? Not that many cars preheat before you get to a charger either afaik.

Grend..

· #19 · 7 d ago

Well I thought the cell voltage in use was 3.3v, 3.6v being the full state on charge. That gives more like the 85kW

simcity

· #20 · 7 d ago

4EV-ER said:
Not just Tesla. Heating and cooling is used during charging to make it more effective, but it will affect efficiency. I keep track of my charges and I can see the difference depending on situation.

Either you use more leccy for heating when arriving at the charger or then you use more while charging.

You can decide which way is better, but you can't really turn it off. BMS manages the heating either way.

Tesla's battery preconditioning and overall temperature management is pretty well sorted, and copes well in all manner of ambient temps, pretty remarkably actually.

The only material advantage to not preheating on the way, and doing it at the charger, is if you have something like free lifetime supercharging so you're not paying for the leccy from the SuC. Otherwise the penalty is a longer charge time. The battery simply needs to be warm (not too hot) to accept a fast DC charge.

Reactions: 1

1 - 20 of 55 Posts