Case for the 800 mile Cybertruck

[ldjessee]

Whether we wish to charge to 100% depends on circumstances. &

Whether we wish to drain to 5% depends on circumstances.


If I was driving my CT around for everyday use, for sure, 80% charge is fine, and when it gets down to 20%, charge up again. Either way, I probably wouldn't care.

But

But definitely, If I am towing my RV, I will charge to 100%. I'ts not that I'm towing for weeks on end. 10 to 30 mins extra waiting.. Suits me.

If it gets me to a spot where I will be spending 3 weeks with 8% left... fantastic.
These recommended charging limits are arbitrary. The degradation to battery is pedantic to me.

Its good it suits your style, but for me, I would rather not wait, get backon the road, than stop again, and for less than the time it takes to charge the last 10% (usually 20-30 minutes on most EVs I have seen tested on State of Charge by Tom Moloughney), I will charge up and arrive with more charge.

 

[Edphonse]

Uh... you'll have to show me some citation for that assertion. I'm an avid EV aficionado and have NEVER heard anyone knowledgeable in Li ion batteries say discharging below 10% hurts the lifespan of your battery. What IS true, it that you shouldn't STORE a Li ion battery at a low state of charge (and by STORE we mean for periods of months or more) but on a road trip you'll only be at a low state for minutes/hours before charging back to a healthy state of charge. Similar goes for charging to 100%. The best practices strategy is to hit your 100% SOC as close to departure time as possible. Either schedule your charge the night before departure to start charging in the wee hours, or better! ramp down your charging amps so that a slow charge all night gets you to full at departure time.

The primo strategy for road trip charging is to leave with 100% and go to the farthest charger you can get to. Charge just enough to arrive at your second charging stop at as low a state of charge as you, and your travelling partner, are comfortable with (my S/O demands a >12% buffer, I aim for <2%), then do the same until your final DC fast charging stop for the day. This last DC stop is where you have a decision to make. Will you be staying the night at/near a level 2/destination charger? Or will you need some range at your next stop for local trips or to hit a DC fast charger the next morning? Because THAT will dictate how high to charge then.

Arriving at a DC fast charger at minimal charge allows you to add the most miles in the least time. Charging rates at below 30%-50% (depending on vehicle) will be at the highest kWs, then the taper starts, so unnecessarily charging above those levels along the way is going to slow you down.

So, I would minimize the amount of time your battery is at 100% or 0%, i.e. don't leave it overnight at either extreme, although doing it occasionally won't do much damage to your battery. If you plan to SuperCharge at your intermediate layover, I'd arrive at your hotel at >5% and top up in the morning while you're eating breakfast.

I did 2.5 years of r & d at the University of California at Riverside on growing LiFePO4 cathodic material and while it is true that completely draining a li ion battery isn't nearly as devastating as a lead acid battery, it can wear the "battery" out faster. Why did I put that in quotes? Because when most people speak of a li ion battery they are talking about multiple cells, not a single cell. It is an important distinction since a single cell degradation or failure will cause other cells to compensate.

Now, the 2 things that I spent a lot of time analyzing my cathodes were how to best control their growth (during the synthesis process) and what caused them to degrade through use. The 2 biggest factors for degraded cells are how many cycles the battery has gone through and how aggressive were they charged or discharged?

The cycles portion is self explanatory but the charge/discharge is a little less intuitive. Li ion batteries that are slowly charged and discharged will have a better cycle capacity than ones that are operated inversely. So for quick math you can use Power (P) = Voltage (V) x Current (I). This isn't 100% because as you put a load on a li ion pack it will have voltage droop and generate heat, which for most materials, increases resistance which just means you lose even MORE energy to waste heat. So if your tesla is using 40kW to drive down the road on a 400v pack, at 100% SOC, the voltage will usually be higher than its rated (I have several large 12 v li ion packs that are rated at 13v but are actually 13.5 at 100% soc but I can't speak specifically on the serial and parallel arrangements of teslas) but for ease of calculations, let's just say it is 400v max, so the car is discharging the batteries at 100 amps. Li ion batteries are great at maintaining a relative flat voltage through its SOC at a constant discharge rate, until about 11-18%. Then the voltage drops off quickly, by upwards of almost 1v (the typical operating ranges I put my 12v banks through range from 14.4v to 12v) per cell at 0% soc and go any lower can start to cause damage, doesn't mean it will. Meanwhile at the low but greater than 0% soc, to draw the same power, the batteries has to supply more current, which generates more heat, which means even more current is now needed to overcome to higher resistances. So now at low capacity, the battery could be as low as 300v. That means to have the same power output, you have to draw ~30% more current excluding heat losses.

Will it cause a notice change in health of the battery pack? Most likely not if not done regularly. But if it is done excessively and the packs are consistently recharged at high rates, cell degradation is more likely to happen on that pack than a pack that is driven between 20% and 80% capacity along with using level 1 or level 2 charging vice level 3.

I don't work in the li ion battery field anymore (over 10 years at this point), just nuclear power, so some technology could have progressed. So the research I did maybe a little dated, but the physical properties should still be applicable.

 

[Ogre]

Its good it suits your style, but for me, I would rather not wait, get backon the road, than stop again, and for less than the time it takes to charge the last 10% (usually 20-30 minutes on most EVs I have seen tested on State of Charge by Tom Moloughney), I will charge up and arrive with more charge.

I usually only mess with 80 - 100% when I’m prepping for a long trip not even always then.

 

[Crissa]

I usually only mess with 80 - 100% when I’m prepping for a long trip not even always then.

Alot of Battery Management Systems require you to get to 100% to do cellbalancing, so keep that in mind.

-Crissa

 

[ldjessee]

Alot of Battery Management Systems require you to get to 100% to do cellbalancing, so keep that in mind.

-Crissa

I have heard once a year, maybe even once every 6 months do a recharge to full 100%, if you are really cycling the battery hard by draining it very low for the cell-balancing you mention.

 

[Crissa]

I have heard once a year, maybe even once every 6 months do a recharge to full 100%, if you are really cycling the battery hard by draining it very low for the cell-balancing you mention.

Yeah.

My old Zero needs it about once a month at least, sometimes a few times in a row...

But it's eight years old. And the management is rudimentary.

-Crissa

 

[ldjessee]

Yeah.

My old Zero needs it about once a month at least, sometimes a few times in a row...

But it's eight years old. And the management is rudimentary.

-Crissa

You see the new stealth fighter looking 2023 model yet?

 

[Crissa]

You see the new stealth fighter looking 2023 model yet?

Which one? I haven't. The black FXE? The S looks pretty much the same as mine.

New ones are much too rich for my blood.

-Crissa

 

[ldjessee]

It was the FXE reveal photo, but looking at the material on their website, it looks like the production bike is gray and black.

I never thought I would buy such an expensive motorcycle as I have now when I bought my previous one, but after riding it for 10 years, we were better off financially, so could afford it.

Now when I look at the prices of the LiveWire, etc... just think that is crazy... but then remember no oil changes, engine maintenance, chain/belt inspections and adjustments, etc...

Just wish someone would make an electric bagger. I want a fixed front fairing (some work could be done on making that a bit better aerodynamic compared to most on the market right now), a good seat, a detachable rack, and hard bags. But still have not see one offered... atleast in the US and for something less than a one off custom build.

 

[Crissa]

It was the FXE reveal photo, but looking at the material on their website, it looks like the production bike is gray and black.

I never thought I would buy such an expensive motorcycle as I have now when I bought my previous one, but after riding it for 10 years, we were better off financially, so could afford it.

Well, they change the color every year or so ^-^

Electric bikes also don't care about being dumped as much, either. The only fluid is the brakes, and those aren't supposed to leak anyhow, so... you can be much more rough with the electric.

-Crissa

 

[Rthardison]

Uh... you'll have to show me some citation for that assertion. I'm an avid EV aficionado and have NEVER heard anyone knowledgeable in Li ion batteries say discharging below 10% hurts the lifespan of your battery. What IS true, it that you shouldn't STORE a Li ion battery at a low state of charge (and by STORE we mean for periods of months or more) but on a road trip you'll only be at a low state for minutes/hours before charging back to a healthy state of charge. Similar goes for charging to 100%. The best practices strategy is to hit your 100% SOC as close to departure time as possible. Either schedule your charge the night before departure to start charging in the wee hours, or better! ramp down your charging amps so that a slow charge all night gets you to full at departure time.

The primo strategy for road trip charging is to leave with 100% and go to the farthest charger you can get to. Charge just enough to arrive at your second charging stop at as low a state of charge as you, and your travelling partner, are comfortable with (my S/O demands a >12% buffer, I aim for <2%), then do the same until your final DC fast charging stop for the day. This last DC stop is where you have a decision to make. Will you be staying the night at/near a level 2/destination charger? Or will you need some range at your next stop for local trips or to hit a DC fast charger the next morning? Because THAT will dictate how high to charge then.

Arriving at a DC fast charger at minimal charge allows you to add the most miles in the least time. Charging rates at below 30%-50% (depending on vehicle) will be at the highest kWs, then the taper starts, so unnecessarily charging above those levels along the way is going to slow you down.

So, I would minimize the amount of time your battery is at 100% or 0%, i.e. don't leave it overnight at either extreme, although doing it occasionally won't do much damage to your battery. If you plan to SuperCharge at your intermediate layover, I'd arrive at your hotel at >5% and top up in the morning while you're eating breakfast.

Thanks for the long response. I was speaking to my lifespan (I.e stress driving below 10% hoping to make it to the next charger is not good for my lifespan). Haha

I agree going below 10% should not hurt the battery. Leaving it there I believe will reduce lifespan the same as charging to 100% and leaving it sitting there at 100%. Both of these scenarios put the battery under stress that will eventually lead to shorter lifespan. This apparently does not apply to LFP batteries, but does on the broad population on the road today.

 

[charliemagpie]

Its the journey not the destination, I don't wish to turn my journeys into military exercises.

Fark it.. if the charger is there, charge the bloody thing and be done with it.. go to the dunny, have a coffee.. watch YouTube. 20 minutes extra not going to kill anyone.

But not saying that's for everyone...

 

[Rthardison]

Another thought here. Tesla Semi. Goes 300 miles pulling 40 tons. Pricing is in the ballpark of what an 800 mile Cybertruck would look like regardless.

As a bonus, you might even get it sooner.

I like the thought. And now, the US is offering 40,000 tax credit. Something to think about. A little challenging parking at the grocery store.

 

[JBee]

Battery cycle life expectancy is directly related to depth of discharge. Typically the less you use a battery the longer it lasts

 

[Ogre]

I like the thought. And now, the US is offering 40,000 tax credit. Something to think about. A little challenging parking at the grocery store.

So is any truck with a 30+ foot trailer.