Structural batteries in electric vehicles

[Piotrsko]

The best example of the forward control batteries underneath concept I know of is the Chinese weego (spelling?)

Shame it's cheap throwaway manufacturing.

[cRiPpLe_rOoStEr]

Originally Posted by Piotrsko

The best example of the forward control batteries underneath concept I know of is the Chinese weego (spelling?)

There were some ancient electric delivery vans which resorted to a similar setup, as they were much quieter for early-morning milk and bread delivery. But I was considering more specifically the fitment of lead-acid batteries enough to provide a reasonable range for daily usage while keeping within the maximum GVWR allowed for a car driving license in my country.

[freebeard]

The best example ... I know of is the Chinese...

There were some ancient electric delivery vans which resorted to a similar setup

The Lohner–Porsche Electromobile

With hub motors just like Aptera FedEx/Bollinger.

[JSH]

Originally Posted by Isaac Zachary

My intuition tells me that the batteries in EV's are a lot like cellphone and laptop batteries. Those seem to lose capacity and die after 5 years or so. And they don't sit out in the elements like a car does. That and I've had an impossible time finding decent aftermarket replacement batteries. Half the time they have the same or worse capacity as the aged original and die within months.

I wouldn't base much on cellphone or laptop batteries. While the cells are similar the battery designs and usage are very different.

Design:
Cells: Phones and laptops have one to 4 cells. If one fails for some reason it has a huge hit to the performance of the battery back. EVs have hundreds to thousands of cells in their battery packs so if one fails the effect is very minor.

Temperature: Phone and laptops have no cooling or are air cooled. They frequently get too hot and are run outside of their optimal temperature. Heat is death for a battery. EVs have liquid heating / cooling. The BMW will heat or cool the battery to keep it in an optimal temperature range for performance and longevity.

Reserve Capacity: Most personal electronics allow a customer to use almost all the capacity in a battery. The design goal is maximum battery life with the smallest / lightest battery. With EVs this varies by manufacturer. Most traditional automakers are conservative and hold back 10 - 15% of the battery capacity to increase battery life. Tesla is the outlier here and typically allows 98% of the battery to be used. (This also helps them get those long EPA range ratings and high efficiency ratings)

Design Life: Personal electronics have a 2 to maybe 5 year design life. Designers go for maximum performance for that short life because there is no reason to hold back on a product that will be obsolete in a few years. Cars have a 15 to 20 year design life. People expect a car that costs tens of thousands of dollars to last for decades.

Usage:

People abuse personal electronics batteries. A lot of what we consider normal usage is really hard on a battery.

• People charge to 100% every charge - for long life we should charge to 80% or 90%.
• People discharge to 10% or even 0% - for long life we shouldn't discharge past 20%
• People let their phone cook at 100% on the charger overnight. Phone manufacturers have only recently have started putting in features to smart charge overnight.
• People fast charge every charge. The faster you charge a battery the more heat is generated and heat is death for a Li-Ion battery.

With an EV a lot of protection and smarts are build into the car. Most will let you set a maximum charge percentage and that is on top of the reserve the manufacturer builds in.

The usage is also very different. Phone batteries are sized so that the typical person is going to use most of the battery capacity every day. With cars the maximum capacity is rarely used. The median person drives 40 miles in a day. The typical new EV has a 250 mile range today so in a typical day less than 20% of the battery capacity is used. Then it can be slowly charge overnight

[Piotrsko]

I'll add: your phone doesn't draw 800 amps to produce a couple hundred KW dissipated. And 100% indicated charge is about 4.2v per cell, mine is 3 cell in parallel but still 4.2 max voltage oyherwise you'd need a buck inverter in the phone because supply maxes out around 5 volts except for the really new stuff running USB "C".

[JSH]

Originally Posted by Piotrsko

I'll add: your phone doesn't draw 800 amps to produce a couple hundred KW dissipated. And 100% indicated charge is about 4.2v per cell, mine is 3 cell in parallel but still 4.2 max voltage oyherwise you'd need a buck inverter in the phone because supply maxes out around 5 volts except for the really new stuff running USB "C".

No phones don't draw 800 amps but I wonder about the ratio of maximum current draw to battery size.

My iPhone XR has a 2.94 Ah battery. When it came out a Model 3 long range had a 230 Ah battery.

[Isaac Zachary]

One thing about phone battery cooling is that the outer surface area to volume ratio is much greater making it cool much better without the need for external cooling.

Originally Posted by JSH

No phones don't draw 800 amps but I wonder about the ratio of maximum current draw to battery size.

My iPhone XR has a 2.94 Ah battery. When it came out a Model 3 long range had a 230 Ah battery.

Amp-hours are kind of a funny way to compare a single cell pile to a multi-cell battery. Watt-hours would seem to be a better metric. Same thing with current vs power.

The 2.94Ah iPhone cell has a nominal voltage of around 3.6V. So that's almost 10.6Wh.

The Model 3 Long Range battery is around 79,000Wh, or 7,464 times bigger.

[JSH]

Originally Posted by Isaac Zachary

One thing about phone battery cooling is that the outer surface area to volume ratio is much greater making it cool much better without the need for external cooling.

My legs say otherwise when I try to stream full screen with my laptop on my lap. My phone gets physically hot to the touch when charging. Both are well outside of the optimal temperature range for Li-Ion batteries (60 to 95F)

Originally Posted by Isaac Zachary

Amp-hours are kind of a funny way to compare a single cell pile to a multi-cell battery. Watt-hours would seem to be a better metric. Same thing with current vs power.

The 2.94Ah iPhone cell has a nominal voltage of around 3.6V. So that's almost 10.6Wh.

The Model 3 Long Range battery is around 79,000Wh, or 7,464 times bigger.

kWh works too. Phone batteries usually have capacity in mAh while cars usually have kWh ratings. Easy enough to convert back and forth.

[Isaac Zachary]

Originally Posted by JSH

My legs say otherwise when I try to stream full screen with my laptop on my lap. My phone gets physically hot to the touch when charging. Both are well outside of the optimal temperature range for Li-Ion batteries (60 to 95F)

kWh works too. Phone batteries usually have capacity in mAh while cars usually have kWh ratings. Easy enough to convert back and forth.

A lot of the heat in a laptop comes from the CPU and the GPU. Those are usually activally cooled (on laptops at least) and that's with a thermal limit of nearly 100⁰C (212⁰F).

Ah need to be multiplied by the voltage to get Wh. So yes, that's pretty easy.

[cRiPpLe_rOoStEr]

Besides cooling, the chemistry of Lithium batteries for a phone or for an EV are different. IIRC a phone battery has a much greater fire hazard.