Comment by londons_explore | Hacker News Reader

Comment by londons_explore | Hacker News Reader

Parent Full thread

londons_explore

Copper as a material is fairly unique in that many things we make of copper have alternatives that could be used if the cost was too high.

For example, copper is used for water pipes. But we also have steel and plastic pipes.

Copper is also used for wiring and electrical conductors - but we can redesign circuits to use higher voltages (double the voltage needs only one quarter of the copper). Or, we can switch to aluminium for wiring, which is also a good conductor.

Plenty of users are already economical with copper. For example, have you noticed that if you buy a USB cable that's 1 meter it is less than half the price of a 2 meter cable? Don't you think that's odd, because presumably there is a fixed labour+materials cost for the connectors, and a per-meter cost for the cable itself? No... The USB specification requires a specific wire resistance, which means longer wires must also be thicker (more copper) to meet that spec. Lately, very cost sensitive USB wires have moved to aluminium conductors.

There is talk of electric cars with 800 volt (vs 400 volt) battery systems... The main reason to switch is to reduce the cost of copper wires and motor coils.

> There is talk of electric cars with 800 volt (vs 400 volt) battery systems... The main reason to switch is to reduce the cost of copper wires and motor coils.

It's not just talk, a number of EVs run at 800V (Porsche Taycan, Audi E-Tron GT, Lucid Air, Hyundai Ioniq 5, Kia EV6). And while there may be a cost benefit for the manufacturer, it also makes a more desirable car for the owner, since they can charge twice as fast. While most 400V EVs top out around 125 kW charging rates, the 800V EVs can hit mid-200s.

Wait what? How does the motor voltage affect charging rate? That's limited by the chemistry in the cells and perhaps heat dissipation, isn't it?

You are correct. The max charging rate of the battery is independent of its voltage, and runs around 2.4 C (Tesla) to 2.8 C (Porsche). You only get this max rate for the first 20% or so of SOC (state of charge). One way to think about this is that each individual cell has a nominal voltage around 3.7, and doesn't care how it's wired into the battery.

The confusion arises because a given DC charger can deliver twice as much power at 800 volts as it can at 400, assuming it's running at its max current. But that's a limitation of the charger, not the battery. This article has a brief discussion:

https://insideevs.com/news/512344/porsche-taycan-fast-chargi...

[ I used to work for a car company, programming battery charge controllers among other things ]

The below link states the peak C rate for modern Tesla batteries is 3C

https://insideevs.com/news/519382/tesla-model3-82kwh-chargin...

It's also a limitation of the specifications the charger designers are working to - CCS2 for example is 500A max.

Which already requires water-cooled cables and connectors.

The charging voltage has to mach your battery voltage, so twice the voltage in the charging cable means you can send more power for the same amount of amps.

> The charging voltage has to mach your battery voltage

Nope, the charging circuitry (most commonly) and/or BMS (less common) inside the car can handle this easily.

In nearly all DC charge setups the charge voltage (ie. the voltage on the wire you plug into the car) does match the battery voltage.

Sure, it's technically possible to do voltage conversion on the car side, but it either requires expensive and heavy hardware (A device that can convert 300 kilowatts from 400v to 800v isn't cheap!), or it requires funky use of the electric motor inverters and coils for voltage conversion instead - which in turn constrains the design and forces compromises.

In either case, you probably with have ~3% efficiency losses, which effectively increases the total energy bill for the customer over the lifetime for the car by 3%, which might be thousands of dollars.

> In nearly all DC charge setups the charge voltage (ie. the voltage on the wire you plug into the car) does match the battery voltage.

Except the battery pack on the car is 300V to 400V depending on the model car, but the grid voltage is 120V (mobile charger) to 480V (Supercharger station). Some EVs are 800V even. So tell me again how the input voltage matches the battery voltage? ;)

The reality is that either the charger or maybe the BMS, either inside the car or elsewhere, is not only stepping up or stepping down the voltage to match the battery, but also rectifying the AC grid input into DC for the battery packs.

> In either case, you probably with have ~3% efficiency losses, which effectively increases the total energy bill for the customer over the lifetime for the car by 3%, which might be thousands of dollars.

There is more than 3% efficiency losses usually and some commercial charge providers handle that differently. Most directly expose the overhead by charging for “kwh used” whereas car shows “kwh stored in battery”, but Tesla does (or did until recently) just charge for what was “stored”.

I expect 95% of chage is done by normal charger, so not so much financial difference by DC efficiency loss.

Twice the voltage = half the current for the same power, and 1/4 the resistive losses in the wiring.

Charging power is roughly battery voltage * charging current. There are practical limits to battery voltage, but higher charging current is expensive.

> but we can redesign circuits to use higher voltages

Rings circuits[0], popular in the uk due to post-wwii copper shortages, use less wiring than the typical radial circuits. Wikipedia says about 25% less?

https://en.wikipedia.org/wiki/Ring_circuit

The US allows sharing a neutral line between two circuits, which also saves copper

This makes sense about the 800 voltage. I've bought COPX because of electric cars. Oddly enough copper has dropped due to recession speculation.

Reply on news.ycombinator.com