4 ms·

I'm confused about why you think the wire would be a challenge. I'm not at all knowledgeable about high voltage/power stuff like this so maybe I'm missing somet

by gpm 6y ago

I'm confused about why you think the wire would be a challenge. I'm not at all knowledgeable about high voltage/power stuff like this so maybe I'm missing something? A quick search tells me that 1000 kcmil wire is rated for 450 amps [1]. Another quick search finds that reasonably sized 1000 kcmil rated for 15000 volts are available and reasonably sized for a vehicle charger [2]. [1] http://wiresizecalculator.net/wiresizechart.htm http://wiresizecalculator.net/wiresizechart.htm [2] (note that kcmil and mcm mean the same things) https://www.lighting-gallery.net/gallery/displayimage.php?pos=-137753 https://www.lighting-gallery.net/gallery/displayimage.php?po...

alacombe 6y ago
For reference, a 1000kcmil wire is a 24mm section of copper wire, that alone over any length would be expensive as hell. If you want to go with aluminium wire, you have to bump your wire to 1750kcmil, or 34mm section. Just moving that beast is a workout, not to mention a nightmare to store, as it won't allow to be coiled is sharp bends.
- octoberfranklin 6y ago
  And stiff! I can't bend a 24mm-diameter solid copper rod with my bare hands. Can you? Going stranded enough to feel even remotely like a "cord" or "cable" will bloat that diameter far, far beyond 24mm. I used to work with ~9mm diameter solid copper and even for that I treated it like EMT and used task-specific benders to shape it.
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conk 6y ago
The higher the voltage the faster the dielectric breakdown of insulators. And the cable/plug needs to be designed for 100k+ operations. 1000 kcmil cable x2 +ground and insulation is going to be one beefy cable. I’m not saying it can’t be done, just that it’s not a trivial problem to solve. Add to this an environment with a wide range of ambient temperatures and untrained humans sure to be yanking on stuff. I just would like to see some details on exactly how these claims will be achieved rather than some marketing puff piece. And Toyota is not alone here, GM pulled the same with the hummer EV and “watts to freedom” marketing buzz with no explanation of what that even means.
amluto 6y ago
That’s the ampacity of wire, field-installed in conduit, per the NEC. This isn’t directly relevant to things in cars. Here’s a table that may be more relevant: http://www.ecswire.com/mmspecs/Specsheets/Belden/leadWireSelectionChart.pdf http://www.ecswire.com/mmspecs/Specsheets/Belden/leadWireSel... So you don’t actually need so big a cable. You also wouldn’t normally be using MV cables for a car charger — getting 15kV safely through a car charger terminal sounds like an interesting challenge. But 450A at 1kV doesn’t sound like a particularly big deal. Keep in mind that there’s potentially a free factor or 2 available. I don’t know how actual DC chargers work, but I imagine you could supply -1kV and 1kV relative to ground without too much trouble, resulting in effectively 2kV while only operating at 1kV relative to ground. AIUI you trigger rather more onerous NEC rules if you get to much higher voltages relative to ground.
- octoberfranklin 6y ago
  The NEC is basically the fire code for building wiring. It's not a general safety code. It's 80% about making sure buildings don't burn down, and 20% about peoples expectations about what parts of their house can shock them if a fork is stuck into them. That's it.
  - amluto 6y ago
    If you look at the actual construction of a Supercharger station [0], the charger stall units don’t have any power electronics. There is a pair of big DC wires from each stall unit running to the big AC-DC units that are usually behind a fence. Regardless of how anyone may feel about the NEC, this is a field installation that needs to follow the rules. So those big cables will be sized per the NEC ampacity tables, and they will follow NEC rules based on their operating voltage. [0] I randomly stumbled on one under construction.

by gpm 6y ago

alacombe 6y ago

For reference, a 1000kcmil wire is a 24mm section of copper wire, that alone over any length would be expensive as hell. If you want to go with aluminium wire, you have to bump your wire to 1750kcmil, or 34mm section. Just moving that beast is a workout, not to mention a nightmare to store, as it won't allow to be coiled is sharp bends.

octoberfranklin 6y ago
And stiff! I can't bend a 24mm-diameter solid copper rod with my bare hands. Can you? Going stranded enough to feel even remotely like a "cord" or "cable" will bloat that diameter far, far beyond 24mm. I used to work with ~9mm diameter solid copper and even for that I treated it like EMT and used task-specific benders to shape it.
deleted 6y ago
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conk 6y ago

The higher the voltage the faster the dielectric breakdown of insulators. And the cable/plug needs to be designed for 100k+ operations. 1000 kcmil cable x2 +ground and insulation is going to be one beefy cable. I’m not saying it can’t be done, just that it’s not a trivial problem to solve. Add to this an environment with a wide range of ambient temperatures and untrained humans sure to be yanking on stuff. I just would like to see some details on exactly how these claims will be achieved rather than some marketing puff piece. And Toyota is not alone here, GM pulled the same with the hummer EV and “watts to freedom” marketing buzz with no explanation of what that even means.

amluto 6y ago

That’s the ampacity of wire, field-installed in conduit, per the NEC. This isn’t directly relevant to things in cars. Here’s a table that may be more relevant: http://www.ecswire.com/mmspecs/Specsheets/Belden/leadWireSelectionChart.pdf http://www.ecswire.com/mmspecs/Specsheets/Belden/leadWireSel... So you don’t actually need so big a cable. You also wouldn’t normally be using MV cables for a car charger — getting 15kV safely through a car charger terminal sounds like an interesting challenge. But 450A at 1kV doesn’t sound like a particularly big deal. Keep in mind that there’s potentially a free factor or 2 available. I don’t know how actual DC chargers work, but I imagine you could supply -1kV and 1kV relative to ground without too much trouble, resulting in effectively 2kV while only operating at 1kV relative to ground. AIUI you trigger rather more onerous NEC rules if you get to much higher voltages relative to ground.

octoberfranklin 6y ago
The NEC is basically the fire code for building wiring. It's not a general safety code. It's 80% about making sure buildings don't burn down, and 20% about peoples expectations about what parts of their house can shock them if a fork is stuck into them. That's it.
- amluto 6y ago
  If you look at the actual construction of a Supercharger station [0], the charger stall units don’t have any power electronics. There is a pair of big DC wires from each stall unit running to the big AC-DC units that are usually behind a fence. Regardless of how anyone may feel about the NEC, this is a field installation that needs to follow the rules. So those big cables will be sized per the NEC ampacity tables, and they will follow NEC rules based on their operating voltage. [0] I randomly stumbled on one under construction.