4 ms·

You're not wrong, but what is an EV going to do with 10,000 volts? You'd have to convert that into something useful to the battery system, so all you've done i

You're not wrong, but what is an EV going to do with 10,000 volts? You'd have to convert that into something useful to the battery system, so all you've done is shove the efficiency drop and heating issues into the vehicle's on-board transformer systems (which would add more weight) instead of the charger.

timerol 7y ago
> “If we increase the voltage on the car side then we can reduce the current we need to push through the cable….so we are looking at higher voltage drivetrains,” says Elshout. Presumably connect the batteries in series rather than parallel, so that the voltage is increased and the current is lessened
- londons_explore 7y ago
  It isn't unreasonable to have a battery which can reconfigure itself. It could switch from parallel to series just by opening and closing a few relays.
- mdorazio 7y ago
  I'm thinking this would probably greatly increase the chance of arcing and catastrophic battery failures in the cell packs, but I'm not certain on that. Also, you still need to get that power into something useful for the rest of the car now - usually 12V for electronics and probably 350ish volts AC for the motor, so you're still going to need to deal with the conversions at some point. There's a reason high-voltage lines are nowhere near people and transformers are chunky as hell. Probably those reasons overlap with EV design constraints.
  - AWildC182 7y ago
    It's entirely doable. Tesla packs are already close to 400V and it's totally possible to go much higher. Keep in mind that every battery is a resistor so the voltage across each one is still tiny, even if the overall series voltage is massive. The reason power transmission equipment looks so weird is A) because it handles 345,000V and B) we have a lot of it and the chunky transformers and bare, massively spaced out conductors are way cheaper than wrapping everything in teflon. Also, pretty much all EVs have a 12v lead acid cell somewhere. It's kinda dumb but it's the cheapest solution to having 12v for relevant systems. The pack/charger voltage is stepped down to charge them.
    - greglindahl 7y ago
      Remember that OP said 10k volts. 400 isn't close to that. For all the "move fast and break things" of Tesla, they haven't moved fast and electrocuted people with a 10k volt battery system.
londons_explore 7y ago
Downconverting voltages is surprisingly easy - a single bank of MOSFETS and an inductor is all you need. A 2MW convertor made of [1] comes out to less than 100 grams (excluding cooling, but that's fairly small at ~100 watts). There are also a lot of reasons to increase voltages in EV battery systems. The current ~400V systems need thick heavy internal wiring, and for all electric (ie. no mechanical) braking and ultra fast charging, they are insufficient. [1]: http://www.ti.com/lit/ds/symlink/csd19537q3.pdf http://www.ti.com/lit/ds/symlink/csd19537q3.pdf
- baybal2 7y ago
  Have you seen voltage rating on that thing? You can't reliably handle 1500V+ voltages in solid state electronics without purpose made IGBTs, or exotic semiconductor materials. Your EE knowledge doesn't seem to be more than cursory.
  - londons_explore 7y ago
    It has a maximum voltage rating of 100V, so you would need 100 in series, with leak resistors to prevent any one avalanching. This is how most modern high voltage switches work, because IGBT's are far less flexible. Take apart a tesla Model 3 motor controller and let me know what you find...
    - baybal2 7y ago
      To begin with, Tesla's "motor controller" is an inverter. The charger on board is AC-DC. DC-DC It's an old, but still not completely solved problem: imagine your stack open, but for a single FET, and your resistor is a little bit off. It instantly pops, and the "tuning" for the rest of it is now completely off, and it will cascade further In case of Tesla, they do use the exotic semiconductor materials I mentioned above. SiC goes to 1500V nominally You need to learn electronics engineering beyond wiring Arduinos There is old, but still quite good and relevant explanation why stacking FETs suck on edaboard https://www.edaboard.com/showthread.php?269261-Is-MOSFET-in-series-is-possible https://www.edaboard.com/showthread.php?269261-Is-MOSFET-in-... There is an even older, but still excellent paper published by Philips called "Power Semiconductor Applications" where they explored nearly all trick to make FET stacks to work reliably. Short: it's near impossible to do it reliably with off the shelf part, and it's better to not to risk if you deal with 600A+ currents. And if are determined to do all tricks necessary, IGBTs or III-V materials will still win on simplicity and cost

timerol 7y ago

> “If we increase the voltage on the car side then we can reduce the current we need to push through the cable….so we are looking at higher voltage drivetrains,” says Elshout. Presumably connect the batteries in series rather than parallel, so that the voltage is increased and the current is lessened

londons_explore 7y ago
It isn't unreasonable to have a battery which can reconfigure itself. It could switch from parallel to series just by opening and closing a few relays.
mdorazio 7y ago
I'm thinking this would probably greatly increase the chance of arcing and catastrophic battery failures in the cell packs, but I'm not certain on that. Also, you still need to get that power into something useful for the rest of the car now - usually 12V for electronics and probably 350ish volts AC for the motor, so you're still going to need to deal with the conversions at some point. There's a reason high-voltage lines are nowhere near people and transformers are chunky as hell. Probably those reasons overlap with EV design constraints.
- AWildC182 7y ago
  It's entirely doable. Tesla packs are already close to 400V and it's totally possible to go much higher. Keep in mind that every battery is a resistor so the voltage across each one is still tiny, even if the overall series voltage is massive. The reason power transmission equipment looks so weird is A) because it handles 345,000V and B) we have a lot of it and the chunky transformers and bare, massively spaced out conductors are way cheaper than wrapping everything in teflon. Also, pretty much all EVs have a 12v lead acid cell somewhere. It's kinda dumb but it's the cheapest solution to having 12v for relevant systems. The pack/charger voltage is stepped down to charge them.
  - greglindahl 7y ago
    Remember that OP said 10k volts. 400 isn't close to that. For all the "move fast and break things" of Tesla, they haven't moved fast and electrocuted people with a 10k volt battery system.

londons_explore 7y ago

Downconverting voltages is surprisingly easy - a single bank of MOSFETS and an inductor is all you need. A 2MW convertor made of [1] comes out to less than 100 grams (excluding cooling, but that's fairly small at ~100 watts). There are also a lot of reasons to increase voltages in EV battery systems. The current ~400V systems need thick heavy internal wiring, and for all electric (ie. no mechanical) braking and ultra fast charging, they are insufficient. [1]: http://www.ti.com/lit/ds/symlink/csd19537q3.pdf http://www.ti.com/lit/ds/symlink/csd19537q3.pdf

baybal2 7y ago
Have you seen voltage rating on that thing? You can't reliably handle 1500V+ voltages in solid state electronics without purpose made IGBTs, or exotic semiconductor materials. Your EE knowledge doesn't seem to be more than cursory.
- londons_explore 7y ago
  It has a maximum voltage rating of 100V, so you would need 100 in series, with leak resistors to prevent any one avalanching. This is how most modern high voltage switches work, because IGBT's are far less flexible. Take apart a tesla Model 3 motor controller and let me know what you find...
  - baybal2 7y ago
    To begin with, Tesla's "motor controller" is an inverter. The charger on board is AC-DC. DC-DC It's an old, but still not completely solved problem: imagine your stack open, but for a single FET, and your resistor is a little bit off. It instantly pops, and the "tuning" for the rest of it is now completely off, and it will cascade further In case of Tesla, they do use the exotic semiconductor materials I mentioned above. SiC goes to 1500V nominally You need to learn electronics engineering beyond wiring Arduinos There is old, but still quite good and relevant explanation why stacking FETs suck on edaboard https://www.edaboard.com/showthread.php?269261-Is-MOSFET-in-series-is-possible https://www.edaboard.com/showthread.php?269261-Is-MOSFET-in-... There is an even older, but still excellent paper published by Philips called "Power Semiconductor Applications" where they explored nearly all trick to make FET stacks to work reliably. Short: it's near impossible to do it reliably with off the shelf part, and it's better to not to risk if you deal with 600A+ currents. And if are determined to do all tricks necessary, IGBTs or III-V materials will still win on simplicity and cost