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I suspect the reason that Tesla has retained a 12v system is because the automotive grade parts largely dont exist at anything other than 12v. Even when the big

by Aloha 3y ago

I suspect the reason that Tesla has retained a 12v system is because the automotive grade parts largely dont exist at anything other than 12v. Even when the big three were making stuff for the military with a 24v system, it was a hybrid 24v/12v system.

sandworm101 3y ago
There are also safety concerns. Any emergency responder cutting into a crashed car isnt going to be killed by 12v, nor are sparks from shorts likely to start fires before a fuse blows.
- Gravityloss 3y ago
  48V was developed for that purpose. For example stage microphones can be powered by 48 V phantom power. Say if there are broken cables or rain, it's not nice to be shocked but it's not dangerous. Many mild hybrid cars use a 48V system for the motor. It's probably going to get more common over time.
  - sandworm101 3y ago
    >> Many mild hybrid cars use a 48V system for the motor. Except they have a 12v solenoid to engage/disengage the drive voltage in the event of a crash, which is why if you leave your lights on you might need a 12v "jump" even if the drive battery is fully charged.
    - Gravityloss 3y ago
      Hmm does 48V really need to be disconnected? What's the reasoning? Honest question: is there something else than path dependence preventing just switching everything in a car from 12V to 48V? Even interior lighting? Ie is there some place where 12V is actually significantly better for physics reasons?
- drzaiusx11 3y ago
  Hasn't this "lower DC voltage is safe" nonsense from the Edison days been thoroughly debunked yet? The safety differences between 12V and 24V are largely trivial. Mostly comes down to wire sizing as 24V can use smaller wires to carry the same power, which some may argue is safer than 12V as the current is halved (but I wouldn't) Modern chemistry batteries are VERY good at providing their stored charge instantaneously across their terminals. Lookup videos of someone dropping a wrench on a car battery for a real life example (spoilers: the wrench welds itself to the terminals immediately and spectacularly.) Humans, as big bags of ferrous liquids, literally have only our skins to help increase our impedance against electrocution when touching ANY metal in series with a battery short. A measley 100 _milli_ amps is enough to stop our hearts. Let's not pretend DC batteries are safe and treat 12V and 24V batteries with the same caution they deserve. I would hope emergency responders are trained against electrocution risks regardless, as fuses can be bypassed when crushed metal is involved near battery compartments in any crash. As for fire concerns it's more about battery chemistry than voltage. Lithium ion being more combustible than lead acid, nickel cadmium.
  - sandworm101 3y ago
    24v is only a little more dangerous than 12v, but so is 48v only a little more than 24v, and 110v only slightly more than 48v. One has to draw a line somewhere. 12v barely penetrates dry skin, and won't do anything across even a cotton shirt. If that is enough for powered windows, why change what isn't broken. As for first responder training, assume they have none. The first person at a scene will be some rando person reaching in to pull a kid out of a burning car, or it is that kid themselves climbing out of the wreckage.
    - drzaiusx11 3y ago
      Since the resistance of human skin is fairly constant (1k-10k ohm without open wounds, limited persperation), increasing voltage increases power absorbed across your body and thus the danger exponentially by a factor of 2: P=V^2/R
  - Grazester 3y ago
    The whole wrench thing has happened to me. It was on the bigger 12 volts marine/industrial batteries connected in parallel series for 24 volts to start a Detroit Diesel 71 series engine. There was a nice arce and the end of the wrench melted.
- Aloha 3y ago
  +48v isnt going to kill anyone either - the Telcos have been using it for a century.
jabl 3y ago
This article claims Tesla is going to a 48V electrical system with the Cybertruck. https://thedriven.io/2023/03/20/why-teslas-move-to-48-volt-electrical-architecture-is-an-industry-game-changer/ https://thedriven.io/2023/03/20/why-teslas-move-to-48-volt-e... It also says Tesla is doing a lot of 48V stuff in house. Likely because they are finding it difficult to source those parts externally?
- 1letterunixname 3y ago
  This specialness causes no end of supply-chain problems often requiring vertical integration of items that might be low volume, complex, and far afield from the main b2c products.

by Aloha 3y ago

sandworm101 3y ago

There are also safety concerns. Any emergency responder cutting into a crashed car isnt going to be killed by 12v, nor are sparks from shorts likely to start fires before a fuse blows.

Gravityloss 3y ago
48V was developed for that purpose. For example stage microphones can be powered by 48 V phantom power. Say if there are broken cables or rain, it's not nice to be shocked but it's not dangerous. Many mild hybrid cars use a 48V system for the motor. It's probably going to get more common over time.
- sandworm101 3y ago
  >> Many mild hybrid cars use a 48V system for the motor. Except they have a 12v solenoid to engage/disengage the drive voltage in the event of a crash, which is why if you leave your lights on you might need a 12v "jump" even if the drive battery is fully charged.
  - Gravityloss 3y ago
    Hmm does 48V really need to be disconnected? What's the reasoning? Honest question: is there something else than path dependence preventing just switching everything in a car from 12V to 48V? Even interior lighting? Ie is there some place where 12V is actually significantly better for physics reasons?
drzaiusx11 3y ago
Hasn't this "lower DC voltage is safe" nonsense from the Edison days been thoroughly debunked yet? The safety differences between 12V and 24V are largely trivial. Mostly comes down to wire sizing as 24V can use smaller wires to carry the same power, which some may argue is safer than 12V as the current is halved (but I wouldn't) Modern chemistry batteries are VERY good at providing their stored charge instantaneously across their terminals. Lookup videos of someone dropping a wrench on a car battery for a real life example (spoilers: the wrench welds itself to the terminals immediately and spectacularly.) Humans, as big bags of ferrous liquids, literally have only our skins to help increase our impedance against electrocution when touching ANY metal in series with a battery short. A measley 100 _milli_ amps is enough to stop our hearts. Let's not pretend DC batteries are safe and treat 12V and 24V batteries with the same caution they deserve. I would hope emergency responders are trained against electrocution risks regardless, as fuses can be bypassed when crushed metal is involved near battery compartments in any crash. As for fire concerns it's more about battery chemistry than voltage. Lithium ion being more combustible than lead acid, nickel cadmium.
- sandworm101 3y ago
  24v is only a little more dangerous than 12v, but so is 48v only a little more than 24v, and 110v only slightly more than 48v. One has to draw a line somewhere. 12v barely penetrates dry skin, and won't do anything across even a cotton shirt. If that is enough for powered windows, why change what isn't broken. As for first responder training, assume they have none. The first person at a scene will be some rando person reaching in to pull a kid out of a burning car, or it is that kid themselves climbing out of the wreckage.
  - drzaiusx11 3y ago
    Since the resistance of human skin is fairly constant (1k-10k ohm without open wounds, limited persperation), increasing voltage increases power absorbed across your body and thus the danger exponentially by a factor of 2: P=V^2/R
- Grazester 3y ago
  The whole wrench thing has happened to me. It was on the bigger 12 volts marine/industrial batteries connected in parallel series for 24 volts to start a Detroit Diesel 71 series engine. There was a nice arce and the end of the wrench melted.
Aloha 3y ago
+48v isnt going to kill anyone either - the Telcos have been using it for a century.

jabl 3y ago

This article claims Tesla is going to a 48V electrical system with the Cybertruck. https://thedriven.io/2023/03/20/why-teslas-move-to-48-volt-electrical-architecture-is-an-industry-game-changer/ https://thedriven.io/2023/03/20/why-teslas-move-to-48-volt-e... It also says Tesla is doing a lot of 48V stuff in house. Likely because they are finding it difficult to source those parts externally?

1letterunixname 3y ago
This specialness causes no end of supply-chain problems often requiring vertical integration of items that might be low volume, complex, and far afield from the main b2c products.