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Siblings covered why 12 V is annoying, let's talk about why 12 V was chosen in the first place. 6 and 12 V electric systems in vehicles came about because lead

Siblings covered why 12 V is annoying, let's talk about why 12 V was chosen in the first place. 6 and 12 V electric systems in vehicles came about because lead-acid batteries made sense in this application, and cetpar. a higher voltage lead-acid battery is overall costlier to manufacture, because it contains more individual cells. Another big thing is that there are many switches and relays in a car, and those often switch significant power. E.g. the light switch for the headlights has to deal with around 200 Watts total for incandescent/halogen headlights, indicators are like 15 Watt each front and back, the starter motor requires a tremendous amount of power, and has a very robust power switch built into it. All of those switches become much more expensive when you increase the voltage. DC at 12 V and sizable currents is something you can reliably switch with mechanical contacts without costs going through the roof. Being able to use 48 V for everything in a car is more or less dependent on using silicon switches for everything, not something that was possible in the past. The reason why legacy ICE cars (all ICE cars are now legacy) stick with 12 V is because everything is 12 V, and everything would have to change for the new voltage.

mcguire 5y ago
I seem to recall, several years ago (when stopping the engine at traffic lights and restarting as soon as the driver released the brake), at least one company was exploring moving to 24V. However, the effort failed precisely because the lifetime of 24V switches was significantly shorter. Naturally, I can't find any links to the info...
- winrid 5y ago
  FWIW Almost no switches in a modern car (turn signals, wipers, door switches) carry a significant amount of current as they are controlled via confuzers. Just built a car without a single relay. I used PMUs (basically boxes of mosfets and current sensors AFAIK).
  - vdqtp3 5y ago
    wtf is a confuzer? I can find nothing via Google.
    - smiley1437 5y ago
      slang for 'computer' made popular by Youtuber AvE
- petre 5y ago
  Trucks and agriculture equipment already use 24V systems, so the point is moot. Vehicle usage during the lifetime of a truck greatly exceeeds the lifetime of a personal passenger vehicle and agriculture equipment is also exposed to dust and grime, yet both continue to operate normally. So I guess it's more of a cost problem than a component issue.
perl4ever 5y ago
>All of those switches become much more expensive Wouldn't a more important question be how does the failure mode change?
- tuatoru 5y ago
  Above 30V - 50V DC, contact arcing becomes a huge problem. (It's a problem below that, but less huge.) With AC, the arc will self-extinguish a half-cycle after the switch opens. With DC there is no cycle, and contacts can be completely vaporised in tens of milliseconds. Commodity switching components are usually rated "30V DC, 250V AC" for this reason. It is possible to design switches so that even DC arcs self-extinguish, but the result is expensive and not as reliable as one could wish. If cars had been invented after 1980, they would probably use solid-state switches except for the very high current circuits such as the starter solenoid and headlights. (Transistors were around a lot earlier than that, but engineers are sensibly cautious about new technologies.) Edit: To answer your question directly: no. Cost is prime.
  - perl4ever 5y ago
    >To answer your question directly: no. Cost is prime I meant to the customer or owner, over the normal lifetime of the vehicle, not to corporate accountants that translate pennies into millions of dollars. "More expensive" presumably is a small amount per car; the average new car in the US is over $40K.
  - boznz 5y ago
    if we are going to 48V then pretty sure all power switching would use solid state relays/MOSFETs, Any mechanical switch would just be the input to a micro at 5V or lower. You could also just switch the HV (400V+) bus directly down to 48/60V as all the high current devices motor/ac/power steering etc run off the HV bus and you would just be left with lights, entertainment and servos on the low voltage side. The 12V battery is probably a bit silly when you have a 50KWH main battery and 97% switching conversion efficiency regulators and I am guessing it may disappear in the next 10 years
    - 5y ago
grecy 5y ago
Plenty of older diesel road vehicles like Land Cruisers run 48V for everything. They've been that way since the 80s (maybe 70s). Note: These were never sold in the North American Market, but they're extremely common in Australia, South Africa, etc.

mcguire 5y ago

I seem to recall, several years ago (when stopping the engine at traffic lights and restarting as soon as the driver released the brake), at least one company was exploring moving to 24V. However, the effort failed precisely because the lifetime of 24V switches was significantly shorter. Naturally, I can't find any links to the info...

winrid 5y ago
FWIW Almost no switches in a modern car (turn signals, wipers, door switches) carry a significant amount of current as they are controlled via confuzers. Just built a car without a single relay. I used PMUs (basically boxes of mosfets and current sensors AFAIK).
- vdqtp3 5y ago
  wtf is a confuzer? I can find nothing via Google.
  - smiley1437 5y ago
    slang for 'computer' made popular by Youtuber AvE
petre 5y ago
Trucks and agriculture equipment already use 24V systems, so the point is moot. Vehicle usage during the lifetime of a truck greatly exceeeds the lifetime of a personal passenger vehicle and agriculture equipment is also exposed to dust and grime, yet both continue to operate normally. So I guess it's more of a cost problem than a component issue.

perl4ever 5y ago

>All of those switches become much more expensive Wouldn't a more important question be how does the failure mode change?

tuatoru 5y ago
Above 30V - 50V DC, contact arcing becomes a huge problem. (It's a problem below that, but less huge.) With AC, the arc will self-extinguish a half-cycle after the switch opens. With DC there is no cycle, and contacts can be completely vaporised in tens of milliseconds. Commodity switching components are usually rated "30V DC, 250V AC" for this reason. It is possible to design switches so that even DC arcs self-extinguish, but the result is expensive and not as reliable as one could wish. If cars had been invented after 1980, they would probably use solid-state switches except for the very high current circuits such as the starter solenoid and headlights. (Transistors were around a lot earlier than that, but engineers are sensibly cautious about new technologies.) Edit: To answer your question directly: no. Cost is prime.
- perl4ever 5y ago
  >To answer your question directly: no. Cost is prime I meant to the customer or owner, over the normal lifetime of the vehicle, not to corporate accountants that translate pennies into millions of dollars. "More expensive" presumably is a small amount per car; the average new car in the US is over $40K.
- boznz 5y ago
  if we are going to 48V then pretty sure all power switching would use solid state relays/MOSFETs, Any mechanical switch would just be the input to a micro at 5V or lower. You could also just switch the HV (400V+) bus directly down to 48/60V as all the high current devices motor/ac/power steering etc run off the HV bus and you would just be left with lights, entertainment and servos on the low voltage side. The 12V battery is probably a bit silly when you have a 50KWH main battery and 97% switching conversion efficiency regulators and I am guessing it may disappear in the next 10 years
  - 5y ago

grecy 5y ago

Plenty of older diesel road vehicles like Land Cruisers run 48V for everything. They've been that way since the 80s (maybe 70s). Note: These were never sold in the North American Market, but they're extremely common in Australia, South Africa, etc.