48v instead of 12v systems in cars

Mercedes put 24v/48v systems in a few of their vans/motorhome things in europe. They were leading the way with that and it never took off. I remember reading it in my electrical books years ago and nothing ever came of it.

 

From what I can see, the true benefit will be to the aftermarket suppliers as they will get to make all new stuff that will be compatible with the higher voltages. The "higher efficiency" BS is just sales spin as the increased efficiency will not really show much in the way of real world benefits for the consumer.

 

Compared to an alternator / battery system of the same voltage, converters are heavy, noisy, expensive, and fragile. Of course, 75v is much higher than anything under consideration, so it's not really pertinent to a discussion on switching to 24 or 48v.

Of course, if they were to tap off one of the alternator windings, feed it through a step-up transformer, and then regulate THAT to 75v, it would be much cheaper and robust. But that's what happens when you graft a 75v accessory to an established 12v system.

 

Www.allaboutcircuits.com/textbook/direct-current/chpt-2/calculating-electric-power/
Which is the long version of what D'urn said. I.e. higer voltage is more efficient at producing power. 12 volt bulbs are dimmer than 48 volt ones

 

There are plenty of benefits of going to high voltage, if only wiring cost per vehicle.

The standardization trap is coming from industry finding ways to keep the 12V standard by lowering part cost. (Or using CAN control also reduces wiring complexity)

Like the Dern mentioned, I'm curious at what voltage DC starts to tickle seriously the human body (you can grab both poles of a 12V battery without effect, not sure a 48V would be so permissive).

 

Higher voltages are more efficient at TRANSMITTING power; lower amperage for the same power = reduced losses through the wires. The same bulb is brighter at 48v than it is at 12v because it has 4x the current flowing through it; a 55W bulb designed for and operated at 12v is pretty close to the same brightness as a 55W bulb designed for and operated at 48v. Of course, a 55W-12v bulb operated at 48v tends to go POOF, as it tries to dissipate 220W ...

 

Don't think this won't happen. I'm not saying it will but I won't be surprised if it finally does. Electronics in cars are developing at an exponential rate. Even cheap compact cars are starting to become loaded with various electronics. IMO, it's only a matter of when, not if. Personally, I welcome the arrival of autonomous driving since the vast majority of drivers totally suck. But, I'd still like the option to drive myself too. Putting the car on auto pilot for a 600 mile interstate trip would be awesome while still being able to throw my Miata around mountain roads myself.

 

Autoweek

 

After a few minutes of Googling, it seems that 60vdc is the max limit before deliberate safety measures are required. The actual currents needed to cause fatal heart arrythmia (fibrillation) are quite small (0.5% nominal probability @ 75mA, 99.5% @ 250mA). This does NOT clear up on its own when the current is removed, and life-saving intervention is required (CPR, defibrillation). Ironically, a brief exposure to >4A may be less lethal than 250mA, as it STOPS the heart, rather than causing fibrillation. If the current is removed before critical damage occurs - burns, localized boiling, "electrolysis causing gas generation" (!) - the heart simply restarts on its own. Respiratory paralysis can occur as low as 30mA, but again breathing starts back up almost immediately when the current is removed.

The saving grace at lower voltages is that the human body is not a particularly good conductor. "The safe DC voltage depends, for example, also on the contact surface, moisture and where on your body the contact is (skin resistance varies across your body)."

 

Thank you. But at least you didn't get called names from some fucktard. Thats what I thought.

 

6v was too low. 12v is just right. 24v is military over builtness. 48v is just silly.

 

It's just plain physics. Something will eventually need to change to support the ever-increasing electronics.

 

I agree to an extent, but like I said earlier they can control things that they want with higher voltage already in a 12v system with no issues.

 

I made my kids 6v hot wheels into a 12V. battery size was not double.

 

I understand that there would be benefits. It is just that I am concerned that those benefits may sound good on sales brochures but will provide little in the way of tangible benefits and just increase the back end costs to the consumer. I really do not know enough about it though.

 

Not to get picky, but a 55w/12v bulb connected to 48v would have to dissipate 880 watts.
As the voltage goes up by 4x, so does the current.

 

I might gently suggest that R_Acree's comment of "dumbass" was a deliberate misinterpretation of TZ_Eric's "dim bulb", and was intended as a joke. The joys of the internet, where you can't see the other person's face or hear their tone ...

 

Not to get picky right back, but I think you scrambled your formulae. P = V^2 / R; P = I^2 x R

Pedantry aside, your point is correct and conceded.

 

Ahhh. Read the same in C&D this morning.

 

Or smell their farts.