Featured Automotive 12v vs 48v Architecture ?

Rat fries?

Bob Wilson

 

Ok, thank you for the correction.

I would have expected that thinner conductors would allow for thinner and lighter insulation with less to cover, and would not have expected that the increased voltage was enough to demand any countering increase in insulation.

I'd still think that reduced current loads would allow for smaller/lighter/cheaper connectors in the branches and bits where pluggability is needed.

 

It would, but we are talking a few pounds per car at the most. It's not that it's a bad idea, it's that the infrastructure change to accomplish it means the ROI would be many decades from now, if ever.

 

Bob is correct, Rat fries and smell - NO fires; unless your accustomed to draping highly flammable stuff over a hot power supply.

I've worked on many 24V, 36V, and 48V UPS systems in the past. It wasn't uncommon to find mouse/rat fries. If a sensor wasn't tripped, the complaint was usually a funny smell in the room.

Nothing like pulling rat teeth out of wire insulation and recoating with liquid insulation. Good times....

If a millennial saw this, they'd probably call in a haz-mat team......

 

I think generally they are because it's rare to burn to death in your car, whereas your house is full of flammable stuff. AFCIs first came about specifically to prevent house first (starting in bedrooms, which is where they were first mandated because they were arcing into beds, behind night stands) but now they are mandated in a lot of places. AFCIs wouldn't have anything to light on fire in a given car except in a few places, because wires are generally out of sight and away from the few things in a car that are flammable. Also, AFCIs add a lot of cost to the electrical system in houses as well.

 

Here is a pretty good break down of the advantages from someone that does cost engineering.

Basically, substantial weight savings & better communications.

 

This was just kind of a goofy puff piece, to be honest. Lot of stuff in here doesn't make a whole lot of sense. Car-wide network rings? Been around since the 90s. Austenitic stainless alloys for body panels? Just for looks, body panels are not stressed. And 73% weight savings from the wiring harness? Color me skeptical - seems awful optimistic. There will be a bit of a weight savings, but we are talking about probably less than 10 lbs on a nearly 7,000lb vehicle.

 

As an amateur radio operator using a buck converter to go from 48V to 12V would not be ideal. For amateur radio the 12V battery acts as a large capacitor drowning out a lot of the RFI going into the tranceiver. A buck converter would only add RFI.

On the other hand, having a 48V system would be a reason to design and build a 48V tranceiver and maybe use those 400W antennas I got to their max power tolerance instead of the standard 100W typical mobile transceiver.

 

• "Car-wide network rings" - versus ethernet, probably 1 Gb rates. The old CANbus was orders of magnitude slower. Also, the huge numbers of custom connectors ends.
• "Austenitic stainless allows for body panels" - beyond that, Martensitic stainless steel.
• "body panels are not stressed" - body on frame is common enough but not with incredibly strong, Martensitic stainless steel. If the exterior is damaged, remove damaged ones and attach new ones. My BMW i3-REx is carbon fiber body and panels over an aluminum frame.
• "73% weight savings" - is probably vehicle wiring savings that eliminate the cacophony of special plugs and mass of wire harnesses.

There are a large number of other features such as:

• drive-by-wire - moves steering drive shaft aimed at chest weight, supports rear wheel steering, makes right-hand drive trivial.
• one piece castings - front and back, saves weight, labor, and stronger than piece parts
• structural battery - allows seats and cabin features installed on the battery platform which is bolted/welded onto the bottom of the body frame, front and rear castings. It also allows firewall forward, side, and rear assemblies without having contortionists line workers.
• Gorilla glass - end to pebble windshield and top cracks and replacement.
• Rubber wheel covers - eliminates 'curb rash.' May have advanced aerodynamic drag reductions.
• two instead of three forward, high resolution cameras - reduces parts count and radar removed already. Not sure about ultrasonic sensors.
• large rear seat - able to handle three, heavy riders in the back.
• HW 4 - faster than HW 3 processor in my Model 3.
• Motors without rare earths - significantly reduce cost and avoids monopolistic, rare earth, providers.
• Adjustable air suspension - easier ingress yet high for rough terrain.
• Easily 'wrapped' - let these artists handle the toxic and expensive body painting to meet customer desires.

Actually, Sandy has a suite of videos that referenced these changes.

Bob Wilson

 

Are we talking about 48v batteries still or is this thread just a puff piece for the cybertruck now too?

 

Still about:

The 48V battery buss not only reduces the amount of copper but also ends huge numbers of unique connectors, The ethernet based communications is simple and fast so complex wiring harnesses complexity is gone. The car is literally software defined which simplifies flexibility and correction of latent defects. Add to that, fewer parts means faster and lower cost labor to assemble. All fallout from going 48V and reinventing the pickup truck.

Bob Wilson

 

I asked Ebay "48V" and got "200,000+ results for 48V" which should temper any concerns. But if you have a specific question, say inverters:

• "48V inverter pure sine" -> "1,800+ results"
• "48V USB" -> "2,200+ results"

A lot of solar panel systems run on 48V. This is really a non-problem.

Bob Wilson

 

What in the world would reduce the number of unique connectors with 48 volts that is different about 12 volts? And how in the world would ethernet not work with 12 volts? Again, cars have had CAN, K-bus, OBD, LIN, and a variety of others for many decades. Since this thread has been fully derailed into a Tesla commercial, I will see myself out.

 

Tesla has reinvented the wheel again? How are you going to drive a 2.5-kW EPS unit with power over Ethernet (PoE)? PoE is limited to about 70 W, which is only about 6 A for a 12-V system—not even enough to operate a radio.

 

It’s pretty unexplored in practice, as the ‘mainstay’ of an automobile’s systems, this higher voltage, and it raises the (sorry, I am just going to say it) alternate mode of making electricity flow and feed useful machines, Alternating Current.

I think it’s fascinating, and surely some bright bods in some universities somewhere(s!) are investigating even deploying 110Vac or a multiple thereof, with a view to avoiding frankly a lot of wasteful efforts in Vehicle to Home or whatever it’s called (Vehicle to Grid?). A lot of converting and transforming.

There seems to be something in the article mentioned here, about keeping the voltages below 60 Volts (so 48V gives you some ‘headroom’ the article suggests), but it all seems a bit backward just to make it fit some arbitrary definition of ‘low voltage’ built into regulations?

Given a clean sheet, it’s kind of a no-brainer to have a crack at an Alternating Current of 110V as the way to go in automotive electrics? I don’t know if there are stumbling blocks, if it’s more or less viable than what we have (12Vdc) or the proposed 48Vdc, but it seems highly unlikely our present system, or the 48V dc system Tesla seem to use for the Cybertruck, is the optimal one.

One’s just what everything already uses, and the other is to fit with that arbitrary definition of ‘low voltage’ I mentioned already. The rationale for 110V ac or a multiple, seems to point to it being worth quite a bit of investment of research effort, is all I am saying.

However, the conversion process of DC to AC and vice versa, seems to be getting more efficient and the inverters etc more compact and lighter, all the time. This might make having a target of one kind of electricity or another, a moot point. You’d literally just use whichever one made the most sense for the unit or purpose in the car, you are dealing with at that time. From one minute’s reading/googling, DC motors are meant to be more finely and accurately speed-controllable than AC motors…but I bet that can be fixed with a suitable feedback loop etc, so I doubt that’s got the draw (sorry again!) it sounds like it has at first sight?

Certainly 110Vac would make Prius camper creation a lot easier! I profess no great knowledge, it just seems the above is clear. I only add the one thing a Merchant Sailor told me, because it’s not obvious…Direct Current if touched by a human, causes their muscles to clamp, and Alternating Current causes them to let go…but, either one at the levels EVs or hybrids incorporate, is probably so debilitating, it’s not clear it’s different enough to affect technical decisions about designing the automobiles.

Genuinely am looking forward to this being a new avenue of exploration.

 

Apparently 48V is a Tesla-skeptic repellant. <GRINS>

Bob Wilson

 

More like a Tesla-fanboy attractant.