Automotive Industry migrates to 48V electrical system

I’m quite happy having modern vehicles that don’t need tune-ups, can typically go 200K or more miles without major repairs (100K spark plugs), have great handling and mileage, great creature comforts and conveniences, and which protect occupants in a crash with crumple zones, multiple airbags and seatbelts.

 

Did you say they'll need a crane?

 

The United States doesn’t use 240 single phase, 120V single phase yes.
Our 240 is technically 2 phase 180deg (in our house) 2 hots, one common and one earth ground.
I use 240 in my hamshack. It works great for the big Astron RM-70 power supplies and the HF amp!
Outside depending on a Wye or Delta configuration in US power distribution
The UK uses single phase 240 volts (50 Hz) one hot, one common and one earth ground.

 

It's just a guess, but I'll bet the auto industry has engineers that understand Ohm's Law as well as we do. In addition, I am guessing the power ports will still be 12VDC for sometime into the future.

 

There will continue to be a 12V Bus. Other systems and accessories aren't going to change to 48V. Aftermarket sytems and accessories, phone chargers, an entire industry built on 12 volt power, inverters, internal computer systems, displays, and other systmes will not go away. The frickin' Tesla's have a 12 battery to drive the computers. 12volt - It's not going away.

 

Could anyone tell me (or make an educated guess) why electric cars have a separate 12V battery instead of a voltage regulator to create 12V from the main propulsion battery? I read a lot of stories about the 12V batteries of Nissan Leafs breaking down, so I wonder, why have this in the first place?

 

Incorrect, the USA uses Single Phase 240/120. It is NOT TWO PHASES. The Transformer is Single Phase Centered Tapped.

 

Couple of reasons. They DO have a DC-DC converter to supply the 12V, but the battery gives you a buffer and some protection should the converter fail - much like it does on a regular car if the alternator fails. And one of the critical failure modes is an accident, where the main HV battery may be cut off and isolated for safety. In this case, you would still want 12V to supply the hazard lights, power locks and windows, airbag deployment, SOS phone (OnStar or similar), etc. A 12V system with a battery is pretty reliable for these sorts of things IF the battery is good.

Bottom line, the 12V bus powers critical systems, and a battery helps insure their availability.

 

I'll give an educated guess.

A power supply will always take a small bit of power just to run itself. Think of the losses from an inverter that produces 120 volts from a 12 volt battery, or a computer power supply that takes 120 volt AC to produce the much smaller DC voltages for the computer. The losses from voltage conversion in a modern power supply might be very small but it's not zero. To minimize the losses on the main propulsion battery it's simple to just have a separate battery for the low voltage accessories to run off of, and charge it up when the car is plugged in.

There's also likely a safety factor here. If there is a battery problem, and there is no accessory battery, then safety systems like signal lights would fail. If the main battery fails then the car can still put on the blinkers and coast off to the side of the road. If the accessory battery fails then a power supply off the main battery can start up to supply power to the accessories and the driver can be alerted with an indication on the dash board.

In cases of an electric car having roadside trouble there might be a need or desire to do some diagnostics. If the battery is dead, or there is concern of taking any power from the battery making things worse, then the on board computers cannot be powered up without some kind of "shore power" for the on board charger or a DC supply that matches that of the main battery. There is some standardization on the charging ports so having the right kind of supply on a tow truck might not be much of a problem, but electric cars are still rare enough that this is far from standard equipment. What is quite standard are 12 VDC jumper cables.

 

And the center tapped, grounded neutral makes both ends 180º out of phase of each other. If you only look at the 240V component, it is indeed one phase. But both ends deliver 120V with respecr to neutral, but 180º out of phase. So we have two phases.

 

Same phase, just measured at different points. If you have a sea-saw, when one end is up, the other is down, right? Same sea-saw, not "2" sea-saws... Split phase is the term commonly used because the center tap "splits' the phase, but it is still a single phase.

 

Incorrect again, still Single Phase. Here is 2-Phase and yes there is such a thing as 2-phase. Most of what I know it is used for is Light Passenger Rails and Electric Trolleys. Phase is shifted 90 degrees.

 

The efficiency of the regulator

 

I see no one has given you the correct answer yet. Life Safety is primary and secondary is Noise/Controls.

1. The LVDC (12 volt) system is a GroundedSystem, and the High Voltage Traction Battery is Floated and forbidden to be grounded. In fact a lot of alarms, bells, and whistles go off if any kind of ground is detected on either polarity. It is done that way to keep from killing yourself. Grounded Systems are dangerous. To electrocute yourself on the EV Traction Battery requires you to get across both Polarities of the battery which is Stupid Simple to do if you bond the battery to the chassis, thus making it a Grounded System. All you have to do is touch the vehicle to make contact with the Negative Polarity. Float the battery makes it much more difficult to get across the battery. So LVDC and HVDC are kept isolated, the LVDC is Grounded, and the HVDC is NOT GROUNDED.

From the FWIW department not even golf cart batteries are grounded. for the same primary reason.

2. The HVDC circuit is very NOISY, EV's use computers and very sensitive electronics to control the vehicle. . LVDC controls and powers all the functions like power steering/braking, Environmental, and CONTROL of the vehicle. There is a high probability the HVDC battery will disconnect and trip off line for a number of reasons and left without any power.










noise

 

Hmm... if this is 2-phase, why then would it suddenly become not 2-phase if the red curve shifts a little bit more until 180º is reached...