I just ordered my first new car since 2013. It has a "mild-hybrid", which uses a starter/generator rather than electric motors on the wheels. It does not, and cannot propel the car exclusively, but it takes a touch of the load from the gas motor (completely ending turbo lag once and for all). And on braking of course, it replenishes the 48v battery.

I have not yet determined if the vehicle has a traditional alternator and 12v battery. I would think not. I'll know in late May early June, because the only way to see one is to order one. Ugh.... 2022...

If you have one, I'd appreciate any info on it you may have gleaned. Specifically, does it have an alternator too?, and a 12v battery?

No info for the OP, but curious what you ordered?

I have a 2021 BMW that has the 48V mild hybrid system. The only thing I dislike is that when BMW added it, they removed the ability to disable the engine auto stop-start system. There used to be a button for it, but now you have to code to disable it. The ASS is annoying at times, especially since I live in Florida, so when you come to a stop light the engine restarts after only about 30 seconds due to the air conditioning needing power. Also, constantly stopping/restarting when you are waiting at a drive-thru as you move forward one car at a time. I don’t really think it’s saving gas.

As for the 48V system itself, it’s transparent. You really don’t notice the boost when you accelerate (it’s only about 10hp max), and the drag from the light regeneration (charging) when you let off the gas isn’t really noticeable either (you get max regeneration as you brake). The car still does have a normal 12V battery, but not sure about the alternator. I think all of the charging for both systems is done by the starter/generator. The 48V system doesn’t power everything, so you still need the old system. It’s mostly used for boosting and the ASS. The initial starting of the car is via the normal 12 V battery.

I've got an X5 45e and even with the larger high voltage battery it still has a 12v system and battery. I believe that the high voltage battery will keep the 12v battery charged while driving in electric mode, and when the ICE is running an alternator will take over charging the 12v.

In this model the transition from electric drive to engine drive is seamless, usually undetectable. Having hated auto start/stop systems for years, this is the first example of it I'm satisfied with.

To Dwill104‘s complaint, I’ve always wondered why they don’t make the AC compressor fully electric, driven from the 48v battery. This would seem better than starting the ICE after 30 seconds on a hot day. In fact, except for compatibility of accessories, the whole car should be 48v. It would be so much better.

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Originally posted by sigcrazy7:
....In fact, except for compatibility of accessories, the whole car should be 48v. It would be so much better.

But...... Switching higher voltage DC with significant current behind it is a problem. Contacts tend to wear out very quickly with higher voltage DC. This is part of the reason why 12V has stayed around for such a long time. With AC, it's not a problem since the voltage goes to zero during the cycle, saving the contacts.

This is the traditional limitation, but tech is always changing, and, just guessing, maybe solid state switching or some other invention will come to the rescue in the future. Big MOSFETs or something like that. You never know what will happen with high technology

The second half of this article has some good info about why higher voltages in cars was a problem......

https://www.popularmechanics.com/cars/a2198/4226979/

The automotive industry found that switching off 42 volts wasn't that easy. Huh? A mechanical switch for, say, the window motor, has two metal contacts (well, a bunch, actually). When you press a switch, the two move into contact with each other and current flows to the motor. When you let go, they snap apart, interrupting the flow of electricity. But this doesn't happen instantaneously--the surface area of the metal contacts that touch doesn't go from something like 10 square millimeters to nothing in zero time. As the contacts move apart, the current density goes up in inverse proportion to the remaining area. And at the last instant of contact, the current density is high enough to melt and then vaporize the surface of the metal as a short electrical arc bridges the widening gap. Eventually, the contacts wear to the point that they don't work anymore. In a 12-volt system, this phenomenon was controlled by careful contact design and attention to the metallurgy of the contacts themselves. Forty-two volts draws a much longer, hotter arc, and vaporizes more metal.

Contact erosion on 42-volt systems was unacceptable, unless automakers upgraded the switches with more expensive metals and stuff such as spring-loaded contacts that jumped apart faster to reduce the arcing. Would you accept a car that had to have the switches for the power windows replaced every 10,000 miles?

Now why exactly isn't this an issue with 120- or 220-volt household switches, running 10 to 20 times the voltage in your car? Because household power is AC, not DC. The AC stands for alternating current. The voltage in AC wiring takes a huge swing--from 120 volts positive to zero and on down to 120 volts negative and back--60 times per second in a neat sinusoidal wave. And the arc just fizzles out as the voltage crosses zero 120 times per second, making for a clean break. DC, or Direct Current, constantly remains at its rated voltage.

Re the Popular Mechanics article that radioman cited, the author of that magazine article needs to do a bit more research.

Electro-mechanical systems such as Step-By-Step, Panel, and Crossbar systems in telephone Central Offices were all 48 volt DC systems. Because these were engineered for busy-hour usage, the relay contacts probably saw a lot more cycles than a typical automotive application.

Bell System Central Office equipment was designed for a forty year life.

quote:

Originally posted by V-Tail:
Re the Popular Mechanics article that radioman cited, the author of that magazine article needs to do a bit more research.

Electro-mechanical systems such as Step-By-Step, Panel, and Crossbar systems in telephone Central Offices were all 48 volt DC systems. Because these were engineered for busy-hour usage, the relay contacts probably saw a lot more cycles than a typical automotive application.

Bell System Central Office equipment was designed for a forty year life.

And back in those days, the metal was thick and hearty. Not light-weighted to the nth degree to reduce weight on the car, and expense and materials.

quote:

Originally posted by P250UA5:
No info for the OP, but curious what you ordered?

BMW X3

quote:

Originally posted by 1gkek:
I've got an X5 45e and even with the larger high voltage battery it still has a 12v system and battery. I believe that the high voltage battery will keep the 12v battery charged while driving in electric mode, and when the ICE is running an alternator will take over charging the 12v.

In this model the transition from electric drive to engine drive is seamless, usually undetectable. Having hated auto start/stop systems for years, this is the first example of it I'm satisfied with.

They did mention a DC-DC converter which I take it converts 48V to 12V.

I gotta find a good BMW forum to get deep in the weeds on the magic under the stupid plastic engine cover.

Due to an unfortunate collision with a horse trailer, our Audi needs replacement. So I ordered an X3 last week. Hopefully, they’ll be able to make me one before summer.

As for the “mild hybrid” setup of the I6, the technology was developed about 20 years ago (I used to product manage semiconductors designed for automotive applications a long time ago), called ISAD (Integrated Starter, Alternator, Damper). Basically, the unit replaces both the starter and alternator (in BMW applications, it’s belt driven, but can be implemented between the crank output and the transmission). This is the only part of the X3 that runs on 48V, so it also has a 12V lithium “main” battery in the cargo area. If these cars need to be jump started, I’m not quite sure how that would be accomplished, but looking forward to experiencing the system.

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I gotta find a good BMW forum to get deep in the weeds on the magic under the stupid plastic engine cover.

Bimmerpost forums are my go-to. Link

Click here if you want to geek out on the original technology paper.

Here’s a post on the system in a X7, but I think it works the same in all of the BMW mild hybrids.

https://g07.bimmerpost.com/for...thread.php?t=1781421

as to the voltage at switches, in modern vehicles you won't find the power that's being directed going to the switches, buttons, knobs.

Most vehicles are run via CAN-BUS systems, all the systems are controlled by multiple modules such as a BCM. Body Control Module. The switches run through a slimmed down harness reducing the amount of wires in the vehicle, and as such, weight, and install times, so the contact points used to run the vehicles systems rarely if ever see the voltage needed to run the items such as heater fan, lights, turn signals, power roofs etc, sort of a digital relay.

I have a 2020 BMW with that system and as mentioned it has a 12v battery in the back and jump points located under the hood if necessary. I don't know how the internals are wired, but I know that if I switch to sport mode the auto start/stop is disabled, and if you run sport individual mode you can run the comfort settings if you prefer, so you can work around not having a button - although mine does have the button too.

It doesn't really add much in power, but it feels more eager than other cars I drove with similar power numbers.

quote:

Originally posted by Dwill104:
Here’s a post on the system in a X7, but I think it works the same in all of the BMW mild hybrids.

https://g07.bimmerpost.com/for...thread.php?t=1781421

THANK YOU! That's a lot of good info. Exactly what I was searching for.

quote:

Originally posted by HRK:
as to the voltage at switches, in modern vehicles you won't find the power that's being directed going to the switches, buttons, knobs.

Most vehicles are run via CAN-BUS systems, all the systems are controlled by multiple modules such as a BCM. Body Control Module. The switches run through a slimmed down harness reducing the amount of wires in the vehicle, and as such, weight, and install times, so the contact points used to run the vehicles systems rarely if ever see the voltage needed to run the items such as heater fan, lights, turn signals, power roofs etc, sort of a digital relay.

There are still contacts in the relays which are subject to the same principles radioman pointed out.

The CAN Bus systems tend to use MOSFet's, not mechanicals. The "slimmed down" harness constitutes a coax cable transmitting data from a dash control unit recieving inputs to the outboard actuator switches which handle the local current to the fixture - brake lights, turn signals, backups, etc.

When you push the turn signal to a direction, it closes the circuit, sends a low sensor current voltage to the control unit which then sends a packet instruction to the units to flash that turn signal. It uses multistrand plated sensor wiring a lot more than a single copper wire until you get to the powered output unit, which receives a battery voltage cable and directs the current in "normal" wiring to the bulb.

Littlefuse offers this for the aftermarket under the "ISIS" branded CAN Bus product line. It's commercial vehicle capable and some kit car builders are adopting it. It can reduce a wiring harness installation from a 65 pound boa constrictor to 35 pounds, and also features troubleshooting live at the power distribution points - lights up if the circuit is defective. Adding heated mirrors at the last minute to an ambulance? Give them an hour or two, done. It's that simple.

It also offers a lot of the luxury car features, just program the controller. Blinking stop lights, theater dimming interior lights, just order it and it arrives pre programmed. The one thing it doesn't do is EFI/ABS but those are separate systems in a lot of vehicles.

Initial costs for a kit to wire a Daytona kit car were $1200 when I looked into it years back, that's likely more but it's far superior to running dozens of skanky old school 14v wires (12V is nominal, not working) and then troubleshooting all the involved circuits. Its one coax run to either end and a 10ga power supply, it can be mounted and run much more accessibly and protected from undercar or interior abuse.

How BMW engineers it will likely be proprietary, MB uses it too, and most commercial vehicles over 5 tons likely, too. Tractor trailers adopted it a long time ago - imagine running a 12v turn signal wire from the cab to the end of a 40 ft trailer thru a number of disconnects. Voltage drop galore in the old days. No longer.

quote:

Originally posted by trapper189:

quote:

Originally posted by HRK:
as to the voltage at switches, in modern vehicles you won't find the power that's being directed going to the switches, buttons, knobs.

Most vehicles are run via CAN-BUS systems, all the systems are controlled by multiple modules such as a BCM. Body Control Module. The switches run through a slimmed down harness reducing the amount of wires in the vehicle, and as such, weight, and install times, so the contact points used to run the vehicles systems rarely if ever see the voltage needed to run the items such as heater fan, lights, turn signals, power roofs etc, sort of a digital relay.

There are still contacts in the relays which are subject to the same principles radioman pointed out.

Yup - currently, all vehicle body electrical sub-systems are sourced from a 12V power bus. Only the data signaling comes through the CAN (or LIN in the case of sub-sub systems, like wing mirrors and switchgear), MOST, or Flexray depending on the system. This allows reliable connectivity and reliable power.

Most body controllers have on-board regulation to bring the 12V down to the 5-5.5V range, which most automotive semiconductors are spec'ed at (although some higher tech stuff runs at 3.3V or 1.8V)

quote:

There are still contacts in the relays which are subject to the same principles radioman pointed out.

Yes, but relays are typically made to handle the stress of whatever voltage they are "relaying" previously it was said that the higher voltage would wear out the metal contacts in switches, however nobody builds vehicles with the power going through the switch/knob.

Today it's all CAN-BUS with ECM/BCM making the decisions and instructing relays or power distribution blocks to move that power. Even Harley Davidson when this way several years ago, which was a major change in control systems and wiring requirements.

The inside of your car never sees the full voltage mainly because of the amount of sensitive electronics and screens now in vehicles and because they don't have to do it anymore.

CAN-BUS eliminates that, and is the point, it insulates the controls from the higher voltage demand/supply be it 12, 24 or whatever V designed into a system, car, truck, boat, plane, motorcycle.

I drove the Mercedes GLE53 AMG which is a turbo-charged inline six with close coupled 48V mild hybrid last year as well as two Audi's (Q7 and SQ7). They really do strike a balance between fuel economy and performance that's terrific. The close-coupled electric gives instant torque and offsets a higher RPM spool turbo for maximum top-end power and fuel efficiency.

RAM even offers a similar system on their 1500's....came out two years ago as I recall. Definitely becoming more mainstream and no need to call them "hybrids" really, at least in the traditional sense.