No CAN Bus, No 12V for Model Y

[Garlan Garner]

Another way to reduce half of the wiring for power is just use the chassis as the ground return. Don't even run a wire for negative / ground.

One positive wire to things that need power... or, PoE to smart devices that need moderate power... and run no separate power lines.

Now that makes sense. PoE. Especially in a small environment such as a car.

 

[Tam]

In the old days, GM EV1 had 12V battery. So did Nissan Leaf.

But at that time, Tesla is no GM nor Nissan, so why would it want to conform to the conventional wisdom of 12V battery for its brand new Roadster.

Tesla got bad press due to the lack of 12V battery for the Roadster bricking problem:

Tesla Battery Failures Make ‘Bricking’ a Buzzword

Since then, it learned its lesson from the lack of 12V battery in Roadster, and it has included 12V battery for subsequent models, S, X and 3...

But it looks like the learning is over and Tesla won't need 12V battery any more in future?

I am really confused!

 

[stopcrazypp]

In the old days, GM EV1 had 12V battery. So did Nissan Leaf.

But at that time, Tesla is no GM nor Nissan, so why would it want to conform to the conventional wisdom of 12V battery for its brand new Roadster.

Tesla got bad press due to the lack of 12V battery for the Roadster bricking problem:

Tesla Battery Failures Make ‘Bricking’ a Buzzword

Since then, it learned its lesson from the lack of 12V battery in Roadster, and it has included 12V battery for subsequent models, S, X and 3...

But it looks like the learning is over and Tesla won't need 12V battery any more in future?

I am really confused!

The bricking has nothing to do with the 12v battery. The "experts" they brought in for that article was talking about something else other than bricking: that if the HV battery is dead, then the vehicle displays and other subsystems can't boot up. However, this is not necessarily true for the Roadster either. For the earlier versions without a 12V battery (later versions had it), they used two dedicated sheets to serve similar to a 12V battery.

The actual "bricking" is permanent damage from overdischarging the battery by leaving it unplugged for too long. Even for the later Roadsters that had a 12V battery, they are still susceptible to bricking. This is because the older Roadster BMS didn't have an anti-bricking buffer in the bottom.

The way the Model S fixed the problem is by locking out the bottom of the SOC window. There is a 4kWh bottom buffer for the larger packs and if I remember correctly 2.5 kWh for the 60 kWh.
Plug It In

 

[Model 3]

But it looks like the learning is over and Tesla won't need 12V battery any more in future?

I am really confused!

Keep in mind that Elon said it will not have a 12v battery, not that it would not have a low-voltage battery/system. He said that 12v was not the right tool for almost anything (or something similar). So they will probably have a low-voltage battery/system but it will not be 12v. The most likely is as others have mentioned a 48v battery/system, but it does not need to be it.

 

[jelloslug]

Years ago there was a push to replace 12V batteries with 48V batteries in all cars. These made sense for larger motors that drive A/C compressors, electric power steering, brake boost, heated elements within the cabin, and even smaller motors, etc. Thinner wires, less weight, less copper, cheaper motors, and a little more energy efficiency. I don't know what happened with this trend, but it would seem to make sense for electric cars. Maybe that's why Tesla may be going in that direction.

Regarding the electronics, with modern voltage converters, it doesn't make much difference whether they convert down from 12V or 48V.

And 48V is still low enough to not be much of a shock hazard in most situations.

Still, it would seem in bad form to not provide at least one robust 12V outlet for accessories...and make the damn fuse easy to replace!

I think the emphasis will be on USB connections rather than 12V outlets in the future.

 

[Tam]

...if the HV battery is dead...

Thanks for the explanation that it is not 12V battery that causes Roadster bricking but it is the prolonged unplugging.

So let's talk about when main battery fails for any kind of reasons:

If I understand correctly, the advantage for a lower voltage battery is: You can power the non-propulsion accessories much easier by just either recharging it, jump starting it, or just replacing it.

Without a lower voltage battery, the dead main battery must be replaced first in order to power up non-propulsion accessories (lights, neutral gear, tow mode, turning on Battery Management System to allow recharging main battery pack...)

It looks like you suggest to solve the problem for powering up non-propulsion accessories without a second battery is to make sure there is a reserved energy in the main pack all the time and the main pack will never go to zero?

 

[Tam]

...not that it would not have a low-voltage battery/system....

It sounds like a reasonable solution: Instead of using 12V battery, it can use 48V battery as a second battery just in case the main battery fails.

That is because it is easier to jump start or replace a second smaller battery than replacing a big heavy main pack.

 

[Tam]

I think the emphasis will be on USB connections rather than 12V outlets in the future.

USB provides 5V but currently, I am using tire inflator that requires higher voltage than that.

 

[Saghost]

Thanks for the explanation that it is not 12V battery that causes Roadster bricking but it is the prolonged unplugging.

So let's talk about when main battery fails for any kind of reasons:

If I understand correctly, the advantage for a lower voltage battery is: You can power the non-propulsion accessories much easier by just either recharging it, jumping starting it, or just replacing it.

Without a lower voltage battery, the dead main battery must be replaced first in order to power up non-propulsion accessories (lights, neutral gear, tow mode, turning on Battery Management System to allow recharging main battery pack...)

It looks like you suggest to solve the problem for powering up non-propulsion accessories without a second battery is to make sure there is a reserved energy in the main pack all the time and the main pack will never go to zero?

All the computers and lights run on low voltage, and that's not changing. Given that, I don't think there's any possibility that the car won't have a low voltage wiring system.

Since that will be driven off of a DC DC converter from the high voltage system, you need a bunch of capacitance to stabilize the voltage and calm the ripples from the converter. This can either be a big capacitor stack, or a fairly small battery, which had other benefits.

I think the most likely outcome is a 5-6 Volt low voltage system, with battery, but Tesla might go to 48V instead.

The others going to 48V are doing it for high power devices - starter-generators with mild hybridization, electric steering, electric A/C. Tesla has 400V for that, so I'm not seeing a value to them in going up.

There could be some value in going down, since most of the things they drive off of 12V are converting that down to lower levels, though power steering and brakes might require other solutions and it will be annoying for folks with 12V accessories.

 

[stopcrazypp]

Thanks for the explanation that it is not 12V battery that causes Roadster bricking but it is the prolonged unplugging.

So let's talk about when main battery fails for any kind of reasons:

If I understand correctly, the advantage for a lower voltage battery is: You can power the non-propulsion accessories much easier by just either recharging it, jumping starting it, or just replacing it.

Without a lower voltage battery, the dead main battery must be replaced first in order to power up non-propulsion accessories (lights, neutral gear, tow mode, turning on Battery Management System to allow recharging main battery pack...)

It looks like you suggest to solve the problem for powering up non-propulsion accessories without a second battery is to make sure there is a reserved energy in the main pack all the time and the main pack will never go to zero?

Sorry, I should clarify. The Model S fixed the bricking problem (where the pack is permanently damaged) by locking out the bottom of the pack so that it never goes zero. However, I do not mean to suggest this buffer is used to power up non-propulsion accessories. If this is allowed, it goes back to square one: the pack might possibly be overdischarged.

As others put it, Tesla might still use a separate accessory battery, just perhaps a higher voltage one. Or they might have a separate low voltage feed come out of the main pack (although this eliminates physical separation, it still allows HV to be cut somewhat independently).

As for the case of a dead main battery, I don't think even in the case of without lower voltage battery that the pack has to be replaced to recharge main battery from empty. In the worse case they might need the service center to connect it to a power supply to boot up BMS, but I imagine they would design it so that shore power can be used to wake up the battery.

 

[mongo]

All the computers and lights run on low voltage, and that's not changing. Given that, I don't think there's any possibility that the car won't have a low voltage wiring system.

Since that will be driven off of a DC DC converter from the high voltage system, you need a bunch of capacitance to stabilize the voltage and calm the ripples from the converter. This can either be a big capacitor stack, or a fairly small battery, which had other benefits.

I think the most likely outcome is a 5-6 Volt low voltage system, with battery, but Tesla might go to 48V instead.

The others going to 48V are doing it for high power devices - starter-generators with mild hybridization, electric steering, electric A/C. Tesla has 400V for that, so I'm not seeing a value to them in going up.

There could be some value in going down, since most of the things they drive off of 12V are converting that down to lower levels, though power steering and brakes might require other solutions and it will be annoying for folks with 12V accessories.

Assuming that there will be a minimum of two converters between the battery and the end load (regulation and protection at the device necessitating a local converter), the higher the intermediate voltage is the better. Higher voltage allows smaller wires to supply the load. Or, like the Y may do, higher voltage allows more loads to be fed by the same power circuit (less total wire length).

 

[jelloslug]

All the computers and lights run on low voltage, and that's not changing. Given that, I don't think there's any possibility that the car won't have a low voltage wiring system.

Since that will be driven off of a DC DC converter from the high voltage system, you need a bunch of capacitance to stabilize the voltage and calm the ripples from the converter. This can either be a big capacitor stack, or a fairly small battery, which had other benefits.

I think the most likely outcome is a 5-6 Volt low voltage system, with battery, but Tesla might go to 48V instead.

The others going to 48V are doing it for high power devices - starter-generators with mild hybridization, electric steering, electric A/C. Tesla has 400V for that, so I'm not seeing a value to them in going up.

There could be some value in going down, since most of the things they drive off of 12V are converting that down to lower levels, though power steering and brakes might require other solutions and it will be annoying for folks with 12V accessories.

I can see a 5 volt system for computers and input devices and a 48 volt system for actuators, motors, and other higher current devices.

 

[mongo]

I can see a 5 volt system for computers and input devices and a 48 volt system for actuators, motors, and other higher current devices.

A 5 V bus isn't advantageous. The wire would be too thick and voltage drop would be too high. I'm working with a 1 meter USB charge cable, and it is dropping .4V at 1. Amps from the charger to the tablet. The AP2 computer pulls ~200W, to source that at 5V would take over 40 Amps. A 12 gauge wire is 1.588 mOhm per foot. Assuming a perfect body ground, and a 6 foot power circuit, you would have a drop of 6*40*1.588/1000 = 0.38 V or almost 8%. You would still need a regulator at the load to get a stable supply.

 

[jelloslug]

A 5 V bus isn't advantageous. The wire would be too thick and voltage drop would be too high. I'm working with a 1 meter USB charge cable, and it is dropping .4V at 1. Amps from the charger to the tablet. The AP2 computer pulls ~200W, to source that at 5V would take over 40 Amps. A 12 gauge wire is 1.588 mOhm per foot. Assuming a perfect body ground, and a 6 foot power circuit, you would have a drop of 6*40*1.588/1000 = 0.38 V or almost 8%. You would still need a regulator at the load to get a stable supply.

Then maybe 48 volts for everything and stuff that needs a 5v bus can do it internally.

 

[mongo]

Then maybe 48 volts for everything and stuff that needs a 5v bus can do it internally.

That is what I am thinking. With lights and such locally switched to reduce power feeds.

 

[jelloslug]

That is what I am thinking. With lights and such locally switched to reduce power feeds.

That would certainly reduce the AWG of the required wiring throughout the car.

 

[mongo]

That would certainly reduce the AWG of the required wiring throughout the car.

With reduced cross section requirements, they could go with more of a tape (wide/thin) design as opposed to a cylindrical bundle.

 

[jelloslug]

With reduced cross section requirements, they could go with more of a tape (wide/thin) design as opposed to a cylindrical bundle.

A ribbon setup would allow for tighter placement under panels and around more intricate sections of the car. You could also have faster termination of the connectors which could reduce costs.

 

[Saghost]

A ribbon setup would allow for tighter placement under panels and around more intricate sections of the car. You could also have faster termination of the connectors which could reduce costs.

We know Tesla's been experimenting with flexible circuit boards for things that are typically wired (remember the patent for the flexible circuit boards connecting all of the cells in the battery pack.

Maybe that's how they'll get the length of wiring down so much - they'll have a single flexible printed circuit board running to any area of the car, with channels designed into it for whatever needs to happen near there.

 

[Kmartyn]

So I guess this is now confirmed, with the recently announced patents. No 12 VDC , no CAN bus. Very simple semi rigid wiring that can be installed by a robot. There are entire manufacturing plants that do nothing but make the complicated wiring harnesses used in the industry now. Should save a lot of cost and manufacturing time.

Tesla keeps upsetting the Apple cart for the old school auto makers.