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[Crissa]

That's because Tesla doesn't repeat things.

Elon's tweeted about it a few times.

https://twitter.com/elonmusk/status/1392429457038667777

-Crissa

[flynnstig82r]

Can anyone enlighten me on why manufacturers choose to use separate 12v batteries instead of DC-DC converters? From my layman’s POV, I don’t see any advantages. It’s a separate point of failure with an incompatible charging system that’s heavier than a DC-DC, but you still need one of those to keep it charged which introduces yet another point of failure. Yet there must be some advantage because Zero went from a DC-DC on the S/DS(R) bikes to a separate 12v battery on the newer range.

[Crissa]

DC-DC conversion isn't very efficient.  Especially at high amperage, but also each has a minimum draw as well, the remainder is wasted.  So it's a poor choice for low-variable power applications.

A battery can - without transfer loss - produce any amount of amperage arbitrarily, small or large.

Having a secondary power source also is needed for anti lock brakes.

-Crissa

[Oldun]

Thank you Crissa, that is helpful info.

[NEW2elec]

Can anyone enlighten me on why manufacturers choose to use separate 12v batteries instead of DC-DC converters? From my layman’s POV, I don’t see any advantages. It’s a separate point of failure with an incompatible charging system that’s heavier than a DC-DC, but you still need one of those to keep it charged which introduces yet another point of failure. Yet there must be some advantage because Zero went from a DC-DC on the S/DS(R) bikes to a separate 12v battery on the newer range.

The 12V battery is needed if they want OTA updates and app connection status info ect.  The things a SRF/S can do that the gen 2 bikes can't.
Tesla has it's sentry mode which will record camera footage if people get too close.  It has pre heat and cool options but I don't know if it closes the battery contactor in order to use that function.

It seems to be the main contactor that is issue.  When it's closed and charging the DC-DC makes all the 12V power it needs.  It is when the main battery is full and opens the contactor that the 12V function is either off or on it's own with only the aux battery to use.

[staples]

DC-DC conversion isn't very efficient.  Especially at high amperage, but also each has a minimum draw as well, the remainder is wasted.  So it's a poor choice for low-variable power applications.

A battery can - without transfer loss - produce any amount of amperage arbitrarily, small or large.

Having a secondary power source also is needed for anti lock brakes.

-Crissa

There is no such need to have ABS. For example, the FX and FXS do not have an auxiliary 12V battery, but still have ABS. The ABS is just powered by the DC-DC converter while the bike is on.

The efficiency and durability of the DC-DC converter are, I believe, the larger reasons for limiting the runtime of the converter and adding the auxiliary 12V battery.

[flynnstig82r]

Thanks Crissa and others, that clears up a lot!

[DonTom]

DC-DC conversion isn't very efficient.  Especially at high amperage, but also each has a minimum draw as well, the remainder is wasted.  So it's a poor choice for low-variable power applications.

A battery can - without transfer loss - produce any amount of amperage arbitrarily, small or large.

Having a secondary power source also is needed for anti lock brakes.

-Crissa

All three of my electric motorcycles have ABS with no 12V battery.


Besides the fact you can get 12V DC2DC converters at just about any rate.


And efficiency  is around 80%. Fine for any EV.


  EV batteries, I think are mainly for doing things when the vehicle is off  and/or in deep sleep. Such as automatic updates in my Tesla. And the 12V battery  is charged  by a DC2DC converter. And that battery seems to do nothing at all while the car is awake, as shown by my testing yesterday.


BTW, in the Tesla forum I found out it charges the battery even while in deep sleep. Just once in a while to bring the voltage back up on the 12V battery. I guess while it is in deep sleep it is still checking the 12V battery voltage. 


-Don-  Auburn, CA

[Crissa]

There is no such need to have ABS. For example, the FX and FXS do not have...

ABS is required to have a backup power source.  I did not say it had to be a 12v battery.  There are other ways to make something work for longer than its main power source.  Battery is just easiest.

Also, I don't think small bikes like the FX are required to have ABS yet, so they would not have the same regulatory requirement for backup power.

-Crissa