Cybertruck low voltage 48V battery capacity

[ituner-HF]

Most Teslas use 12V/45Ah batteries, about 0.5kWh capacity.
Considering that CT will have steer-by wire and other power accessories, what do you think the capacity will be in Ah?

1) 0.5 kWh
1) 1 kWh
2) 2 kWh
4) 4 kWh

My take -- while a bigger battery might seem as deadweight, I think that there are benefits to moving some of the main battery capacity, I think that 48V pack + HV pack can be seen as one when calculating overall efficiency. Thoughts?

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[ÆCIII]

Your post evokes some interesting thoughts and questions, because if it's steer by wire, we're talking about 4-wheel steering by wire, and some other possible features like winch support and not to mention the compressor that activates the air suspension and possible alternate air compressor(s) too. There are also more cameras on board, and the climate systems will depend on it too. For these reasons I would guess at least the 2kWh or the 4kWh or even more, but I have no idea really.

Some of the golf cart 48V batteries I've noticed out there are fairly large needing about a 9"x11"x21" box to hold them, but they're 100 AH or around 4.8KWh. But there are also smaller ones available for E-Bikes ranging as low as 0.5 - 2KWh.

Another possibility (just wondering) if Tesla is going to just make a designated portion of the main pack to just provide a 48 Volt current source (tap), which would mean that a 48-52 volt charging system would not even be needed at all (like the 12-14 volt charger circuits in the battery pack penthouse configuration they have now). Software and the battery management system could possibly control and compartmentalize the reserves in the battery pack to make this feasible? Just brainstorming a little here, but it would save complexity and give options for how much power to allocate to 48 volt systems for different situations. Again, I don't really know, but am just throwing it out as speculative questions considering Tesla's aim to reduce complexity with increased versatility.

- ÆCIII

 

[Crissa]

Probably half a kWh, since the current one is about that. But their lithium replacement is 0.1 kWh.

https://insideevs.com/news/546087/tesla-liion-12v-auxiliary-battery/

-Crissa

 

[ituner-HF]

It is impossible to have drive-by-steering or winch operation with a 0.1Kwh battery, which would equate to a ~20C discharge rate, and for all practical purposes, it requires a 10-20C charge rate, having a 2-4Kw step-down converter is not easy or lightweight... By my calculations, min 48V battery capacity should be ~1kWh. Might sound counter-intuitive, but a larger 48V pack can actually (slightly) increase range., if you consider the total battery capacity to be the sum of 48Vdc + HV packs.

 

[ituner-HF]

Your post evokes some interesting thoughts and questions, because if it's steer by wire, we're talking about 4-wheel steering by wire, and some other possible features like winch support and not to mention the compressor that activates the air suspension and possible alternate air compressor(s) too. There are also more cameras on board, and the climate systems will depend on it too. For these reasons I would guess at least the 2kWh or the 4kWh or even more, but I have no idea really.

Some of the golf cart 48V batteries I've noticed out there are fairly large needing about a 9"x11"x21" box to hold them, but they're 100 AH or around 4.8KWh. But there are also smaller ones available for E-Bikes ranging as low as 0.5 - 2KWh.

Another possibility (just wondering) if Tesla is going to just make a designated portion of the main pack to just provide a 48 Volt current source (tap), which would mean that a 48-52 volt charging system would not even be needed at all (like the 12-14 volt charger circuits in the battery pack penthouse configuration they have now). Software and the battery management system could possibly control and compartmentalize the reserves in the battery pack to make this feasible? Just brainstorming a little here, but it would save complexity and give options for how much power to allocate to 48 volt systems for different situations. Again, I don't really know, but am just throwing it out as speculative questions considering Tesla's aim to reduce complexity with increased versatility.

- ÆCIII

Unfortunately tapping HV battery to 48VDC can cause a BMS imbalance, even if solved by BMS algorithms or by a separate 'tap' 48V charger, the aging of the 48V portion will be significantly higher, in terms of ESR. Because the 48V is in a series configuration, your entire HV battery pack will age at the rate of the 48V tap.


x20=~1000v

 

[Nanodot]

[snip]

Another possibility (just wondering) if Tesla is going to just make a designated portion of the main pack to just provide a 48 Volt current source (tap), which would mean that a 48-52 volt charging system would not even be needed at all (like the 12-14 volt charger circuits in the battery pack penthouse configuration they have now). Software and the battery management system could possibly control and compartmentalize the reserves in the battery pack to make this feasible? Just brainstorming a little here, but it would save complexity and give options for how much power to allocate to 48 volt systems for different situations. Again, I don't really know, but am just throwing it out as speculative questions considering Tesla's aim to reduce complexity with increased versatility.

- ÆCIII

After replacing my 12v AGM "motorcycle" battery (twice) in my golf cart (for lights and radio only) i put in a 48v to 12v DC-DC voltage reducer unit in its stead. After several years use now i wish i had done this sooner. Maybe this approach would work on the CT as well?

BTW, i assume their is no such thing (yet) as 3rd party after-market 48V winch for the CT either ...

 

[android04]

Probably half a kWh, since the current one is about that. But their lithium replacement is 0.1 kWh.

https://insideevs.com/news/546087/tesla-liion-12v-auxiliary-battery/

-Crissa

Just want to state that the lead acid 12v battery and the lithium ion 16v low voltage batteries have equivalent useable capacity. If the lithium ion battery is 0.1 kWh, then most of that is useable (let's say 90% of it). The lead acid battery is not a deep cycle battery (at least Tesla does not treat it as such) and only 15-20% of its 0.5 kWh capacity is useable. Which ends up being about the same useable capacity.

I would prefer that Tesla put a higher capacity battery in Cybertruck if only to keep the high voltage battery contactors from cycling as much to charge it up when not being driven.

 

[ÆCIII]

Unfortunately tapping HV battery to 48VDC can cause a BMS imbalance, even if solved by BMS algorithms or by a separate 'tap' 48V charger, the aging of the 48V portion will be significantly higher, in terms of ESR. Because the 48V is in a series configuration, your entire HV battery pack will age at the rate of the 48V tap.


x20=~1000v

True - unless the tap is possibly [Virtual] via software and BMS, and thus all the cells of the pack are used for the 48Volt tap at possibly different times distributed evenly. This would of course require more wiring or busses inside the pack, but again just creative thinking a little.

That was the configuration I was speculating, but we really don't know. Good discussions.

- ÆCIII

 

[ÆCIII]

[snip] ...
BTW, i assume their is no such thing (yet) as 3rd party after-market 48V winch for the CT either ...

I don't think it's that difficult for 48 Volt winches to become commonly available. Tesla may be working with Warn and other companies to get this started.

There are already 48 Volt motors being made by different manufacturers. Tesla will be (or are) making 48 Volt motors already for their Steer by Wire in the CT, and there are already 48 Volt motors being made for various purposes. Both Toro and Snapper have 48 Volt motor string trimmers, there are E-Bikes with 48 Volt motors in them, and you can even just buy 48 Volt electric motors on Amazon right now.

Look at how fast all the electric walk behind and riding mowers have come on the scene. It's been very easy for companies to make implements with varying DC electric motors and get them to market fast. I think it's been very easy to produce 48 Volt winches all along, but until now there has not been a reason to. I don't think we'd have to wait years for them, more like months IMO.

- ÆCIII

 

[ituner-HF]

True - unless the tap is possibly [Virtual] via software and BMS, and thus all the cells of the pack are used for the 48Volt tap at possibly different times distributed evenly. This would of course require more wiring or busses inside the pack, but again just creative thinking a little.

That was the configuration I was speculating, but we really don't know. Good discussions.

- ÆCIII

Yes, this would be a solution. Usually, the chassis is tied to the GND of the low voltage battery (for EMI shielding purposes, etc) while the HV battery is 'floating'. However, there is an absolute need to have power in case the HV battery pack fails -- you need to open doors, deploy airbags, the computer needs to be up and running to report the accident, etc.

 

[Crissa]

It is impossible to have drive-by-steering or winch operation with a 0.1Kwh battery, which would equate to a ~20C discharge rate, and for all practical purposes, it requires a 10-20C charge rate, having a 2-4Kw step-down converter is not easy or lightweight... By my calculations, min 48V battery capacity should be ~1kWh. Might sound counter-intuitive, but a larger 48V pack can actually (slightly) increase range., if you consider the total battery capacity to be the sum of 48Vdc + HV packs.

This is patently untrue, since you'd be operating off of whatever current the DC-DC board would provide, not the accessory battery.

The accessory battery just powers the radio while the vehicle is asleep.

-Crissa

 

[ituner-HF]

This is patently untrue, since you'd be operating off of whatever current the DC-DC board would provide, not the accessory battery.

The accessory battery just powers the radio while the vehicle is asleep.

-Crissa

IMHO, there are legit situations when you need power steering and others w/o the main HV battery pack. Example: Pyrofuse blows, HV disconnects while driving. Very stressful for the LV pack, if not impossible to get 10C discharge rates, even for short periods of time.

 

[Crissa]

If the high voltage pack drops, the car stops. The motors end up with very high resistance.

If you think they're under-sizing the battery pack, well, you should take up the argument with them.

As it is, my LFP provides ample CCA without being massively huge in kWh. You're not operating the battery at 10C for an hour, but for seconds.

-Crissa

 

[Bill906]

Probably half a kWh, since the current one is about that. But their lithium replacement is 0.1 kWh.

It is impossible to have drive-by-steering or winch operation with a 0.1Kwh battery,

Current Tesla vehicles already have steer by wire, it just works in conjunction with steer by mechanical linkage. And they (presumably) power that function with a 12V 500Wh battery. I don't see full steer by wire using much more (if any) power than the current system. Unless your argument is less about steer by wire, and more about having 4 wheel steering, which would require more power.

 

[ituner-HF]

true.

Current Tesla vehicles already have steer by wire, it just works in conjunction with steer by a mechanical linkage. And they (presumably) power that function with a 12V 500Wh battery. I don't see full steer by wire using much more (if any) power than the current system. Unless your argument is less about steer by wire, and more about having 4 wheel steering, which would require more power.

Current Teslas use hydraulic power steering with an electric pump and all kinds of reservoirs to buffer the power. Steer-by-wire uses an electric motor for steering, which is more efficient but might require larger power swings, 12V systems cannot easily cope (hundreds of amps!) but 48V will work very well.

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