Tesla packaged trailer upgrade kit

[Tinker71]

I don't think Tesla should get in the trailer business. But what they could is build a fully compatible trailer upgrade kit that any manufacturer or most existing trailers could be retrofitted with.

This would consist of:
1.) a single hub motor in roughly the 20 hp range
2.) A scalable battery pack Say 20 Kwhr increments.
3.) A super capacitor module.
4.) A software/bluetooth interface with the truck.

A small hub motor is all that is really needed to account for the addition of drag and rolling resistance on a trailer. It might be able help get rolling but would be tuned for 45 MPH and greater speed. 20 hp should capture 90% of regeneration (due to the trailer) except for emergency or very hard deceleration. The supercapacitor would help get that mass going again in stop and go without taxing the main battery and maybe protect the batteries from hard stop overvoltage charging. The batteries could be moved from trailer to trailer or where ever you have power needs. That would be the major cost of this system. An onboard 240 volt charger should suffice for everyone who doesn't tow 80% of the time. Forget the DC supercharging on the trailer. The software could have 1000s of trailers preprogrammed to interface with the CT trip computer. On a sustained down grade you might be able to optimize regen to allow the trailer to take it all. The software could anticipate the topography and decide when to apply or conserve power from the trailer, maybe even charge on the flats.

Yeah you might wear out one tire quicker but this would fix most of the problems with pulling trailers for a relatively small cost.

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[ajdelange]

You really need to think about this. It's well known that putting a trailer of any size behind a vehicle cuts its range approximately in half (if you are lucky). This means that the trailer is imposing a load approximately equal to the load imposed by the vehicle itself. For example, a Trimotor CT will have about 800 HP worth of motors on board and a 200 kWh battery pack. A 20 HP motor increases the power available to 820/800 = 1.025 i.e. by about 2.5%. A 20 kWh battery addition increases total energy by 220/200 = 1.100 i.e. by 10%. It would be much more practical to throw 2.5% more current to the motors in the truck and/or add 10% more battery to it than to think of a kluge such as you are proposing. The only benefit a system such as what you are suggesting might offer would be an couple of percent increase in energy collected by regen. Definitely not worth it in terms of added interface complexity.

You also need to understand why super capacitors, at the current level of the SOA, have no role in BEVs (except perhaps in their sound systems, clocks etc) and why PMSRMs are the most efficient motors for use in BEVs.

 

[Crissa]

I think, instead of figuring out ways something is impossible, we should take atesla as an example and think of what is possible.

Yes, the motor needs to be at least what's in a single-motor Tesla. But that would vary by trailer size. As would any pack that came with.

And as pointed out, much of the loss in a trailer is just air resistance. So this wouldn't affect that at all. But not having regen or flywheel would make it worse.

-Crissa

 

[Tinker71]

I think, instead of figuring out ways something is impossible, we should take atesla as an example and think of what is possible.

Yes, the motor needs to be at least what's in a single-motor Tesla. But that would vary by trailer size. As would any pack that came with.

And as pointed out, much of the loss in a trailer is just air resistance. So this wouldn't affect that at all. But not having regen or flywheel would make it worse.

-Crissa

Thanks Crissa - Adjelange is often negative with a superiority complex. Probaly French Canadian . My point is why upsize the tow vehicle for your worst case need. And I do disagree, you don't need a lot of motor power on the trailer. Say you burn a constant 8000 watts just working to overcome drag from the trailer. You would still consume consume 64 KWhrs over an 8 hour road trip which would otherwise have to come out of the CT battery pack. The CT has plenty of power for hills. In my mind the question is how do you maximize range with the lowest cost while trailering. Using the smallest motor/inverter is one place to start. Only spending $10k upgrading your trailer to work with your CT vs spending $20k on the next battery level on the CT might be another or say you bought a lesser model and now you want to pull a trailer. Heck this trailer configuration could work with your current ICE.

The software would optimize the trip. You know your destination, the topography, trailer characteristics and charging opportunity locations. You could even add expected wind. It would generally be foolish to charge your trailer by dragging it unless you knew you were going to supercharge your main pack to 80% at mile 200 on a 300 mile trip. In the case of a camper you might want power in your camper battery for accessories at your end destination.

 

[FutureBoy]

Thanks Crissa - Adjelange is often negative with a superiority complex. Probaly French Canadian . My point is why upsize the tow vehicle for your worst case need. And I do disagree, you don't need a lot of motor power on the trailer. Say you burn a constant 8000 watts just working to overcome drag from the trailer. You would still consume consume 64 KWhrs over an 8 hour road trip which would otherwise have to come out of the CT battery pack. The CT has plenty of power for hills. In my mind the question is how do you maximize range with the lowest cost while trailering. Using the smallest motor/inverter is one place to start. Only spending $10k upgrading your trailer to work with your CT vs spending $20k on the next battery level on the CT might be another or say you bought a lesser model and now you want to pull a trailer. Heck this trailer configuration could work with your current ICE.

The software would optimize the trip. You know your destination, the topography, trailer characteristics and charging opportunity locations. You could even add expected wind. It would generally be foolish to charge your trailer by dragging it unless you knew you were going to supercharge your main pack to 80% at mile 200 on a 300 mile trip. In the case of a camper you might want power in your camper battery for accessories at your end destination.

I do want to have a Tesla provided solution like this for trailers.

At the same time though, I’m not sure such a solution is in Tesla’s best interest in the short term. Right now there is a battery shortage that restricts the total number of vehicles that can be produced. Under these circumstances it seems like Tesla would use all their available batteries for building vehicles.

Once the battery recycling system that Tesla talked about at battery day is in place I could imagine them recycling some into trailer packages. If not, then perhaps once enough batteries can be produced to no longer be a limiting factor on the other projects already under way at Tesla.

Or perhaps Panasonic will make a trailer package.

 

[Tinker71]

I do want to have a Tesla provided solution like this for trailers.

At the same time though, I’m not sure such a solution is in Tesla’s best interest in the short term. Right now there is a battery shortage that restricts the total number of vehicles that can be produced. Under these circumstances it seems like Tesla would use all their available batteries for building vehicles.

Once the battery recycling system that Tesla talked about at battery day is in place I could imagine them recycling some into trailer packages. If not, then perhaps once enough batteries can be produced to no longer be a limiting factor on the other projects already under way at Tesla.

Or perhaps Panasonic will make a trailer package.

Valid point. Unless you supercharge, the batteries could be 1850 or any light chemistry really. Hub motors aren't their forte as far as I am aware. Maybe the software interface is their only participation.

Some participation from Tesla would only help overall EV adoption. If you own a $100k airstream and wanted to pull it with your future $60k CT this would help seal the deal.

 

[ajdelange]

Thanks Crissa - Adjelange is often negative with a superiority complex.

Well I do tend to be negative about dumb ideas. If that makes for a superiority complex, so be it.

Probaly French Canadian .

BELGIAN, dammit.

My point is why upsize the tow vehicle for your worst case need.

Because it's the only practical way to do it.

And I do disagree, you don't need a lot of motor power on the trailer.

That's because you didn't do any calculations as I suggested you should. Had you done so your folly might have been apparent.

Say you burn a constant 8000 watts just working to overcome drag from the trailer.

60 mph is 0.438573*60 = 26.31 m/s
The density of air at sea level on a normal day at 15 °C is 1.225 kg/m^3
The Cd of the CT is probably going to be about 0.4
It's frontal area is probably going to be about 4 m^2
Put all this together and you have drag at 60 mph of 26.31^3*1.225*0.4*4/2 = 17,848 kW corresponding to 297.5 Wh/mi. Over an 8 hour trip at 60 you would consume 17.848*80 = .2975*480 = 142.8 kWh. To get the drag load down to 8 kW you would have to go 60*(8/17.8)^(1/3) = 46 mph.

Now this is for the drag of the CT by itself. Do you think the trailer will have smaller frontal area. Or lower Cd? If you had a trailer with Cd of 0.2 or frontal area of 2 m^2 or Cd of 0.28 and frontal area down to 2.8 m^2 then you could get the trailer drag load down to 8500 W at 60 mph but you won't be able to do that for any trailer that weighs 2 -3 times what the CT does. And why are you neglecting rolling resistance and gravitational potential load?

At cruise on level ground drag is the biggest load. Trailer drag is going to be larger than tractor drag hence 50% or more reduction in range when towing. This is why you can't tow a trailer for 8 hours at 60 mph.

You would still consume consume 64 KWhrs over an 8 hour road trip which would otherwise have to come out of the CT battery pack.

So you are proposing to put a 64 kWh battery pack and a 20 hp motor with inverter and controller into a trailer as a means of cost reduction?

Only spending $10k upgrading your trailer to work with your CT

Can I get some of what you are smoking?

In my mind the question is how do you maximize range with the lowest cost while trailering.

If you have enough math ability to understand what I posted above you will realize that drag consumption, Wh/mi, goes down as the square of the speed. Does that suggest anything?


Try to understand the physics and then revisit.

 

[ajdelange]

I do want to have a Tesla provided solution like this for trailers.

Common sense says they wouldn't touch it with a ten foot pole but then the common sense in this thread is as thin as it is, alas, in most other places.

 

[Tinker71]

Ha. The Belgian spent 20 minutes customizing math on my comment and he is still wrong/doesn't get it. 30 seconds - out.

 

[ajdelange]

Hey. I'm here to learn. Where am I wrong? I'll fix it.

 

[Newton]

Hmmmmmm

Basically adding more money to the trailer to help the range while towing. Seems fine to me.
Although it would have to have a fantastic system, I would think integrated into teslas to know when and how much to help.

 

[ajdelange]

One of the things that would make such a system impractical would be the difficulty in the interface. The truck's software has a detailed dynamic model of it that Tesla will spend many many engineering man hours on refining. It would have to do the same for each combination of truck and trailer. I can perhaps see them doing that with a trailer for the Semi but certainly not for the CT. The market just wouldn't be there.

 

[firsttruck]

I think the direction you are thinking is good. But we could do even better for new trailers.

No motorized wheels in front. Motorized wheels with regen should be on at least one of axles of the axles in the back of the trailer. More axles possible.
Extra batteries under the trailer.
Before Semi arrives to pickup, each trailer is already charged based on load, trailer aerodynamics/drag, trip distance.
Solar panels on the roof.

 

[firsttruck]

One of the things that would make such a system impractical would be the difficulty in the interface. The truck's software has a detailed dynamic model of it that Tesla will spend many many engineering man hours on refining. It would have to do the same for each combination of truck and trailer. I can perhaps see them doing that with a trailer for the Semi but certainly not for the CT. The market just wouldn't be there.

I think Elon already said Cybertruck would in realtime sense some towing load characteristics. The Cybertruck will already know if it is traveling on level surface or up/down hill. Based on increased torque needed to accelerate, regen when braking Cybertruck & trailer, increased power usage needed for steady cruise with trailer vs none, up/down hill power needs the Cybertruck would have a lot of info

Could Cybertruck detect wind direction & speed?

 

[Crissa]

Ajdelange is right that for regen, the motor needs to be of appropriate wattage.

But I don't think it's as big of an ask as he seems to. He's making it sound impossible when it's actually quite simple... You just have to make sure draw and regen never exceed the battery's rating, and it has a limit how much regen it can take. But you can dump that to a radiant resistor or just use more brake. That's not rocket science.

-Crissa