Tesla towing 27' Airstream

[FilmGuy]

Originally Posted by Howard L.

Andy at CanAm is a smart guy. But here is a real time comparison of the Ford Lighting and a Chevy gasser towing the same trailer. I can’t imagine many people wanting to deal with the charging hassle. But to each his own.

https://insideevs.com/news/594871/fo...single-charge/

I think one of the biggest takeaways from this InsideEVs.com link, compared with the Tesla article is how important aerodynamics are to towing. That gets magnified with an EV. But the Denali gasser got only 8.9 mpg? Where are all the advances in fuel economy? My 2004 Denali with a 6 liter engine got 11 mpg most days while towing our Airstream.

[KK4YZ]

Originally Posted by Dsner

Perhaps by the time Tesla’s Cyber Truck finally becomes available, so too will Airstream’s re-gen charging for the TV

All EV’s and all or most gas-electric hybrids that I know of already utilize regenerative breaking to charge the batteries while slowing down or coasting down a hill. Not sure what adding regenerative breaking on the trailer adds to range or efficiency (beside a more balanced breaking approach).

Here are a few things to know about this topic:

1) batteries generally have a limit on how fast they can be recharged. Adding more generators to the charging path may not help.

2) when coasting down from altitude A to altitude B, there’s only so much energy that can be recaptured. It can all go to the EV battery, the AS battery or split between both. If the AS has a large enough traction battery then this could help with #1 above. Of course larger AS battery = more weight……

3) in normal towing on a relatively level road you wouldn’t be charging batteries (except in moments while you’re slowing down). It takes power to turn a generator, and the more power you take from it electrically, the more mechanical power is required from the wheels. This would represent a drag on the TV. There’s no free lunch.

4) These processes are not 100% efficient. That means on the downhill run you will capture a lot of the uphill energy but not all.

Take this from a guy who put over 300K miles on gas-electric hybrids over the past 10 years or so.

I’m telling you this because the EV salesman who haunts these forums won’t volunteer the balancing info. Again. I like the idea of EV’s but you have to look at the whole picture.

[RickBullotta]

The fundamental problem I have with most EV (and even some ICE) range/performance analyses is the "hypermiler" mindset in which the person travels on interstate highways and turnpikes at well below the speed limit. In even the slightest bit of traffic, this will lead to backups and traffic "clots", and overall reduced flow for the highway. IMO it's selfish, unsafe, and not reflective of real world range at normal speeds.

[DewTheDew]

Originally Posted by FalkTheHawk

T

I think it's amazing that going over mountains you recapture the uphill energy expended on the way down!!!

Thermodynamics suggest that there is an error in Andy's measurements. There is just no way that you gain more going down than you lose going up. There is always aero drag and mechanical losses that will prevent this gain.

[KK4YZ]

Originally Posted by DewTheDew

Thermodynamics suggest that there is an error in Andy's measurements. There is just no way that you gain more going down than you lose going up. There is always aero drag and mechanical losses that will prevent this gain.

Correct. In fact going through hills will decrease your range since you will not recapture all of the uphill energy on the downhill side. These machines are not 100% efficient.

[BT2513]

Originally Posted by RickBullotta

The fundamental problem I have with most EV (and even some ICE) range/performance analyses is the "hypermiler" mindset in which the person travels on interstate highways and turnpikes at well below the speed limit. In even the slightest bit of traffic, this will lead to backups and traffic "clots", and overall reduced flow for the highway. IMO it's selfish, unsafe, and not reflective of real world range at normal speeds.

Are we talking 45mph or going 65 in a 70?

[kscherzi]

Originally Posted by FalkTheHawk

I am currently putting a 3000W solar system on my 2003 Classic.

How do you fit 3,000 watts of solar on the roof of an Airstream trailer?

[gypsydad]

Originally Posted by FilmGuy

I think one of the biggest takeaways from this InsideEVs.com link, compared with the Tesla article is how important aerodynamics are to towing. That gets magnified with an EV. But the Denali gasser got only 8.9 mpg? Where are all the advances in fuel economy? My 2004 Denali with a 6 liter engine got 11 mpg most days while towing our Airstream.

I put a little over 10,000 miles on this summer towing the 28' AS with our 6.7L 2017 F250 4x4, and averaged 14.2mpg in the Rockies of NW-WY, MT, UT, ID and the flatlands of AZ, NM and TX. This is the first time I made a conscious effort to try and keep under 65mph. When not towing, I averaged 16-17mpg, usually at these speeds. Last few years I towed above 65...sometimes 70-73mph...averaged 12-13mpg towing...sometimes 10-11 even when climbing. Lesson for me is how much I was able to increase by slowing down...diesel was pretty expensive this year! Forgot to add...I am not thinking about an EV anytime soon to replace the TV....

[jcl]

Originally Posted by DewTheDew

Thermodynamics suggest that there is an error in Andy's measurements. There is just no way that you gain more going down than you lose going up. There is always aero drag and mechanical losses that will prevent this gain.

Originally Posted by KK4YZ

Correct. In fact going through hills will decrease your range since you will not recapture all of the uphill energy on the downhill side. These machines are not 100% efficient.

I didn't see evidence of an error. There was no claim that the laws of thermodynamics were being altered.

The article stated that the battery increased in charge by 8% on a descent. It didn't say what was expended on the ascent. But it was more than 8%.

The on board computer displaying average consumption between charges showed that the average consumption on a mountainous section was better than the average consumption for the whole trip. That's all. While regen on the descent would have helped, the take away is that other factors came into play, the most likely being travel speed, possibly headwind. Andy wondered if the thinner air helped as well. Perhaps there was an ambient temperature difference. But regardless, the elevation change did not create an issue as it can do with a conventional ICE powertrain.

If we assume 90-95% efficiency for the electric motor, both in propulsion and regen modes, and consider that the energy that could be recovered was only that related to the altitude change, and not aero or mechanical losses, we can deduce that the aero effect, as noted in the article, is bigger than many realize.

[jcl]

Originally Posted by KK4YZ

All EV’s and all or most gas-electric hybrids that I know of already utilize regenerative breaking to charge the batteries while slowing down or coasting down a hill. Not sure what adding regenerative breaking on the trailer adds to range or efficiency (beside a more balanced breaking approach).

Here are a few things to know about this topic:

1) batteries generally have a limit on how fast they can be recharged. Adding more generators to the charging path may not help.

2) when coasting down from altitude A to altitude B, there’s only so much energy that can be recaptured. It can all go to the EV battery, the AS battery or split between both. If the AS has a large enough traction battery then this could help with #1 above. Of course larger AS battery = more weight……

3) in normal towing on a relatively level road you wouldn’t be charging batteries (except in moments while you’re slowing down). It takes power to turn a generator, and the more power you take from it electrically, the more mechanical power is required from the wheels. This would represent a drag on the TV. There’s no free lunch.

4) These processes are not 100% efficient. That means on the downhill run you will capture a lot of the uphill energy but not all.

Take this from a guy who put over 300K miles on gas-electric hybrids over the past 10 years or so.

I’m telling you this because the EV salesman who haunts these forums won’t volunteer the balancing info. Again. I like the idea of EV’s but you have to look at the whole picture.

Good list. Here are a few more.

When talking about a trailer with regen capacity, the benefit to me isn't the battery recovery, that can be done with a tow vehicle as long as there is sufficient regen capacity. The benefit is that braking the trailer keeps the combination taut, which means safer and better handling. You don't want the trailer pushing the tow vehicle.

Regen (TV or trailer in the future) will be limited when the battery is full, or thermal limitations are reached. Wouldn't want to charge up at the top of a summit and then expect regen on the descent. In very cold or very hot ambient temperatures, or when the battery is close to 100%, we get a dash warning that regen is unavailable.

For efficiency, if we assume 90% motor efficiency in propulsion, so 10% losses, then the same again on regen, so compounded to 81% efficiency for the motors alone, it would be worth knowing what the rest of the system losses are.

The reason for a trailer with a battery is alluded to in your point 2. Larger and heavier battery packs not only cost more, but they decrease efficiency due to weight, and that penalty is there for all miles of operation. For other than a dedicated tow vehicle, a larger battery for towing range would likely only be required when towing, so it makes sense to me to put the additional battery capacity on the trailer, whether the trailer is powered or not.

One of the useful takeaways for me was learning that the EV tow vehicle in this case had sufficient regen capacity to brake an AS27 on a steep grade for several miles. I think we should see published specs on regen capacity in EV tests, that would help consumers. I play around with regen on a steep descent (the Coquihalla grade through the snow sheds, a regular route for us). If I use a light throttle, the vehicle maintains the speed limit fine. I get a certain amount of regen showing up as increased battery charge level at the bottom of the hill. If I accelerate to 20 km/hr over the limit, and remove throttle sharply, the vehicle brakes more aggressively with regen, and on that descent I will gain back more battery charge than if I held a steady speed. This suggests that the vehicle programming isn't linear, and also that there is more regen capacity than I am normally accessing, but I couldn't put that into context with a larger Airstream, until now.

[Countryboy59]

Originally Posted by RickBullotta

The fundamental problem I have with most EV (and even some ICE) range/performance analyses is the "hypermiler" mindset in which the person travels on interstate highways and turnpikes at well below the speed limit. In even the slightest bit of traffic, this will lead to backups and traffic "clots", and overall reduced flow for the highway. IMO it's selfish, unsafe, and not reflective of real world range at normal speeds.

No one does this anymore. Speeds are so high on the freeways that “clogs” are caused by people who dare to follow the speed limit.

[AlbertF]

Originally Posted by jcl

Good list. Here are a few more.



When talking about a trailer with regen capacity, the benefit to me isn't the battery recovery, that can be done with a tow vehicle as long as there is sufficient regen capacity. The benefit is that braking the trailer keeps the combination taut, which means safer and better handling. You don't want the trailer pushing the tow vehicle.

I can see it now. Generators and battery packs integrated with axle assemblies, even as an aftermarket option for existing trailers. The biggest issue is the cost of the batteries to gain the extra range. An extra 100 kWh wouldn’t be cheap.

[KK4YZ]

Originally Posted by Countryboy59

No one does this anymore. Speeds are so high on the freeways that “clogs” are caused by people who dare to follow the speed limit.

From what I’ve seen “clogs” on the highway are mostly caused by people in the left lane driving along side someone in the right lane, preventing anyone from passing. Used to drive me crazy when I was commuting to/from work.

[Daquenzer]

I still haven’t heard what modifications are made to the Tesla. I just don’t see how they can be safely made to a vehicle with a payload of only 1000lbs and a towing capacity of 5,000lbs.

As to efficiency I would completely agree that aerodynamics is more important than gross weight. I experienced that with my square cargo trailer. When I moved, I would fill that cargo trailer and if it got 9 to 10mpgs I was lucky. And it weighed half as much as my Airstream. Pull the AS along the same route and I’m at about 11 to 12 mpgs.

If tow vehicles could be more aerodynamic it would have to make a difference.

[mikeinca]

Originally Posted by jcl

If we assume 90-95% efficiency for the electric motor, both in propulsion and regen modes, and consider that the energy that could be recovered was only that related to the altitude change, and not aero or mechanical losses, we can deduce that the aero effect, as noted in the article, is bigger than many realize.

Just for the sake of accuracy, the 90% efficiency number that you quote for EV propulsion is considered more or less standard. However, on the regen side efficiency is more on the order of 60-70% due to losses in the regeneration process and when converting that recaptured energy back into propulsion. This is one reason why some manufacturers engineer their EVs to do more "coasting" under certain conditions when the throttle is lifted to take advantage of the momentum that has already been built up in the vehicle. FWIW, this also make driving the EV feel more "natural" rather than having heavy regen every time you take foot off the accelerator. That last part is just my opinion.

https://electrek.co/2018/04/24/regen...5%20efficient.

[DewTheDew]

Originally Posted by jcl

I didn't see evidence of an error. There was no claim that the laws of thermodynamics were being altered.

The article stated that the battery increased in charge by 8% on a descent. It didn't say what was expended on the ascent. But it was more than 8%.

Ah yes, I mis-read; thank you for pointing that out. What he said is that going up and down was more efficient with energy use than driving in the flat. I still think that is against thermodynamics and is either measurement error or something else weird (the thinner air argument seems weak, but I would imagine that a 20 mph headwind/tailwind would make a difference like that).

[jcl]

Originally Posted by DewTheDew

Ah yes, I mis-read; thank you for pointing that out. What he said is that going up and down was more efficient with energy use than driving in the flat. I still think that is against thermodynamics and is either measurement error or something else weird (the thinner air argument seems weak, but I would imagine that a 20 mph headwind/tailwind would make a difference like that).

I don't think much of the thinner air argument either. I think it is most likely that they were travelling 10 mph or so slower, but that is just speculation.

I think the take away is that things like headwinds and travel speed matter more than whether there are mountains involved. That is consistent with my non towing EV experience crossing the Rockies through Revelstoke, Golden, and Banff. Our consumption goes up when we get out of the mountains and closer to Calgary, where incidentally there is a higher speed limit. It seems that EV energy consumption when towing is consistent in that respect with EV solo operation.

[richard5933]

Originally Posted by AlbertF

I can see it now. Generators and battery packs integrated with axle assemblies, even as an aftermarket option for existing trailers. The biggest issue is the cost of the batteries to gain the extra range. An extra 100 kWh wouldn’t be cheap.

Doesn't seem like it should be that difficult to accomplish, at least not on the axle drive assemblies. I can see a two-axle assembly that gets mounted in place of the existing two separate axles, complete with some reinforcement of the frame to cope with the torque.


It's the batteries and associated cables that would be the tricky part, as there is not much free space in most of our trailers. Considering all that plus the live axles and there will be quite a bit of weight added to the trailer that has to be accommodated. For this to pay off, the added boost to the overall rive efficiency has to be more than the loss due to the extra weight.

[Mullers]

Originally Posted by AlbertF

I can see it now. Generators and battery packs integrated with axle assemblies, even as an aftermarket option for existing trailers. The biggest issue is the cost of the batteries to gain the extra range. An extra 100 kWh wouldn’t be cheap.

but does it need to be 100 kWh? with the eStream, Airstream talk about the technology being scalable from 20kWh to 80kWh. [ source: https://www.airstream.com/blog/the-a...and-adventure/ ]

There's going to be a cost/benefit, and somewhat diminishing returns from adding more capacity.
e.g. during testing in the alps with a similar system added to SOB trailer, an Audi E-Tron's range increased from 218miles to 240 miles with 2x 40kWh batteries in the trailer [ source: https://www.greencarreports.com/news...ers-the-future ]

For our needs I've got a 4 year old, so ~2-2.5hrs between stops is about all we're going to want to do. That would be a range of around 150 miles. Maybe that just needs 40kWh in the trailer?
That really is the beauty with electric, it'll be pretty straightforward to make it modular and retro-adjustable.

and then 15 years from now when battery technology has improved significantly could swap out our hypothetical trailer's 40kWh pack for a 80kWh pack that weighs less and charges faster.

[skyguyscott]

Originally Posted by Dsner

Perhaps by the time Tesla’s Cyber Truck finally becomes available, so too will Airstream’s re-gen charging for the TV

Elon Musk reportedly has said that the Cyber truck should finally enter production in 2023*, but even working at full capacity, they would not be able to meet all the existing pre-orders for three years. So 2027?

*I can't recall a single announced date Musk has ever met, let alone beat. So I would wager even longer.