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Towing and off-road

Anything to do with the electric or hybrid world

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gruntguru
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Re: Towing and off-road

Post by gruntguru »

Kevin Johnson wrote: Wed Dec 04, 2019 4:55 pm https://youtu.be/-cvNfmL7XQg
Not surprising when you think about it. Very high conversion efficiency (onboard energy store -> wheels) is one of the big advantages of EVs and this efficiency stays high under all driving conditions.

However this becomes a chink in the EVs armour when it is used for heavily loaded operation because it suffers in comparison to combustion engine vehicles where conversion efficiency IMPROVES as load increases. For example:

In the video it is apparent that towing the horse trailer at highway speeds requires about three times the energy as the unladen Model X. For the BEV this means 1/3 the range.

For a gasoline vehicle, the conversion efficiency of the ICE would improve from say 25% to 35% comparing unloaded to loaded so the range would reduce to 1/3 x 0.35 x 0.25 = 0.466 ie 46% or about 1/2.

In addition, the video uses a sedan with low aerodynamic drag. This suffers dramatically with the huge frontal area and poor Cd of the trailer. Something like a large pickup truck would get poor highway mileage in the first place - the energy required might only double when adding the trailer. Furthermore the truck (due to its poor economy) will have large fuel tank. This vehicle is designed to tow and is a good choice for towing.

The takeaway is - this is the wrong marked for rolling out EV technology. The prime market for EVs - especially at the "emerging technology" stage, is inner city commuting.

Unfortunately the world's biggest economy has a huge market for SUV's and pickup trucks, so EV startups in the US are in many cases trying to penetrate that particular market - which is unfortunate.
adam728
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Re: Towing and off-road

Post by adam728 »

gruntguru wrote: Wed Dec 04, 2019 7:03 pm In addition, the video uses a sedan with low aerodynamic drag. This suffers dramatically with the huge frontal area and poor Cd of the trailer. Something like a large pickup truck would get poor highway mileage in the first place - the energy required might only double when adding the trailer
Yup, and many don't think about that. I often tow a 6x10 enclosed trailer. Empty it's pretty light, maybe 850 lbs. But the drag can be killer, depending on the vehicle profile.
  • My car, 2.4L GMC Terrain. Pulls it just fine, but I wouldn't want to do over 60 mph with it. Lots of drag. Haven't towed it long distances with this one, but takes the mpg average down insanely fast even on shorter (15-30 mile) trips.
  • Wife's van, 3.6L Town and Country. Gets around 22-25 mpg on the freeway. Plenty of power. With the trailer that drops to a worst of 10.5 mpg, to around 12 mpg. And it likes to stay in 4th and rev rather than go to 6th.
  • Truck, 1992 C2500 with a 350. Gets a little over 12 mpg empty. Gets about 11 mph with the trailer.
  • Camper, gutless 1982 Chevy G30 with a 350. Gets 11 mpg empty. Gets 11 mpg with the trailer. Can't tell it's back there. Camper profile dwarfs the trailer.
And at that, they all end up using nearly the same amount of fuel (energy) to do the work of pulling that thing through the air. Diesels are a bit more efficient, and I've gotten 14 mpg pulling it with an overkill 1 ton Ram dually. Point is, trailer towing will crush an EV's range. But for some reason I've talked to people that seem to think 400 miles is 400 miles, whether it's tooling along 35 mph roads, or towing a camper at 75 mph through the mountains.

Another thing, we really need more aerodynamic trailers! Many have tried, but consumers just don't take em.
peejay
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Re: Towing and off-road

Post by peejay »

Towing is the worst thing for EVs and hybrids. They shine at recovering wasted braking energy. There is (very little) wasted braking energy in long-haul towing, there is just a long slog of fighting the wind. This is where you'd want an engine with high efficiency at moderate loads like a Diesel, which happens to be what we already have, so using it is easy.

Now, on the other hand, the garbage truck I encountered yesterday sounded for all the world like it was an electric. All gear and motor whine, no engine noise at all. A bit of Googling suggests that Mack is working with Republic Waste (the corp my city has contracted to) to create an EV garbage truck, and the new briefs are too recent to be "old news".
gruntguru
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Re: Towing and off-road

Post by gruntguru »

exhaustgases wrote: Thu Feb 06, 2020 10:48 pm The real fun is being stuck in snow and running the heater to keep warm. So how many miles of battery charge are lost running the heater just sitting there for say 5 hours?
Depends on a lot of factors. Assume it takes 1500W to heat the cabin. If the EV uses resistive heating only, that works out to 3 - 5 miles of lost range per hr.

If you leave the engine running to heat your combustion car the range reduces by 10 - 20 miles per hour.
gmrocket
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Re: Towing and off-road

Post by gmrocket »

gruntguru wrote: Wed Dec 04, 2019 7:03 pm
Kevin Johnson wrote: Wed Dec 04, 2019 4:55 pm https://youtu.be/-cvNfmL7XQg
Not surprising when you think about it. Very high conversion efficiency (onboard energy store -> wheels) is one of the big advantages of EVs and this efficiency stays high under all driving conditions.

However this becomes a chink in the EVs armour when it is used for heavily loaded operation because it suffers in comparison to combustion engine vehicles where conversion efficiency IMPROVES as load increases. For example:

In the video it is apparent that towing the horse trailer at highway speeds requires about three times the energy as the unladen Model X. For the BEV this means 1/3 the range.

For a gasoline vehicle, the conversion efficiency of the ICE would improve from say 25% to 35% comparing unloaded to loaded so the range would reduce to 1/3 x 0.35 x 0.25 = 0.466 ie 46% or about 1/2.

In addition, the video uses a sedan with low aerodynamic drag. This suffers dramatically with the huge frontal area and poor Cd of the trailer. Something like a large pickup truck would get poor highway mileage in the first place - the energy required might only double when adding the trailer. Furthermore the truck (due to its poor economy) will have large fuel tank. This vehicle is designed to tow and is a good choice for towing.

The takeaway is - this is the wrong marked for rolling out EV technology. The prime market for EVs - especially at the "emerging technology" stage, is inner city commuting.

Unfortunately the world's biggest economy has a huge market for SUV's and pickup trucks, so EV startups in the US are in many cases trying to penetrate that particular market - which is unfortunate.
Exactly,,except why is it unfortunate about the worlds largest economy liking what they like?

I couldn't get by without my pickup.

It's not unfortunate.. it's a fact the EV manufacturers have to overcome... they need to overcome that challenge... not the other way around
gruntguru
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Re: Towing and off-road

Post by gruntguru »

It is unfortunate because:
a) folks that need trucks will not have an (equivalent) electric option for the time being
b) "Liking what we like" (as opposed to "need") often has unfortunate consequences (think cigarettes, drugs, firearms, eating exotic wildlife . . . )
gmrocket
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Re: Towing and off-road

Post by gmrocket »

gruntguru wrote: Mon Feb 17, 2020 12:25 am It is unfortunate because:
a) folks that need trucks will not have an (equivalent) electric option for the time being
b) "Liking what we like" (as opposed to "need") often has unfortunate consequences (think cigarettes, drugs, firearms, eating exotic wildlife . . . )
we could all give up our hobbies and life's little pleasures to accept the EV's as they are now... then the manufacturers could stop all R&D, sit back and produce a stagnant product.

Or, we could live our lives, enjoying what we do and have manufacturers meet OUR needs... it will be a better product in the end.
gruntguru
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Re: Towing and off-road

Post by gruntguru »

gmrocket wrote: Fri Feb 21, 2020 5:21 am
gruntguru wrote: Mon Feb 17, 2020 12:25 am It is unfortunate because:
a) folks that need trucks will not have an (equivalent) electric option for the time being
b) "Liking what we like" (as opposed to "need") often has unfortunate consequences (think cigarettes, drugs, firearms, eating exotic wildlife . . . )
we could all give up our hobbies and life's little pleasures to accept the EV's as they are now... then the manufacturers could stop all R&D, sit back and produce a stagnant product.

Or, we could live our lives, enjoying what we do and have manufacturers meet OUR needs... it will be a better product in the end.
Totally agree.
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