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RoyJ

Vancouver, BC

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Posted: 08/16/19 01:27am Link  |  Quote  |  Print  |  Notify Moderator

Reisender wrote:

wanderingaimlessly wrote:

For the electrical engineers that really want to get into the weeds on this, real question for you.
IF you had a Tesla truck and TT and ran out of power in the desert southwest. And you had a trailer with 400 watts of solar, and a 430 Amp/hr battery pack. Along with a 1500 watt inverter.
How long would it take to generate enough power to get the truck, without the trailer, 20 miles, to a real power source for recharging if you dont run anything else in the trailer?
It may be a lot better than I am guessing, but I really do wonder if there is an optimistic answer.
That there is a self sufficient method is a positive, just curious if the method would be real world useful.


Well, a kw will take you about 6.7 km in our cars. So 30 km is around 20 miles. So let’s say you need 5kw total. I’ll leave it to someone else from there.


I'm going to guess it takes from than 1 kwh to drive 6.7 km when TOWING.

Let's say you tow at a very conservative 90 km/h, or 56 mph. It takes 0.0744 hrs to drive that distance. Your average power output would be 1kwh/0.0744hr = 13.42 kw, or 18.01 hp.

There're very few trailers you can tow with an average of 18 hp.

Drag = Cd*A*rho*V^2/2

Assuming a small 7' wide 8' tall trailer, your frontal area is 5.17 m^2. The combined Cd of a truck and trailer would be lucky to hit 1. Rho of air is roughly 1.2. Plugging in the numbers, drag at 56 mph is:

Drag = 1973N

Power = F*V = 1973N x 25m/s = 49.33 kw, or 66hp

In conclusion, the required power is far greater than the 18hp assumed. Re-calculating with 66hp, it takes 49.33 kwh to drive 56 miles, or 1.13 kwh per mile. A 1.5kw generator + 0.4 kw solar makes 19 kwh in 10 hours, assuming PERFECT charging.

You can tow 21.47 miles after 10 hours of generator + solar. In real life, with charging inefficiency and less than 10 hrs of perfect sun, you'd be lucky to get 15 miles.

ShinerBock

SATX

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Posted: 08/16/19 06:37am Link  |  Quote  |  Print  |  Notify Moderator

afidel wrote:



I'm hopeful that my retirement tow vehicle will be a used Class 8 electric truck. The Tesla semi is now testing at 600 miles for the full range model with a 75k pound payload (albeit jersey barriers so way less drag than a 5er) link


At this point, I would not trust what Tesla range when towing. Especially when it is something with a drag coefficient of a brick like a 5th wheel. So I will take the 600 miles with a grain of salt.

Reisender

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Posted: 08/16/19 06:51am Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

Reisender wrote:

wanderingaimlessly wrote:

For the electrical engineers that really want to get into the weeds on this, real question for you.
IF you had a Tesla truck and TT and ran out of power in the desert southwest. And you had a trailer with 400 watts of solar, and a 430 Amp/hr battery pack. Along with a 1500 watt inverter.
How long would it take to generate enough power to get the truck, without the trailer, 20 miles, to a real power source for recharging if you dont run anything else in the trailer?
It may be a lot better than I am guessing, but I really do wonder if there is an optimistic answer.
That there is a self sufficient method is a positive, just curious if the method would be real world useful.


Well, a kw will take you about 6.7 km in our cars. So 30 km is around 20 miles. So let’s say you need 5kw total. I’ll leave it to someone else from there.


I'm going to guess it takes from than 1 kwh to drive 6.7 km when TOWING.

Let's say you tow at a very conservative 90 km/h, or 56 mph. It takes 0.0744 hrs to drive that distance. Your average power output would be 1kwh/0.0744hr = 13.42 kw, or 18.01 hp.

There're very few trailers you can tow with an average of 18 hp.

Drag = Cd*A*rho*V^2/2

Assuming a small 7' wide 8' tall trailer, your frontal area is 5.17 m^2. The combined Cd of a truck and trailer would be lucky to hit 1. Rho of air is roughly 1.2. Plugging in the numbers, drag at 56 mph is:

Drag = 1973N

Power = F*V = 1973N x 25m/s = 49.33 kw, or 66hp

In conclusion, the required power is far greater than the 18hp assumed. Re-calculating with 66hp, it takes 49.33 kwh to drive 56 miles, or 1.13 kwh per mile. A 1.5kw generator + 0.4 kw solar makes 19 kwh in 10 hours, assuming PERFECT charging.

You can tow 21.47 miles after 10 hours of generator + solar. In real life, with charging inefficiency and less than 10 hrs of perfect sun, you'd be lucky to get 15 miles.


Yah. I forgot about the towing part. Our 6.7 km per kWh is on paved roads no load other than us and a chihuahua. [emoticon]

rjstractor

Maple Valley, WA

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Posted: 08/16/19 08:31pm Link  |  Quote  |  Print  |  Notify Moderator

wanderingaimlessly wrote:


For the electrical engineers that really want to get into the weeds on this, real question for you.
IF you had a Tesla truck and TT and ran out of power in the desert southwest. And you had a trailer with 400 watts of solar, and a 430 Amp/hr battery pack. Along with a 1500 watt inverter.
How long would it take to generate enough power to get the truck, without the trailer, 20 miles, to a real power source for recharging if you dont run anything else in the trailer?
It may be a lot better than I am guessing, but I really do wonder if there is an optimistic answer.
That there is a self sufficient method is a positive, just curious if the method would be real world useful.


You don't really have to get into the weeds or be an engineer to figure this out. Regardless of your available 110V power, Tesla Level 1 charging only provides a max roughly 3 miles of range per hour. TFL testing shows that towing uses roughly 3 times the battery energy as non-towing, so figure 1 hour charging time per hour of range. With a 400W solar panel trying to charge a battery pack powering a 1.5 KW inverter, you're going to be there a LONG time. Even with a gas generator (would probably take a 2kw generator at a bare minimum) figure 20 hours charging time and about 7 gallons of gas. (Honda EU2000i uses about 1/3 gallon per hour at full load) Not very good mpg at all! And if you were using this little generator you would have nothing left over to run anything in your RV. I'd say Tesla has a bit of work to do before they produce a viable vehicle for RV use. But in time it will happen, as sure as the internal combustion engine replaced the horse.

noteven

Turtle Island

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Posted: 09/03/19 04:57pm Link  |  Quote  |  Print  |  Notify Moderator

Towing up grades like “the Ike” and in 40mph crosswinds reduces the “range” on my gasohol and diesel trucks. The salesman shoulda told me.

The Tesla Camper Trailer is coming out with thirty eleventeen kWh’s in its skateboard chassis battery that plugs into the tow Tesla or your Tesla wall at home. Charges from a Supercharger, wall socket, it’s solar, or regen from the Tow Tesla. Low c of g. Optional powered wheels will be available.

thomas201

Eastern Panhandle WV

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Posted: 09/03/19 07:08pm Link  |  Quote  |  Print  |  Notify Moderator

I also doubt that 75k payload. Gross maybe. Payload no. With an 80K gross on a normal truck, you are lucky to get 45k payload. A payload of 75k would leave you just 5k for the truck. Most cars weigh about 4k.

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