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Travel/camp trailer test methodology?

Discussion in 'Model X: Driving Dynamics' started by BerTX, Oct 23, 2015.

  1. BerTX

    BerTX Member

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    One of the things many of us will want to do with the MX is to tow travel or camping trailers on trips requiring stops at Superchargers. If one is in the market to get a trailer, how will we know what to get so that this will be successful? I hope we can get some community learning to share here, but what is the information we really need?

    I don't own a Model S, but I read lots of stuff about travelling between Superchargers. It seems that (simplified), with a given state of charge, to get to the next SC one will have to average x Wh/mi during the drive. Some conditions will allow us to drive 80 mph and achieve that usage rate. Sometimes, with a headwind or cold weather or elevation change, we may only be able to go 55 mph.

    I'm proposing that towing is just one more variable increasing the power use. However, since we still have a fixed(ish) distance between Superchargers and nobody want to sit at a SC waiting for a range charge, the thing that will have to change while towing is the speed.

    So, just to throw out some made-up numbers (nobody has real ones, so no complaints, please), lets say that we are comfortable driving our non-towing MX on the highway between Superchargers at 70 mph and charging for 30 minutes at each SC. Maybe that gives us an average Wh/mi of 350. So when we attach our trailer, we will want to still spend the amount of time charging that we already do, and the average distance is still the same between Superchargers, so we will still have to get 350 Wh/mi during our drive to get to the next one. The question is, how fast can we go, pulling this particular trailer, and get 350 Wh/mi?

    Obviously, all the other factors affecting range will still be there, and some of them will probably be of even more importance (like wind speed and direction), but it seems to me that if we agree on a "standard" Wh/mi rate calling for a reasonable amount of charge time, then different trailers could be tested by towing them on flat ground with no wind and simply reporting how fast that particular trailer can go (up to the 65 mph limit of trailer tires) and still achieve the required Wh/mi (350 in the example).

    It seems like if we can settle on some standard, then we can start to build a database of trailers showing what speed that particular model can be towed at, and we can decide if that travel speed is workable for our particular travel style. Also, with a standard Wh/mi goal in mind, owners can hook up to a trailer they are considering purchasing, tow it on the highway for a few miles and have some idea how it will work out for them.

    Reading ICE mpg info while towing a trailer reported on various trailer forums is totally worthless -- they all have different towing vehicles with different driving styles and they don't accurately remember their mpg or don't even know how to measure it. Yes, and sometimes they lie about the mpg they get. We will have the advantage of a fairly fixed performance on the tow vehicle (although the difference with a Performance model vs. standard in towing will probably need to be tested).

    Thoughts or ideas?
     
  2. santana338

    santana338 Member

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    BerTX, I think this is a good idea. I think what you are proposing is going to be the only way to get a good set of data. One thing though. Changing the aerodynamics would have a big effect on the Wh/mi numbers. So adding 1 (or 4) bikes on top of my pop-up I would suspect would change the numbers. We would need to make sure all measured numbers are in a stock configuration to minimize variance. Adding more drag would be an interesting extra data point if it can be quantified.
     
  3. BriansTesla

    BriansTesla Old school meets new tech

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    Some comparisons can be made to towing with an ICE vehicle but it is helpful to remember that an ICE wastes most of the energy in the fuel it burns. chart_ICE_efficiency-1024x293.jpg

    An electric vehicle because it is very efficient in its energy usage, is affected much more by added loads, higher speeds, elevation gains, etc.

    I would look for a very substantial increase in Wh/mi with a trailer. I believe 350WH/mi would only happen with a very small trailer in ideal conditions. With say a 3500lb trailer at 65mph, I think you might be looking at 450-600WH/mi. Keep in mind also that the MX will lose a lot of the possible regeneration because it will exceed the maximum when slowing and stopping.
     
  4. Uncle Paul

    Uncle Paul Member

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    Since most Highways restrict vehicles towing trailers to 55 MPH this might be much less of an issue than trying to tow at 70-80 mph.
     
  5. BerTX

    BerTX Member

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    Only California and a handful of other states have this restriction. The vast majority of states have no towing speed limits other than the posted speed limit.

    Obviously testing in California would be limited to the towing speed limit, unless someone wanted to temporarily risk having to explain to the officer that it was "all in the name of science". Honestly, I have driven in California quite a bit at the posted speed limit, and I definitely felt like I was the only one. Maybe they enforce the towing speed limit more vigorously -- no data.

    - - - Updated - - -

    What did I say about criticizing my fake numbers? :biggrin:
     
  6. ohmman

    ohmman Maximum Plaid Member

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    I've given this a little thought, and my feeling is that for the majority of Supercharger spacing, you're going to be able to hit one a day on road trips, and you'd have to be pretty strategic about the RV camps you choose in order to maximize daily distance.

    The idea is that you'd wake up with a full charge from a 14-50 RV outlet, and make it to the first Supercharger at nearly empty. Range charge, then make it to the next campground for the day. I mean, theoretically you could do a 3-4 hour stop and make it to the next Supercharger if you space it well and need to get some distance, but I just don't think long-haul camper drives are going to be very quick. Distance-wise, I wouldn't be surprised if that implied about a 250-300 mile per day in my first scenario, and maybe - maybe - 400 or 500 if you include a long stopover for a non-Supercharger charge. Plus, don't forget that after having to unhitch your trailer at each Supercharger, you're probably going to be fine with only stopping at one a day...

    Still not terrible, and impressive that it's doable with an electric vehicle.
     
  7. cantdecide

    cantdecide Member

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    Wh/m is a decent measure, so I expect the basic statement will be wh/m at a certain speed... Most commonly 55 to go at reasonable speed with long range. An alternative would be using the trip planner which said I would use x rated miles or percent, but actually used Y... That will give a ratio. Of course this will need to be reported for each trailer.
    Of course if the Tesla software is really smart then it will combine measurements of speed, slope, acceleration, and power usage ... Over the first few minutes of a journey to profile the weight, rolling resistance and air resistance of the vehicle trailer combination and figure the rest out itself.
     

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