Charging While Driving?

[Crissa]

1. I don't need to have a large battery in trailer that isn't being used 95% of the year. I'll take that money and spend it on a bigger battery for CT.

Or you could use it as a powerwall for the rest of the year?

-Crissa

 

[Crissa]

The type of wire coming off of a decent-sized PV array is probably going to look a lot like this heavyweight 50-amp 6-gage wire running at whatever voltage the PV array produces.

...You're going to have 50a at what voltage from solar on the trailer? That would be at minimum ten 600W panels, which would be a tad larger than a large RV.

Anyhow, hanging charging cables is a solved problem.

https://store.clippercreek.com/ev-charging-cable-retractor


-Crissa

 

[Luke42]

Anyhow, hanging charging cables is a solved problem.

https://store.clippercreek.com/ev-charging-cable-retractor

...You're going to have 50a at what voltage from solar on the trailer? That would be at minimum ten 600W panels, which would be a tad larger than a large RV.

If you boost the voltage from whatever the panels produce, you can use a lighter wire - but then you need a big DC boost converter on the trailer.

Designing and building one of those is very possible. However, designing a big DC boost converter that matches the the economic and mechanical requirements of a trailer is harder than it looks, and definitely a nontrivial engineering project.

The big question is whether it makes sense to put this expensive piece of electronics on the truck O(1) or on the trailer O( n). Anything that makes the trailer more expensive means fewer trailers will incorporate that feature.

Anyhow, hanging charging cables is a solved problem.

https://store.clippercreek.com/ev-charging-cable-retractor

With the constant 60+mph wind, weather, debris, and constant movement in 3 dimensions, I'd give that thing an MTBF of about 24 road-hours.

Running a wire like that out into a 60+mph breeze to the corner of the vehicle is going to be quite likely oscillate like a mofo in the breeze.

At $550/ea, it's going to add up quickly even if my intuition is off by an order of magnitude.

It's possible to solve this problem, but the existing trailer-towing tech stack already worked out all of these problems decades ago -- at least for the limited vehicle/trailer interconnection they have. It's the design to beat.

 

[JBee]

My thoughts on the subject of charging from a trailer with solar are based on the below rough calculations and assumptions:

1. The cable connection to the CT is not as difficult as it first seems. There are many caravans here in Australia that use a simple 50-175A Anderson plug. Depending on the voltage used this could handle between @ 48V = 2600 - 9100W by itself. If you use a higher voltage setup, via a 240V solar inverter for example, to plug into the existing L2 charging circuit, you'd be able to get around 11kW. The cable and connector can easily be specified to work at the power levels required and described below.
2. The interconnection to the battery pack is however more difficult. From what I understand the Tesla plug is not active and won't accept charge whilst driving. If it did then supplying it with 240V from the RV solar would be trivial, and not require any further components to control charging, as the Tesla would handle that itself using the 240V charge cable. An internal plug could be wired into the CT so it's not hanging off the side, or a flat plug used.
3. If one wants to charge directly into the battery bus, then technically this is also possible and would require wiring to some sort of RV connector rated at the voltage being tapped (400V?). You could then use a solar MPPT charger with a PV string voltage rating and output of similar voltage to directly charge the battery using the right MPPT charger settings to fit the battery min/max voltage. Most MPPT allow you to configure this within the chargers specification. There does not however have to be any interaction with the Tesla system as such, and if the car was on full regen and the voltage was beyond max pack voltage the MPPT would simply throttle it's output as it already does whenever connected to any other battery when it appears full.
4. Due to the surface area required its only really possible to install 4-5kW of PV on a 8 x 2.5m 20sqm (215sqft) RV roof area.
5. If we take 11kW as the power level, you will need 48sqm (516sqft) of solar panel area using high efficiency Sunpower panels (22%). That's 8m (26ft) long and 6m (20ft) wide, so about 2.5 times the width of a RV trailer, meaning it would have to telescope out to expand the solar collection area to achieve this level of power. A stationary expanding Solar array with RV battery storage will be much more productive and easier to incorporate. You can then charge normally whilst stationary. But lets continue on the "charging whilst driving route for now:
6. If we can produce 5kW from a roadworthy RV roof mounted solar array whilst driving, we would get per full day and using trailer consumption rates:
   1. In Phoenix in Summer: 30kWh @ 600Wh/km = 50km of range (31miles)
   2. In Phoenix in Winter: 11kWh @ 600Wh/km = 18km of range (11miles)
   3. In Portland OR in Summer: 25kWh @ 600Wh/km = 41km of range (26miles)
   4. In Portland OR in Winter: 4kWh @ 600Wh/km = 7km of range (4miles)
7. 5kW of Sunpower cells would weigh 252kg (555lb), say another 70-100kg for framing, 25kg inverter etc with no batteries at least around 400kg (880lb). The extra weight will reduce range, to the point that in Portland in winter on average you will have reduced your effective range whilst towing by adding the solar setup
8. Seeing a lot of people travel with RVs in the summer though, you would likely end up with about 30-40km of max. effective extra range by charging with a 5kW system whilst driving with a trailer
9. This however requires the solar to be exposed to sunlight throughout the whole day, so no parking in the shade, no tunnels, trees, trucks or building etc casting shade across the road when you drive.
10. In this best case scenario you would be adding around 5-6km (4mile) of range per hour whilst driving whilst the trailer alone is consuming some 3-4 times more than it can produce
11. Given that this use case is specified by "charging whilst driving" the ToU (Time of Use) is ridiculously small in comparison to the annual park time. So assuming the solar setup costs $7-10k, and you can effectively drive around 1500km (937mile) using this setup in a 30day holiday period, with your RV in tow (which is generous), you end up with a cost per km of around $1 per km over a 6 year period or $1 per mile over a 9 year period.
12. The same range per day, at half the per mile cost could be charged in a couple of minutes at a Supercharger and would not require any capex or effort whatsoever. The ROI is therefore comparatively less than zero and you would be adding the system only so you could pat yourself on the back for creating a solution that just created more problems!
13. Now ToU and ROI is annoying or at best fair depending on your individual use case, obviously the setup could produce power all year long if left out in the open in a good sun exposure location. Adding an expanding array makes even more sense to get those kWh in, and you can even use it to power your home. Even a tracking array (adds 25%) would work.
14. The problem with using any of the RV solar power directly though is that the CT would have to remain connected to make use of it, or the RV needs to have enough battery onboard so that the RV can store what it generates during the day. That adds further cost and weight, but has the benefit of also powering the RV, which in turn will however result in less range being added. You could reduce the RV battery size if you stop 2-3 times during your drive to charge, which will in turn cycle the RV battery more. Somewhere in between there's likely to be a useful and usable balance of systems.
15. BUT a RV battery storage also completely negates any reason at all to have a system to "charge whilst driving".

So overall the short answer is NO it does not really make sense to charge whilst driving, mostly because of the variability of sunlight exposure, the limited space for mounting PV modules and the ability to use even a relatively small RV battery instead, to charge from when parked and can power the RV as well which leads to an overall much better ToU and therefore ROI.

 

[JBee]

If you boost the voltage from whatever the panels produce, you can use a lighter wire - but then you need a big DC boost converter on the trailer.

Designing and building one of those is very possible. However, designing a big DC boost converter that matches the the economic and mechanical requirements of a trailer is harder than it looks, and definitely a nontrivial engineering project.

The big question is whether it makes sense to put this expensive piece of electronics on the truck O(1) or on the trailer O( n). Anything that makes the trailer more expensive means fewer trailers will incorporate that feature.



With the constant 60+mph wind, weather, debris, and constant movement in 3 dimensions, I'd give that thing an MTBF of about 24 road-hours.

Running a wire like that out into a 60+mph breeze to the corner of the vehicle is going to be quite likely oscillate like a mofo in the breeze.

At $550/ea, it's going to add up quickly even if my intuition is off by an order of magnitude.

It's possible to solve this problem, but the existing trailer-towing tech stack already worked out all of these problems decades ago -- at least for the limited vehicle/trailer interconnection they have. It's the design to beat.

You don't need a DC boost converter to increase the voltage, you can just plug the PV panels in series until you get the string voltage you need to supply the pack. Off the shelf PV charge controllers go up to 1200V.

As per my post above the energy level available from the RV surface area (5kW) makes the trailer hitch connection a non-issue whatsoever.

 

[Bill906]

If you boost the voltage from whatever the panels produce, you can use a lighter wire - but then you need a big DC boost converter on the trailer.

The power is going to have to be boosted to battery voltage (≈400VDC probable, ≈800 or 900VDC maybe) at some point. I’d suggest boosting it to either 120VAC or 240VAC from the trailer and have the built in charging circuit take it from there, but I don’t want to start a side debate comparing efficiencies of DC-AC-DC vs DC-DC converters.

Making this work is far from impossible, but some real engineering is going to be required to make it happen.

With the constant 60+mph wind, weather, debris, and constant movement in 3 dimensions, I'd give that thing an MTBF of about 24 road-hours.

Cables have been developed to handle way worse conditions than connecting a trailer. It’s a cable, it’s not landing someone on the moon. Worst case just beef up the wire and/or insulation on the cable currenly used for brake power. We have the technology.

Hhow do you run a high-amperage/high-voltage electrical cable through there without abrading the insulation and while protecting it from road-damage?

Just how much power are you thinking? If it’s just solar panels, I’m guessing in the realm of about 1-2 kW. So typical extension cord. If you are talking power wall type setup, I’d be surprised if the cable needed to handle more power than say a level 2 charger, so roughly an RV 240V 50A extension cord at the absolute most. Yes there are cables made of that size that can handle the weather and being constantly flexed and moved, even in all three directions. Higher voltages do require more insulation, but the difference of insulation between 200V vs 400V vs 900V is not that significant. I work in the industrial world, we consider anything below 1000V as low voltage.

 

[Crissa]

Running a wire like that out into a 60+mph breeze to the corner of the vehicle is going to be quite likely oscillate like a mofo in the breeze.

Why is it running around the corner? Are you imagining that an in-motion charger plugs into the port on the side of the truck?

-Crissa

 

[Bob Anderson]

Or you could use it as a powerwall for the rest of the year?

-Crissa

Yeah, I guess some people could (lucky!). I definitely could not based on where our rv is stored. Most in the city store their rv off-site.

 

[Zabhawkin]

Those are hollow hoses and very light.

The type of wire coming off of a decent-sized PV array is probably going to look a lot like this heavyweight 50-amp 6-gage wire running at whatever voltage the PV array produces.

Making this work is far from impossible, but some real engineering is going to be required to make it happen.

Many solar systems run in the 400v range, which is the same as the charging system for the Teslas.

The max practical solar for a very large 5th wheel might be as high as 5kw.

At 400v we are looking at less than 15 amps. A heavy duty 12-10ga extension cord can handle that easily.

 

[Luke42]

Why is it running around the corner? Are you imagining that an in-motion charger plugs into the port on the side of the truck?

Where are you going to plug in the additional cable?

The rear bumper basically means you need to run it through the hitch, the same way you do with the rubber-armored 7-pin plug -- but carrying a lot more power one way or another.

The center of the tailgate is no-go because you'd have to route heavy cables through the tailgate hinge on the truck-side.

 

[Bob Anderson]

Where are you going to plug in the additional cable?

The rear bumper basically means you need to run it through the hitch, the same way you do with the rubber-armored 7-pin plug -- but carrying a lot more power one way or another.

The center of the tailgate is no-go because you'd have to route heavy cables through the tailgate hinge on the truck-side.

I was picturing adjacent to the trailer plug. Like many others have pointed out, this cable would be roughly same size of extension cord.

 

[JBee]

I somehow feel like nobody has bothered reading my 15 point post above except Bill, thats should end these debates and assumptions?

Charging from solar on a trailer is simply not a financially viable idea, that is why no-one will do it. ?

 

[charliemagpie]

I liked what Cybertruck Guy said, to carry a dual fuel generator. I will likely have 2 9k gas cylinders anyway. A handy thing if I decide to overstay in a remote location.

But, as far as putting very high amps into trailers and RV's etc.. we really don't see the future well imo. We will have chargers everywhere. 10 times more than the fuel stations we see today.

They will be in destination places. They will be in parks. General parking spots, people's houses, supermarkets, shopping centers , they will be stand alone. They will be mobile : they will come to you.

If desperate, you could even beg the guy parked next to you to give some charge.

Tesla intends to triple over the next 3 years ? and probably triple again over the next 3. Plus others will get their act together.

Before we know it.. progressively, it will be a totally different landscape rendering such overthought initiatives redundant. imo

Unless spending $10,000 is worth not having to waste 20 minutes of your day charging.

 

[JBee]

I liked what Cybertruck Guy said, to carry a dual fuel generator. I will likely have 2 9k gas cylinders anyway. A handy thing if I decide to overstay in a remote location.

But, as far as putting very high amps into trailers and RV's etc.. we really don't see the future well imo. We will have chargers everywhere. 10 times more than the fuel stations we see today.

They will be in destination places. They will be in parks. General parking spots, people's houses, supermarkets, shopping centers , they will be stand alone. They will be mobile : they will come to you.

If desperate, you could even beg the guy parked next to you to give some charge.

Tesla intends to triple over the next 3 years ? and probably triple again over the next 3. Plus others will get their act together.

Before we know it.. progressively, it will be a totally different landscape rendering such overthought initiatives redundant. imo

Unless spending $10,000 is worth not having to waste 20 minutes of your day charging.

Critically, it's the "charging whilst driving" part that is not useful.
Using an array mounted on your RV to charge whilst you are parked works easily.

 

[charliemagpie]

Critically, it's the "charging whilst driving" part that is not useful.
Using an array mounted on your RV to charge whilst you are parked works easily.

Yes,I was not dismissive of using whatever solar might have been collected. If your having a rest break, and its the middle of the day and your RV batteries are full, use it don't waste it.
800 to 1500wh of panels is plenty imo.
If you run out at night, just top up from the EV.

The machinations of dealing with exceptions will be short lived.