openinverter forum

I am in the very early stages of planning a build of an electric travel trailer. Some companies out there are proposing these types of products such as Airstream e-Stream, Pebble, or Coastrv. I think most of these companies are missing a golden opportunity to sell these as mainly a Home Energy Storage system...with an electric trailer attached. The price of a large battery on the order of >35kWh to fully cover the needs of Home Energy storage + Solar does not currently have a return on investment. Using an EV for this could have merit, but if you drive during the day and park at night it is limited. I happen to be a Powertrain System Engineer at an automotive company (but mostly mechanical knowledge) and want to potentially expand my knowledge outside of my professional life. I also own a truck EV and love to camp with my family. This trailer would help eliminate any challenges with BEV towing, while expanding the camping options (boondocking for days).

Soooo....Electric Self-Propelled Travel Trailer with ability to use battery for Home Energy Storage.

I would like to consult the forum for advice, but here are my current initial thoughts on components to be used for the system:

System Spec Targets:
- Peak Drive Power: >80kW to support a continuous load of around 40kW (typical trailer at 70mph)
- Battery Capacity: Ideally ~80kWh to support around 2hrs of driving, and reduce duty of daily charge and discharge of home wear on battery (~35kWh MAX/day, average 15kWh/day throughout the year)
- Charging: Should have AC and DC Fast charging capability (speed is not super critical)
- DCDC converter to support 12V DC Low Voltage --> 3.6kW AC single phase needs of RV

Base Travel Trailer:
- 20-25ft typical 3000-5000lb dry weight (logically I will need a dual axle that is at the lower end of weight spectrum to handle the added mass, but I have a single axle now that I could convert)[/list]


Donor EV:
- I was thinking Model 3, but are there better options that are more easily repurposed and/or reasonably priced as donor?

I am well mechanically inclined, I am educated in basic electrical engineering and interested to learn, so I am looking to lean on this forum to help me in certain electrical/software areas where I may need support to complete this project. Thanks in advance!

This is an ambitious project. There is a lot to work out.

How does the drive / braking happen? I suppose you could make up a tongue sensor as throttle input. A brake light input as a secondary brake input too.

The suspension will be complicated and likely overloaded. A solid able with an independent suspension might get tricky.

48v or high voltage home inverter input?

Are you planning V2x or some high power battery plug?

40 / 80kw is a lot of power to have in a thing pushing you. Traction control, abs, how to control are all questions that need good answers.

Does this thing need to be inspected as a pusher trailer? What requirements do you have for your motor vehicle department for that?

jrbe,

Thanks for your feedback and ideas!

For the drive and regen I am thinking a tongue sensor or a redundant set of G-sensors. Anything would need to be programmed to a small board that would effectively replace the throttle pedal signal. For brake pedal my idea would be to not change the functionality of the trailer brake signal from the tow vehicle. Keep drive/regen separate from braking as it is on the truck.

For the suspension, you are right I need to spend some time thinking and planning this out. Luckily I have a background in related things so I should be able to work out a solution. My main idea is to create a DeDion type suspension utilizing the current trailer geometry with the drive unit sitting behind. It will likely require new custom knuckles and extended CV shafts that I will need to engineer up and everything will need to be beefed.

I am planning V2x for sure as V2H at a minimum would be important to be able to utilize the battery capacity for home energy. Does anyone know of any bi directional charger units that could be used here?

It may sound like 40kW is a lot but that is about what it takes to push the trailer down a level road at 70mph. For safety of course you wouldn’t want to ever “push” the trailer more than the tow vehicle is pulling, so there will need to be some study of the exact road load profile in order to create the upper limit power profile as a function of vehicle speed. Regarding traction control/abs, most trailers don’t have such tech and my thought is that it’s great if easy to add, but as I mentioned earlier I don’t plan on messing with the brake system (other than possibly turning up the gain).

Regarding regulation, I think it’s an unregulated gray area, based on that I would take full responsibility for my safety and the safety of others on the road. Certain safeties will need to be considered and added.

For safety of course you wouldn’t want to ever “push” the trailer more than the tow vehicle is pulling

Ehn, there's been some back and forth about this. To my mind, it's no different than braking while the trailer pushes. To others, it's a catastrophe waiting to happen and the sky will fall if you attempt it.

It's happened a bunch of times, but here's a conversation:

https://www.diyelectriccar.com/threads/ ... ar.204610/

JB Straubel (Chief Techknowledgy Officer of Tesla), made a gas-powered pusher-trailer 15 years ago or so. And it wasn't just to not be a drag, it was to push and charge the towing vehicle while on long trips.

One of the guys at the Seattle DIY EV club bought it years ago and restored it, and has done several other pusher trailers since. And he drives the hell out of them. 20,000 miles a year. His pusher trailers most often get used pushing him through mountain passes.

Thank MattsAwesomeStuff, that information and thread is very interesting and helpful. Didn’t realize the breadth of history regarding gas powered pusher trailers!

I'm assuming a toungue sensor produces a signal proportional to the push or pull force on the tow hitch? If that signal is accurate it should be quite easy to run a "net zero" controller on it that essentially makes the trailer disappear

Damien is currently hacking an MG charger that has V2L

For rapid charging we've got Foccci which also allows taking energy out of the battery.

40 kW sounds like a lot for typical trailor speed and partly obscured by the towing vehicle

I will be watching this quite closely. Please keep us updated with lots of details! I am considering a very similar project. It's actually a bit of a funny story how I got to thinking about it. You see I was just originally thinking about doing a bit of car camping in my Chevy Bolt EUV. There are still quite a few free level 2 chargers around so I was figuring I could travel on the cheap by sleeping at free level 2's while charging overnight. I was searching for a trifold mattress that I could use in my bolt. I think if I slide my front seats all the way forward, take all the headrests off, lean the front seats back all the way, I could build a little platform to extend the flat area in the back with the seats down to where I need it to sleep on. It would go across the center console and arm rests I'm thinking.

Anyway I was searching for an appropriate mattress, and I knew I wanted an 80 inch mattress because I sleep on my stomach and my toes hang off of 75 inch mattresses and I hate that. I was originally just thinking I would do a single width mattress with just the passenger seat down, but I couldn't find a single single trifold mattress that was 80 inches long, they were all 75 max. The only 80 inch ones were twin xl trifolds, which would just about perfectly fit in my space, but then I wouldn't have room for basically anything else in my car, so I started looking at putting a hitch mount and cargo box on the back of my bolt to carry all my shit so that I could sleep like a king on my twin xl inside. But then I got to thinking, if I'm already putting a trailer hitch on it, maybe I should think about a trailer. Then of course I had the bright idea to think, well if I'm going to do a trailer, why not put enough solar panels on it so that I can charge my car anywhere? I was already planning on spending most of my time on public land if possible, and that would let me stay on public land instead of having to head back to the city to find a level 2 to sleep at. Then I thought, if I'm going to put a bunch of solar panels and a battery pack in my trailer, why not add an engine to it so I can use that battery to extend my range? So for want of an extra 2 inches of toe room, I started thinking about building a pusher trailer lmao. This is how you know I'm mad I suppose.

I wasn't planning on making an account on this site for another, I don't know, year or so considering I don't have a technical background or much experience with electronics. I bought a book on electronics and I've started reading it, but I'm only on page 20 of over 1000, so yeah it will be a while, but seeing this thread, I just couldn't resist jumping in to share my own plans and to ask some questions, especially about the one part that is vexing me the most, (because my googlefu is failing me) specifically what hitch to use to handle the "push". What's this about the tongue sensor? Wouldn't some extra push be desirable? When I had this idea I searched on youtube to see if guys had done it before and it does appear to be a thing that works fine (as already mentioned upthread).

I was planning on going as small and light as possible. My panels would be a little smaller than 4'x6', so I was thinking I would make the trailer as close to those dimensions as possible with the vertical dimension being around 4' I'm thinking. I would want a water tank, hot water heater, 12v fridge/freezer, and a toaster oven, 2 induction burners, sink, and shower head as well as a full sized spare. (trailer would match my car). I'm thinking I would have 3 "levels", the bottom level for the traction battery, 12v battery, inverter/dc-dc converter for traction battery, fresh and grey water tanks, then a "hybrid" inverter/solar charge controller for charging the battery, level 2 would be the panels on a slide out, then level 3 would have all the other shit and a drain that I could set my pop up shower tent over. If I did this though, the battery would have to be low voltage considering all these types of inverters are designed for 48 max (which in a 16s LFP is actually 51.2). Now I was only thinking about trying to do a 36kwh battery with an engine that could do 10kw max only for the highway. Probably 7-10kw. Even at that relatively low power that's a lot of amps at 48 v. I looked up some charts for BLDC motors and depending on the motor it's something like low 200's to 270 amps which will create a lot of heat and losses to said heat, so I keep having this battle in my head of whether I should go low voltage or high voltage and ditch the convenient all in one hybrid inverter and invest in a solar charge controller made for high voltage packs. I did find a few of those somewhere on the internet. I was hoping I could use the hybrid inverter to charge the battery off of 240v level 2 chargers since it can take 240 shore power and charge the battery. If I go HV, then that's yet another component I need to add. All this would add weight.

The bolt EUV has no official tow rating, but the hitches they sell it for recommend a max of 2k lbs, so that's what I would be targeting to stay under. The batteries would weigh ~500 lbs, the solar panels would be slightly heavier depending on how many I do (I'm thinking 12 400w at ~46lbs each which would be ~560 lbs). I would be doing an either or for water/panels. Find my camp site, unload the panels, go get some water, dump it before I pack up the panels and leave (yes I'm planning on some sort of security system). That leaves me precious little weight for the motor and inverter and all that so I need it as light as possible.

I'm thinking I could maybe use the gen 3 prius transaxle and inverter as a fairly simple drop in solution, but I don't know if the gearing would be appropriate. I'm hoping going up from the 15 inch wheels the stock prius to the 17 inch wheels on my bolt could give me the buffer I need for highway speeds without any overspeed issues on mg1, but IDK. If there was some way to use MG2 from a third gen in everything else second gen while ditching MG1 that might do it, IDK. Either way, if I go that route then I couldn't use a low voltage battery pack. Even with the boost converter I don't think I could get what I need from 48v although that's just a guess on my part. How are you planning on balancing the needs between an appropriate pack voltage for solar charging and for using as a traction battery? Your power is much higher so I assume you're going HV no matter what.

Anyway, back to the issue of the hitch, I was thinking I want something that would allow me to position the trailer as close as possible to the car for aerodynamics. I saw this video of a pusher range extender trailer and whatever they are using has the trailer very close to the car. Do you know what sort of hitch this is and how the trailer manages not to hit the car when turning and if there's any special differences between a normal hitch and one designed to take a push? I definitely would like to push it if I can and extend my bolt's range from 3.5 hours of driving time at 60mph to as long as possible. Are you just going to use a normal ball hitch and use this tongue sensor thing to make your trailer "disappear" rather than try to get some push from it?

Sorry if that was a lot I just got excited seeing someone planning something very similar to me. Makes me feel like I might not be a total idiot for thinking about something like this.