Planning to convert a 6x12 cargo trailer.

[rebelrider.mike]

That's true.

I think I've decided on the battery voltage. Six cells in series will give me the voltage range I need for the solar charge controller. Also, I picked out a mini fridge I like, and contacted the manufacturer about its startup current. They were kind enough to answer, and it looks like the fridge can draw up to 6A when it first starts up, but runs on a little less than 1A.

The 500W inverter I was looking at may or may not work for that. I asked that manufacturer about it and didn't get an answer. So I'm looking at a slightly larger 600W inverter. Also pure sine. It claims to be able to handle 1200W of peak current, though the reviewers don't agree on whether that's actually true. Maybe it depends on how long the peak lasts. But if the fridge only peaks at 720W, hopefully that will work. Just have to try it and find out.

I've also been looking at stuff for the grid connection. I'd like to use a surge protector, but they don't seem to make them for 20A hookups. I've been thinking I could get by with just a 20A hookup, but maybe I should bump it up to 30A. I plan to have two 15A breakers inside the trailer. Even if I ran everything at the same time, the current would still be less than 20A. Of course the microwave would only be used for a few seconds at a time. I don't think 700W is enough to do any actual cooking. Just the convenience of heating things up a little. For cooking we'll have propane and propane accessories.

I put a lot more detail in my circuit diagram.


After adding up power for all the things running off the battery, I made an estimate of how long each device would run per day. I used the kW/year rating for the mini fridge. Looks like the fridge will take up 2/3 of the power consumption. Haven't taken conversion inefficiencies into account yet, but It looks like about 1,300 Wh may be used per day. The battery should have about 1,500 Wh, so it should last up to a day without any charging. If we need to conserve power, the fridge could just be turned off, and we can put a tub of ice in it. That could stretch the battery across maybe 3 days. Also, we'll have solar, but sun is never guaranteed.

[flboy]

May want to get meter to measure your microwave consumption. 700W is power to the target food. They use about 1000W of power to get that. I have a kill-a-watt meter and my 700W microwave was not so efficient.

Good luck with your electrical setup. Not seen one like that before with so many conversions.

Since you have decided on a 24V battery, why not just use a 24V inverter. Why down convert? Also, it will use alot more than 8.5A at 500W or 600W.


Also, never seen DC and AC on same switch. Need one outlet for fridge with a transfer switch between inverter output and 120V shore/Gen. You are making this alot more complex than it needs to be for the functionality and power requirements.


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[rebelrider.mike]

I understand what you're saying. I'll try to explain my thought process. Some of this stuff is happening only because more common hardware that I've been able to find is prohibitively expensive for me. Probably the one that affects my design the most is the solar charge controller. I have yet to find a programmable one for lithium batteries that isn't crazy expensive except for this weird little one I hope to use. But it's a boost converter rather than a buck converter, and I have to have something at least 15V or higher in order to work. That means I need a LiFePO4 battery with at least 6 cells, which gives the voltage range I'm looking for.

Similar issue with the inverter. I've looked for 24V pure sine inverters, and they are few and really expensive. Also, none work with the voltage range of the battery, so I'd have to use a converter regardless. Seems everything is still designed for lead acid battery voltage. I do not want lead acid batteries. Yeah, the inverter will only deliver 90% of the power that goes in, and it will draw power even when the fridge is off. The converters will also have inefficiencies and phantom power draw, but I just wanted a rough estimate. I expect the plan will change before I actually build stuff.

I did look into the microwave, and it uses around 1100 Watts. According to the owner's manual I found. So I rounded the Amps up to 11 for some reason. It works out to 9.2A, so I'm actually not sure now where I got 11A from. I'm not too worried about the power consumption of the microwave and air conditioner since they'll be on AC power only. Just want to get an idea of the sizes of wiring and breakers I'll need.

The fridge is the only device I want to use on either AC or DC. Yet again, the product out there designed for this sort of thing are crazy expensive. While I have some experience wiring AC and DC things, I'm a total noob when it comes to RV type stuff. Maybe the transfer switch you mentioned is what I'm actually looking for? My thinking is that I don't want the fridge to be connected to both AC and DC at the same time. The On-Off-On switch is meant to prevent that, and to shut of both the fridge and the inverter at the same time. Since the inverter is only there for the fridge. I'll look into the transfer switch and see what I learn though.

You do make a good point about all the converters. My thinking on having several small ones is that each one will generate less heat than one big one. Also, they're small and inexpensive. I suppose I could look into getting one big one withe the capacity to run all the 12V stuff. Maybe that would be more efficient? I'm concerned about how much heat it might generate.

Anyway, I appreciate the feedback. I don't mean to sound argumentative, I just want to explain my thinking. I expect that the plan will keep changing as I learn stuff, right up until I start actually building.

[flboy]

I am on the road now, but if you are interested, I can send you a schematic of my setup. Uses LiFePo4 and Solar. 24vdc going into controller charging at 14.6 volts. It is a relatively inexpensive MPPT controller thatis somewhat programmable. You can get any old power supply locked on 14.6vdc to charge LifePo4. The BMS in the LiFePo4 setup manages the charge. In any case, I understand what you are trying to do.. Best wishes.

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[rebelrider.mike]

Yeah, I'd like to see your schematic. Whenever is convenient.

I looked around and found a 750W buck converter made for truckers that can handle a 75A peak current. This could handle all the 12V devices, including the inverter for the mini fridge. Also found USB ports that can convert the battery voltage themselves, so they won't need a buck converter.

I've planned a little relay circuit to send 5A to the trailer from the truck. This setup will ensure that the power will only be sent if the truck is running and if I want it on.


I don't really want a battery isolator. I think it's overkill, and this way I can control it from the dashboard. Speaking of which, I removed the radio/cassette payer since I never use it anyway, and am making a custom panel to go in there instead. Here's a mock-up I made on a piece of cardboard:

The wiring behind the radio should be plenty adequate for what I want to use it for.

Well, I'm off to a vacation for a week. Sadly, not camping, but should still be fun. I'm taking the old motorcycle!

[rebelrider.mike]

Back from my road trip.


Got stuck in a spot of loose sand, but my brother-in-law was kind enough to pull me out.


I've been working on the wiring plan some more. Biggest thing is that I noticed the mini fridge was going to have two power cords the way I had it worked out. If one were to be unplugged for whatever reason, it would end up being one of those suicide cords that are really dangerous. So I moved the transfer switch after the inverter, so only one output to the fridge will exist. I guess if i'm on grid power, I'll just have to remember to shut the inverter off myself.

I've also found some new products that will simplify things. There's a 24V-12V converter capable of handling all the 12V devices at once, even when the mini fridge has its startup peak. And I found a better inverter for the fridge too. I did need to add a cell to the battery to get it in the voltage range of the buck converter, but it also adds Wh to the battery, and is still cheaper than trying to match the inverter directly.


I've also read that whatever generator I might use needs to have a bonded ground. I'll have to keep that in mind before I hook one up.

For above the bed, I want a shallow shelf to stash things like glasses, phones, books, veeeery small monkeys, or whatever. Below it, I've planned out a sort of convenience panel that will have some of the bits from the electrical diagram. Still working out the details.


I'll have to work out an electrical floor plan soon. Like what switches I want by the door, and where all this stuff is going to go.

[tx2sturgis]

I think I've seen this OP over on the Soviet Steeds forum awhile back....small world we have right here on the web!

[rebelrider.mike]

Tx2sturgis, hi! I remember your name from Soviet Steeds. In fact, someone over there sent me over here a couple years ago.

Flboy, I finally had a chance to read through your 6x12 build, and got a lot of useful ideas from it. I see you have videos available too, so I'll be checking those out. I'm particularly impressed that you were able to run the air conditioner off the solar and battery. If I could pull that off, that would be fantastic.

[rebelrider.mike]

I've been playing with parts I've got laying around. I have a few COB LEDs made for 14V, and I wanted to see if they would work as dimmable reading lights. I found a PWM controller to hook them up to, and it works!




This controller is overkill for these lights, so I'll get some smaller ones at some point maybe make a diffuser and a filter so they're not so harsh white. I did that once with an old pill bottle. Makes a good tent light.

[rebelrider.mike]

First floor plan.

I've had a design like this in mind for a long time, but finally got it drawn up. Not everything is to scale. Like, I don't know the exact position of the door, or what the interior dimensions will be after insulating and stuff. But this will help with figuring out where the wiring has to go, and if I'll have room for everything I want in there.


Here is the front and back of the trailer. Front is kitchen, and I found while doing this that the microwave will not fit in the electrical closet, so I moved it to the kitchen. Which means I'll need the microwave outlet there too. May as well double as a convenience outlet. The microwave will only work through grid power anyway. Two of the six ceiling lights will actually be mounted under the upper cabinet thing that holds the microwave and water jug. I don't know yet the exact size or height of the windows.

In the back there are the cargo doors, a window, and a bed with storage underneath. I plan to have the storage accessible from both the inside and through the doors. The little convenience console thing will be at the head of the bed at an angle, and above will be a flat spot for glasses and phones and small things.


On the left is a fold-down table, and some overhead storage and a window, which I don't know the sizes of yet. The headboard console thing is way bigger here than it will actually be for real. Just keeping it recognizable. I plan to have a fresh air fan by the bed, and an exhaust in the kitchen. The roof will be entirely taken up by solar panels, so no room for a vent up there. And a CO detector is always a good idea.


On the right will be overhead storage at the foot of the bed, and the electrical cabinet. I got dimensions for the A/C and fridge online, and the battery/electrical area is based on what room is left. You see why the microwave won't fit, LOL. I may need to find a shorter refrigerator, and I'd like to maybe put the A/C a bit lower so I have more room in the back for venting. I figure I can't go wrong with a fire extinguisher and first aid kit. And a long time ago, I saw someone hang a waste basket on their camper door. I thought this was pretty cool. It's available inside and outside with the door open, and I won't have to worry about accidentally kicking it over.

That's it for now. Lots of changes to the wiring diagram, but I won't post that for now, since it will probably change yet again. Also, I may be buying the trailer sooner than I thought. Have to see how things work out first though.

[rebelrider.mike]

The trailer company I want to buy from makes them as they're ordered. Looks like I'll be going in soon to make a deposit and get mine started.

I've been looking at how I want to make the a/c cabinet. I'm thinking along similar lines as Don's build:
http://www.tnttt.com/viewtopic.php?f=42&t=73788&start=75

Separating the hot from the cold outside air flow, and putting in some drains for condensation and in case some rain manages to get in through the vent.


The kind of vent I want to use can be opened to insert a filter. Instead of a filter, I want to see if I can make a couple of inserts. One that is open, like a sort of end cap for the dividers inside, and one that is closed and sealed to help keep weather out of the cabinet while driving or not using the a/c. I plan to do something similar with the vent fans.

[rebelrider.mike]

The truck's custom panel is close to being finished.


Still need to add a relay and circuit for the trailer, but now I have a clock, sound system, USB quick charge, and some other stuff.

Looks like I'll be going in next week to order the trailer. They say 8-12 weeks for delivery. That might be enough time to finish up some other stuff.

[rebelrider.mike]

Got the deposit and order done today. Now I just have to wait 8-12 weeks for them to build it.

[flboy]

Got the deposit and order done today. Now I just have to wait 8-12 weeks for them to build it.

Will be the longest 8-12 weeks ever! LOL tough to wait,,, been there!


BTW... nice job on the accessory panel in your truck.

[rebelrider.mike]

Thanks!
I got the panel installed in the truck yesterday and mostly hooked up.


Still needs some details, but it all works! Now I can run the power cable and relay to the trailer hookup whenever I'm ready to. The little dual temp gauge, I plan to put the sensors on the engine and transmission. I don't know if they'll reach, but I can get extensions for the sensor wires.

I just saw a thread for a 6x10 build that only weighed 1,600 lbs when done. I hope I can keep my weight below 2,000 also. With all the things I'm not putting in, like wast tanks, propane, and lead-acid batteries, hopefully I can keep the weight down. Also saw today a fellow install a medicine cabinet in his trailer. I like that idea, as I take 5 meds, and my wife takes about 600. Also, we'll want some regular stuff like vitamin I (Ibuprofen) in case of accidental hiking.

Here's the trailer I picked out:

https://www.olympictrailer.com/2022-cargo-mate-challenger-6x12-with-cargo-doors-Gz5i.html

Turns out it has all sorts of options since they don't make it until you order it. I left everything stock except the side door, which has an RV latch option.