6x12 cargo trailer conversion for camping.

[rebelrider.mike]

I took some pictures of my temporary setup trying out the inverter, fridge and A/C. Only one of them turned out any good:


I later figured out that I could "fold" the battery in half and save a lot of room on the table. It's connected up with fuses for now, since I don't have enough bus bars.

Today, I got out my solar charge controller since I have the battery temporarily assembled. It's a PowMr 60A. People seem to love it or hate it. I don't have solar panels yet, so I can't test it at full power, but I hooked up my benchtop power supply to stand in for panels, and I was able to get it programed for my lithium battery. The directions were difficult to follow at first, but after reading them about 10 times, I finally started to follow the logic of what they were talking about.


I remembered that I have a pocket oscilloscope, so I brought that out to see how pure my pure sine wave inverter really is. Once again, I took several pictures, but only one turned out good.


I had my little 12A space heater plugged in at the time, and whether it was running or off, the energy meter I had plugged in measured 60.18 Hz. The sine wave also didn't seem to change when the inverter was under load. The wave looks a bit pointy, but it's also a very cheap device. In fact, its a cheap knock-off of a cheap device. And I know it doesn't work exactly right. So take the readings with some skepticism.

For a comparison, I put the scope on an old UPS inverter that I converted to a portable power box a while back. You can see a huge difference.


A fun little device, but no good for precision oscilloscoping. That's fine though, I wouldn't know how to use a full sized one anyway. What's important though, is that these technical parts seem to be working together ok. That's a bit of load off my mind.

[rebelrider.mike]

I've been wanting to test out my battery and inverter to see if they can run a 5000 BTU A/C and a 1A mini fridge for the trailer. I got the battery temporarily put together today, and hooked up to the inverter. Since it's still cold out, I had to run a space heater for a while to get the A/C compressor to kick on.

The short answer is yes. The battery voltage barely moved under the peak load of both units switching on at the same time. And the inverter had no issues whatsoever.

To get the A/C blower and compressor to turn on at the same time, and also the fridge, I put them on a heavy duty power strip and just turned the strip on. The A/C is using less power than I thought it would. I was expecting it to need 4A, but it's only using 2.84A. Just 0.36A with the blower only. The fridge uses about 1A, as expected.

These are old units though that I happen to have on hand. The trailer will be getting new ones. I don't expect a new A/C of the same BTU would use more power than the old one, but for all I know, it's possible. I bought that old mini fridge USED when I was in college over 20 years ago. The A/C is only about 10 years old.

So a nice proof of concept anyway. On sunny days, the solar array will make more than enough power to run everything and charge the battery. But I can also run everything off the battery in the evening.

[rebelrider.mike]

I don't think there is a single right way to do this stuff, but there is a right way for me. Basically, I'm going for simple.

The only really effective air conditioners that I know of, run on 120VAC. Swamp coolers can work in dry climates, but the PNW is not one of those areas. Also, our living space will be small, and I'm concerned about humidity buildup inside the trailer. An inverter and a 120V air conditioner is a pretty simple setup, and isn't super expensive. I'll have to build a special cabinet for the A/C, but if it or the inverter were to break, they'll be easy enough to replace. The inverter will cause some efficiency loss, around 10%, but I figure a 5,000BTU A/C shouldn't have to run very long to cool a well insulated 6x12 area.

The DC refrigerators I've seen either use thermoelectric cooling, which is extremely inefficient, or use a traditional coolant pump, but one that runs on DC, which as far as I've seen is very expensive. Regular 120V mini fridges use very little power, and I'll have an inverter for the A/C unit anyway, so it's pretty easy to power. Also, I want a front access fridge, and not a top access fridge. Top access is more efficient as the cold air inside doesn't fall out when you open it like a front access does. But for me, front access is a personal preference. So far, all the DC fridges I've seen don't have a front access option.

As for propane, I won't have anything else in the trailer that needs it, so I don't want to mess with it. In such a small space, I'm not comfortable using any propane devices inside. This is just another personal preference of mine.

I'm afraid I don't have much of an update to share. But while I'm here, I can say that I've had more practice towing the trailer, and backing up has gotten a bit easier. I also found that the truck gets about 14 mpg, with the trailer. Down from about 22 mpg without it. Also finally got the license plate and title in the mail. I've got at least one more cargo run before I can start the conversion, so I've been focusing on other projects lately.

I hadn't thought of the differential getting hot. But that makes sense. I'm sure my cheap little temperature senser won't reach that far, so I'll have to think about that. It was built for larger loads than the transmission was, so hopefully it won't be a problem. But I'll keep it in mind anyway.

[bcroe]

I hear the new DC fridges especially designed like a cooler with top access are outstanding. The rv I'm working with is propane/dc/ac and although it sips propane it guzzles ac at 260 watts when running and the duty cycle seems t be mostly on. It seems if on DC it will kill an average battery overnight and I hear that's common. My mini ac fridge only uses 70w but I hear the new DC can get down to just a few watts. Don't know why but so far I hear the triple power ones like mine are only efficient at all on propane.

My guess, you are entirely right. That basically propane fridge uses the flame
to operate it. An electric heater might be substituted for the flame, but this is
an extremely inefficient way to use electricity. You want the latest tech heat
pump fridge on electricity, boosting efficiency many times. However I doubt if
these can run on propane at all. Bruce Roe

[Mike90250]

........
But I installed a temperature gauge anyway that I want to route down to the transmission to see how hot it's getting. I'll also have to find out how hot a transmission is supposed to be.

Differential is also a "power" based piece of gear and they overheat too, might want to meter that. Either trans or diff getting over 200F would be higher than normal. Thy make HD differential covers with heat dissipation fins in them

http://www.xegu.americanrebelmfg.com/odc/

[nomadh]

I interesting article. https://www.mortonsonthemove.com/12v-air-conditioner/

[nomadh]

As a beginner I like the sound of what your doing. I'm helping a friend setup a big 80s rv and looking to update it. I do have a few questions. It seems you are going very ac centric. Is there a reason that with DC solar and DC batteries and for weight savings you dont stay full DC and the only conversion you do is ac to DC when hooked up? I hear the new DC fridges especially designed like a cooler with top access are outstanding. The rv I'm working with is propane/dc/ac and although it sips propane it guzzles ac at 260 watts when running and the duty cycle seems t be mostly on. It seems if on DC it will kill an average battery overnight and I hear that's common. My mini ac fridge only uses 70w but I hear the new DC can get down to just a few watts. Don't know why but so far I hear the triple power ones like mine are only efficient at all on propane.
I wanted to add that a mini swamp cooler can replace ac many times and runs off of USB 2.0 power. I haven't checked yet but isn't there some very efficient DC air cond units based on the new DC fridge tech? If so I'd stick to DC.
also I love the idea of a second panel of solar under the first that you could pull out maybe either side to doubl your solar and also aim at the sun and give porch shade when parked. Also with shade issues possibly anywhere but the desert maybe you should make mire seperate strings of solar so as shade shifts you have the best chance of some panels still producing. I use a solar panel camping but with trees I'm busy moving the panel constantly. Maybe even I charge controller per panel? Is that possible?

[SunEagle]

I took the trailer on a cargo run this weekend.
5751bcd861e36842c942b24b588a2fd5.jpg
The truck did pretty good. I don't know how much weight it had, but the truck had no problem pulling it, or stopping. Backing up a hill is pretty hard on the clutch though.

All 16 cells have now been tested. They all passed with an average of 50.5 Ah. Plenty for what I want. I've also got the inverter in the mail. So time to hook it up to a mini fridge and an A/C, and see how it goes.

I am glad your trailer is working out well for you. Thanks for the update.

[rebelrider.mike]

I took the trailer on a cargo run this weekend.
5751bcd861e36842c942b24b588a2fd5.jpg
The truck did pretty good. I don't know how much weight it had, but the truck had no problem pulling it, or stopping. Backing up a hill is pretty hard on the clutch though.

All 16 cells have now been tested. They all passed with an average of 50.5 Ah. Plenty for what I want. I've also got the inverter in the mail. So time to hook it up to a mini fridge and an A/C, and see how it goes.

[chrisski]

FWIW, I skipped the capacity test on the 2 X 8S 24 volt lithium batteries I’m making. First, I go them from a reputable vendor where I saw their tests of my actual cells and others had tested and posted about this vendor. Second, would not really change the way I put this battery together, Third, capacity testing those 16 cells would have taken two weeks.

I’m also looking forward to your progress and wish to build something like you’re doing, just a little bigger to put a shower in. I will likely not act on that wish.

[SunEagle]

Trailer is finally here! I picked it up yesterday. Also, the cells came in the mail. I'll do a capacity test on each one first, and then a load test. They're rated for 180A continuous discharge, but I'll only need them to hold a decent voltage for a few seconds at 40A. I'll rig something up later to test that.

Thanks for the update. Keep us posted on your progress.

[rebelrider.mike]

Trailer is finally here! I picked it up yesterday. Also, the cells came in the mail. I'll do a capacity test on each one first, and then a load test. They're rated for 180A continuous discharge, but I'll only need them to hold a decent voltage for a few seconds at 40A. I'll rig something up later to test that.

[Mike90250]

Putting "filters" on LED's to make them "warmer" is a waste. to get them warm enough you will loose half the light output. Just get warm white LED's in 2500-3000 K lighting range.
The phosphor mix is what changes a blue LED to some version of white. Cool white (daylight) 5000K phosphor mix is cheap, warm white is a couple cents more expensive.

[rebelrider.mike]

I plan to have a little shelf above the bed for glasses, phones, very small monkeys, books, keys, that sort of thing. Underneath it I'll be making a sort of diagonal panel so we can have USB ports, power sockets, and reading lights. I haven't worked out the exact positioning or scale yet, but here's the wiring diagram:
3c58728936bbbd8cee91537ac02ac0df.jpg
I have all the parts I need, just need to build it. It will have the USB ports and the 24V power socket for my CPAP, running directly off the battery, and the lights and 12V power socket running off the 12V regulated power. The switches normally wouldn't need a ground, but these ones light up to show when they are working, so the little LED inside needs a negative wire. The reading lights I already had left over from another project, and I found some nice little dimmers that work perfect for them.
403e0d9b6fe37149c5edc6f8142f24d0.jpg
They're plenty bright, so the dimmers will be very handy. I'll also get some filters for them both for protection, and to warm the color up a bit.

I found a solar charge controller that I think will work with putting my panels in a 5s2p conviguration:

https://smile.amazon.com/dp/B0719PGGBS/?coliid=ICZJ2GH990UPB&colid=1E6B1UUZBLNWO&psc=1&ref_=lv_ov_lig_dp_it

It can handle 160V of open circuit voltage from the panels and can handle more current than I'll get from the panels even in full sunlight. And it's able to work with LiFePO4, and can even be programmed if I decide to change the preset parameters for some reason.

I've been working on a floor plan. Not everything is to scale yet, and I don't know the exact position of the wheel axle, but this is the layout I'm imagining.
0ee06cae03f492ac8b2e293022506f6e.jpg
I know the width of the side door, but not it's exact position either. Though I think I'm pretty close. I'll be able to measure everything once the trailer actually gets here.

[rebelrider.mike]

Thanks for the feedback!

I hadn't thought of slide out panels. At $600 I'd definitely have to make my own. They would have to be put away on windy days, but that's still a neat idea. Maybe I'll leave some space under the fixed ones so I could try this out some time in the future. I thought about tilting the panels, but since I'll never know how I'll be parked from one place to the next, I didn't figure it would be worth it.

My plumbing will be dead simple. A jug of water, gravity fed cold only faucet to the sink, and a drain into a little bucket. I'll also stash a composting toilet under a cabinet for emergencies, but that's it. I plan to keep maybe 4 gallons in the trailer, and any extra we might need, I can put in the back of the truck. There's nearly always a water source where we camp though, so it's never been an issue.

I agree that LiFePO4 is the way to go. It has it's drawbacks, but I think the pros outweigh the cons by far.

I've been working on a wiring diagram for a while, and here is what I've got so far. Remember that the solar part is not done yet:
d004615d63b1f4b922c579b00ac531ef.jpg
Red wires are DC+ (left out the - for simplicity)
Black wires are AC
Green things are sources of power
Purple things use power
Blue things are just various components.

Not a professional wiring diagram, but it's something I can follow. I figure the solar will be connected all the time, and there will only be 1 power inlet for the generator or grid power. I'll have a little power coming from the truck while I drive. Should be enough to power the fridge and inverter if I'm driving at night. I'll have that set up so power is only available if the truck ignition key is on.

One big manual switch between the battery and everything else. Maybe it will double as the junction box I have shown separately. There's a transfer switch so the fridge and a/c can get power from either the inverter or grid power, but never both. I think the peak current draw from the microwave may be a bit much for a 15A circuit breaker, so I'll probably upgrade that to 20A. The inverter will be loaded with safety features, but I'll put it on an external DC breaker anyway.

Here's the circuit that will send power from the truck:
1a107a9a86de84f5ea459e0d47e2f6e5.jpg
The ignition switch and the manual switch will have to be on for the relay to send power from the alternator to the trailer. I'm not sure how many amps I'll be sending. This will be a long cable going all the way back to the trailer, so there's going to be voltage drop. I hope to lessen that a bit by using 12 AWG cable. I've already make a custom panel in my truck with a switch for the trailer power:
4912928f23e14c3551a49052204f6f35.jpg
The clutch plate is the limiting factor in my truck as far as how much weight I can tow. But I installed a temperature gauge anyway that I want to route down to the transmission to see how hot it's getting. I'll also have to find out how hot a transmission is supposed to be.