6x12 cargo trailer conversion for camping.

[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.

[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?

[nomadh]

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

[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/

[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

[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.

[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 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]

Looks like I may have enough money to finally buy the solar panels. This has renewed my interest in figuring out exactly how to wire them up. I'm still a noob at solar, but I've watched a lot of videos, and done a lot of reading. I think I have a viable plan:


Took a while, but it finally dawned on me that a "12V" solar panel has nothing to do with 12V. The numbers in the diagram are rounded somewhat for simplicity. These particular panels happen to be the perfect shape to cover the whole roof. Vents and other traditional roof things will be on the sides of the trailer. I've never heard anyone complain of having too much solar, so I decided to take advantage of the whole space.

Here are the specs for the panels I found:


Hopefully the diagram makes sense. The idea is to have 5 sets of 2 panels in series, and then connect those 5 sets in parallel. This setup will need a 5-into-1 pair of connectors, and I think a 10 or 12 AWG cable to connect it to the charge controller. The controller I bought recommends a breaker between the panels and the controller. I'm looking into the din rail style ones.

I've also read that inline fuses are sometimes needed to protect the panels from themselves if one gets a short circuit. Makes sense. We fuse our individual battery cells on the bus bars, so a similar concept for solar panels. Not sure if I need any fuses in this case, but I'm thinking 10 or 15A fuses on each series, so that if one series goes nuts, the others can't just dump power into it.

Anyway, have I missed anything?

[chrisski]

The easiest way for inline fuses is to buy branch connectors and the fuse attachment for those. 5P2S is difficult in finding a branch connector. A combiner box would work and you could put circuit breakers in versus fusing. Circuit breakers are a bit more expensive but can shut the panels off prior to powering down the system. Also helps in troubleshooting.

Five fuses or circuit breakers are needed.

Don’t know if its been discussed, but you could save a bit of cash by buying larger panels. Locally, there’s usually a dozen panels for sale new or used at much cheaper prices than 100 watt panels. Also, I can locally purchase from San Tan Solar and pick those up in my truck.

[rebelrider.mike]

Yep, that is kind of what I had in mind. Right now I'm thinking inline fuses on the branch connectors, and a breaker to separate the whole array from the charge controller. I plan to have some other breakers in the system too, so I can put them all together on a DIN rail.

Unfortunately, I haven't been able to find anything cheaper locally. The panels I'm looking at are $95 each, or $0.95 per Watt. All the bigger panels I could find are $1.25 per Watt or higher. Also, their shape won't allow me to fit 1,000W worth on the roof. It's like playing 4 dimensional Tetris. Hight, width, price, Watts. Finding the right combination has been a bit of a brain buster, LOL.

[rebelrider.mike]

Well I bit the bullet as they say, and bought the solar panels. painful on the wallet, but this way I can be sure they all match. Final bill was $1,034.49 after tax. Shipping is free. so about $1.04 per Watt. As far as I can tell, that's pretty good for smaller panels.

I've been running my old mini fridge for almost a day from the battery and inverter. The battery voltage has barely moved. It may be a couple days before the battery gets low enough to test the charge controller again. I figure that's a good problem to have.

I've made the first video of my series for this project. It's not much; just an introduction. But if anyone is really bored, you can watch it:
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[rebelrider.mike]

My BMS has arrived! It's a Daly 8s 80A. It's my first "smart" BMS, so there has been quite the learning curve. I can monitor and change settings over Bluetooth, which is great. However, the app is in poorly translated english, and it's been difficult finding specific information and explanations about the settings. I think I'm getting it figured out though.

Apparently there are better BMSs out there that have similar features, but I wasn't aware of them at the time I bought this. It may work for the trailer battery, but it's got a couple characteristics that I'm not liking.

First, it has a "time out" feature, where if no current is going into or out of the battery for a settable amount of time, the BMS will not only shut off the Bluetooth, but also the whole battery connection. It wakes up when there is a lode or charge put on it, but in the case of a solar battery that could be potentially problematic. See, without power to the charge controller, the solar power can't get to the BMS to wake it up. However, you can put a very long amount of time into the setting so it won't go to sleep overnight.

The Bluetooth connection seems to be on an independent timer though. It will shut off after a minute or so of no battery current regardless of the timer setting. I've seen suggestions for a workaround, so I'll try that. But otherwise, you have to push the little button on the Bluetooth dongle or make sure the battery is experiencing some kind of current. The tiny amount of current needed to run the solar charge controller doesn't seem to be enough.

The second issue, is that the Daly seems pretty picky as to the conditions that need to be met before it will balance the cells. The minimum cell voltage can be set, as well as the voltage difference between the highest and lowest cells. Those are two of the conditions. The third though, is that balancing will only occur if the battery is being charged by a certain amount of current. Like an Amp or so, but I'm not sure. Also, balance current is limited to 30mA. Doesn't seem like enough to balance large capacity cells.

Good news is that it seems easy enough to physically hook up to the battery.


The battery is still only temporarily put together. I'm expecting more parts in the mail tomorrow.


More good news; the BMS seems to be measuring the voltage and current pretty accurately.


I finally got the whole battery down to about 22V, so I could test the behavior of the solar charge controller. It still only needs about 2.2V difference to charge the battery. I'm glad I got the BMS when I did though, as the cells are getting quite out of balance as they approach their bottom voltage. I'm charging the whole battery back up now, and I'll see what the balance looks like back at the top.

I wonder if they have different internal resistances. I may try to measure that. They all have the same capacity though, and behaved the same during the discharge test. Anyway, back to tinkering...

[chrisski]

For balancing most BMS have a setting to start charging. Also, a separate setting to balance only when charging. Mine is set to only balance when charging and 3.40 volts and greater. My SCC charges at 3.475 per cell.

For my BMS to balance, that’s basically only a few minutes a day after the pack has hit absorption. Lithiums are much shorter with the absorption cycle. Also, the cells settle after charged. I forget mine, but it’s less than 3.4.

Top balancing cells prior to install is important. If you did not, the BMS would take weeks or months.

Theres a whole debate over whether adding active balancers are worth it.

My opinion is if that balancer is balancing all the time and your cells spend most of the time below a full SOC, than it could throw the top balance off. This is someone who gets his batteries to 20% every night.

After reading that I was happy with the BMS balancing only after 3.4 volts.

If you only use these batteries a few days a month and the rest of the time they’re fully charged, than a active balancer could good.

[rebelrider.mike]

That all makes sense to me. I noticed when I tested all the cells that they settle to around 3.4V after charging to 3.65V. I've wondered if that is normal for LiFePO4. I'm used to working with Li-Ion, and they hardly settle at all. I picked LiFePO4 for this project because it's a more sable chemistry, and the voltage range is more compatible with all the components I want to use. I wonder if it even makes sense to charge them all the way up to 3.65V? I could see that if they settle anyway, trying to keep them topped up might take more energy than what is lost if they're just charged to say, 3.5V or something. I let my cells sit for a few weeks after charging and they never went below about 3.4V.

I've set the BMS balancing for 3.4V for now. My concern is that I don't want the BMS shutting off the battery except in a bad situation. The solar charge controller may take damage if the solar power is connected, but the battery is not. According to the manufacturer anyway. I have already top balanced my cells before connecting the BMS. I just hope the very short balancing time will be enough to keep them in balance. I am hoping to keep the battery above 20% SOC as much as possible. I'm thinking of having the controller only charge the cells to 3.6V. That would keep the battery at 28.8V, and I won't have to worry about the BMS shutting off.

The workaround for the Bluetooth time out seems to be working. I read on the internet that entering 65,535 in the timeout setting disables the Bluetooth timer, and keeps the BMS from shutting off the battery due to inactivity. My concern here is that the solar charge controller won't reactivate the BMS if the BMS has shut of the battery due to inactivity. The charge controller can only function if it already has power from the battery. It won't run on solar at all. The Bluetooth part of the workaround works. Even if the second part doesn't work, that number of seconds is a little over 18 hours, and being on the solar charge controller should be enough to reset the timer by then. If I were to "winterize" the trailer, I can set the timer back to a small number. I think the default was 3,600 seconds.

Anyway, I think this BMS will be fine for the trailer battery. And I love that I can change the settings and monitor what the BMS is doing via a phone app.