Planning to convert a 6x12 cargo trailer.

[nsfr1206]

Still waiting for the actual trailer to be ready. Any day now... Or next month.

My wife asked an interesting question: Should we get insurance on it? I don't know. I suppose with the money I'll be putting into it, it's probably a good idea. Progressive does my motorcycle insurance. They're happy to insure my trailer, but I'll have to figure out what the stuff I add to it is worth. So I've added prices to all the things on my weight spreadsheet. I'll be able to add it all up as I go. I don't know if insurance is even required in Washington on a cargo or camping trailer. I'll have to go look.

It seems the planning is pretty much done. I haven't thought of anything lately to add or change. I've started buying a few parts while I wait for the trailer itself. I've got the battery cells ordered, and found a charge controller for the solar panels. I'll be buying them next, I think.

I've been helping my grandpa clean out his shed the last couple months. Unfortunately, he won't be around much longer and he doesn't want us all stuck with his accumulated stuff after he's gone. So we're doing it now as a sort of early inheritance. I found a small sink in his stash that will fit the trailer perfectly. He's got all sorts of interesting things tucked away, and almost everything has a story behind it. I found a box of tiny 0.8 cc model airplane engines that were seized up and hadn't been run in 45 years. I got them apart and cleaned up, and had enough good parts to put one working engine together. Grandpa got a kick out of seeing one run again.



Anyway, we're still going through stuff, so who knows what I'll find that can be used in the trailer build...

Looks like a Cox Babe Bee? Oh the memories of those line control airplanes. And getting my finger thwacked by the prop. :-)


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[rebelrider.mike]

Yep, I found a company in Canada who helped me identify it. And they still have parts! One works now, and I should be able to get the other two running also.

[rebelrider.mike]

Looks like the trailer may actually be delivered some time this week! Not gonna hold my breath though. Especially since I'll be away for Thanksgiving. But still, it will be nice to actually have it available to work on and measure.

As far as the cells I bought... no idea where they are or even if they exist. If I don't get them by Christmas, I get my money back. I think they're out of stock and the seller just hasn't told me yet, LOL. But I'm not in a hurry. Good, cheep, and fast. Pick two.

I'm planning to get the solar panels next. They went up in price, but they're still reasonable. And available at the hardware store. I'm about all planned out until I can actually start working. But I keep looking at the electrical and considering possible improvements. I decided to eliminate the DC circuit breakers. I've just read too much bad stuff about them and don't trust them to actually work. I don't remember if I mentioned it, but I found a single solar charge controller that will work with all 10 panels hooked up. So that simplifies things. So here it is now:


I decided to limit the power output from the truck to 7A. My understanding about engines is that the horse powers that you get are all you get. And it takes some to power the alternator. The heavier the electrical load on the alternator, the more power the engine uses to turn it. Which means less power left to turn the wheels. I want as many horses as possible for the wheels, which means limiting the load on the alternator. I'm also thinking of converting the headlights to LED. Those halogen ones us like 50A each or something. Anyway the headlights are the single biggest electrical draw on the alternator that I know of. Unless you count the popcorn maker.

That's where things are now. Weather is terrible for working outside and will probably be the same until April. Gives me time to collect parts and wait on those cells. They seem to be out of stock everywhere. I guess I'm not the only one who noticed how cheep they are, LOL.

[rebelrider.mike]

Cells finally arrived in the mail!



They all arrived physically intact, and all were around 3.2V. A good voltage for storing these guys. So now I get to test each one to find out if they are really 60Ah. Chinese companies tend to exaggerate a bit on their cell capacities, so I'll be happy with anything around 56Ah or higher. I'm all set up to test lots of small Li-Ion cells, but not these large LiFePO4 cells, so this is going to take a while.

Another good bit of news, is that the trailer is now in stock and ready to roll. I may pick it up as early as tomorrow. Next big purchase will be the solar panels. I can't afford to buy them all at once, so I'll be getting a couple per paycheck.

Some sad news though, is that my grandfather has passed away. So the first use of the trailer will be to help clean out his house so we can sell it, or whatever mom decides to do with it.

[pchast]

Sorry to hear of your loss.

[rebelrider.mike]

Thanks.

This weekend I actually took the trailer up North to help my son move. Not sure how much weight was actually in the trailer, but the truck did really well. Just had to down-shift a little more often going up hills. Backing up a hill seems to be a bit 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.​

[featherliteCT1]

I really like your electrical system.

I have been researching Lifepo4 batteries for a while. What was your reasoning for choosing 61 Ah batteries, rather than larger Ah batteries?

[rebelrider.mike]

Thanks!

I had two reasons. At the time, two 60 Ah cells cost less than 1 120 Ah cell. Not sure that's the case anymore. Second reason is that putting two cells in parallel lets me share the current between the cells. So my theoretical limit of 80 Amps for the whole battery would only need 40 Amps from each cell. I'm hoping that will reduce the Voltage drop in the rare event that both the A/C and the fridge kick on at the same time.

Since each cell tested at about 50 Ah (Chinese manufacturers tend to exaggerate their cells' capabilities) I'll have a 100 Ah battery, which should be plenty for what I need. If not, I can buy 8 more cells and put them 3 in parallel without having to spend a huge amount of money. I'm hoping not to have to though in order to save weight. But we'll see.

[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.

[featherliteCT1]

Thank you for posting and explaining your electrical system.

Am I correct to understand that you have 24v nominal going into your inverter with 120v output from the inverter?

[rebelrider.mike]

That's correct. The inverter is 24V nominal, and can accept a voltage range from around 19V-30V. The battery has a voltage range of 20V-29.2V, so they are pretty much a perfect fit.

[featherliteCT1]

Thanks!

I think I read somewhere that it is difficult to use a vehicle’s alternator with a DC DC converter to charge a 24v battery bank.

I would like to reconfigure my lead acid 12v battery system to a 24v LifePo4 system like yours but I really need to charge my battery bank from my truck’s alternator. I currently charge my batteries with a 12v DC DC converter in addition to my solar panels.

How are you planning on doing this with your 24v system?

[rebelrider.mike]

There may be better ways to do it, but I'm think of building something like this:


I want to have power only available while the truck is running, and I want to be able to turn the circuit off manually. Like for when the trailer isn't hooked up. So I'll be using a relay to connect the power from the alternator to the charge controller. The relay will get it's "on" signal if the ignition is turned on (truck engine running) and if the manual switch is also on. I put the manual switch on my dashboard.

The charge controller will be a simple constant-voltage, constant-current boost converter. I'll limit the output voltage to 29.2V, the top charge of the battery, and I'll limit the current to about 7A input. You certainly don't have to limit the current so severely, but in my case, I've got a small pickup truck, and I don't want the alternator taking to many horse-powers away from the wheels.

There will be some voltage drop between the truck and the trailer over such a long cable, so the charge controller will either need to be close to the battery, or I'll have to bump the voltage a little to compensate. I'm leaning towards putting the booster in the engine compartment, and running the higher voltage cable from it to the trailer. The higher voltage will help mitigate the voltage drop a little. I also plan to us a thick cable, like 14 or 12 AWG, also to help limit voltage drop.

You can have multiple devices charging the battery at the same time as long as the devices are matching the battery voltage, and the total current from all of them doesn't exceed the maximum charge current of the battery. I also need to make sure the CVCC converter can handle the Watts going through it. In my case, 7A x 14V is 98W, so I'll need to make sure it can handle at least 100W, or maybe 120W so it doesn't overheat.

Something like this maybe:
https://www.amazon.com/Converter-Module-Step-up-Constant-Current/dp/B07TMF4JC8/ref=sr_1_56_sspa?crid=2J32R49S4PBL8&keywords=120w+boost+module&qid=1645592366&sprefix=120w+boost+module%2Caps%2C112&sr=8-56-spons&psc=1&smid=A2K5DI8VX12AN1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUE2TkNPVTMwVEZBR04mZW5jcnlwdGVkSWQ9QTEwMjgzNjVLNTk0QzhVTkkwTzUmZW5jcnlwdGVkQWRJZD1BMDI1NjM2ODExUVE5N0xNUkFJWkgmd2lkZ2V0TmFtZT1zcF9idGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Hopefully that makes some sense. I've only gotten to the switches so far, so I don't know how well it will actually work.

[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?