Planning to convert a 6x12 cargo trailer.

[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:

[flboy]

Solar panels look nice. Should charge your batteries quickly. Instead of a 5 into 1 connector, you could build a junction box. I did that on my 7x18 build and it works well and allowed me to extend wires from the panels that needed to be longer without having to crimp on the connecter and etc..

I have 900W of solar on one build and 420W on another. Both have large battery banks. What I find frustrating on the east coast of US is finding nice campsites that are not shaded most of the day. I have all that solar and depending on how long I am camped, the trusty Honda comes out for a few hours to charge. I was just out West in my 6x12 camping in the desert.... generator just got dusty and batteries recovered via solar most every day by 2pm. That was with 50% efficiency due to the lower sun angle in winter. Would increase significantly if I could tilt the panels.

Bottom line, if you need 1000W of panels because you are using that much power and need to recover that quickly, depending on where you camp, I'd have a generator as a backup. I use mine alot in Florida due to shade.

On the fridge, If you are using LiFeP04 batteries, as you probably already know, the voltage will remain reasonably stable during the very large and flat part of the discharge curve between ~20% and 80%. To see the state of charge on the batteries you'd have to hook up a shunt and use a culomb counting type meter.

I appreciate the video. Good luck with the actual build.

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[onehoser]

i have 5, 100watt panels and 2 lifep04 100ah batteries that i leave loose, so that i can manually move the panels into the sun and in many cases have to follow the sun through the day. on the rare occasion we camp at a hydro site i can leave everything at home, less clutter.

[rebelrider.mike]

I appreciate the feedback Don. I've referenced your videos several times now, since a lot of what you did in your 6x12 is similar to what I want to do.

Onehoser, what do you mean by hydro site? Do you have a hydro generator? I thought about portable panels. A lot of people do that. I just don't want to have to worry about hunting good sunlight all day. I'm the sort of person who would set it up, and then forget to move it.

Sometimes I type faster than I think, and forget that you all don't know the details, LOL. For discharging the battery, I'm not looking to see how long it will run the fridge. I'm just using the fridge to draw power so I can get the battery down to certain voltages.

What I really want to test is the behavior of the solar charge controller. I bought one of those cheap PowMr controllers, and it doesn't come with much info. I think it will work like a basic CV-CC buck converter, in that as long as the solar panels are a few volts above the battery, it will continue to charge. So I started with the battery at 26.5V, and the controller seemed to work fine with a benchtop power supply simulating solar input (since I don't have the panels yet) at about 28V.

My guess is that when the battery voltage drops to say, 24V, the charge controller will continue to use the "PV" power down to about 27V. Which right now it won't. I plan to take the battery down to 22V (I figure it will be pretty much depleted at that point. 20V would be depleted, but that's under load.) and I'm hoping the controller will accept power from 25V. Just looking for different data points to see if I can see a pattern. I could draw it down faster with a space heater or something, but I'm not in a hurry.

This all comes from the idea that, as suggested, the panels will spend a lot of time in shade or pointing the wrong direction, or blocked by clouds. In ideal conditions, I wouldn't need 1,000W of solar, but I expect to be camping in less than ideal conditions. So even 20% power from the panels will help the battery drain slower. And if it's cloudy or shady, I expect I'll use the A/C a lot less, or not at all. Which eliminates about half the power consumption for the day. It's a crazy balancing act, eh?

Oh, and yes, I'm using a LiFePO4 battery. After testing all the cells, I know it is about 100Ah, and a little over 2,000Wh. I may have overestimated the power consumption of the fridge and A/C, but I'm not sure yet. I did some math, and without the A/C running at all, the battery should last about 40 hours without any help from solar or other inputs. But this is all based on my best guess at how much energy I'll actually be using. I have a spreadsheet, but it's all still just math and theory.

As you say, worst case, I'll have a little generator. Should be able to fully charge the fully depleted battery in about 4 hours. Plus a little extra time for inefficiencies. And if it got worse than that, we could always throw an ice block in the fridge and live without power. That's what we do now when tent camping.

[onehoser]

Onehoser, what do you mean by hydro site? Do you have a hydro generator? I thought about portable panels. A lot of people do that. I just don't want to have to worry about hunting good sunlight all day. I'm the sort of person who would set it up, and then forget to move it.g, but I'm not in a hurry.ce block in the fridge and live without power. .

i meant campgrounds that have hydro, water etc. between my girlfriend and i we have 3 inverter generators that we use when the solar panels can’t keep up due to shade or overcast days

[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...

[flboy]

I have the same Daly brand with Bluetooth. It works well and the limits work well once you set them per the datasheet that comes with the batteries.

I think the balance current is only 50mA so if your pack is not top balanced very well, it may take forever or maybe never get perfectly balanced.

I top balanced and let the pack set a few days and the did it again. I did that 3 times and now they stay within a few milivolts of each other.

I really like the way the BMS works and is all monitored via bluetooth. The low temp charge and discharge work well. I was in -5F weather and it shut me down. Lol

Also like how I can monitor each cell individually and watch thier performance.



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[rebelrider.mike]

I found a workaround for the Bluetooth timeout function. Apparently, entering 65,535 seconds will keep the Bluetooth signal on all the time. And maybe also prevent the BMS from shutting off the whole battery due to inactivity. I've also read that 4s Dalys use 15,300 seconds for that function. Don't know why, or even if it's true. Even if the second part is not the case, that's still something like 18 hours. And there's bound to be some kind of current going in or out of a solar battery by then. But the Bluetooth on my BMS is now on whether I've got the battery hooked up to anything or not. That was my main concern.

Good to know the temperature functions work. I'm thinking of setting mine more conservatively than the manufacturer's spec sheet. The balancer, while picky, is working. I've got the battery on a charger, feeding it 0.75A, and that seems to be enough for the balancer to work. Any lower, and the BMS doesn't seem to recognize that there's a charge going on, and the balancer shuts off.

I've just discovered that when the BMS cuts off charge, it still somehow sends power to the solar controller. I see from the display that the charge MOS is off but the discharge MOS is still on. I don't understand what electronic magic is happening, but that is darn cool. I had the battery charging directly from a power supply, but I've connected it back up through the solar controller instead. Same result. Even though the BMS cut off charge, it still sends power out to the controller. That is fan-flipping-tastic!

Also, I got my final data point for my little experiment with the charge controller. Here's what I found:
Batt V PV in Difference
28 30.3 2.3V
26.6 28.9 2.3V
25.9 28.1 2.2V
24.4 26.6 2.2V
22.3 24.5 2.2V

With the battery voltage being anywhere from 28V-22.3V, as long as the PV input on the solar charge controller is at least 2.3V higher than the battery, it will attempt to charge it, and actual current will happen. There seems to be no set cutoff voltage within the range of the battery. Good news for cloudy days. I may only get a couple of Watts, but that's better than zero. Can't wait to set up actual panels and give it a try.

[flboy]

It has to do that else controller output circuit could be in an unknown state when a solar charge arrived. I think the BMS keeps 10.5VDC with very little current on the 12V models..As soon as it sees a charge coming in, it will turn back on full current as needed.

A solar controller manual will tell you to always hook the battery up first before connecting the panels. This is why. The BMS has to accommodate that scenario.

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[rebelrider.mike]

New video:


Just me talking again. This time I'm giving a brief overview of how I plan to do the electrical. I've updated my wiring diagram too, based on some new stuff I've learned lately about my battery and solar panels in general.


I've been thinking about grounding lately. Specifically, what to do with the ground wires that lead up to my isolation switch, and the ground post on the body of the inverter. I've made a diagram showing much more detail of the AC side of things to maybe help me figure it out.



So here's what I think I know:

-If the trailer is connected to a service connection somewhere, there should be a physical ground rod buried in the actual dirt somewhere.

-If the trailer is connected to a generator, there should be a bond between the ground and neutral. Either inside the generator or via an adapter.

-If the trailer is connected to nothing, there will be no ground connection to either neutral or earth.

-The neutral bus bar in the breaker panel needs to be isolated from ground.

-The trailer body needs to be connected to ground.



Here's what I'm not sure of:

-The solar panel frames (being aluminum) and mounting hardware should be grounded to the trailer body?

-The solar panel frames should also be grounded to the inverter via the ground connector on the inverter's body?

-The inverter body should be grounded to it's AC output ground?

-All the ground wires meeting up at the isolation switch should be connected together?



Vaguely related: I plan to use GFCI breakers, or maybe the GFCI/AFCI combo breakers.



Anyway, does it mater that sometimes the trailer will be connected to a ground rod, and sometimes just boded to neutral, and sometimes neither?

[hankaye]

rebelrider.mike, Howdy;

I know nothing, therefore I ask a ton of questions.
Here is a link to a site devoted to RV electrics;
https://rvelectricity.com/author/mikes/
and then there are the You Tube videos
https://www.youtube.com/channel/UCVcjUs ... uwWeaqdHNg

Good stuff.

hank

[rebelrider.mike]

Thanks for the links. Mike Sokol has been one of the people I've been learning a lot of this stuff from. Didn't realize he had a You Tube channel too.

Well, I've done more digging around, and I still think that what I know is correct. As for the things I'm not sure of, it's looking like the solar panel frames and any mounting hardware should indeed be grounded to the trailer body. What's more, a lot of aluminum products are anodized, which causes high resistance, so any ground points should be connected to actual bare aluminum. It looks like the ground lug on the inverter body should also be grounded to the trailer body. And from what I've seen, all the ground wires meeting up at the transfer switch should be connected.

I guess there's some inverters that bond the neutral to ground on the AC output side to simulate a path to ground. Some appliances and electronics won't work if they detect an open ground. I think this is what my inverter does. So in my case, I definitely need to have both the hot and neutral wires isolated at the transfer switch. This will prevent having more than one neutral/ground bond in the system at a time.

I've also just learned that there is supposed to be a bond between the AC ground and the DC negative. But only one. When the trailer is hooked up to the truck, The AC ground will be bonded to the truck's negative through the chassis. But that goes away when it's unhitched. My battery is a different voltage than the truck's, so I've been planning on keeping the DC isolated from the AC. Not sure now if that is still the best way to go or not.

[flboy]

I think my Solar panel frames are grounded by default because the mounting racks are screwed into the trailer's frame; however, no need to be grounded. Grounding the frame would be for safety in case something in the panel with potential were to short to it, but 12V or 24V is not going to even jingle you. The negative or black wire is a return.. but not a ground reference.

Think about the free standing panels... they just connect to a controller and set on the grass or etc..

If these panels had micro-inverters embodied and put out 110vac like household panels do in most cases, then I'd suspect you'd want a safety ground.


Also, if you were dealing with RF or very sensitive Electronics where a few milivolts would make a difference, then I'd worry about anodization. If something needs to be grounded, just use the toothed washers which will bite through the anodization. In reality, just the act of turning the screws most of the time bites through and the threads themselves cut the metal as they are screwed in.



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[Gulfcoast]

Nothing is grounded to the frame in my trailer.... I simply run a positive and negative wire to every item in the 12-volt circuit, including every light. I don't run a positive wire and connect the other wire to the trailer frame like some do.

[rebelrider.mike]

I appreciate the responses. I also plan to ground the panel frames and mounts to the body of the trailer via all the nuts and bolts. As long as I get continuity on a multimeter, I'll call it good.

Think about the free standing panels... they just connect to a controller and set on the grass or etc..

Well of course they don't need a ground wire. They're already sitting on the ground. Ok, now I'm just being facetious, LOL.

But seriously, I don't mean to obsess over grounding. I just want to take my time and do it all right. I plan to run DC negative wires to finish all the circuits, rather than depend on the body of the trailer as a return. I've had too many bad connections in the past trying to do that with extra lights and such on vehicles. I'm mostly interested in the AC grounding though. But from what I've seen, it's not much different that grounding a house. I just have to make sure the generator I use has a bonded neutral and ground. And make sure the inverter is shut off at the transfer switch if I've got AC power coming in.