24v of solar to a 12v battery

[mtbikernate]

I just want verification that what I think I'm reading is true.

Looking to upgrade my solar array (currently have just a 40w Zamp panel).

I am planning to get 200w of panels (2x 100w Renogy) and am looking at MPPT controllers and wiring.

I would like to have at least a little possibility of upgrading if I want to put a fixed panel on the roof of my trailer later. Right now, I plan to set up my panels as portable ones, mostly for simplicity's sake.

Looking at a Rover Li 20 MPPT controller. Looks like if I wire the panels in parallel, the controller doesn't really have any upgrade capacity for me. However, the impression I'm getting is that if I wire the panels in series (so now I'm getting a 24v input), this controller DOES give me the capacity to add more panels later, and the controller can then step down the voltage to 12v for my battery. is this correct?

I've also read that it seems most MPPT controllers begin charging when the solar input voltage is +5v above the battery voltage, and then continue charging so long as the solar voltage is +1v above the battery voltage, does make any practical difference for charging a 12v battery?

This also appears to have a side benefit of being a touch more efficient? For example, under the specs for the controller, it says the consumption is:

Power Consumption:＜100mA/12V; ＜58mA/24V

so the controller itself uses less power at 24v? Is this referring to the solar panel voltage, or the battery voltage?

[edgeau]

There are several things in that but bottom line is yes 24v is fine. I have nearly 40v going into my mppt. That is part of it's job, to take all the watts produced and use them effectively.
12v will not charge a 12v battery, you need at least 14v. But the power (forgive the pun) is understanding watts. Volts x amps gives watts.
Feed 24v direct to the battery and it will charge but you don't get the benefit of all the watts as you are wasting 10v. It will also overcharge. This is where your controller shines (yes another pun). It will take say, 24v and feed the battery 14. But the amps also change so you still get all your watts. 24v in at 2amp is 48w. Battery still gets 48w but as 14v and 3.4amp minus the tiny bit the controller uses itself.

Now the series vs parallel. Remember watts stays the same so in series higher volts and lower amps. This is more efficient as amps create heat and you lose some of your energy. At least in a perfect situation. Bring shade over one panel and parallel is ahead. Trade offs.

Clear as mud?

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[mtbikernate]

There are several things in that but bottom line is yes 24v is fine. I have nearly 40v going into my mppt. That is part of it's job, to take all the watts produced and use them effectively.
12v will not charge a 12v battery, you need at least 14v. But the power (forgive the pun) is understanding watts. Volts x amps gives watts.
Feed 24v direct to the battery and it will charge but you don't get the benefit of all the watts as you are wasting 10v. It will also overcharge. This is where your controller shines (yes another pun). It will take say, 24v and feed the battery 14. But the amps also change so you still get all your watts. 24v in at 2amp is 48w. Battery still gets 48w but as 14v and 3.4amp minus the tiny bit the controller uses itself.

Now the series vs parallel. Remember watts stays the same so in series higher volts and lower amps. This is more efficient as amps create heat and you lose some of your energy. At least in a perfect situation. Bring shade over one panel and parallel is ahead. Trade offs.

Clear as mud?

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Ha! Sure. FWIW, my battery is a 100Ah LiFePO4.

The way I bought everything, I can plug my panels in either series or parallel, I guess only changing the inline fuse between the panels and the controller and moving some wires around.

If I read this correctly, I won't need to do anything to the fuse between the controller and the panel because the controller will be feeding the battery the same thing either way.

Another question I have is about wiring things together later on if I want to add a permanent panel to the roof of the camper later. So let's say in that scenario that I put my 2 portable panels in series at 24v so the controller has a more extra wattage to work with for expansion. And let's say I add a 100w panel to the roof. Does that panel also need to be 24v or could I put a 12v panel up there? Would I have to wire all 3 panels in series to pull that off? Would it be a whole lot easier to use a 24v panel and wire that one in parallel with the 2 panels that are in series? The other option I have is to keep the panels wired in parallel at 12v, I guess, and put a small 60w or less panel up there to stay within the capacity of the controller.

For now, since I won't be in any danger of sending too much juice to the controller, I'll probably just wire the panels in parallel. And it's entirely possible that these 2 panels will supply the vast majority of my power needs. The only thing I see as being a little bit of trouble is if I decide to do another long road trip, where I might want charging while driving to keep things topped up (especially if I have food in my dometic fridge) and don't always have shore power for recharging at night.

[tony.latham]

Your electrical questions are a bit over my head, but make sure you work out attachment points for the panel and how you plan to run the wires for your planned roof-mounted fixed panel.

Otherwise, your cabling will look like an afterthought.





I'm also wondering why you might need 3, 100-watt panels? What are you planning on powering?



Tony

[mtbikernate]

Your electrical questions are a bit over my head, but make sure you work out attachment points for the panel and how you plan to run the wires for your planned roof-mounted fixed panel.

Otherwise, your cabling will look like an afterthought.

I'm also wondering why you might need 3, 100-watt panels? What are you planning on powering?



Tony

Yeah, all that stuff is running through my head. And that's part of the reason I'll be installing the 2 100w panels I ordered as portable. In an ideal world, one could mount to the roof of the trailer for on-the-road charging, but could also be removed later. I just haven't seen an install method that I like for that.

And since the camper has been long-built, running the wires cleanly has been part of that thought process. My battery is in a tongue box, so I don't think a gland on the roof to clean things up would really work.

For everything I ordered yesterday, I've decided that I'm putting an SAE plug in the toolbox (gotta find a good way to permanently mark/distinguish this SAE plug going to the Renogy controller and the Zamp plug that looks the same, but assumes the controller is attached to the panels), and using an SAE-to-solar converter cable to switch to the panel cords.

As for my loads, here goes:
Dometic CFX3 55IM fridge is currently the biggest
MaxxFan and light ring
Small LED lights in galley
12v and USB outlets in the galley and cabin

All my exterior lighting is self-contained solar lighting that I put away for travel.

On a sunny summer day, my current 40w suitcase solar has been enough for me to get through a 3 day weekend. I doubt it's fully recharging my battery at the end of the day, but it's extending it just enough that I can make it through. I wouldn't know with my detail, however, because my electrical system is basic enough that I don't have the ability to monitor my loads or battery discharge, and the solar controller for my zamp suitcase doesn't log charging over the course of the day. It's worth noting that I live in the eastern part of the country and often end up with shady campsites. One of my goals with my camper is to be able to boondock for awhile and I don't want my battery charge to be the limiting factor.

I do want to add heat to extend my camping seasons a bit, though. Not going to use a buddy heater inside, even for a few min to warm things up, because I don't want to add to condensation. I have also been working hard to eliminate the use of those damn green propane cylinders. Adding a diesel heater or a propex would increase electrical demands on my system a bit and I want to make sure I have enough charge capacity to be good. So I needed more charging capacity first. I think for now, I'm going to give a 12v heated blanket or two a try (at home, the wife and I prefer very different temps on our heated blankets, so having 2 zones is kinda necessary).

Another addition I'd like to make eventually is a propane water heater (with a battery-powered pump). I've been making do with heating pots of water on the stove for dishwashing, but a warm shower would be oh-so-nice. For now I will probably make a DIY PVC pressurized solar shower akin to one of these:
https://www.rei.com/blog/camp/diy-car-t ... amp-shower
but I don't exactly have high expecations of the water getting really warm inside it. Realistically, I will probably have to help it out by preheating at least some of that water on the stove.

Long term, I want to have enough charging capacity to be able to fill the battery during the day from any overnight use.

Once I get this Renogy kit installed, I'll have 240w of portable panels (including my 40w zamp suitcase that has its own charge controller already). I could always replace that zamp suitcase with a bigger suitcase (with its own charge controller) without impacting the Renogy controller I will be using for the new panels I bought. But as a cost-per-watt consideration, that's a much more expensive solution.

Maybe I could take care of trickle charging on the road with a 50w panel mounted on the lid of my toolbox? That would simplify cable routing to the controller inside said toolbox and avoid the issues of wanting a better rooftop mounting solution, but I'd have to pay a lot of attention to sealing any holes I put in the lid. And my Renogy controller does have room to add that easily enough. I'd just need to dig around a bit to find a 50w panel with suitable dimensions.

[Tom&Shelly]

... It's worth noting that I live in the eastern part of the country and often end up with shady campsites. One of my goals with my camper is to be able to boondock for awhile and I don't want my battery charge to be the limiting factor. ...

Yes, we had that problem a lot in the East last Summer. That justifies the three (or however many) panels right there, as you may want to spread them out a little to catch the sun between the trees at different times of the day. (Especially if you want to leave the set up unattended for a few hours.) In that case, paralleling them probably works better, as Edge mentioned above.

Tom

[mtbikernate]

That all makes sense. The wiring I bought won't let me spread the two Renogy panels out much from each other. And I may wind up attaching them to each other with hinges, anyway, to make setup and teardown a little easier.

Now it appears the fun part is going to be figuring out how to safely pack them up and keep them from being damaged. Poking around the interwebs, I don't like what I'm seeing and I think I'm going to be making use of my sewing machine to make a case. I have some leftover fabric from other projects. Not sure if I have enough heavier nylon for an exterior, but I do have a good bit of softer fabric for the inside. Should be some foam sheets in the packaging that I should be able to repurpose, too.

And then legs to prop them up. Most of what I'm seeing is made for RV roofs and building roofs where you want to really clamp down the panels. I don't want all that bidness. So again, that's going to require some creative rigging.

[edgeau]

Just a word of caution, avoid having two controllers trying to charge at the same time. They will confuse each other as to the state of the battery. So use the folding 40w by all means but bypass the controller bolted to it and feed the main controller.

Another thing to consider is rather than solar while driving, use a DC to DC charge controller and run power from the tow vehicle. Renogy do a separate unit like this https://au.renogy.com/renogy-12v-dc-to- ... y-charger/ for a situation like this where you already have a solar controller.
There are units with both for those that plan it from the get go.


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[edgeau]

For what it is worth, I have similar loads, a fridge, fan and lights. I find my 200w solar blanket ample. But I am in a different climate, Eastern Australia

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[mtbikernate]

Just a word of caution, avoid having two controllers trying to charge at the same time. They will confuse each other as to the state of the battery. So use the folding 40w by all means but bypass the controller bolted to it and feed the main controller.

Another thing to consider is rather than solar while driving, use a DC to DC charge controller and run power from the tow vehicle. Renogy do a separate unit like this https://au.renogy.com/renogy-12v-dc-to- ... y-charger/ for a situation like this where you already have a solar controller.
There are units with both for those that plan it from the get go.


Sent from my Pixel 6 using Tapatalk

From what I have read elsewhere, it is possible to have multiple solar controllers.

I've read into the DC to DC thing. I ruled it out based on statements from the trailer manufacturer that getting sufficient power to charge the trailer battery isn't possible with the equipped 7 pin connector (the manufacturer equips the 7 pin connector just to charge the breakaway device). I know of folks who have done it, but they're basically taking a whole new run of (heavier gauge) wire from the TV battery and using separate connectors (like Anderson Powerpole) to the trailer and to the DC-to-DC charger.

The extra cost and work involved with doing it that way surpasses the effort of adding a panel permanently mounted to the trailer to trickle charge it.

[mtbikernate]

For what it is worth, I have similar loads, a fridge, fan and lights. I find my 200w solar blanket ample. But I am in a different climate, Eastern Australia

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I live in the Southeastern US, which does trend to be a bit sunnier. But that said, I also live in an area that amounts to a temperate rainforest, so we do get some respectable cloudy/rainy periods and thick tree cover in some places.

[TimC]

...
And then legs to prop them up. Most of what I'm seeing is made for RV roofs and building roofs where you want to really clamp down the panels. I don't want all that bidness. So again, that's going to require some creative rigging.

I'm not sure of how "creative" this is but thought I would show how I created a set of legs to prop the panels at different angles. Easy to do and cost virtually nothing. The aluminum frames of these 50 watt panels serves as a anchor point and there are two legs that can swing down from their storage position (glued on velcro strips). The hinge is left over living hinge from my hatch.

[tony.latham]

Maybe I could take care of trickle charging on the road with a 50w panel mounted on the lid of my toolbox?

I've got a Renogy 30 watter on my tongue box.



The cabling was easy-peasy.

Tony

p.s. A Propex heater uses considerably less electricity than the diesel heaters. We swear by ours It's something like 2 amps for a night of usage.

[Tom&Shelly]

I've read into the DC to DC thing. I ruled it out based on statements from the trailer manufacturer that getting sufficient power to charge the trailer battery isn't possible with the equipped 7 pin connector (the manufacturer equips the 7 pin connector just to charge the breakaway device). I know of folks who have done it, but they're basically taking a whole new run of (heavier gauge) wire from the TV battery and using separate connectors (like Anderson Powerpole) to the trailer and to the DC-to-DC charger.

With an AGM battery, charging at a maximum of about 15 amps or so, that's not correct. Our Tacoma has a stock 10 gauge cable running to the 7 pin connector. There are calculators on the web where you can compute the voltage drop over about 15 feet or so and it's negligible. Folks who put in larger cable aren't really gaining much of anything (maybe a few tenths of a volt at the maximum current).

Perhaps you can tell, we were warned about this, and I spent more time on it than I should have before we decided to charge from the TV in exactly this way. We don't use a DC-DC converter, but then we don't use much to draw our battery down either, and we're satisfied (for now) with the battery taking a day's driving (5-6 hours in our case) to charge back up from 85%. If we ran a refrigerator, we probably would also install a DC-DC converter to boost the charge voltage at the teardrop's battery.

But that wire gauge thing is mostly an internet myth. (Stand by for rebuttals...)

Tom

[mtbikernate]

It's worth noting that I have a 100Ah LiFePO4 battery in my camper, so diff charge behavior than an AGM or otherwise. My Ford Ranger also has quite a few electronics onboard that can behave funny with different loads (I have also read about "smart" alternators being problematic with these kinds of systems). It would go nuts if I didn't have a legit DC to DC charger. Going back and reading the comments from the trailer manufacturer about it, they're pretty strong about the fact that you should be using 0-2 AWG wire from the TV battery to the DC-to-DC controller. Not just for current sake, but also things like fire risk and making sure the battery is able to get the appropriate charge profile.

It's SO MUCH EASIER to put a solar panel on the roof of the camper, or on the lid of the tongue box if I wanted to do that.

Those wooden legs look like they're worth a shot. I've got some scrap pine sitting around leftover from other projects that I could probably use to cobble together for similar sorts of legs. I've seen pictures of similar when google searching and it might be the best I can realistically do. I saw one example where the guy used aluminum instead. Bah, too expensive for minimal gain.

My tongue box is longer and could probably fit a bigger panel if it had the right dimensions. That's a later item, though.

I'm aware that Propex heaters use less juice than diesel ones. I actually did some digging and found an example where a guy measured out actual consumption of his diesel heater and I was surprised how much more power it used than I expected. With that in mind, it probably is well worth it to save and spend more on a Propex for the improved efficiency alone (and the fact that I already bring propane with me). I was actually thinking of getting a diesel heater before buying solar panels (which were already on the list as a want). Seeing the power consumption (as well as the fuel consumption, and the cleaning and maintenance needs) on them just solidified that solar should be higher on the priority list, and that I'd be better off with a propex when it came time to add real heat.