New small solar set up for caravan - opinions/advice please!

[AussieSun]

Hans, you're right that I cant go any bigger.. I was still in the mindset of when I was looking at smaller panels 🙄 That said, these panels are well oversized for my power needs already so shouldn't be an issue. Having the PV slightly oversized (for the cc) should give me enough voltage for a good charge in iffy conditions.

Also, do like the idea of the water cooling. might design space for it at least under the panels

[PNW_Steve]

Can you expand on how the CC limits current pls? I am assuming you have a MPPT, but I am curious as to how the CC does this? Are you setting a max battery voltage? Does it start "dumping" extra watts as heat through the heat plates? Does wire size between the CC and Batts affect this? Would wire size provided false readings on Batt voltage to the CC if undersized?

Just trying to understand how my MPPT CC operates, and trying to decide if I need to upgrade my wire. 40 Amp MPPT CC, <15 ft run from batt to CC (currently AWG12), 12 volt system, 100 watt panels, 2s2p so max amps in is 11 amps and 36 volts in. For some reason I'm thinking (in perfect conditions, from CC to batts the MPPT CC could be pushing nearly 30 amps. Am I wrong, as I'm thinking to upgrade wire to AWG 6.

The Midnite Classic, when used in conjunction with the Whizbang Jr gives you the ability to set a Max charge amps.

[Mike90250]

The Midnite Classic, when used in conjunction with the Whizbang Jr gives you the ability to set a Max charge amps.

I think the combination of the two pieces of gear, give you the ability to precisely terminate ABSORB when you reach a specific battery amps
The classic alone, can be set to limit output amps

The current shunt measures battery current, because you cannot rely on the classic measuring total amps (Loads & Charging) and guessing what share the battery is.

[HansWT]

Sorry, I think some misunderstood my question.

I'm trying to understand how MPPT CC work versus PWM CC, so I can size my wires to the battery correctly.

Full sun during summer for flat panels is going to put out nearly max watts.

That means for me, 400 watts in will be nearly 30 amps at 13+ volts (for a 12 volt system).

Thats the difference with PWM vs MPPT CCs, as they won’t push say 24 volts x 18 amps into a 12 volt system.

The AWG 12 I installed is rated in the 15 amp range, so I’m looking at AWG 6.

when I was finalizing my panel connections, I noted it was not straight line additive for each panel added for overall watts (I did in full sun, morning... so if anything it should have been increasing). For example, 40, 80, 120 & 160. It was losing some with each panel added in my test.

so I’m wondering if the CC is degrading produced watts or possibly my undersized wires to batt.

[Mike90250]

PWM is simply a switch connecting and disconnecting the panel from the battery.
Amps from the panel = amps into the battery.
A 12V battery is generally used with 19V panels

MPPT is a dc-dc conversion process where high voltage from panels (usually 25 - 120Vdc) is converted to proper charging voltage with a proportionate increase in amps
A 6A 80V array, would convert to a 15V 32A charge to the battery.
Watts from array = watts into battery
Nearly all MPPT controllers only "downconvert" PV array voltage to battery voltage.

As a battery charges up, it accepts less amps from the controller.

If you have a 400w array (wired in series) , and are charging batteries at 14V, expect to have about 28A . A #10 ga wire should be OK, you don't need to go to 6ga. 6ga would work, but the expense would hurt your wallet.

Does this help ?

[littleharbor]

All this info is assuming you are using a real MPPT controller. If you have a cheap fake MPPT controller you only get amps in = amps out. The higher the input voltage the higher the losses.

[HansWT]

Mike90250 Thanks!

i am obviously overthinking this all.

i wired my panels 2s2p, but from what you are saying 18 volt panels are designed more for PWM then for MPPT. My bad early on.

I went with an excess amount of free AWG 12 to start with, screwing myself in essence. Now that we're moving out of peak solar, I have time to wait on rewiring, but for the future a few $ extra for AWG 6 will be a better option in the end.

a 5x7 trailer is .... ah, a bear. Everything comes down to quarter inch clearances (or less) and every new add adds a redo of the adds prior. Oh well.


@littleharbor... yes, it is true MPPT. Cheap, yes. But it is MPPT, not PWM branded as MPPT. It's a OOYCYOO 40/100

[PNjunction]

AussieSun -

For Caravaning with your simple power needs - go old-school off the shelf. I'm taking into consideration your skill level. No offense, but the objective is not to over-complicate it, and have you kill a system prematurely. Ie, a "practice" scenario is called for that won't empty the wallet.

Common-mistake: using a "conventional" so-called deep-cycle agm touted by many caravan shops. Not ideal for solar.

Go with a "pure-lead" AGM battery, rather than the conventional agm's you are looking at. Pure-lead types such as Optima, Odyssey, and others in your region are easy to find from *reputable* dealers. Even brick-n-mortar walk in. NO, they are not true-blue deep-cycle batteries, but for your first time out - better to kill one of these as a practice battery.

Why "pure lead", rather than the so-called "deep cycle" conventional agm's which are NOT pure-lead that you are looking at?

It's all about internal resistance, and charge efficiency. The ones you are looking at are at least 4-8 times more INefficient than the pure-lead agm's. Optimas (yellow or blue top with LIGHT gray casings - NOT black casings) are easy to find. Other brands are similar, like Odyssey. The whole point is to get the battery charged as fast as it can with your solar setup.

Expensive? You bet. BUT, you have an "off the shelf" chance of bringing them back if you kill them and revive them in time. An off the shelf solution would be an Optima digital 400 charger. Or one of the Odyssey chargers. Or a Tecmate-Optimate 6 or larger. Since it is probably guaranteed that you won't always get a full charge from solar, you can hit up your battery with one of these when you are near AC power once in awhile.

These pure-leads have a wide CV voltage range - anywhere from 14.4 to 15.0v. So if you or your controller is not the best quality, you still have an acceptable range window to work with. Not that I'm suggesting to go cheap with the controller.

AND, being pure-lead, they can handle up to 0.5C or even 1C in some cases - meaning that you can hammer them with up to a half to one time their capacity rating with solar. Ie, you can hit up a 100ah pure lead with 50-100ah (heh, if you actually had that large of an array) without harming the batt. So you can expand a bit more in your paneling if you feel the need. A "conventional" agm like the ones you were looking at - you are limited to about 0.25c max charge current before you start to warp the plates, and quite frankly they are not that good of quality to do that all the time before the casing starts to bulge.

Misjudge your actual power use and bought a too-small capacity pure-lead battery? If you haven't totally abused it, you can possibly sell/give to others for use in their vehicle, or just keep as an auxiliary. Kill your diy-lifepo4 batt? Do us a favor and just recycle it.

I'm not trying to be an Optima salesman, because there are other good pure-lead batt manufacturers, I'm just trying to keep it simple, but pointing out that most caravaners get hoodwinked into buying those HIGH-IMPEDANCE conventional agm's.

Later you can specialize with componentry and TRUE deep cycle batts. But for a first time out, or just to have some kicks learning with solar, don't use those alarm-box / ups style agm's. Go pure-lead for the LOW impedance they have.

If it doesn't work out, you can use the batt, chargers etc for normal vehicular rv type use as sell / giveways with a good conscience.

[PNjunction]

Forgot -

That *first* charge is extremely important! Don't rely on solar for that.

Another common mistake - For the battery's first-birthday, charge it right. And don't use your typical auto-store "speed charger", which are often too aggressive or have poor actual *at the terminal* voltage CV settings. Schumachers are ok for hitting up dead / dying batts, but I don't recommend them for normal maintenance.

The Tecmate-Optimate 6 or higher, Optima digital 400/1200, or Odyssey charger will properly charge that agm - the most important being the first. In fact, don't rely on solar at all until I've had about 5 normal cycles in them. Normal - means not a total discharge, but say no more than 25% of the total capacity. Then you can go to town with solar.

So yeah, still off-the-shelf, with a high survivability window with limited initial skills.

[Wrybread]

Just my views. Panels on roof are going to be a disappointment. They never work well as the vehicle is alot of times in shade or the angle is not right. They really are a gimmick I'm sorry.

Good lord is that bad advice! And typical of this forum for some reason. Panels works *beautifully* on RVs and are an absolute necessity. When you flat mount your panels you'll loose 15 to 20% efficiency, depending on time of year, but that's no big deal since you can load up that roof with panels.

Get modern high powered panels and an MPPT charge controller. This one for example is awesome and cheap:

https://www.amazon.com/dp/B07KW5W49J

This one is more pricey but awesome, and lets you do fun things like monitor your solar via your phone:

https://www.amazon.com/SmartSolar-MP.../dp/B073ZJ43L1

I'd recommend at least 600 watts of panels (two 300 watt panels) or 900 watts or even 1200 watts. That way you're always getting a nice full charge even in overcast conditions and winter.

If you read the manual for that charger you'll see what the maximum amount of *input* watts is, I forget the specifics but it's more than 1200 watts. It'll never output more than 40amps of course (480 watts at 12 volt, 960 watts at 24 volt).

I've found four Trojan T105 batteries (450 amp hours @ 12 volts, aka 5400 watt hours) give me all the power I need while living almost full time in my RV, and I never drive it or start the engine and don't have or need a generator. And I'm on the Northern California coast where it's very commonly overcast. And I get seagulls crapping on my panels all the time.... And I never ever have power issues.

If I was installing a new system I'd seriously consider wiring those batteries for 24 volt, or using lithium battery packs built for electric bikes and scooters...

[Wrybread]

If you have a cheap fake MPPT controller you only get amps in = amps out

The charge controller he linked to isn't fake, works awesomely. And it's awesomely cheap!

https://www.amazon.com/dp/B07KW5W49J

[Mike90250]

Depending on your location, flat panels may only harvest 50% of nameplate. You loose the first 20% because they are in the sun and get hot (heat makes power go down) As you loose direct aim perpendicular to the sun, power is lost because it's reflected off the glass and never makes it into the active part of the panel.

Any shadows on the RV roof, like a vent, antenna or air conditioner, will shade a panel, and mostly take it out of action.

So if you can fit 900w of panels, you can expect to harvest 450w, more or less.

I'm giving you an objective view, some folks get better harvest, some are at lower latitudes, conditions vary.

[Wrybread]

Depending on your location, flat panels may only harvest 50% of nameplate.

In my experience I get about 15% to 20% less harvest from flat mounted panels versus correctly tilted panels. That's real world numbers from a few different installs I've done and from experiments when I had my panels on the roof but not yet mounted. And with flat mounted panels I can just install another panel to easily offset that 20%, no biggie. And having a panel permanently mounted means I'm harvesting *at least* 20% more power than if I was setting them up temporarily each time I go to use them. Not to mention the massive convenience factor of having them always working without setup.

Any shadows on the RV roof, like a vent, antenna or air conditioner, will shade a panel, and mostly take it out of action.

A little bit of shade from an antenna or whatever doesn't kill all the power from modern panels, but it's easily solved by wiring the panels in parallel. I do that on all my RV installs these days for the reason mentioned above, and also because I occasionally strap boats or surfboards to a rack that's over one of my panels. And I have a semi permanently mounted chair on my roof that shades one of my panels from morning sun. Just have to remember to use fuses if you're using 3 or more panels in parallel.

[Wrybread]

Just my views. Panels on roof are going to be a disappointment. They never work well as the vehicle is alot of times in shade or the angle is not right. They really are a gimmick I'm sorry.

I literally have to laugh at how wrong that is. Modern solar in an RV works well enough to be able to live full time in an RV without ever starting the engine or a generator. I'm proof of that, I've been living in an RV most of the time for years and now full time (I'm now a campground host), and I'm off-grid and the camper never moves, I never start the engine for charging, and I don't have a generator. And I'm not miserly with power, I use all I want, I literally never give a thought to power consumption. And my system is dirt cheap and simple.

930 watts of panels (3 310 watt panels)
4 Trojan T-105 batteries (5400 watt hours)
Morningstar MPPT 60 charge controller (previously the Tracer 40 amp charge controller, which also works beautifully)
Xantrex 1000 watt inverter

[NCmountainsOffgrid]

while my situation back in 2017 was for a solar array while visiting ALASKA for several months, being off-grid many overnights, I also wanted to keep my panels in more of a 'portable' mounting so that I not only could make use of the best angle to the sun, but also so that I didn't have the typical problem that most RVs have when they mount their panels on the roof - parking IN the sun. We want to park in the shade, but make use of the sun for our solar, and the two don't always go hand-in-hand.

I devised a use of an old 4-bike articulating rack, which we had previously used at the rear of the coach, to mount and carry the two 100w 12v panels. This allowed me to not only carry the panels, without dealing with the roof, but also to easily 'tilt' the panels, when parked. As my coach charges my House batteries(4-6v FLA type) while driving, the incoming solar power was basically only needed as a way to minimize generator run-time when parked off-grid. I could choose to simply tilt the panels where I was parked, or take them off the rack and place them in a better place if parked for several days.

For me, it was about limiting generator run-time, not trying to 'do everything' without the generator... knowing that cooking and air conditioning and even supplemental battery charging would still need the use of the generator. It's a very efficient power source, but most of us would agree that a 'silent' power source makes us feel better, when possible.

My financial consideration was whether these panels, with the 20a charge controller, would sufficiently offset the purchase cost, if solely for a several month trip to Alaska. My calculations at the start were that we would be off-grid every other night, and at an rv park or campground with electricity most other nights, on average. I knew that my alternator would provide supplemental House battery bank charging while driving, which would be most every day, during the morning to mid-afternoon time frames, and that we would still use the generator when off-grid for hot days, or cooking a special meal, etc. We certainly have propane for cooking, but the wife enjoys more her instant-pot, crock-pot, blenders, and 'special' cooking devices. The fridge is a 120v residential type, and the Inverter is a 2000w 'whole house' Magnum brand which is wired via a sub-panel to all the outlets in the coach. Our boys come with the typical teenage devices, computers, smartphone chargers, and even full size desktop computers while on the trip, so many things are constantly in use, whether while traveling, or while parked. It doesn't change much either way.

If the package system cost $300, then my calculations would need to come close to bearing out $300 'less' of generator run-time cost, which is basically the additional FUEL.
Diesel is not the same cost everywhere, especially when in the rural areas of the Yukon and Alaska, but a 'guesstimate' of $...... would give me an average cost basis to calculate from.
The generator, like most, is a very economical engine, and actually gets very good 'mileage' from the diesel fuel. Running at 50% capacity, for most off-grid needs, would use about 1 gallon of diesel every 2 hours, or so.
If off-grid every other afternoon/night, and using the generator late evening, early morning, the fuel cost would then be about $.... for each of those days.

in the end, my 'guesstimates' were that a 200w solar package purchase to 'test' this solar power economics might come close enough to offsetting the upfront cost with the lower generator fuel cost, if my average held somewhat true.
The actual trip confirmed that 'guesstimates' are just that. Sometimes diesel was a higher, or lower, cost than assumed. Sometimes the sun was not available as much for the off-grid days. Sometimes the sun was very available, but we were parked at a full-service park or campground. Sometimes, as much as we wanted the sun, we were parked at a dry-camp state park, but with so much shade that even trying to use the panels in a remote location would not prove successful. Sometimes, we had the sun, and hardly needed to use the generator at all.
It's such a hit-and-miss that even the best calculations and assumptions just can't match the 'real world', when it comes to solar, and the mobile nature of RVing..

What would I suggest for your camper? In your situation, where you may be parked extensively and can make the best use of solar everyday, and your rather limited needs for power, a simple 200w system might work just fine, especially if you pair it with two 6v deep charge GolfCart type batteries, in series, for a 12v output. A small 120v watt Power Inverter easily found on the shelf at many big box or auto parts stores, which plugs into your 12v outlet, or clips directly to those batteries, can provide you what you need for 120v power. If you 'must' use a blender, even the 300w type, you'd then need a 450 watt power inverter, which is still only $30 or so.

Also, unless you already have this capability, you can find devices that allow your alternator on your vehicle to charge the House battery bank while you are driving, or could even be the 'emergency' capability to charge them should the sun not shine for several days.