Solar charging of 12V

[William Deak]

Looking for a solar charger to use as back up for battery in my Scamp 13. Harbor Freight has these in 25 W and 100 W, about $65 and $185 respectively. What would be the minimum needed for this purpose? Thanks.

[PatrickTXFL]

I am sure those with more than reading experience can help more. I am on same search and seems as 100 watt or more would be best for daily recover of a 1 battery system with basic light draw down over night. Many models to pick from on Amazon or Ebay, I have been shopping the briefcase style that use two 50 watts hinged and come with every needed. Use a quick connect like used on trickle chargers for motorcycles or lawn mowers that will leave you a pig tail to quickly plug in so you don't have to open battery box.

[Jann Todd]

Originally Posted by William Deak

Looking for a solar charger to use as back up for battery in my Scamp 13. Harbor Freight has these in 25 W and 100 W, about $65 and $185 respectively. What would be the minimum needed for this purpose? Thanks.

If you are looking to just keep it topped off the small one works. Some of the people in our local Casita group hook up the small one in the back window of the trailer or a window that would be in the sun most of the time. Since our group is not together any more I can't tell you how to do it but I do know the ones that had them were very good with electric, etc. We have one and a voltage controller from Harbor Freight that will keep a battery topped off. Before we found our problem our pickup battery would die in 2-3 days so we kept the panel in the windshield. It worked just fine. It most likely wouldn't recharge a dead battery enough but it kept on it most likely it wouldn't die.

[John in Santa Cruz]

I think a 100W panel is a good match to a single 12V marine/rv style battery, and 160-200 watts is a good match to a dual golf cart battery setup.

[CarlD]

Solar panel selection depends on your load, battery capacity and how you plan to use it. There are many variables associated with solar panel efficiency. Location, orientation to the sun, cloudy days, shade, etc. If you only run lighting and use a few amp-hours a day then I would recommend a 25-50 watt unit, and you may only need it every few days. If you have a furnace and run fans for cooling and use 15-25 amp hours a day you will probably want a 100 watt unit. Once again it depends on your load.

As an example, I have a compressor refrigerator that uses around 30-40 amp hours per day, plus a heater, fan and LED lights. I have 2 100 watt units and also charge from my truck while driving. We spend around 4 months traveling in the last year and did not plugged in to shore power and never run out of power.

As a backup, which I have yet to use, I have a 1000 watt inverter that I can connect to the truck battery which I plug my camper into to recharge the camper battery. I have a LFP battery which I recharge at 35 amps, so I don't have to run the truck very long to put some charge in the battery. It is a lot easier than carrying a generator. This configuration is not as well suited for a lead acid battery due to the limited charge current.

[PatrickTXFL]

One reason to over size has to do with when and where you want the benefit of use. If you are using during winter up north where you have high demand from heating and short cloudy days for charging the extra size helps.

[ZachO]

You can see that the answer is "it depends". For people dipping their toes into solar (or for anyone, for that matter) the advice to get a 100W panel and see how that goes can't steer you wrong.

Now if you want to actually match a panel to your power use, and save money by not buying more panel than you need, then you need to do some calculations.

But an easy answer for a typical camper (whatever that is) is that if you'd like to be able to recharge your single battery with solar, a 100w panel is a pretty decent "one size fits all" answer.

I have one 100w panel on my roof, and I spend a lot of time in my trailer. Between May-September, it's plenty of power.

[AC0GV]

Originally Posted by William Deak

Looking for a solar charger to use as back up for battery in my Scamp 13. Harbor Freight has these in 25 W and 100 W, about $65 and $185 respectively. What would be the minimum needed for this purpose? Thanks.

Yes, the 100 watt is a better choice. But part of a solar lifestyle is conservation. No running the refrigerator on the battery, shift that to gas, and replace the interior lighting to LED. Note also that the furnace fan uses a fair amount of power when running. A 100-watt panel can recharge from the nights use by mid-morning and has some reserve production to recharge on a partly cloudy day. Do not cheap out on the wire from the panel to the battery and controller, number 14 – 12 should be OK for most installs and watch out for aluminum wire that looks like copper called CCA in the fine print (yes I fell for it). Harbor freight prices have gotten better but amazon is still the place to buy. (Although their delivery has been slow on some resent orders.)

[Byron Kinnaman]

Missed points..
First It's a good idea to know what your usage is. then size the solar accordingly For some a 100watt is way over kill for me 65 watt if over kill.
You might be able to get by with a smaller solar system to carry around. Do some research.

[ZachO]

Originally Posted by AC0GV

But part of a solar lifestyle is conservation.

Blasphemy!

When I took a solar design/installation course in 2015, that was the mantra. For someone wanting to install solar (at home, on camper, wherever), the first step was to determine power usage, then figure out how you can cut down that usage as much as reasonable. Then design the system around that reduced use.

Judging by the size systems I see around a lot of towns, the mantra has changed to "how can I do keep doing whatever I want?".

Which is reasonable, and not everyone who wants to switch to solar cares that much about reducing use, being green and all that. Sometimes solar just makes sense for other reasons, and the more people using solar, the better.

But it's sort of too bad to see solar almost divorced from the idea of conservation.


Anyway, not everyone wants to design a system. For someone who can afford $200, and just wants to buy a panel and be done, it's really hard to go wrong with getting a 100w panel and forgetting about it.

[Byron Kinnaman]

Originally Posted by ZachO

Blasphemy!

When I took a solar design/installation course in 2015, that was the mantra. For someone wanting to install solar (at home, on camper, wherever), the first step was to determine power usage, then figure out how you can cut down that usage as much as reasonable. Then design the system around that reduced use.

Judging by the size systems I see around a lot of towns, the mantra has changed to "how can I do keep doing whatever I want?".

Which is reasonable, and not everyone who wants to switch to solar cares that much about reducing use, being green and all that. Sometimes solar just makes sense for other reasons, and the more people using solar, the better.

But it's sort of too bad to see solar almost divorced from the idea of conservation.


Anyway, not everyone wants to design a system. For someone who can afford $200, and just wants to buy a panel and be done, it's really hard to go wrong with getting a 100w panel and forgetting about it.

Spoken like a true lase comer into solar. I've been and electronic engineer for a number of years, now I'm retired. It looks to me like several peopl studied solar systems without any understanding.

[Raspy]

It's so easy to tell an honest questioner to add up your loads, and style of using them, and there's your answer. Easy Peasy. Not.

How does someone new to the game know very clearly what their desired usage will be, beyond a water pump and lights and charging a phone and computer? How do they decide what a practical limit is? And how do they relate a 100 watt system to actual amps and hours, including the charging efficiency of the battery, to arrive at the available power? Without a battery monitor, not too easily.

That's why the OP's question makes a lot of sense and is sincere. And that is why some general starting point makes sense. Some can get by with almost nothing, but that is not what I'd call normal. Others want hair dryers, electric coffee makers, and all kinds of stuff. Again, not what I'd call normal, or desirable in the beginning. So what does one need for the basics, that will get them going and provide a reasonable amount of useful energy? A group 27 deep cycle 12v battery, (or two) and a 100 watt suitcase with controller, that requires no installation. A simple answer to a sincere question.

That is a good starting point that will do a lot and will give the person a real feel for how it all works. Then more can be added if needed. And if it is enough, fine, oversized a bit never hurts. If more is needed, it's much easier to decide twice as much is needed, or just a little more is needed. Base it on what you have and how it works, then add a percentage if needed.

For instance, bragging about 65 watts being all that is needed, tells the OP nothing without mentioning what that will actually run, what size battery it is charging, can the panels be aimed at the sun, and what if any controller is being used.

An advantage of the 100 watt suitcase/group 27 (or two) is that it is a common size system, that is easy to buy, install and carry around. And again, no installation besides connecting a couple of wires. An excellent starting point with a reasonable amount of usable power.

[David B.]

Originally Posted by William Deak

Looking for a solar charger to use as back up for battery in my Scamp 13. Harbor Freight has these in 25 W and 100 W, about $65 and $185 respectively. What would be the minimum needed for this purpose? Thanks.

What I found when I purchased the 100 watt solar set-up from Harbor Freight was the size. I later discovered that a 100 watt monocrystaline panel from Renogy was the size as one of the 25 watt panels from Harbor Freight. Since I only had a 13’ Scamp, I gave away my HF kit and went with the Renogy. It would power our NovaKool 12 volt danfoss compressor refrigerator and a few lights without ever needing an external power source.
Best of luck with your project.
Dave & Paula

[redbarron55]

For my money I fitted 100 watt panels to the roof of my 16' Scamp. less power might be OK, but marginal conditions might leave marginal performance.
Also the orientation cannot be optimized with fixed mounting.
300 watts and MPPT controller gives me the best chance to keep everything running and as a retired maintenance engineer something to overdo.
I did just change out an old Norcold DE704 that used ~ 4 amps when running for a slightly smaller, but much quieter and newer Norcold DE490 that draws ~3 amps.
Both have swing compressors and run on 12 or 120v electric power.
By the way I find that the MPPT with the solar cells in series starts charging earlier and keeps charging longer than the old PWM controller and is an essential part of overkill.

[Peder_y2k]

100W YES, best way to begin.
I've used https://www.batterystuff.com/solar-chargers/ with good results. Dont think harbor freight solar panels are good quality or long lasting.

[kolocar]

I purchased the 4-25 watt panel kit from Harbor Freight before our trip to Alaska last summer. Only brought 2 of the panels with us and they worked great. My first solar purchase and was intentionally on the cheap side. By the way, that kit comes complete with mounting brackets and a 10 Amp controller. No frills but it worked admirably..

Also, FYI I am selling the kit for $50 if anyone is interested. Cash and carry only, from western NC.

Don

[Rockytop]

Look up Renogy. They have good prices and sales, and their customer service Reps are knowledgeable and helpful.