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New to Solar. Conect directly to battery ????

TenOC
Nomad
Nomad
I am completely new to solar panels. I know almost nothing about them. We boondocks and dry camp about 50% of the time in our 5th wheel. We have 2 deep cycle lead acid batteries. When the batteries need recharging, we have a Champion 3100W Inverter Portable Generator that we plug the power cord from the RV into by the use of a 50 amp to 30 amp adapter.


I want to add a portable solar panel such as Harbor Freight Underbolt Solar100 Watt Solar Panel Briefcase


Harbor Freight 100 watt

Can I connect this solar panel directly to my battery with a alligator clips or do I need some type of controller to keep the panel from overcharging my batteries. I think the output of the solar panel is 14 to 22 volts..
Please give me enough troubles, uncertainty, problems, obstacles and STRESS so that I do not become arrogant, proud, and smug in my own abilities, and enough blessings and good times that I realize that someone else is in charge of my life.

Travel Photos
15 REPLIES 15

profdant139
Explorer II
Explorer II
For whatever it's worth, we boondock a lot and have a 120 watt folding portable panel. It has a built in controller -- the panel puts out almost 14 volts in bright sun. We hook it right to the battery (group 31) with alligator clips.

The panel supplies all of our power almost all the time. We've been using it this way for many years with great results.

We have a portable panel (not rooftop) because we usually park the trailer in the shade. We use a long ten gauge cable so we can park the panel in the sun without a lot of voltage drop due to the long cable run.

The twelve gauge cord that came with the unit did cause a measurable voltage drop because of the resistance in the thinner wire. So we replaced it with ten gauge.

The panel is a "no name" Chinese imitation of a Renogy briefcase unit.
2012 Fun Finder X-139 "Boondock Style" (axle-flipped and extra insulation)
2013 Toyota Tacoma Off-Road (semi-beefy tires and components)
Our trips -- pix and text
About our trailer
"A journey of a thousand miles begins with a single list."

pianotuna
Nomad II
Nomad II
Dusty R,

My panels are from 2005. They still work well. They have paid for themselves several times over.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

Dusty_R
Explorer
Explorer
I've read that Michigan ranks 47th in the 48 continental states for available sunshine. With this in mind, how well do solar panels pay?

Vintage465
Nomad
Nomad
The most important thing about solar is to be flexible with your listening.....There are those that say, "you're wasting time not having tilting panels".......Or, here's an old favorite"PWM controllers vs MPPT controllers, PWM's are useless".........If you're buying new, I fully recommend a MPPT. If you want to and have the coin, tilting panels will aways give you the most harvest. But I've had panels screwed to the roof and a PWM charging four six volt batteries for 6 years and never want for power and never need the emergency genny I have on board. I think the most important thing is to have the controller as close to the batteries as possible to minimize charge voltage loss.
V-465
2013 GMC 2500HD Duramax Denali. 2015 CreekSide 20fq w/450 watts solar and 465 amp/hour of batteries. Retired and living the dream!

wa8yxm
Explorer III
Explorer III
Solar panels are not voltage regulated in another forum someone is comlaining his batteries were overcharged to the point of failure. Turns out his charge controller is shorted or miswired and the panels are kicking out 17+ volts.

I have 5volt panel or so it says. Hits 12 in partial shade.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
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Sage_Rat
Explorer
Explorer
With regard to the need for a controller, years ago I remember West Marine opined a 1/60 ratio. If the amp output of your solar was less than 1/60th of your battery amp hour rating, a controller wasn’t needed. This was way back when lead-acid was just about the only show in town, and panels were modest in their output. Probably no longer applies. Not applicable to lifepo4!

bucky
Explorer II
Explorer II
Another factor is where you like to camp.
State parks and Federal campsites love trees. Solar hates trees and shade.
If you like open fields go for it.
Puma 30RKSS

SJ-Chris
Explorer
Explorer
An excellent component to add to your RV/TT is a battery monitor. There are very suitable ones for $20-50 that will give you some indication as to HOW your power gets used, what each device in your RV uses for power, and a whole host of other great things. There are also more expensive battery monitors that interface through your phone. Just depends how fancy you want to be.

Here's a link to a newbie solar install I did about 3 years ago. Lots of info, pics, steps. Was very inexpensive and it still is working great!
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30217540.cfm

WARNING: Solar is addictive...

Stay charged!
Chris
San Jose, CA
Own two 2015 Thor Majestic 28a Class C RVs

pianotuna
Nomad II
Nomad II
Hi TenOC,

You can use minimal solar of about 15 watts per 100 amp-hours with no controller. Of course that is only good for maintenance between trips.

I'd recommend over sizing the charge controller. That way it is quite cheap to add more panels.

This series of articles may help:

https://freecampsites.net/adding-solar/

Make your own folding panels hinges and metal screws are cheap.

May I suggest adding a dc to DC charger? Mine works like a charm while I trundle down the road.

Welcome to the wonderful world or solar and free power!
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

TechWriter
Explorer
Explorer
TenOC wrote:
I want to add a portable solar panel such as Harbor Freight Underbolt Solar100 Watt Solar Panel Briefcase
Harbor Freight 100 watt

For $10 more you get a Charge Controller (which you must have): Thunderbolt Solar
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CapnCampn
Explorer III
Explorer III
Regarding that HF 100W briefcase, I see nothing wrong with it other than the price per watt. I haven't looked at briefcase type panels much, so maybe the price isn't too bad either - you do pay for that form factor.

You will need a separate controller to protect your batteries at this wattage, you can get super cheap PWM controllers off Amazon or Ebay that will work just fine with it. I wouldn't direct connect anything over maybe 20 watts.

As SJ-Chris says, you can find panels much cheaper -for example, this one is $120, includes a cheap controller, wires and mounting brackets and will ship to Lowes and maybe your home for free.
Renogy Starter Kit
Further searching & the used market could likely save more, but that one ain't too bad.

I disagree that HF panels are junk - in general, panels are panels and 100W is 100W.

SJ-Chris is correct in that you should take a look at how much power you need before purchasing: 100W may be perfect, or leave you frustrated with lack of performance. There are lots of threads on here (and people to opine 🙂 )about how to do a power audit and estimate your needs.

Good luck!

SJ-Chris
Explorer
Explorer
You mention you have 2 deep cycle batteries for your boondocking. Depending if their size, and whether they are 12v batteries or two 6v batteries in series, you likely have ~200-220AHs of battery capacity.

The first question is: Are those batteries still good? Or are they at their end of life? If they are old and at their end of life, then getting new batteries is your first step. You can have them tested at a local auto parts store for free (usually).

Regarding solar panels...On a good, sunny day, a decent 100w panel can provide ~20-35AH back into your battery bank. An inexpensive, foldable Harbor Freight solar panel may produce a fair amount LESS than this.

It is a good idea for you to first figure out approximately what your actual battery needs are before starting to add solar. For example, do you find that you can boondock with your existing batteries (starting fully charged) for 3-4 days before they are getting low? If that is the case, then maybe you only need 100-200w of solar to help you extend that time to 4-6 days. Or, do you wake up every morning and your batteries are close to empty? In that case, you might need 400-600w of solar panels to get them charged back up the next day.

Here is a good tip to save a LOT on adding solar...Buy used solar panels. As long as you test them with a volt/amp meter before buying, you will be able to buy 5-10yr old solar panels for $0 to $50 each, saving you 60-90% on your panels. Solar panels have no moving parts and can last a long time. For example, I bought/installed several 250w residential panels that only cost me $35 each and they work great. Depending on what part of the country you are in, solar panels can be found easily on craigslist or facebook marketplace.

To answer your specific question.... There are some "toy/junk" solar panels that are very low power that you could probably hook up directly to your battery terminals. I've seen some 10-20w panels for this. They could possibly be useful for putting a very small trickle charge on your batteries for when in storage. That 100w Harbor Freight panel might be similar (it will show you on the packaging). But if that is the case, the entire setup will be very low power (basically junk) especially if you are thinking about using it for boondocking. The proper way to add/use solar is to get proper solar panels (new or used) and then hook them up to a solar charge controller (there are different types depending on the voltage of the solar panels) and then the output of that solar charge controller hooks up to your batteries. The solar charge controller will properly adjust its output voltage and charge your battery correctly (as opposed to a flimsy solar panel with alligator clips to go to your battery). If you hook up a solar panel's output directly to your batteries you could damage your batteries.

Good luck!
Chris
San Jose, CA
Own two 2015 Thor Majestic 28a Class C RVs

Boomerweps
Explorer
Explorer
Tom/Barb wrote:
You will need some kind of controler there are several on the market.. victron .. is a good one.


Used with Harbor Freight panels. Like buying a new F550 to pull an A-liner.
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ScottG
Nomad
Nomad
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