Dual Battery Solar System

The system in Ol’ Blue has a very basic 100 watt solar system and a second battery. It took me (Austin) a couple days to install all the wiring, battery and solar.

The worst part and most daunting task along the whole process at least for me would have to be doing all the internet research. The hardest thing, as with all internet research, is filtering out all the information that is absolutely worthless. The best ideas on what I would actually need, came from retailer websites. I would spend countless hours reading through forums and DIY websites; ultimately I would always come back to the same conclusion, that people on the forums are idiots and very few actually know what they are talking about. I ended up just looking at the retailers webpages, figuring out the capacity I would require, then search for the individual products or similar and building up my Amazon list. Finally, after what seemed like months, I had come up with a very rough plan of how I could lay out my solar and dual battery system. I’m sure some who read through my build will come to the same conclusion that I did many times, but I’m ok with that because I’ve built a system all by myself, at a reasonable price and well guess what, it works just fine!

The following is a list of the parts that went into my DIY dual battery system. Please note that not all the parts I used were purchased, due to this being built at my fathers shop.

  1. ACOPOWER® 100w Solar Panel
  2. Jay Corp True Smart Dual Battery 140A Isolator (VSR Voltage Sensitive Relay)
  3. Intelligent 30A PWM Solar Panel Charge Controller
  4. Car Audio Inline Circuit Breaker Fuse (80A)
  5. Copper Battery Terminal Lugs 4 Pack
  6. Stinger 4 Gauge Matte Blue OFC HPM Series Power Wire
  7. Stinger Pro Series 8 Gauge Translucent Red Power Wire 25′ Cut
  8. Optima Batteries 8016-103 D34M BlueTop Starting and Deep Cycle Marine Battery
  9. Blue Sea 5029 ST Blade Fuse Block w/Cover – 12 Circuit w/out Negative Bus


  1. Triple Function Dual USB Charger + LED Voltmeter + 12V Outlet Power Socket
  2. 43 Qt Portable Compact Refrigerator Freezer – EdgeStar
  3. Schumacher 750 Watt Power Inverter

For a basic idea of what is entailed in the dual battery I referred a funny thread on Expedition portal. Expedition portal – Dual battery setup. The first thing I can say about this thread, is that it’s a good start into what will need to be built.

The basic run down of how the system is wired up goes as follows:

Starter battery -> Circuit breaker -> Isolator -> Second battery -> Fuse block -> Accessories (fridge, lights, USB chargers, ext…)

I’ll leave the technical bits out of this write up due to the fact that I don’t want any responsibility if something is done incorrectly. This CAN be done by any person with any bit of understanding of electricity. However, here is some elaboration into the little bits of what makes my system work for me.

Standard US 3 prong plug

Panel Connection:

The reason I decided to add in a standard US 3 prong plug was due to the MC4 connectors. When looking into purchasing the extensions, I was blown away at the cost and was very turned off by the fact that it is two separate wires. Doing a cost comparison of outdoor 10 gauge/2 conductor wire versus a singe 10 gauge wire with MC4 male/female connectors was just about equal price; so two cords would cost double. Now the big difference…. adding in extensions. The use of the 3 prong connection makes putting on an extension SUPER easy; just add in an extension cord. They are accessible just about anywhere that sells anything that uses electricity.

I started out with 25 feet of cord. I have purchased two very cheap extension cords since being on the road and can now put my panel roughly 75 feet away from the vehicle. This is great because I can stow away the extensions when they are not needed; making the cord much less to coil up and deal with on a daily basis.

Solar Panel storage location

The Panel:

The panel we use is a 100 watt panel that I found on Amazon for a good price. The main constraints for my panel purchase was the size and capacity. My goal when I started was to find a panel that was slim enough to fit between my DIY roof rack and the base of our Tepui roof top tent.


The Isolator:

One the more costly parts of the whole solar system was this little gem. I had purchased a Cole Hersee continuous duty solenoid to later realize that it wouldn’t work safely.  As you can see, this Jay Corp True smart isolator will open the charging connection when the starting battery reaches 13.4V. Even better there is a small blue LED that will turn on when the connection is open; so it is very obvious to know that it’s working. This is a product that I would rate a 10/10.


Blue Sea fuse block:

The fuse block is a 12 terminal block with out the ground terminal. Blue sea makes great products and really there is no comparison. This comes with a cover and is made of quality materials that wont leave you stranded.

Circuit breaker:

A circuit breaker or a fuse? Well the easiest explanation is that the circuit breaker has two functions, where the fuse only serves one. The breaker is able to disconnect the second battery from the starting battery with the press of the button. Also if it ever blows, I don’t need to carry extra fuses. The circuit breaker is a very generic open/close made in China product. I decided to use the 80 Amp size due to the maximum loads that the wiring can handle. When choosing a fuse or circuit breaker please look to the max amp rating for the size and quality of wire you are using; this is where DIY builds can become dangerous.


For all my wiring I used Stinger brand. Mostly because I knew that I would be buying a quality product. I simply don’t trust the random brands that are found in the jungle of Amazon shopping. I wanted to guarantee that I could maintain amp loads over the length of the wire. There is big difference in the quality of oxygen free, copper and aluminum wires sold online; so do your research and buy quality wire!


Optima Battery:

I decided to use a Blue Top Optima battery due to the connection terminals. This is technically a marine battery, but it is identical to the yellow top; however it has the marine style and automotive style connections. As you can see the battery only has one power and one ground; all the connections to auxiliary components are run from the fuse block.  The size of this battery is 34, it will keep the refrigerator and electronics powered for 2 days before it needs charging.

Charge Controller:

The charge controller  we used is a very basic model that met the capacity needs of our solar system. There are no fancy bells or whistles with this one. If I had to purchase one again I would spend a few dollars more to get one that would tell me more information with a display. This one works and we have had no problems with it as of this point.


USB Plugs:

This USB volt panel was a nice add-on that we installed due to the accessibility and full time function of charging at the rear of the vehicle. The power lines run directly to the battery and can handle a very good load without the possibility of fire or failure. The unit sits on the box around all the wiring for the solar panel and charge controller. It is directly tied to the power wiring heading back to the battery from the charge controller; please note that there are two power wires, one for the refrigerator and one for accessories/solar.

Power Inverter:

Just before leaving, we decided that we needed a power inverter for all sorts of things; mostly the charging of our computer and haircuts. We picked up a 750 Watt inverter that has been amazing. It would be worth a purchase if you are in the market!