Solar Project: Part-4a, Wiring

Projects like this are hard enough without fighting the weather. Adding last minute design/equipment changes to the project increases the difficulty from hard to insane. This is why the Smart thing would have been paying to have this installed by a professional. But, where’s the fun in that?

It’s been raining off and on for the last month. I actually work on my TT in the storage lot because there isn’t room where I live to do the work here. So I have to take the time to drive there with my tools, set up, do some work, break down and pack up. Even tougher when it might rain. It has actually SNOWED in Sonora (Central Sierra) TWICE, which it rarely does at my altitude. (2000ft) I can’t catch a break!

I was still able to mount the Backboard and do a little routing of the wires, but it was here I had a Hard Stop. I realized I needed two major changes. I had wanted a true Battery Monitor, and trying to save money I ordered one from Hong Kong. The pictures looked OK and it had nice Specs, but when it finally arrived (5 weeks) it was crap; A poor design in the Shunt and a Butt-Ugly head unit. It was unusable and a waste of $40.

So I bit the bullet and ordered a decent one: Victron BMV-712 Battery Monitor. At $206 it was a hard decision, but I felt I really needed a true Battery Monitor. The reason is that this doesn’t just measure the battery voltage; it monitors the Energy State of the battery. It knows exactly how much draw there was in amps and exactly how much charging current there was from the Solar Panels during the same period and calculates the % available. So I always have an accurate gauge of the charge-state of the battery, unlike the Voltage based “Battery Gauge” built-in to the TT. (usually wrong) This is incredibly important to me both to see how effective the new Solar Charging system is and when to fire up the Generator! The icing on the cake? It has Bluetooth. (Geek out!)

The other major change was that I decided to install a Transfer Switch/Relay after all. (Another $65…) Originally I was just going to install one outlet near the bed for a CPAP machine or other small usage, like chargers or an amplified speaker. The rational was the Bed is right next to the storage where the Inverter is and wiring would be easy. Also, the existing Battery capacity and the 1,000 watt Inverter wouldn’t handle the whole trailer. Or so I thought.

Looking at the AC loads: there are the Air Conditioner, Microwave and the TV. The Air Conditioner is out, (too much draw) the Microwave is rarely used, and I don’t watch much TV. However I remembered the Refrigerator also works off of AC! The RV fridge is dual use: AC and Propane. When I’m Dry Camping somewhere I run the fridge off of Propane and things are great. But what do I do when I’m driving? Running things on Propane while driving is flat dangerous. It works, and I’ve done it, but it’s not safe. But, hey! I now have this nifty Solar Charging system that runs great during the day even while driving down the highway. I believe it will handle the Fridge, at least while the sun is shining. When I’m parked I can cut back to Propane.

So this necessitated installing an automatic Transfer Switch/Relay that cuts the whole trailer over to the Inverter. Sounds great, but there is a catch: The AC Power Panel is at the far rear corner of the trailer. Fishing a 12/2 cable from the front corner through the underfloor cover to the opposite rear corner will be a stone cold Bi!ch and is why I was avoiding it in the first place. Routing past/over all the holding tanks in the center of the trailer being the biggest problem. This will be a wiring phase all by itself.

The final wiring phase is drilling a hole in my roof and routing the Solar Panel cables. I cannot do that with the rain, snow AND the cold weather. I use a putty called Dicor that waterproofs the roof after adding screws and things and it needs at least 60degs F to flow well and bond properly. Once I have the Solar Panel wiring in, I need to route that with the wiring from the Inverter Remote, Victron Head, and the Transfer Switch as a bundle to the Backboard. (Fished through the bottom of the trailer)

Finally, once the cables are in, I hoist 64lbs of Solar Panels to the Roof, (32 lbs each) mount them, and test the system.

What I’ve done so far:

  • Mounted the Backboard and drilled the hole for the cables
  • Mounted the 500 amp shunt the Battery Monitor uses
  • Rewired the cabling to the batteries and upped the gauge from 6ga to 2ga (more than doubling the size)
  • Added a temperature monitor on the batteries for the Charge Controller
  • Mounted the Inverter Remote
  • Mounted the Victron Head unit
  • Added a Battery Switch that cuts off the trailer when in storage

To Do:

  • Install the Transfer Switch and rewire the Power Center
  • Route the 12/2 cable from the Transfer Switch to Inverter
  • Route the Inverter Remote and Victron Head cables
  • Mount the Solar Cable Entry Housing
  • Install and route the Solar Cables
  • Mount the Panels
  • Test system

Damn…glad I’m retired…

Batteries with Shutoff switch
Not finished...needs more wiring
Backboard mounted, not finished…needs more wiring

4 thoughts on “Solar Project: Part-4a, Wiring

  1. Hi Mike, Just quickly. I would really like to see you put a couple large amp slow burn fuses (100 amps) directly connected to your 12V positive post on both sets. (Battery – Fuse – All Services). This is to prevent fire if that positive wire right next to the battery gets grounded, Again, I don’t see it but knowing you, you’ve thought of it, if not, don’t depend on your circuit breaker feed.


    • A point. Every addition like that has to weigh against complexity and additional points of failure. Adding an extra >100A fuse from the battery sounds simple, but Class-T fuse holders aren’t waterproof. Not sure of any ANL type that are either. I’ll think on it. Thanks.


  2. Hey Buddy, good reading about you. Keep it up.
    Doesn’t have to be like this particular one but notice the lugs. 1 lug no the Positive wingnut post and nut / bolt to supply cable to the battery only now to the fuse. I have a 50 for my houseboat, lots of water sloshing around, no problems. . 2 – 6 VDC 240 amh Trojans.


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