My funky power system build

[Skyjim73]

We should take delivery of our new 3124KB in February, and I've begun acquiring the major hardware for the solar charging system. Since I'm going slightly against the grain with a few of my choices, I'll list what I'm using and then once we get some experience with the system next year, let any interested forum members know if my system is working for us or if my theories have crashed and burned...

We'll hopefully be all over North America, but we do a lot of dry camping in the desert southwest. I am a pretty serious amateur astronomer, so I like to go to fairly isolated places for dark skies. My wife enjoys many of the national park campgrounds when we do "normal' camping, and at least in the western states most campgrounds in the parks lack hookups. I have a Honda EU-2000 we've used with our old hard-side trailer, which had four 6V golf cart batteries and a 2KW Heart inverter-charger with a 100 amp four stage charger. I've gotten used to managing my battery bank, doing regular equalization charges, and so forth, and my last set of Trojan T-105s lasted 8 years. But one thing we learned was that we really did not use the AC power capability except for stuff like wall chargers that a tiny, cheap inverter could have handled. But having a good DC charging system is a must for me.

I'm not going to take my new lightweight TM and burden it with a huge battery bank - at least not right away. But I will need reliable 12 volt power since I'm committing to a 12VDC/115VAC compressor fridge rather than the 3-way. So my version 1.0 battery bank is going to be a pair of 6 volt Trojan T-145 "tall" golf cart batteries giving me a 260 amp/hr bank to draw from. Trail Manor has agreed to fab me a slightly lower slung set of battery rack rails to get me an inch lower so the T-145s in their boxes are out of the way of the forward bed section when it folds down.

At first I figured I'd buy a Magnum inverter/charger, but I really don't need most of it's capability - and it's a really pricey way to get a good charger into the system, and the only one they have with a 65 amp or under charger output (using the 25% rule of thumb for charging rate vs bank size) only has 20 amps of AC pass-through rating. That worried me when looking at air conditioner startup loads - wanted to allow at least 30 amps to match the AC service the system is designed for and the common low amperage hookup in most RV parks. So, I could spend a lot more money for a bigger inverter/charger than I needed, and deal with the complexity of an AC sub-panel for the fridge and air conditioning, which I would NOT want pulling power from the inverter. We would only use the air with AC hookups and the fridge will only switch from DC when AC power is present - no point in incurring conversion losses making AC power via an inverter. Anyway, I'm instead going to try another setup.

I also REALLY didn't want to completely redesign the DC setup, but wanted at least some control over the battery charging. The converters typically installed, including the WFCO TM uses, have three stage charging now incorporated, but they taper out of bulk charge stage VERY quickly - just the opposite of what you want for quick replenishment in a campground via small generator. I knew I'd want some solar charging capability to extend my dry camping endurance and offset the power the fridge consumes en route to a campsite, but there just isn't that much roof area available on a TM, and I didn't want to deal with portable arrays. So, I want a fixed set of panels, preferably with pretty high low-light/partial shade performance to better deal with the variety of sun exposures in typical campgrounds.

So, Version 1.0 of my system:

Batteries: 2 x Trojan T-145 (260 amp/hrs at 20 hr rate)

Custom battery rails, 2 Sea sense tall GC battery boxes.

Replace the charger module of the factory 12 volt converter with a 55 amp Progressive Dynamics 3 stage unit, with PD control pendant installed to allow me to manually control charge stages during short AC availabilities. Automated but very conservative charging option for longer term hookup situations.

TM is upgrading the DC charge cabling - still waiting to confirm whether we can go to my desired 2 gauge from the factory 10 gauge, but as Fun Pilot has found out, at least 4 gauge is definitely possible. Happy to pay for this type of upgrade at the factory!

2 x Unisolar 64 triple junction amorphous solar panels. Unisolar made these panels, as well as sheet-style flexible arrays with self-adhesive backing for metal roof setups, in Michigan before they went out of business after the 2008 economic meltdown and the flood of cheap Chinese panels. The design isn't as efficient in full sun as typical crystalline arrays, but they have really excellent shade-tolerance and low light performance. You can still find new in box US-64s on E-bay last time I checked.

Morningstar Sunsaver 15 Max Power Point Tracking charge controller. Went with the pricier MPPT controller to run the panels in series for higher voltage to minimize wiring losses to the controller, which can down-convert to the needed voltage while utilizing more of the panel output, since MPP for the Unisolars is 16.5V. Normally it's more cost-effective on small systems to buy more panels and use a cheaper controller, but I want the panels hard mounted to the roof and I've got mass and space constraints, so I'm going to try for max real-world efficiency in less than ideal light conditions. Theoretically ought to work, but we'll see how it goes in practice. I might be wrong on this choice but I want to test that.

Edit: Almost forgot:Morningstar battery temp monitor cable and remote monitor. May not give me as much information as I want, andI could wind up wanting a Trimetric monitor for comprehensive info, but this was a good deal and I'll see how it goes.

Can't wait to get things assembled after delivery and see how it all works!

Jim