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Walkthrough of my solar setup

jonrickardjonrickard Member Posts: 7
in Battery/Electrical & Solar

Background:

Each year I attend a number of motor races with my father, until now we have been tent camping but wanted something a little more comfortable. In January I purchased a 2019 T@G Boondock Edge. Camping at a motor race is about the same as boondocking with no connections for water or electricity, and also generally in the middle of a field with no shade. All of this meant that solar was not just an option, but necessary to keep everything going, and so I set about researching options.

I found a website with a youtube channel (http://www.beginningfromthismorning.com) which I credit here as they were a primary source for information about solar, batteries, tools and other items. It’s not that I relied only on this website, but they were the largest source of information and design for my system.

My use case for the design was to build a system which would last from Friday afternoon until Sunday evening, with enough power to charge phones, cameras, run lights, the fridge plus an electric cooler, and on some very hot weekends to run the air conditioning overnight. I needed a large inverter and because solar produces no power overnight I needed enough battery to store ample power during the day which could run the AC overnight.

Battery:

I started by looking at new lithium batteries but concluded that the cost was more than I was willing to pay given my significant storage needs, this led me to used EV batteries, and while I looked very hard at Chevy Volt batteries I ended up with Nissan Leaf battery modes due to their lower cost, and the ease of installing a battery management system (BMS). Nissan Leaf batteries tend to experience greater loss of storage capacity with age than other EV batteries like Chevy Volt (~$1800USD) or Tesla (~$2600USD), but they are quite a bit cheaper ($1120USD for 2G). I chose second generation modules which would be newer than first generation modules and I expected therefore to have greater remaining capacity (I can’t confirm if this is true or not since I only bought 2G modules).

Once I had decided on a battery modules I needed to design the rest of the system, fairly quickly I decided to go with a 3000w inverter in order to power the AC, these were available in 12v, 24v, and 48v versions, and given the high power output I consider higher voltage an advantage since it results in lower current draw and therefore would reduce the cost of items like wiring, circuit breakers etc. Nissan leaf battery modules have 2 cells in series and a nominal voltage of about 7.5v, this meant 12v was impossible, 24v was difficult, but a 48v system running 7 modules in series (14 cells in series) would have a nominal voltage of about 52v and the max (58v) and min (45v) would be within the operating range of a 48v inverter (with 6 modules in series the min voltage (~38.5v) would be below the low voltage cut-off of most 48v inverters making part of the otherwise usable storage in the batteries inaccessible). Since I was not using the BMS that came with the Nissan Leaf I chose a high power BMS which could be controlled by a smartphone app and which was compatible with 14 cells (7 modules) in series. To have sufficient storage I purchased 14 modules and put each module in parallel with a second module and each pair in series. Brand new these 14 modules would have a total of 6500w usable storage, and in testing I have since confirmed about 4700w of actual usable storage capacity in my battery.

While the BMS is able to provide a lot of information about the cell charge, and control low/high voltage cutoff, I also wanted information about discharge rate, state of charge etc and purchased a Victron BMV712. The BMV712 has a temperate sensor, and can send the temperate information to the solar charge controller to shut down charging when the ambient temperature is below a set level, I have set this to 3 degrees celsius (37.4f).

Picture of assembled battery with BMS wires attached
(short copper bars down the centre are connected to the voltage sense ports between the first and second series cell in each module) :

Picture of battery with BMS connected and plastic shields over the copper bus bars:

Inverter and Air Conditioner:

Given my desire to run the AC off the inverter I knew I needed a pretty hefty inverter, not for the ongoing use but in order to accommodate the surge current of the compressor starting, I figured a 2000w inverter would not be enough since general a 2000w generator is not enough, so applying the same logic I decided on a 3000w inverter. I strongly considered a Victron 3000w Multiplus, however once I had decided on a 48v system the 3000w multi-plus was not compatible and due to both cost and size I did not want to upgrade to a 5000w Victron inverter. I searched Amazon for other options, and I ended up with a cheap 3000w high frequency inverter from Reliable Electric, reviewing a number of online reviews left me with the impression that as long as I got a good Reliable inverter (reviews suggested quality control was a risk) it should be able to run my AC. In fact I found when I had it installed it would not start the AC and though testing confirmed the over current protection kicked in at about 1500w, perhaps because I overloaded it trying to run the microwave, or perhaps because it came that was from the factory, I’ve checked all of the fused which are fine, so I’ve concluded something internal is broken. My recommendation is to go with a low frequency inverter, they weigh more, are more expensive, and are bigger, but if you want to run something which creates a large inductive load like an air conditioner, you will have more success. Ultimately I bought a Micro-Air Easy start soft-starter for the AC which allowed it to start on my now 1500w inverter. An interesting note is that the AC consumes just under 400w while running and once the power for the AC fan (for the cowbells) is included the total power from the battery including efficiency losses in the inverter is around 410w. After I had setup the AC and tested it, I ended up replacing it with a very similar model but which has an internal thermostat so it turns off when the trailer gets down to temperature, this causes the AC to be off about 1/2 the thereby reducing power consumption overnight significantly.

Charging (solar and shore power):

With my use case being about having enough power storage to run for a weekend, I was fine with starting the weekend with full batteries and ending with empty batteries just as long as the batteries could be recharged over the course of the week prior to my next trip, I see solar during the weekend as simply a way of extending the battery capacity but do not expect to collect enough energy each day to recover the batteries fully. I wanted as much solar as posible but between the stargazed window, the roof vent, the roof rack, and the front facing flood lights I had difficulty finding enough real estate for more than 400w. On the other had 400w was enough to recharge the battery over 5 days in time for the next weekend trip. I higher battery voltage means needing to have a higher solar output voltage (Victron solar charge controller require the solar voltage to be 5v higher than the battery voltage to start charging), and so I went with 8x 50w semi flexible panels which I connected in a series/parallel configuration (2 parallel sets of 4 in series). I have read a number of threads (in various places) comparing roof mounted to portable solar and have certainly found shading is an issue, however my plan is to recharge the batteries when my trailer is parked in a parking lot where I store it and I therefore needed panels which would not be stolen so I accepted the compromise.

I have found that on a sunny day I can collect as much s 1100w of power through the 400w of solar panels on the roof, however due to my desire not to worry about battery capacity I have also purchase 4x 100w panels which can can put on top of my awning for over 2000w of collection on a sunny day, I use these extra panels on very hot weekends when I expect to use the AC longer than normal.

Layout of the solar on the roof
(green = solar panels, grey = stargazer window and roof vent, yellow = roof rack, front facing flood lights and rear running lights):

Picture of the solar panels mounted on the front and back of the trailer
(I have since this picture moved the awning to the outside of the roof rack support and mounted it below the cross bars so as to reduce the shading on the solar panels):

For shore power charging I could no longer use the built-in charge converter since the 12v systems is separated from the batteries by a 48v to 12v DC-to-DC converter, because of this and because I was worried that I might run into issues with cloudy days which might prevent me from fully charing my batteries from solar, I wanted a high capacity 48v lithium battery charger. I considered a number of options I ended up choosing a Chargery 25a variable voltage charger, this can be programmed to the correct charging voltage and at 25a and 58v allowed me to charge my batteries at up to 1450w, in fact I found that with a long extension cord, my 15a AC breakers at home pops if I don’t turn down the current. This charger was expensive, but charges the batteries quickly (~4h from empty to full charge) and is very flexible.

Putting it all together:

Picture of the power system main board:

Picture of the battery, main board, and inverter installed inside of my replacement tongue box
(Lund 9460WB - 60” wide x 24” deep x 18.5” tall)

Picture of wiring diagram with parts identified
(I should note that I made a few changes after this diagram was created, they were: the solar charge controller pictured is not compatible with a 48v battery and was replaced by a Victron 150/35, I replaced the 32a AC breaker with a 24a breaker, removed the 13a DC breaker as the 48c to 12v DC-to-DC converter is already fused, and finally removed the switch before the 13a breaker which I may end up adding back in since the converter itself draws a small amount of power even when the output is disconnected)

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