I am asked numerous times about my system. I performed this upgrade in spring 2000. The COVID quarantine gave me plenty of free time, and it achieved my "5 C" goals of Capacity, Cubic Inches, Cost, Conservation, and Connectivity.
Capacity
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We enjoy boondock camping, and abhor KOA-style facilities. We also enjoy the quiet, non-generator environment. I calculated that about 10kWh of storage capacity is required to power our two CPAP machines, a small continuous oxygen concentrator, along with the standard Norcold DC compressor refrigerator, and other small loads overnight, and be usable over at least 4 days of zero sunshine. Upgrading the inverter to 3kW capacity would also allow the dogs to be in air-conditioned parked comfort while we spent a couple hours away shopping or hiking.
Cubic Inches
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Maybe your copilot is different, but mine did NOT want to forego any of the great storage capacity we found in our lightly used, pre-owned 2018 Navion. This meant not filling the storage bays with batteries. Research found the Tesla car batteries to have the highest power per volume (cubic inches). All Lithium batteries are also about 1/3 the weight of a comparable lead acid battery. Good. They also charge 3x faster, and can be nearly fully discharged without significant damage. Lead acid batteries can only be discharged to 50%.
Cost
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So ka-ching, we have decided to purchase a larger inverter, and "go Lithium". But Lithiums are generally much more expensive vs comparable lead acid. We saved a bunch of money buying a used RV, can we do the same buying a slightly used Lithium battery? Yes! Besides, Ebay, there are many sources of less expensive used lithium batteries. However and per above, the Tesla battery is the most efficient in terms of volume, and can be readily found for the ~$1,000 range. Two Tesla Model S battery modules will provide 2 x 233Ah at 24V storage capacity for a total of 10.4kWh. They weigh 58 lbs each, and are 27" x 12" x 3". Thus with some minor trimming, two of these will fit into the Navion's existing battery box below the top entryway step. By comparison a typical Battle Born-style lithium battery are each 29 lbs, 12.8" x 6.8" x 9.0", and have 1.2kWh of capacity. So ten Battle Born batteries, at ~$1,000 each, and total weight of 290 lbs, with have the same storage capacity as two Tesla batteries at ~$1,000 each and total weight of 116 lbs. This is ~$8,000 in savings, plus take less space and less weight! I imagine used Tesla batteries cost will also decrease with time when replacement is needed - 10+ years from now?
A Tesla battery has a built-in proprietary Battery Management System (BMS) that communicate with the car's computer to control charging, discharging, and internal battery temperature. Although many alternative BMS providers are available, I chose the
ElectroDacus for its low cost ($121), flexibility, and awesome customer support. A good review is seen here:
https://diysolarforum.com/threads/wi...urce-bms.4649/
Conservation
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Repurposing a used Tesla battery is also good for our environment. Each module is made from 444 toxic cells. Each cell is slightly larger than a AA battery. Whether you are a tree-hugger or not, you have to admit this is also a good thing.
Connectivity
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If you want to spend the least amount of money, and have time to research, you can likely save a few dollars by mixing and matching devices to make this work. But with about $8,000 of battery cost savings jingling in your virtual pocket, it is prudent to look into the best full-system solution available. There would be no band-aid mixing and matching. Victron is among the most prestigious providers, and makes everything required with good instructions. Their customer service is done through resellers, and you WILL need help, so don't skimp by saving a few dollars through Amazon. Buy from a reputable brick and mortar business, especially one that thoroughly knows RVs and/or solar.
How
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This is not a detailed "How To", but a list of suggested components and details needed to achieve the full system goals. I plan to double my 800W available PV power so I have upsized various systems.
Tesla Batteries, 2 x $1,000 + BMS, $121
All batteries are affected by temperature. The Tesla car uses electrical heaters and coolers to control antifreeze fluid temperature which is pumped through the battery modules. The lithium battery is best charged at about 65F, and that's where I keep mine. Aluminum plates were added to fully enclose the current battery compartment exterior. There is room to insert both batteries, plus 2" of blue construction foam inside. The opening at the top needs to be enlarged by about 1/2" on the upper/lower sides, and 1 inch on each remaining side to fit the batteries in. New top step rubber moulding was supplied by WBGO and cut for the larger opening. The top step was lightly modified to seal. The main battery cables, BMS cables, and heated fluid lines pass through bulkhead seals at the rear of the semi-sealed battery compartment. RV antifreeze fluid is kept in a Tupperware tub under the kitchen sink, heated by an aquarium heater, and pump flow is controlled with a Buck converter to about 10V DC. Bulkhead gland nuts pass all cables and insulated fluid lines into the front outside storage bay behind the passenger.
Victron BMV-712 Battery monitor, $220
Although not strictly "required", this provides a quick way to monitor the overall battery health and State of Charge (SOC) either through the display, or Bluetooth connection to your smartphone. You can quickly see how much time in hrs/days that you have left with your battery at the current usage and SOC. I suggest having something like this for any RV coach battery! It allows you to perform an energy audit at any time.
Victron MultiPlus (24/3000/70-50 Inverter/Charger, $1,200
Inverter/Charger - since committed to supplying higher inverter power (3kW), and the need to properly charge a 10kW lithium battery, both the stock inverter and converter must be replaced. Victron has numerous solutions, but this unit also provides several unique features. Among these are a "Power Assist" setting which allows control of shore power level. This is especially handy when "mooch-docking" and you are connected to your benefactor's wall outlet which has a 15A breaker. You can set the Power Assist to any value, like 12A, and the inverter will only draw up to that value from the wall outlet. Any additional power requirement will come from your batteries. Therefore you can likely run your air conditioning getting most of its power from the wall outlet, while sipping power from your battery. Another feature is automatic switch-over for shore power. You simply rewire all 120VAC loads to come from the inverter, through the existing circuit breaker box. The 120VAC loads, like microwave, etc. will always work, regardless of whether shore power is being used. The Multiplus is controlled via the Electrodacus BMS. If the Tesla battery voltage reaches the upper charging limit, the charger section is stopped. If the battery voltage ever drops below the lower limit, the inverter is stopped. You need to purchase the $75 Victron Mk3-USB adapter to initially program the Multiplus from your laptop.
Victron Color Control GX, $516
Not required, but it provides two great features. 1) Single location to quickly view any Victron device state, control, and modify certain parameters, like the "Power Assist" value above; 2) It stores your past energy history on the Victron portal website for review by connecting to the internet via WiFi.
Victron Energy MPPT 150/45 TR SmartSolar charger, $450
The solar charge controller is enabled by the BMS when the batteries need to be charged. It displays status and history on the Color Control GX or via Bluetooth on your smartphone.
Victron Orion 24/12-70A (24VDC-12VDC converter), $265
This 92% efficient converter powers all the 12VDC loads through the existing fuse box. It will be disabled by the BMS if the battery voltages are at the low voltage limit setting.
Victron Energy Orion-Tr Smart 12/24-15A Isolated Dc-dc charger, $260
Not required. This device allows you to charge the Tesla lithium batteries using the chassis alternator. This can be handy if driving at night, or any other time you want to add a little more charge than your solar can provide while driving during the day. Typically my 800W solar array will provide about 600W at 24V, or 25A of charging power as the panels are not pointed directly at the sun. This DC-DC charger allows an additional 15A to be charging the battery. Thus about 30A at 12V is drawn from the vehicle alternator system, but only when manually enabled. I think any more power draw can stress the alternator, especially when the headlights are on.
The attached images show:
- The Victron equipment bay behind right front wheel.
- The two Tesla batteries mounted within existing under floor battery box, but sealed to exterior, and with insulated interior.
- Required programmable Battery Management Systems, one for each Tesla battery, below the DVD player at entryway. These give full disclosure of all parameters including battery internal temperature. They can also be integrated via WiFi into various custom monitoring systems.
- 4x200W @ 12V PV panels, upgrading to 24V panels soon with over/under slide mounting. They are tilted for better morning sunlight capture in this picture.
- 60W Battery heating system mounted below sink with Tupperware holding tank for RV antifreeze, aquarium pump, and heater. Draws about 3A when heating, and tested useful at 7F outside.
- Upgraded control panel above refrigerator.
Linear Mode
