Tag: Batteries

RV Power Center: Final Results

This is the ninth post of a series of articles documenting and describing our RV electrical upgrade. Our previous post in this series described a simplified model of our battery bank, the wiring of our system, the resistance contributed by each component and associated cables, and the expected system voltage drop. Our goal is to keep our voltage drop to 2.5% or less as recommended in Victron’s Wiring Unlimited. This post describes the outcome, reports actual voltage drop measurements, and compares these with those calculated previously. Finally, we evaluate our final results regarding our initial goals, point out a few things we’d do differently, and conclude. For those interested, this page lists the parts, equipment, and tools we used to build our power system.

Initial Design

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Figure 1 illustrates the power system proposed in a previous post.

The power system we built, illustrated in Figure 1, was initially proposed in one of our first posts in this series. In our previous post, we introduced the critical path of this system consisting of the circuit from the battery bank to the inverter/charger and back, illustrated in Figure 2.

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Figure 2 illustrates the components and cables that make up our system’s critical path and associated resistance values.

Figure 2 includes the measured resistance of each cable and component, such as the 400 A class T fuse, battery disconnect switch, shunt, 400 A mega fuse, and the Lynx Distributor busbar system. These resistances are assumed to be worst-case values as we rounded up measurements and the measurement device’s connection to each component was simply the tension applied by the spring-loaded probes. The total measured resistance of components and cables around our system’s critical path is 1.77 mΩ. With this resistance, we concluded that our system should be capable of providing just over 180 A while remaining at or below our 2.5% voltage drop goal.

Final System

After considerable cold winter work, our design came to fruition. As previously described, our power system fits within the left pass-through storage area, illustrated in Figure 3.

Figure 3 illustrates our complete power center providing 800 W of solar, 360 Ah of Lithium-ion batteries, and a 3kVA invert/charger.

Figure 3 illustrates the major components of our system. There are seven major components illustrated from upper left to lower right:

  • Solar PV disconnect switch
  • Victron SmartSolar 150/45 solar charger
  • Victron MultiPlus-II 2x 120V inverter/charger
  • Victron Cerbo GX monitoring system
  • Victron SmartShunt
  • Blue Sea battery switch
  • Victron Lynx Distributor

Our battery bank is behind and to the right of this location. The solar charger and the SmartShunt attach to the Cerbo GX via VE.Direct cables. The battery voltage monitor (mounted on the battery bank) and the MultiPlus-II connect to the Cerbo GX via two VE.Bus cables.

We used a Victron MK3-USB device to program the inverter/charger for our specific setup and then used the remote console provided by the Cerbo GX to monitor the initial startup. After turning on the battery switch and the solar PV switch, the system immediately started providing inverted power to the RV, and the solar charger started charging the batteries. Next, using a halogen light and my wife’s toaster, we applied some moderate load to the system and took some readings, found in Table 1.

Battery VoltageInverter VoltageVoltage DropCurrent (A)Resistance mΩ
12.8812.840.04251.6
12.7112.610.10731.4
12.2812.040.241571.5

As expected, as the system current increases, the voltage drop experienced by the inverter/charger increases. We divided the voltage drop by the associated system current to calculate the system resistance. Averaging these three values, we note that the system resistance is 1.5 mΩ which is 0.27 mΩ lower than the measured 1.77 mΩ.

The system experienced a 0.24 V voltage drop with a 157 A load. A voltage drop of 0.24 V is a percentage voltage drop of just 1.9%, well below our limit of 2.5%. With a resistance of only 1.5 mΩ, we should be able to load our system to nearly 215 A without exceeding our 2.5% goal. These 5-10 minute load tests resulted in almost no heat generation by the inverter/charger or any system components. I am looking forward to more extended tests to see how hot things get.

Summary: How Did We Do

Nearly three months ago, we outlined our goals for our new power center in our first post on this subject. We desired the ability to use our microwave, television, and other 120 V AC systems without having to ruin our camping solitude with a generator. In addition, we wanted to minimize the intrusion of our generator while recharging our batteries. We determined that to meet our needs, we needed several items:

  • 400 Ah of lithium-ion batteries
  • 800 Watts of solar power
  • An inverter that is capable of producing nearly 3000 Watts of 120 V AC power
  • A battery charger that is capable of consuming our entire generator output to minimize charge time

We have nearly met each of these requirements. Instead of 400 Ah of batteries, we have 360 Ah, and instead of 3000 W of inverter power, we have 3000 VA or 2400 W continuous. We believe each is close enough to call this project a success. Perhaps more importantly, we learned a lot on the journey and had a lot of fun. If our RV needs to be restored to what we had before this project, here is a brief description of the required tasks.

We did a couple of things right and a few we’d do differently with the new knowledge we possess:

  1. We can’t properly express how great the copper bar approach to connecting the battery disconnect switch and the SmartShunt to the Victron Lynx Distributor is. Using a short segment of 4/0 wire and a lug at each end results in a rather long connection. The copper bar approach saves space, looks clean, and in our cramped environment made our layout possible. You could save ten bucks if you want to make your own, but we saved ourselves the cutting, drilling, and the likely mistakes and bought a pair.
  2. I wouldn’t have initially skimped on our torque wrench purchase. Our fitst purchase had a torqu range of 10-100 ft-lbs and barely registered when being used at the low end. We ended up twisting a bolt head on a battery lug clean off. This was dangerous and could have resulted in a bolt being unretrievable from an expensive battery. Fortunately, just enough bolt was left to enable its removal with a pair of vicegrips. We love our second torque wrench, the Park Tool TW-6.2.
  3. We would definitely use boat/marine wire instead of the 6/3 Romex that we installed. Our RV, like most, is full of Romex making us comfortable that this was a reasonable choice. In addition, 6/3 Romex contains stranded conductors, but not like ultra flexible boat/marine wire such as Ancor’s Triplex Cable.
  4. We would have used lugs suggested by Victron Energy. The 4/0 sized lugs we used are great, but don’t fit very well within the Victron Lynx Distributor. I suspect, but have no evidence that the lugs they suggest would fit much better.

We’re done, it looks clean and neat, and above all else, it works!

RV Power Center: Design

This article is the second of an ongoing series of posts documenting and describing our significant RV electrical upgrade. In our previous post, we outlined our requirements and created a schematic of a system that would meet our needs. We also discussed our desire to do the work incrementally, leaving the trailer in working order after each sub-project. Finally, we discussed our desire to build a 24 V system. In this post, we discuss a potential need for an alternative design and present its schematic. We also discuss the need to model our finished product, and we share our results.

Alternative Design

While we desire to build a 24 V system to reduce currents, Victron Energy does not currently produce a 24 V version of their MultiPlus-II 3000 VA 2x 120 V inverter/charger. However, we are hoping they announce such a device at the METS 2021 conference.

Figure 1 illustrates a schematic for a 12 V system that meets our requirements.

In case a suitable product does not become available, we have designed an alternative 12 V system. This version would not need a 24-12 V DC-DC converter, but increased system currents require larger wires to connect the battery bank to the inverter/charger. Figure 1 illustrates the schematic for our alternative design.

Modeling the System

Our desire to make incremental progress without wasting time or money requires us to see the outcome before taking our first steps. If we don’t know where each component will go and how it will be oriented, we will likely make mistakes that waste resources.

To visualize our project, we used Autodesk’s Fusion 360 3D modeling software to create a model of our RV’s pass-through storage space, our under-bed storage area, and the significant components of our system. Then, by placing the scale versions of the desired components into the modeled spaces, we can arrange and rearrange them to ensure the best overall final implementation. We can then undertake small projects without worrying about them negatively impacting future work. We can also simultaneously work on multiple projects that don’t interfere with one another.

RV Storage Spaces

We initially thought we would put both the power center components and the battery bank in the pass-through storage area. However, we decided to place the battery bank in the under-bed storage to reduce the temperature extremes it would otherwise experience.

Figure 2, The pass-through storage area, under the bed drawers, and storage space beneath the foot of the bed. Immediately above these modeled objects is where the mattress sits within the trailer.
Figure 3, The pass-through storage area is on the left, and the under-bed storage space is on the right.

Figure 2 illustrates the pass-through and under-bed storage areas of our trailer. It might be helpful to note that the mattress sits immediately on top of these modeled objects. The under-bed storage comprises two drawers, and immediately above them, a small storage space accessible by lifting the foot of the bed. The area illustrated in Figure 3 seemed to be an ideal place for our battery bank.

Figure 4, The space between the drawers is sufficient for four Lion Energy UT 1200 batteries.

However, we discovered some completely wasted space between the two drawers during our modeling efforts, see Figure 4. This space is almost large enough for four Lion Energy UT 1200 batteries. Some modifications will be necessary, but using this space will leave both the under-bed and pass-through storage areas free for their intended purposes.

This example points out the sound practice of measuring things out and opening up places in your RV to determine what is there and what’s available. You never know when you may need a bit of space for one thing or another.

Modeled Components

Modeling the trailer spaces gave us a great reason to learn a bit about Fusion 360. While we aren’t experts, we learned enough to model each of the major components we’ll use in our system. These models are not precise, but their overall dimensions and appearance are accurate enough for our purposes.

Victron MultiPlus-II 2x 120V
Victron SmartSolar MPPT 150/45
Victron SmartShunt
Victron Lynx Distributor
Victron Cerbo GX
Victron Orion DC-DC Converter 70A
PV Circuit Breaker Box
Lion Energy UT 1200 Battery
Blue Sea Class T Fuse Holder
Blue Sea 300 A Battery Disconnect Switch

This modeling effort enabled us to place each component, move them around, ensure adequate spacing, etc. The implementation illustrated in Figures 5 and 6 was achieved by adding a wall in our pass-through storage space and placing the modeled components. As previously mentioned, we may have to implement a 12 V alternative by removing the DC-DC converter and adjusting fuse values appropriately.

Figure 5, This is the front view of the RV Power Center showing the layout of all major components. The solar charge controller and PV breaker are in the upper left. The DC-DC converter is in the lower left. The inverter/charger is in the center of the figure, while on the right side, we have from top to bottom the Cerbo GX monitoring system, the SmartShunt, battery disconnect switch, and the Lynx Distributor.
Figure 6, This top view of the RV Power Center component layout demonstrates sufficient clearance from all devices, walls, doors, etc.
Figure 7, The four batteries fit nicely between the drawers with the 300 A Class T fuse nearby.

As previously mentioned, the battery bank will be located between the drawers in the under-bed storage area. In addition, we’ll build a small shelf near the batteries where our 300 A Class T fuse will be located. The battery cables will pass through the thin wall between the under-bed area and the pass-through storage area and then travel down to the left in Figure 7 until they reach the battery switch and SmartShunt.

Summary

In this post, we discussed our alternative 12 V design and modeled the physical spaces and components in the hope that we get it all right the first time around. This may be an optimistic goal, but having this detailed plan in hand will enable small projects to fit more seamlessly together. Now the work begins.

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