Tag: Outdoor RV

Making an RV Fan Reversible

Most, if not all, RVs have several vent fans on their roof. Our 2016 Outdoors RV 240 RKSB has one in our bedroom, one in the bathroom, and one in the kitchen. Our fans all have wall-mounted remotes that allow the fan speed to be adjusted, but our fans only draw air from the trailer and exhaust it to the great outdoors. On many occasions, I have desired to draw air from outside and exhaust it into our living space. Many newer fans have this capability as a standard feature, but I was uninterested in the expense and labor of purchasing, installing, and sealing new units when our current fans were fine.

Fan Basics

A basic controllable fan circuit consists of a DC motor M, a DC voltage source VS and a switch S. A fan of appropriate size and style is then connected to the motor shaft. When the switch is depressed, the motor spins, and the connected fan moves air.

Our current RV fan is only slightly more complicated than the basic circuit described above. The constant DC voltage source depicted in the previous figure is replaced by a variable or pulse width modulated DC voltage source VV and the switch is replaced with a push button switch SC that completes the circuit and drives the motor and fan MF when the fan cover is open.

DC motors are easily reversed by reversing the polarity of their power source. This is easily accomplished using a double-pole double-throw (DPDT) switch, as shown in the figure. By adding the DPDT switch SDPDT after the voltage source VV and switch SC, we don’t have to concern ourselves with how and when the appropriate power is delivered; we simply need to provide it to the motor MF in one of two directions. With the switch in the upper position, a positive voltage is connected to the upper motor connection, and the negative source voltage is connected to the lower motor terminal. When the DPDT switch is in the lower position, the polarity is reversed.

Our Implementation

A fun part of every project is tearing things up and being creative. After removing the internal trim of the fan box and the fan cover, it became apparent that this project would be easier than expected. There was plenty of room on every side of the fan to accommodate an additional switch, and the wiring was straightforward.

With plenty of available space, I selected a DPDT switch with appropriate voltage and current characteristics. I knew from previous measurements that our fans draw far less than 10 A of current and run off the 12 V supply. I chose a rocker switch that met these requirements and has a low profile. Notice that this switch has six blade-type connections. The center two connections are connected to two outer connections in position one and the other two outer connections in position two. We connect our variable voltage source to the center two connections and then wire the fan motor to the others.

The two wires that connect to the fan motor come from the fan controller illustrated in the figure on the right. The red and white wires of interest were easily traced around the fan housing, up through the fan box, and across one of the cross-arms holding the motor in place.

In the following figure, you can easily see the same red and white wires. As previously mentioned, these wires come from the fan controller and up through the fan box, across a cross-arm, and connect to the motor. Notice that the white wire goes through a silver cylinder which is the switch that completes the circuit when the fan cover is open.

While our initial intention was to wire our implementation according to the schematics previously discussed, it would have been much more challenging to get to the wiring on the motor side of the fan cover switch. While our wiring doesn’t match the presented schematics, it is functionally equivalent. The fan cover switch is connected to one of the motor terminals, while the other terminal of the fan cover switch is divided and attached to the DPDT switch.

We cut the red and white wires. The pair of wires from the fan controller are connected to the center two connections on our DPDT rocker switch. These two connections were made with crimp-on blue spade connectors and can be seen in the figure to the right. The red and white wires that go up to the fan motor are doubled, resulting in two red wires and two black wires. We changed from white to black because I didn’t have any white wire. These connections were made using solder seal wire connectors; these things are amazing. These pairs of wires can be seen in the figure. One pair is connected to an outer pair of contacts on the rocker switch, while the other pair is connected to the remaining outer contacts in the opposite direction. These connections were also made with crimp-on spade connectors.

The rectangular hole for the rocker switch was made in the thin plastic fan trim with a sharp chisel. It is essential to cut the initial hole small and then increase the size slowly while repeatedly trying to snap the switch in place. It’s much easier to make the hole slightly larger than smaller!

The switch was snapped in place before the wiring was finalized so wires could be appropriately routed. The mounted switch and the associated wiring can be seen in the figure to the left.

After ensuring everything worked as expected, the wiring was neatly tucked away, and the fan cover and trim were replaced. The final product can be seen in the figure to the right.

With a few connectors, a couple of feet of wire, a $3 switch, and an hour of time, I was able to make my RV fan reversible. The result looks fine, works great, and saves me time and money in the long run.

RV Power Center: Insulation and Storage

This post is the seventh of an ongoing series of articles documenting and describing our RV electrical upgrade. Our previous post in this series described the original shore power wiring and our improvements. In addition, we discussed a severe flaw that was difficult to find but eventually corrected. In this post, we describe non-power-related improvements to the pass-through storage area. These improvements include thermal insulation and an acquired storage system.

Thermal Insulation

Figure 1 illustrates our pass-through storage area and shows how the ceiling and rear walls of this area are adjacent to the living areas of the trailer. The ceiling of the storage area is the bottom bed support.

Only thin materials separate the ceiling and rear wall of our pass-through storage area from the bedroom area of our trailer, as illustrated in Figure 1. These materials provide little thermal insulation between the near outdoor conditions of our storage area and our living quarters. During colder weather, the front and top of each nightstand and the sides and bottom of the upper portion of the bed get cold.

Figure 2 illustrates the foam panels added to the rear wall and ceiling of the pass-through storage area.

Jason Evans‘ post inspired us to mitigate this issue by insulating our pass-through area. Jason reported using R 1.93 insulation panels, while we chose to use R 3.85 panels that offer twice the insulation at, you guessed it, nearly twice the price.

Our space required nearly two 4′ by 8′ sheets of material. First, we used a box cutter and straightedge to subdivide each panel. Then, we gently pushed each piece into position and caulked them to keep them from falling out of place. We thought this was particularly important for those loosely hanging from the storage area ceiling. Figure 2 illustrates the complete installation. We also used expanding foam to seal around the 120 V outlets and USB port outlets on each nightstand. These modifications should help keep the cold and heat out and reduce the noise of our soon-to-be-added inverter/charger.

Sliding Storage Tray

When we built our power center, we inadvertently created a bit of a storage dilemma by adding the wall visible at the far end of the pass-through storage area in Figure 2. As a result, we eliminated easy access to the far end of the nearly 7′ deep remaining storage space accessible only via the remaining hatch. This depth would make it very difficult to get items from the far end of the area.

To facilitate retrieving items from this area, we have acquired a MORryde CTG80-2672-2DW 80% extension cargo tray, illustrated in Figure 3. This tray is 26″ wide and 72″ long, perfectly fitting our space. In addition, the tray walls are 4.3″ tall, and the tray floor comes pre carpeted. The structure bolts to the bottom of our storage area, and the tray rides on heavy-duty roller bearings and can support 500 pounds of gear. Working on electrical wiring in that area is now simple. I pull out the cargo tray, lay on it with my tools, and pull myself in.

Figure 3 illustrates the MORryde CTG80-2672-2DW fully extended.

MORryde offers 60% extension trays that only move in one direction, and while they support heavier loads, they also cost a bit more than the 80% extension trays. The 80% MORryde extension trays are intended to slide in both directions, but we won’t use this feature in our application. With the tray extended to 80% of its length, as illustrated in Figure 3, little of the tray remains within the storage space, making the extraction of items simple. Less drawer would stay within the storage space in some installations, but we chose to set ours back from the door nearly 8 inches (see Figure 4).

Figure 4 illustrates the MORryde cargo tray locked into place.

Another nice feature of the MORryde cargo trays is that they lock into place when stowed away. It is a simple matter to lift the blue handle on the unit’s left while pulling the tray out. When you push the tray back in, it locks in place. Figure 4 also illustrates how we chose to mount our tray towards the rear of the RV to leave space for long items we don’t often access. We’ll also take advantage of the wall space to the left and right of the tray for hanging light and narrow items such as axes, hammers, jack handles, etc. While this is an unexpected additional cost to our power upgrade project, it will create a better storage experience.

Summary

This one was the most obvious and straightforward of all the projects we’ve tackled thus far. We cut some foam to size, put it in place, caulked the seams, and installed a pre-constructed cargo tray. Frankly, it was refreshing to begin a project with few unknowns, with an obvious list of steps to accomplish, and resulting in an end product that will add value to our camping experience.

RV Power Center: Wiring

This post is the sixth of an ongoing series of articles documenting and describing our RV electrical upgrade. Our previous post in this series described the Victron Energy Lynx Distributor and a minor modification we made to it to meet our needs better. This post describes the original shore power wiring and our improvements. In addition, we discuss a severe flaw that was difficult to find.

Shore Power

Figure 1 illustrates a typical 50 A shore power connector.

Figure 1 illustrates a typical 50 A RV shore power connector. A power cord may connect this outlet to a shore power pedestal that provides 50 A AC power to run appliances such as air conditioners, microwaves, televisions, and power converters for charging batteries. In addition, a 50 A connector can be adapted to a 30 A or 15 A power source using appropriate converters or dogbones. Alternatively, this connector may be connected to a generator when shore power is unavailable.

The connector illustrated in Figure 1 connects to the RV circuit breaker panel via appropriate conductors inside the RV. For example, our Outdoor RV 240 RKSB has 6/3 Romex that connects the shore power outlet to the main breaker in the circuit breaker panel, as illustrated in Figure 2.

Figure 2 depicts a typical RV circuit breaker panel with a 50 A service.

6/3 Romex has three 6 AWG conductors and one 10 AWG bare copper wire. The 6 AWG red and black wires are connected to the 50 A breaker. The white wire is the associated neutral wire connected to the neutral busbar. The bare copper wire is attached directly to the ground busbar.

The left side of the circuit breaker panel distributes 120 V AC to various trailer components, including 120 V AC outlets, television, microwave, air conditioner, and the power converter located beneath the circuit breaker panel, as illustrated in Figure 2. The power converter converts 120 V AC into the appropriate DC voltages to charge our 12 V RV batteries.

The right side of the circuit breaker panel acquires power from the 12 V RV batteries and distributes this through blade fuses to various RV components such as lights, pull-outs, pumps, USB ports, audio systems, etc. In addition, the power converter output connects to the batteries via this side of the panel for charging.

Inverter/Charger Power

The ability to use all of our 120 V appliances without needing shore power or a generator is the primary objective of this project. Including an inverter/charger in our power center will accomplish this goal. The desired inverter charger will pass through shore or generator power when available and provide 120 V power when they are not. The inverter/charger requires shore power as an input, and its 120 V AC output must be connected to the circuit breaker panel to enable this feature.

We desired to leave the shore power outlet in its original location, requiring us to run 6/3 Romex from the shore power connector to our new power center and another strand of 6/3 Romex from our power center to the circuit breaker panel. Rather than running these two strands to two different locations, we determined to run both from our power center to just behind the circuit breaker panel.

Rather than fussing with the RV underlayment, routing the cables around tanks, and through the frame, we hired this out to Stewart’s RV, our local RV service center. We purchased 125 feet of cable and delivered it to the service folks at Stewart’s, who did an excellent job in all but one aspect. We’ll address the one flaw in the next section.

Figure 3 illustrates conductors of 6/3 Romex spliced using two-conductor Morris connectors.

Once the wiring was in place, we made the right connections. First, we detached the original shore power connection from the circuit breaker panel and spliced it to one of the new 6/3 Romex strands using four two-conductor Morris connectors. These connections are illustrated in Figure 3. Next, we combined the two strands of 6/3 Romex in our power center using four additional Morris connectors. Finally, we joined the remaining conductors to the circuit breaker panel. With these modifications, shore or generator power comes in through the shore power connection, over the original 6/3 wire, through a new strand of 6/3 Romex to our power center, back through the second strand of 6/3 Romex, arriving at the circuit breaker panel. The before and after connections are identical, but the path has increased by roughly 50 feet.

The spliced 6/3 Romex cables in our power center will be separated when our inverter/charger is installed. The 6/3 cable coming from the shore power connector will be tied to the inverter/charger’s input. The remaining cable will be connected to the inverter/charger’s 120 V AC output.

Testing, Debugging, Repairing

Before connecting shore or generator power to our RV, I tested for short circuits within the circuit breaker panel. Unfortunately, I found a low resistance short circuit between the ground and neutral busbar. As a sub-panel, this should not be the case. I looked for obvious wiring flaws but didn’t find any. I returned our trailer to the service center, reporting a short circuit between ground and neutral.

They made a thorough inspection of their work and found no flaws. They did what I should have done after installing the wires and before wiring things together. They tested the continuity between each possible conductor pair of both strands and found no short circuits. I accepted their findings and began a tedious search for the truth. I completely rewired the circuit breaker panel and eventually convinced myself that perhaps it was a strange interaction with the power converter, etc.

I determined to plug the trailer in and see what happens. I knew it wouldn’t be a disaster, but I wanted to see if it would work. Unfortunately, immediately after plugging in the trailer, the GFCI outlet tripped. After much more work, I determined to plug it into a non GFCI protected outlet, and the trailer worked great. I carefully measured the potential between the trailer frame and ground to ensure my safety; everything was fine, well, it seemed fine.

GFCI outlets trip because the current on the hot wires differs from that of the neutral wire by more than 5 mA. In other words, GFCI trips when current is flowing through some undesirable path, like through you. So why was this happening? A considerable amount of literature describes GFCI failures due to long runs, over 100 feet, for example. Essentially, the longer the wire, the more leakage between conductors, and when this exceeds 5 mA, the GFCI trips. Therefore, the longer the wire, the more likely this is. While I had successfully used the failing shore power connection previously, I also recognized that I recently added nearly 50′ to the circuit through my new wiring. Perhaps this was the culprit. I moved the trailer much closer to the outlet and removed more than 50′ of cords, and it still failed.

After disconnecting the cable from the circuit breaker panel and removing the Morris connectors, I rechecked each conductor to ensure independence. Still no short circuits detected. Finally, in a last-ditch effort to find the flaw, I checked each wire in each cable for connectivity to the trailer’s frame. I found the elusive, obvious, and now embarrassing culprit. When the service center installed one of the new cables, its neutral wire was inadvertently electrically connected to the trailer’s frame.

The circuit fails as follows. The ground busbar in the circuit breaker panel is appropriately attached to the trailer’s frame. However, when the faulty neutral wire is connected to the neutral busbar, the trailer’s frame connects the neutral and ground busbars, which is inappropriate for a subpanel.

The test for this condition is simple and easily recreated. I returned the trailer to Stewart’s RV, demonstrated the test described above to them, and they accepted responsibility for the issue. They removed each cable clamp assembly installed, inspected for damage, and repaired where the wire insulation was cut and shorted the neutral wire to the frame. They demonstrated great integrity and excellent service through this ordeal and were consistently friendly and polite. They will get all of my future business.

Summary

Our new AC wiring is in place and works perfectly. One of our goals was to end each sub-project with our trailer in order and available for camping. With this project done and working, we’ve reached that goal. Several takeaways:

  • Morris connectors are amazingly awesome and much easier to work with than junction boxes.
  • Vendors, such as Stwart’s RV, with integrity are a pleasure to work with even when things seem tough.
  • Most importantly, check continuity between each conductor and between each conductor and the trailer’s frame! This one simple test would have saved dozens of hours of searching, poking, disconnecting, etc.

This project was our least understood because of the difficulty and uncertainty of physically dragging cable from the very front to the very back of our RV. However, the rest should be easy with this step done and working. Did I say that out loud?

RV Power Center: Physical Space, Wiring, and Solar Upgrade

This post is the fourth of an ongoing series of articles documenting and describing our RV electrical upgrade. In our previous post, we described our battery bank design and discussed where we would place it. In this post, we describe creating the physical space for our power center, our initial wiring, and our solar upgrades.

Power Center Space

Figure 1, This is a 3D model of the pass-through storage space we intend to use to house our power center.

To house our chosen electrical components, we need to build a space similar to what we previously presented. Our proposed power center is illustrated in Figure 1. Component placement will likely change as we deal with surprises and take advantage of opportunities. However, the basic structure seems sound, and the creation of this space will allow progress.

Figure 2 illustrates the physical space we’re starting with and some essential tools, Dewalt impact drill and a Diet Coke. First, we constructed a 3/4″ plywood wall that stretches from the bottom to the top of this compartment and lies flush against the short wall near the top.

Figure 2, This is the space we’re using for our power center. In this picture, we have already run some wires that we’ll describe in the next section.

This approach required a cleat, see Figure 3, attached to the floor to support the plywood wall. To determine the location of the cleat, we held a small piece of plywood against the upper wall and marked the bottom of the compartment with blue tape where it landed when square.

Figure 3, This figure illustrates the lower cleat to support the plywood wall.

The cleat, made of 1-1/4″ by 1-1/4″ lumber, was built by drilling screw holes and countersinking them to allow some 1-1/4″ screws to reach well within the 5/8″ flooring. We also had to add a top cleat, made of the same material, on the right-hand side of this space. The upper cleat was attached to the rectangular aluminum framing using 1-1/4″ self-drilling screws. Finally, before the plywood wall went up, we needed to run a few electrical wires and rescue the Diet Coke.

Initial Wiring

As mentioned in a previous post, our RV is a 2016 Outdoor RV Blackstone 240 RKSB. The floorplan of this model is illustrated in Figure 4. Our new power center will be located in the left-hand side of the pass-through storage area in the upper right-hand corner of Figure 4. Our shore power outlet is located at the left rear of the trailer, while our circuit breaker panel is located just under the refrigerator in the lower left of the figure.

Figure 4, This is the layout of our RV, a 2016 ORV 240 RKSB.

120 Volt AC Wiring

The shore power electrical outlet is wired directly to the circuit breaker panel. However, in our design, the shore power connector must be wired to the inverter/charger, and then the inverter/charger is wired to the circuit breaker panel. We ran Southwire 6/3 Romex from the circuit breaker panel area to the power center to accommodate this need. This line will carry the 50 A shore power to the inverter/charger. We then ran a second piece of 6/3 Romex from the power center back to the circuit panel area. This wire will carry inverter/charger output to the circuit breaker panel to energize our appliances.

Many discussions in RV forums berate Romex because it shouldn’t be used in high vibration environments like RVs and boats. However, Southwire Romex larger than 10 AWG uses stranded wire for three conductors and a solid ground wire. Therefore, we used Romex instead of running a PVC conduit and pulling eight strands of 6 AWG THHN wire through it.

We intended to run this wire ourselves, but it was a task I was not looking forward to. However, our local RV center, where we purchased our trailer several years ago, was willing to run the Romex for a few hundred dollars. That was a deal we couldn’t pass up. They ran the wire neatly and securely and left extra wire coiled behind the circuit breaker panel and in our power center.

Solar PV Wiring

The original solar setup on our trailer was a single 150 W panel on the roof. The installer fed the PV cables through the roof and into an upper cabinet in the bedroom. An inexpensive PWM solar charge controller was installed in that cabinet and then wired down through the trailer cap to the a-frame-mounted batteries.

Soon after purchasing the trailer, we upgraded this setup by replacing the single 150 W panel with three 200 W panels and the PWM controller with an MPPT controller. This upgrade used the existing wiring, and the new controller remained in the bedroom closet. This work aims to improve all aspects of our solar setup and get the solar charge controller out of our cupboard.

We ran new 10 AWG PV cables from the roof through the portal and into the trailer attic near the front of the trailer. Next, we routed the PV cables behind the trailer cap and into our power center. Unfortunately, we purchased 20′ lines with MC4 connectors on each end. We intended to cut the connectors off of one end and fish the cable to its destination. However, we inadvertently cut off the wrong connectors and ended up having to install our own. We should have purchased cable and installed MC4 connectors after they were in place.

Battery and House Wiring

Eventually, as described in our previous post, we will move our battery bank and will need to provide 12 V from our power center to the rest of our trailer. For now, the batteries remain on the a-frame and feed the rest of the trailer from there. Therefore, we need to tap into the existing 12 V and ground line so our new solar charge controller can charge the batteries. Our completed project will eliminate the lines to the batteries.

Figure 6, Power and ground distribution travel through this space from the battery bank to the trailer.

On the underside of the subfloor near the a-frame of our trailer, we found several auto reset circuit breakers. The breaker illustrated in Figure 6 has a direct connection to the positive terminal of our batteries. The positive terminal of our batteries and the trailer emergency brake are attached to the shown stud. We attached a 6 AWG THHN wire with a lug to that terminal and fished the wire into our power center.

Figure 7, We used a Morris connector to connect a ground wire from the existing ground to our power center.

A ground wire also travels through this area from the negative terminal of our batteries and into the trailer. We obtained ground by cutting the ground wire that travels through this space and connected both ends and a new 6 AWG THHN wire with a 3 position Morris connector, illustrated in Figure 7. These connectors are amazing and easy to use. Finally, we fished the new ground wire into our power center.

After the 120 V AC, solar PV, and 12 V DC wiring were complete, we installed the plywood walls. With this done, the power center is ready for the addition of components. The empty power center can be seen in Figure 8.

Figure 8, The empty power center is illustrated with 120 V AC, 12 V DC, and solar PV wiring in place.

Solar Additions

On the roof of our trailer, we installed a fourth 200 W solar panel, as illustrated in Figure 9. We couldn’t obtain another panel identical to the three we had, so we chose a panel with similar voltage characteristics and a current capability that slightly surpassed our existing panels. This panel will not constrain our system or be significantly limited by our existing panels; it should be a good match.

Figure 9, A fourth 200 W solar panel was added to the roof and connected in series to the existing panels.

Before celebrating the installation of our new panel or our wire routing prowess, we measured a voltage of 60 V across the PV cables. The addition of the fourth panel increased the PV voltage to approximately 80 V; success!

We connected the PV cables to a disconnect switch/circuit breaker mounted in a DIN breaker box in our power center. Next, we used a couple of short lengths of PV cable to run from the breaker box to our Victron SmartSolar 150-45 solar charge controller. Finally, we connected our 12 V DC lines to the solar charger, and we’re back in business. Figure 10 illustrates the result.

Figure 10, The completed power center with solar charge controller and PV disconnect switch installed.

The End Result

We’ve reached the end of another sub-project, and the trailer is once again ready to be used. We successfully created our power center space prepared to receive additional components. In addition, we routed all necessary power cables to this new space. Finally, we added a solar panel and upgraded our MPPT solar charge controller.

RV Power Center: Battery Bank Space

This is the third post of an ongoing series of articles documenting and describing our significant RV electrical upgrade. In our previous post, we discussed a potential need for an alternative design and presented its schematic. We also discussed a 3D model of our finished product, and we shared our results. In this post, we describe our battery bank design, discuss where we intend to place it, and the details of making space for it.

Battery Bank Design

Our first article of this series discussed our requirement for a 400 Ah battery bank to meet our electrical needs. However, our 400 Ah requirement assumed a 12 V system. We have since determined that we’d like to implement a 24 V system that reduces our Ah requirement. To enhance clarity, we should discuss our needs in terms of Watt-hours (Wh). A 12 V system capable of delivering 400 Ah is a 4,800 Wh system. A 4,800 Wh 24 V system delivers 200 Ah. We need a battery bank design for both a 12 V and a 24 V system until we determine whether or not Victron will produce a 24 V version of their MultiPlus-II 2x 120V inverter/charger.

Whether we implement a 24 V or 12 V system, we intend to use four Lion Energy UT 1200 lithium-ion batteries to implement our battery bank. We would use their newer UT 1300 batteries, but we already own two of the UT 1200s and found two used UT 1200s for less than half the price of new units. The UT 1200s are rated at 1,152 Wh, while the UT 1300s are rated at 1,344 Wh. So while our goal was 4,800 Wh, we’ll settle for the 4,608 delivered by our four UT 1200s.

24 Volt Battery Bank

We will connect two UT 1200 batteries in series to create a 24 V set. This set can deliver 2,304 Wh, which is well below our goal. Two of these sets can be connected in parallel to yield our desired 24 V battery bank, providing 4,608 Wh. Figure 1 illustrates this configuration. This implementation also adds redundancy in case a battery fails while in the field.

Figure 1, This is a 24 V series-parallel battery bank configuration built using four 12 V Lion Energy UT 1200 batteries. The fuse holder on the left of the figure will hold a 300 A Class T fuse.

Because wire resistance is nonnegligible in these types of systems, it is essential that the circuit length from the positive terminal of any battery, through the load, and back to the negative terminal of the same battery be equal for all batteries in the bank. In practice, this means that the connecting wires between batteries should be of equal length, and the positive and negative connections to the load should be from opposite ends of the battery bank. For example, Figure 1 shows that the positive connection comes from the upper bank, while the negative connection comes from the lower bank.

According to a comprehensive document published by Victron Energy called Wiring Unlimited, an alternative configuration includes a connection between the midpoints of both sets. This configuration is illustrated in Figure 2.

Figure 2, This is a 24 V series-parallel battery bank configuration built using four 12 V Lion Energy UT 1200 batteries and includes a midpoint connection. The fuse holder on the left of the figure will hold a 300 A Class T fuse.

According to the Wiring Unlimited document, this approach requires midpoint monitoring to detect deviations in voltage between the upper and lower batteries. In addition, when deviations are detected and reported, they must be acted on to deal with potential issues. Batteries in the battery bank may be damaged if reported problems are not resolved. Monitoring the midpoint has the advantage of detecting these issues that might otherwise go unnoticed. The Victron SmartShunt, which we intend to use in our system, can monitor midpoint voltages and raise alarms when problems arise.

12 Volt Battery Bank

Alternatively, four UT 1200 batteries can be connected in parallel to yield a 12 V battery bank, delivering the same 4,608 Wh. This configuration also adds more redundancy in case a battery fails while in the field. The obvious configuration to accomplish this is shown in Figure 3.

Figure 3, This is a 12 V parallel battery bank configuration built using four 12 V Lion Energy UT 1200 batteries. The fuse holder on the left of the figure will hold a 400 A Class T fuse.

Notice in Figure 3 that the positive connection comes from the upper left battery in the bank, and the negative connection comes from the upper right or the last battery in the bank.

In a 12 V system, the currents are double those of a 24 V system. These higher currents demand a 400 A Class T fuse and wire with double the cross-sectional area of wire used in a similar 24 V system.

A cleaner wiring layout that still respects the principle of keeping circuit lengths equivalent is illustrated in Figure 4.

Figure 4, This is a 12 V parallel battery bank configuration built using four 12 V Lion Energy UT 1200 batteries. This layout uses the halfway approach of keeping circuit lengths equivalent. The fuse holder on the left of the figure will hold a 400 A Class T fuse.

In the hopes of reducing system currents, voltage drops, and associated ripple, we desire to create a 24 V system. However, if this is impossible due to the lack of availability of an appropriate inverter/charger, the 12 V layout, illustrated in Figure 4, will be used.

Battery Bank Placement

Our RV is a 2016 Outdoor RV Blackstone 240 RKSB. The floorplan of this model is illustrated in Figure 5. Our new Power Center will be located in the left-hand side of the pass-through storage area that is accessed by an exterior door located in the upper right-hand corner of Figure 5. Batteries should be located as close as possible to their associated invert/charger to reduce voltage drops that may occur over long cables. To keep the cables short but still leave storage areas available for their intended purpose, our battery bank will be located under the foot of the bed.

Figure 5, This is the layout of our RV, a 2016 ORV 240 RKSB.

In our last post, we determined that space between the drawers was available for our battery bank. This open space was found during our modeling efforts and is illustrated in Figure 6.

Figure 6, The space between the drawers is sufficient for four Lion Energy UT 1200 batteries.

The UT 1200 batteries measure 10.2″ long, 8.8″ tall, and 6.6″ wide. We started demolition to determine the best way to orient these batteries within the available space. We knew from our previous inspections that two cross beams were holding up the false floor of the storage area above the drawers. We removed the drawers and, using a jigsaw, removed the portion of the false floor between the beams. This roughed-out hole and the exposed space are shown in Figure 7.

Figure 7, This is the rough cut opening that exposed the space we intend to use for our battery bank.

While the drawers are only 17″ from front to back, the glides they’re on are 18″ long. The distance between the backs of one set of glides and the other is insufficient for two side-by-side batteries to sit between them. Unfortunately, 17″ drawer glides are unavailable, and the next size down is 16″.

The lack of space necessitated converting one of our drawers to 16″ glides and adjusting the drawer to match. After removing the glide supports and drawer glides, we constructed a new and more robust support structure shown in Figure 8.

Figure 8, This is the drawer space with a new support structure and drawer glides in place.

We acquired and installed new 16″ drawer glides. In addition, we disassembled the associated drawer, cut 1″ off the sides and bottom, and reassembled it better than new.

The remaining space between the backs of both drawers is now more than sufficient to hold two UT 1200’s side by side. The distance from right to left in Figure 8 is also more than enough to hold two UT 1200s longwise. There is also enough space for the fuse holder that needs to be located near the battery bank.

Figure 9 shows the battery bank space with two UT 1200s in place between the installed cleats.

To assist in holding the batteries firmly in place, we added two cleats to the floor spaced to allow the batteries to sit side by side with little to no room to spare. The cleats and batteries can be seen in Figure 9. Also, notice in Figure 9 that the roughed-out access hole has been cleaned up using a round-over bit in our router, some chisel work, and a bit of sanding.

To restore the utility of the storage space used to provide access to the batteries, we drilled finger holes in the remaining false floor. We also added another false bottom over the top of what can be seen in Figure 9. This can be seen in Figures 10 and 11.

Figure 10, Finger holes were added to the existing false floor to facilitate the removal of the new false floor.
Figure 11 shows that the new false floor restores the storage area while protecting the hidden battery bank.

The End Result

In the spirit of making incremental progress and leaving the trailer functional for camping, we’ve reached the end of this sub-project. We successfully created an excellent space for our battery bank that will work for either a 24 V or a 12 V system. The only negative impact of this sub-project was one drawer is now an inch shorter. In future posts, we’ll install the batteries, wire them together, create a small shelf for the fuse holder, and wire the battery bank to the battery disconnect switch and the SmartShunt.

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