RV Power Center: Performance

This is the tenth and last post describing our RV power system. Our previous post described the final design and some of its characteristics. This post summarizes the system’s performance on our first overnight outing. First, for convenience, we briefly describe the final system. Next, we describe our outing and associated conditions and finally explain the system’s performance.

Final System

Our power system fits within the left pass-through storage area, illustrated in Figure 1.

Figure 1 illustrates our complete power center providing 800 W of solar, 360 Ah of Lithium-ion batteries, and a 3kVA invert/charger.

Figure 1 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 360 Ah 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.

Our Outing – Red Canyon, Utah

We spent two nights in Red Canyon Campground in southern Utah in late April. This outing is described in more detail in another post. The daytime temperatures were in the mid-60s, and the lows were in the low-20s. The sun was bright the first day. We had a couple of hours of good sunlight on the second day and then overcast with rain.

Performance

With the nighttime temperatures in the 20s, our furnace periodically ran to keep the trailer at approximately 65 degrees. In addition, we watched television for several hours at night, used lights, and charged a couple of phones, watches, and an iPad. With all of these devices running and charging, we consumed nearly 80 Ah of our 360 Ah battery bank. Our batteries were replenished after just a few hours of good sunlight.

Early in the day, the solar charging system produced about 360 W. I decided to check the cleanliness of the solar panels and was shocked to find them coated in mud. It was thick enough that I could not remove it without a significant amount of water. After cleaning the panels, the system produced just over 500 W. A little water and elbow grease pay off.

Figure 2, our electric fireplace.

After a 5 mile hike, we returned to find our RV an uncomfortable 81 degrees. We flipped on the AC and set the thermostat to 75. The AC drew a constant 1100 W and ran for approximately 30 minutes. Later that evening, the temperature in the RV dipped down to about 68 while we were still up and around, so we turned on the electric fireplace. That unit drew nearly 1400 W but warmed us right up. We tried a few other electric devices to see the practicality. The refrigerator on electric power drew about 22 A, my wife’s curling iron was no big deal at 200 W, and I’ve tried the microwave before at just over 1000 W.

It is a pleasure to use all of our systems without generating noise. We can use the AC, microwave, and TV after campground quiet hours without worrying about bothering others. However, it is funny watching us adapt to this new world. Are we content toasting our bread in the broiler? Of course not; we need a toaster because we can have one! I am sure we’ll add a hairdryer and who knows what else. Nevertheless, I am pleased with the outcome and the comfort it has added to our lives.

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!

Electrical Power for Astrophotography

Introduction

Telescopes that slew to, and track celestial objects do so through the use of electric motors that drive their axes of rotation. Portable telescopes, like the Celestron CPC 1100 GPS, depend on either alternating current (AC) line voltage or batteries for their power. In addition, camera coolers, dew heaters and other accessories require power. The remainder of this post describes power requirements of typical astrophotography equipment and the construction of a do-it-yourself (DIY) portable power supply.

Astrophotography Equipment

The equipment I use includes a telescope, camera and dew heaters:

This equipment and their power requirements are listed in the following table.

EquipmentMake and ModelOperating VoltageReported Current
TelescopeCelestron CPC 1100 GPS12 V1.5 A
CameraZWO ASI071MC Pro12 V3 A
Dew HeaterDew-Not DN01212 V1.57 A
Dew HeaterDew-Not DN00312 V350 mA
Dew Heater ControllerThousand Oaks Four-Channel12 VNegligible
Total6.42 A

The reported values were obtained from vendor web sites, while the measured values were observed during operation. The total required current has a maximum value of 6.42 Amperes. The remainder of this post will describe the construction of a DIY power supply to meet these needs.

Power Supply

This section describes the construction of a portable power supply that meets the needs of my astrophotography equipment. This system must be portable and supply 12 Volts at just over 6 Amperes for 4-5 hours. We’ll first list the items needed and then dive into the simple construction.

Tools and Parts

This project is very straightforward and requires very few tools and a handful, a heavy handful, of parts. You’ll need a 1.25 inch hole saw or drill bit, a couple of wrenches, and scissors or a utility knife. In addition to these tools you’ll need the following items or appropriate substitutes:

Construction

Lets start with the green utility box pictured to the right. Remove the inside dividers and then drill two holes in one of the ends. These 1.25″ holes will enable the mounting of the 12 Volt receptacles and can be placed wherever you’d like them. Then install and securely tighten the receptacles in place.

The next step is to make a secure location for the battery to sit in the box. Place a 1/2″ layer of closed cell foam in the bottom of the utility box. Then add two 1″ thick blocks of foam to each end with just enough space between them to squeeze in the battery. Then add 1″ thick foam on both sides of the box to hold the battery firmly in place. In the image to the left you can easily see the indentation in the bottom of the box intended to accept the battery.

The cigarette lighter power sockets include simple wiring harnesses that enable them to be easily connected to a battery. Connect each harness to the battery with two 1″ x 1/4″ bolts with associated nuts and washers. The socket end of the harness simply plugs into the blades protruding from the power sockets. Make sure you tie the positive socket terminal to the positive side of the battery! Once this is done you simply tuck the wires neatly under the power sockets, slip the battery in place and latch the lid closed.

You now have a portable source of 12 Volt power. When the battery needs recharging, you simply open the lid and charge it.

Summary

In this post we outlined the need for 12 Volt power for remote astrophotography and presented a simple DIY power supply to meet the need.

 

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