Volt Meter for RV Direct Reading Battery Monitoring By Minnesota Fergie Since buying a camper trailer last year, like a lot of other RV newbie s, I have learned that unless you are an RV/Boat mechanic or already an expert in the Cield, RV, golf cart, boating or solar power battery care is a much different affair than that we are used to with our cars, SUV's and trucks. Typically RV's, golf carts, boats and solar power installations use "marine" or deep charge batteries to run on-board or household electrical equipment for long periods between charges that are designed for this type of use. They are different than the lead-acid batteries that we use with our modern internal combustion engines that require very high currents for a very short time to start them. Lead-acid vehicle batteries dispense bursts of high current and then start being recharged as soon as the engine is running and have characteristics that support this type of use. Since buying our RV, I have read dozens of entries in the user blog of our T@B teardrop trailer and viewed many YouTube videos on this topic. They cover charging the battery in storage or in use by solar, generator, TV (tow vehicle) or charger plugged into "shore power" (regular electric at home or campground). They also covered the effects of discharging on battery life when "boon docking" (camping not connected to either the TV or campground electricity), parked in the driveway and other scenarios. In all of these situations an important piece of information is the voltage at the battery. While this voltage doesn't provide the Cinal word on how much energy is left, it is an important indicator of the state of charge. For most 12volt RV marine type batteries, experts say it shouldn't get down much below 12.0 volts without being recharged to prolong battery life. That exact voltage depends on the type and make of battery. Research and read your models' specicications for your exact number and its relation to battery life. There are also sophisticated battery management systems such as the TriMetric TM-2030 you can install that measure energy (amp - hours) in and out of your battery and tell you 1
how much more you can safely use before needing to recharge. However, they are quite expensive and can be more challenging to route the needed wires in your rig. Generally these seem to be used by RV's who do a lot of "boon docking" and who use solar panels to recharge their batteries. Of course household solar installations already have sophisticated control systems. Since we mostly stay at campsites with electrical hook-ups, what we needed was a simple voltmeter permanently mounted near the battery with a switch to connect it for a reading. In addition I wanted it connected on the "hot" side of my main battery disconnect switch so I could read the voltage when nothing else was connected to it. Also I wanted a direct connection to the battery terminals with relatively short leads to eliminate any IR voltage drop due to load current under various use conditions, as might be the case if the voltage were monitored inside the camper. The following describes my project to build and install such a meter on my 2015 T@B S Max Teardrop RV Trailer built by Pleasant Valley Manufacturing in Ohio. I hope it inspires you to build one for your RV, boat, golf cart or as an auxiliary unit for your solar house! 2
Comments on Material Sources The heart of the project of course is the meter unit itself. Drok makes a whole line of inexpensive d.c. voltmeters of different sizes with different voltage ranges, case and display colors. I picked this one for the voltage and size of my application. It is available through Amazon. The lighted Uriah 12 volt switch was purchased in the auto section of a local hardware store. The Hammond plastic project box was also ordered though Amazon as my old standby, Radio Shack, doesn't have a store in my town anymore. All the rest of the connectors, wire, black silicon sealer, grommets, cable cover and screws were purchased in the electrical and hardware departments of our local home improvement store, but probably could be ordered online. A basic wire stripping tool with a crimper is needed for the automotive type solder-less connectors. Bill of Materials Drok 0.56 3-30 volt d.c. meter with 3 digit w/green LED display https://www.amazon.com/gp/product/b00c2ntjhs/ref=oh_aui_detailpage_o02_s00? ie=utf8&psc=1 Uriah 12 volt Automotive Style Lighted Red Rocker Switch Hammond 1591BSBK ABS 4.4 X 2.4 X 1.1 Plastic Project Box w/cover and screws https://www.amazon.com/gp/product/b0002bbqua/ref=oh_aui_detailpage_o00_s00? ie=utf8&psc=1 Black and White #16 Stranded Auto Hookup Wire (length to match installation situation) Crimp-type electrical wire connectors: battery post, slide-on and butt connection types Plastic wire clips w/adhesive backs, tube of automotive type black silicon sealer 1/4 Rubber Grommet for exit hole for hookup wires 3/8 Flex Tubing for protecting hookup wires (length to match installation) 3
Wiring Diagram (Excuse the primitive diagram; it is what I used to keep my wiring straight!) The lighted switch is a SPDT model. The light is connected between the central terminal and one of the poles which has to be connected to ground. The +12v. supply is connected to the other pole so that when the switch is thrown to that side the + 12 v. and ground are across the switch light and also to the meter as shown in the above diagram. On this switch model there was a little diagram showing this on the back of the switch. If you don t want a lighted switch you could use a SPST switch between the +12 volt line to the battery and the meter, but you still have to route the ground connection to the meter from the battery. I chose to have the light to remind me the meter was still connected in bright light conditions, although the display is quite bright itself. Comments on Component Mounting and Wiring Cutting the hole for the meter in the project box is probably the hardest part of this project. For both appearance and weather protection I used the back of the box as the top and the cover as the back. I used the meter itself to scribe a hole pattern on the top of the box. I then drilled holes in each corner just touching the scribe lines and then more inside until I could punch out the center. I then Cinished the rectangular hole with a Cile. The meter just Cit, but didn t snap in as I had expected and was a bit loose. I then turned the box over with the meter in place and put a bead of black silicon around the meter inside the box and left it overnight. The next day I put another bead in to make sure it was moisture sealed all around and let that cure also. This seemed to secure the meter to box very well and made it moisture proof. The hole for the switch on the side of the box was drilled with no problems. I bent the tab type contact on each pole out to facilitate putting on the slide-on automotive type connectors as shown in the pictures below. As can be seen, the adhesive backed plastic clips 4
were very useful in securing the routed wiring in the box. The Cinal steps were to drill the outlet hole for the leads to the battery in the cover (now the back ) and put the rubber grommet in the hole to protect the leads from the sharp edges of the drilled hole. The Cinal steps were to thread the leads through the hole in the cover, screw the cover to the box with the screws that came with it and crimp on the battery terminal connectors to the ends of the leads and then put the Clex tubing on to contain and protect the leads. If I were to do it again, I would "irst slide the leads into the Clex tubing and then crimp the battery terminal connecters which would be much easier. Pictures of The Wiring The Finished Meter 5
Meter Installation Every situation is different, but in our T@B Teardrop Camper Trailer I decide to install it on the inside top of the housing in the front of the trailer that houses the propane tank and the battery on the side nearest the battery. The battery cutoff switch I previously installed is near there also. With the housing cover down and locked the meter is fairly well protected. I drilled three holes in the top inside edge of the housing and then used self tapping stainless steel screws to secure the box to the housing as can be seen from the pictures below. I then attached the leads to the battery as shown below and the installation was complete. By installing it there it is very handy and I didn t have to Cigure out a way to neatly and securely route the battery leads inside the trailer. Pictures of the Installed Meter Final Comments With the main battery disconnect switch OFF I can measure the no-load voltage at the battery. With it ON I can measure the voltage at the battery under any electrical system condition regardless of any voltage drops to the loads in the trailer. Both the meter and the light in the switch use less than 100ma of current and, since connected directly to the 6
battery by about 1 foot of #16 wire at each terminal, any voltage drop due to them is negligible and certainly out of the accuracy range of the meter. It was a fun electrical project that anyone can do. It brought back my younger days in early Hi-Fi and "Ham" radio many years ago when I built my own equipment. Besides looking sharp and professional, the meter is handy, protected from the elements by the propane/ battery chest cover, has a lighted switch to remind me when it is on and takes up very little space. This basic meter and its components can be adapted to almost any battery situation on an RV, golf cart, boat or even at the battery site of a solar power installation to supplement meters on control panels that may be remote from the battery. Shielding from the elements would be the biggest challenge for a boat I would imagine, but then innovation is part of the fun of any project! 7