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Project "Build A Solar Battery Bank Monitor"
The purpose of this project is to demonstrate how to build a battery bank monitor from individual components.

In a solar charging and use application, the battery bank accepts power from solar panels and also provides power to items that you have connected to it. In larger solar arrays, a charge controller/regulator (charges the battery bank) may be able to display the current amount of voltage in a battery bank. This is great if you want to have an overall idea of how much voltage is in your battery bank. Unfortunately most do not report individual battery voltage states.

Significance of the Solar Battery Bank Monitor
The advantage of the solar battery bank monitor (versus charge regulators/controllers that display voltage of a battery bank) is that it reports the voltage status of each individual battery in a battery bank. This capability is invaluable because you can quickly identify which battery(s) are losing the ability to hold proper charge; likewise you can quickly identify which battery(s) may be holding too much charge.

In either case, you can replace individual batteries in the battery bank before they prematurally cause other batteries in your battery bank to become defective. In the long term you will undoubtedly save money by being able to monitor the status of individual batteries in a battery bank. If you are interested in calculating the size of a battery bank and solar array based on the number of devices to power, check out the solar calculators.

Let's Make A Solar Battery Bank Monitor
The solar battery bank monitor that will be focused on here is that which contains 12VDC batteries. After construction and integration (since I do not know how far away from the battery bank the monitor will be present at), keep in mind that the length of wire will reduce voltage detection due to resistance of the wire. In this case, you may want to write down the detected voltage of each good battery at the monitor so that you know what a good voltage level is.


  1. Create slots on one side of the 11 x 9 x 3 inch box; the female ends of the Deans 2-Pin Ultra Plugs to be seated and glued in.
  2. Place 1/4 inch acrylic cubes around the perimeter of the acrylic sheet so that when the acrylic sheet is placed over the box, one edge of each cube is in close proximity to the inner wall of the clear box.

  1. Glue the Mini Fuse Style fuse blocks to the opposite side of the box.

  1. Cut off the two plastic snap-clips from the digital voltmeter.

  1. Remove the faceplate from the digital voltmeter.
  2. Apply silicon sealant around the perimeter of the colored, transparent plastic plate and allow it to dry. This will prevent the epoxy from leaking around it.
  3. Reattach the faceplate to the digital voltmeter.

  1. Take a 10 inch strip of packaging tape and stick it to the perimeter of the digital voltmeter. Ensure that it is applied properly so that the epoxy does not leak out.
  2. NOTE: The reason why epoxy is used is to create a seal over the meter's electronic components to help reduce the likelihood of the components degrading prematurally due to moisture, dirt, battery acid fumes (if not using AGM), and so forth.

  1. Mix a portion of the 1:1 epoxy so that you have enough to fill approximately 60% of the volume created by the tape and then pour into that area.
  2. As the epoxy fills in areas of the digital voltmeter you may need to add more to ensure that the electrical components of the digital voltmeter remain covered.

  1. After the epoxy has dried (approximately 24 hours), remove the tape. You will notice that the epoxy has dried into the form created by the tape.

  1. After you've completed with all digital voltmeters, glue each one onto the acrylic sheet.
  2. Be sure to also glue a reed switch below each digital voltmeter and solder wiring as shown.

  1. Solder the positive wire (red) of the reed switch to the blade of the Mini Style fuse block.
  2. Solder a positive wire (red) on the corresponding opposite side of the Mini Style fuse block and solder the other end to the to the positive blade of the Dean 2-Pin Ultra Plug (female).
  3. Solder the negative wire from the digital voltmeter (black) to the negative blade of the Dean 2-Pin Ultra Plug (female).

  1. Since reed switches are being used in place of traditional switches, we need a way to close the contacts of the reed switch. This is accomplished by using a small magnet.
  2. Glue four 1/4 inch acrylic cubes together as shown.
  3. Drill a hole into the center acrylic cube, place silicon sealant into the hole and slip the small magnet inside so that the exposed end of the magnet is flush with the surface of the acrylic cube.

  1. At the top of the clear box, glue a small magnet to the inside and two 1/4 inch acrylic cubes on the outer surface. This is to provide an area for the reed actuator (previous step) to be placed when not in use.

  1. This photo illustrates the placement of the reed actuator so you can see how the two cubes seat the reed actuator and the small magnet inside of the clear box is attracted to the magnet in the reed actuator so that the reed actuator does not move.

  1. This photo illustrates the advantage of the clear box in relationship to the fuse blocks and fuses it contains. Each of the fuses illuminates when it is burnt out; by being able to glance into the clear box you can identify which fuse(s) may be burnt out in order to replace them.

  1. After looking at the front of our solar battery bank monitor, all of the glue adhering the digital voltmeters to the acrylic sheet is visible and may be distractive.
  2. In order to fix this visual "blemish", you can paint borders around each digital voltmeter that will cover that up. It will also provide a solid colored background for writing (which will make the writing easier to see).

  1. With the borders applied and allowed to dry, each digital voltmeter is marked sequentially from 1 to 12. You should also mark each Dean 2-Pin Ultra Plug female plug with the same number as the corresponding digital voltmeter.

  1. Congratulations, the solar battery bank monitor is complete!
  2. In this photo we see that the reed actuator is placed over the reed switch of the first digital voltmeter (closing the circuit) and we see a digital read-out of the voltage of a single battery (in this case, a 9 volt battery for testing).
  3. The voltmeters, in use, are connected to 12VDC @ 100Ah batteries (weighing approximately 70 pounds each) and have operated fine (as you can imagine, the 70 pound batteries are considerably larger than the 9 volt hand-held battery used for testing).

Example of Connecting Meters to Batteries
Usually a battery bank consists of one or more rows of batteries connected together so that each battery in a row is connected in series, while the rows are connected together in parallel. The example below shows (although small battery bank) how to connect meters to batteries in order to get a reading for each battery. If you just have some batteries connected in parallel instead of series, it is not likely you would be able to get an individual voltage reading for each battery. To extend the life of the voltmeter you would probably want to add a switch to it and a small fuse (not pictured in this simple example since the project, above, uses reed switches and fuses); this way the voltmeter is not on all of the time and can last longer by switching it on when you want to get a reading.

Example Schematic Connecting Meters to Batteries in a Battery Bank

Project Materials
[1] #1477 11 x 9 x 3 inch Clear Box
[1] 11 x 9 x .125 inch clear acrylic sheet
[1] #300/11 Clear Amber AeroMarine Epoxy (2 quarts - approximately 1 quart is used in this project)
[1] 60/40 Rosin Core Solder
[2] 22-18 Gauge Insulated Crimp-On Butt Connector (16-Pack)
[2] #47087 Mini Fuse Style 6 Fuse, Fuse Block
[12] #46260 3Amp Violet, 12Vdc Led Blade Mini Fuse Type
[12] #808-0019 High Voltage, High Power Reed Switch
[12] #WSDM1300 Deans 2-Pin Ultra Plug (male and female)
[12] Blue LCD Digital Voltmeter 7.5V- 20V SKU: BP26

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