A little sideline
As a follow up to my post on solar panel installation, here's a little piece on my build of a remote current monitor for those panels.
Initially prompted by some concerns about whether my new solar panels were working as expected, I hatched a plan to install a remote power monitor on the main power board in the saloon. Unable to locate appropriate shunts (at least for a reasonable price) this became a project to make and calibrate my own shunts and to then modify off-the-shelf ammeters to display the required information. Since my solar system is divided into two parallel, slightly differently powered, arrays, this led to two independent monitors.
Each of my two shunts consist of about 65 lengths of nickel/chrome resistance wire, each 3cm long, with an advertised resistance of 13.77 ohms per metre. I squeezed each of those lengths of wire through the tube formed by backing two yellow crimping terminal fittings against each other. I found I could calibrate the shunts quite effectively by adding or subtracting single lengths of wire one at a time. Having done so, I didn't crimp or solder the wires into place, for fear of upsetting their characteristic resistance. In any case, 65 pieces of wire proved to be more than a snug fit and didn't show any sign of dislodging.
In the photo, below, you can see that I've taped the terminal fittings together, but this was only to assist in the general assembly. Some of the individual wire lengths are visible sticking out from each end of the shunts.
Having wired these assemblies into the cables running to the batteries, I began work on the two ammeters required for the job. I began with a pair of 1 milliamp ammeters, for which the shunts had been calibrated to show full deflection at 20 amp of current flowing into the batteries. I removed the face plate from the meters and scanned their dials into a graphics package. With that as a guide I created new face plates displaying the required 0 - 20 amps. Together with the name of the boat and a label indicating the particular solar panel array being monitored, I printed new face plates onto glossy photographic paper and then reassembled them onto the ammeters. When all wired up, the new meters look really quite nice and now give me continuous information on the current being generated by each solar panel array.
