Wednesday, December 3, 2008

Installing the Batmon Resistors

In order to shunt current around each fully charged battery, the BatMon boards use an external 3 ohm resistor. Since mounting these resistors involves drilling holes in metal, I wanted to mount them before mounting the BatMon boards to prevent metal shavings from sprinkling into the electronics.

Here are two pictures in the rear trunk showing the drilled holes for the resistor mounting bolts. The BatMon resistors have mounting holes 2" apart that take 10-24 bolts. The Belktronix instructions suggest drilling holes and then tapping them with threads to support the bolts. Since I had a pile of 10-24 rivnuts and rivnut tool from a prior EV project, I decided to use them instead. The top picture shows two holes just over the large red battery post cover. The bottom picture has two holes in the upper left and two holes over the wingnut in the right side of the picture. Each set of two holes will hold two resistors stacked on top of each other.

Here is a view in the engine compartment where the 12V car battery used to be. I drilled four holes here to mount two pairs of resistors.

After drilling the holes, I used the rivnut tool (in the foreground with red handles) to press in four 10-24 threaded rivnuts.

In order to mount the resistors for the two front batteries (just behind the radiator grille), I had to unbolt the large piece of plastic holding up the charger and controller. With this raised, I could squeeze in the drill to produce the two holes on the inside vertical wall just behind the radiator grille. I'll try to note in the open-source instructions that these holes should be drilled BEFORE mounting the plastic and components. I guess hindsight is 20/20...

With the holes drilled and rivnuts installed, I then used 10-24 bolts 1 1/2" long with lock washers to bolt in each pair of resistors.

Here are the mounted pairs of resitors in the trunk. These resistors have fast-on connectors that will attach to each BatMon board.

Since the resistors get quite hot, I've been informed (thanks to Bob K.) to use bare fast-on connectors with heat-shrink tubing around them instead of the fast-on connectors with a plastic covering. The plastic covering tends to melt or burn, causing a mess.

No comments: