Of note to fellow builders: The Kavlico sensor IS NOT a direct replacement for the VDO sensor … in that the Kavlico sensor requires +5 volts to operate. Newer RV-12 kits shipped with the Kavlico sender have the +5 volt wire. Older RV-12’s converting to the new Kavlico sender require an additional +5 wire to the sender, …this voltage can be obtained from the same source as the +5 volts for the manifold pressure module.
The Kavlico fuel pressure sensor is on the right in this photo. There is socket in the top of the sender that receives a molded plug which has three wires connected to it. The three wires are: red (+5volts), green (signal out from sensor) and black (ground) .
Some have experienced issues with the new Kavlico sensor’s readings fluctuating … fortunately there is an easy fix. Dynon support believes this is from electrical “noise” on the green signal wire and suggests placing a 330 microfarad capacitor rated at 25 volts from the green signal wire to ground. To my knowledge, the additional capacitor has fixed the issue of fluctuating readings for all who have installed it. Some builders have had a hard time locating a 330 uF capacitor and have used 470 uF capacitors instead with good success. Because the DOG Aviation RV-12 is being built as experimental – amateur built, a 330 uF capacitor will be installed now as a preemptive strike. Below is a wiring diagram I made to show how the capacitor is installed.
This diagram shows how the 330 uF capacitor is to be wired to the Kavlico fuel pressure sensor.
The plan is to install the capacitor at the butt splices a few inches from the sender. It is a good location because there are splices here anyway and feel it is better than installing the capacitor on the aft side of the firewall which would require cutting the wires and adding additional splices. However, the engine compartment is a warm environment so the DOG Aviation procurement department took that fact into consideration when choosing which capacitor to purchase.
Friends who know me well, know I have a propensity to over kill a bit at times and this just may be yet another example …as not all 330 uF electrolytic capacitors are created equal. Knowing the max temperature rating of an electrolytic capacitor is typically around 85 degrees C (which equates to 185 degrees Fahrenheit), I just could not let myself knowingly install a capacitor with a 185 degree max rating in an environment where the heat could potentially easily pass 185 degrees on hot summer days during ground operations. The 330 uF capacitor chosen is an automotive grade capacitor and has a temperature rating of 150 degrees C (which is 302 degrees Fahrenheit). The capacitor was ordered through Mouser electronics … which is a great source for some of the electrical parts used on the RV-12 such as connectors, connector pins, etc.
The Nichicon UBX1E331MHL is a 330 uF electrolytic capacitor rated at 25 volts with a maximum working temperature of 302 degrees F and was purchased through Mouser electronics for a couple of dollars.
Of note … electrolytic capacitors ARE polarity sensitive and care must be exercised when installing them to make sure the negative lead of the capacitor goes to ground. In some applications if they are not installed correctly, they can pop like a firecracker. Some electrolytic capacitors are marked quite well and others like the one in the above photo are not marked very well. Typically, for this style of capacitor, the longer of the two leads coming out of the case is the + lead and the shorter of the two is the – lead. Also, looking closely at the above photo, one can see there is a black box printed to one side of the capacitor, this denotes the – lead is on that side.
Three butt splices have been installed onto the wires from the plug for the Kalvico fuel pressure sensor. The positive lead from the capacitor will be inserted into the butt splice on the green signal wire and the negative lead on the capacitor will be inserted into the butt splice for the black ground wire.
I was hopeful that the leads on the capacitor would be long enough so the capacitor could be heat shrunk on top of the butt splices but unfortunately they are not. So as can be seen in previous photo, the capacitor was covered with a bit of heat shrink to insulate the “can” and prevent chafing of the wires passing by the capacitor. Once crimped to the butt splices, two sizes of heat shrink were used to cover the capacitor, wires and butt splices.
The 330 uF capacitor is now crimped to the butt splices along with the red, green and black wires coming from the firewall forward connector. The positive terminal from the capacitor is attached to the green signal wire and the negative lead on the capacitor is attached to the black ground wire.
The grounding for the Kavlico sensor was to also be modified a bit, in that the black ground wire was to go directly to the ground block on the firewall. However, this did not happen as my efforts to make good connections without messing up the capacitor's polarities distracted me enough that I forgot to crimp to the ground wire going to the ground block on the firewall … instead I ended up using the original black wire that is part of the three wire twisted bundle. Discovered this after all the connections were crimped and the heat shrinking finished. Oh well, not a big deal and certainly not worth the effort to tear back into the butt splices.