Monday, February 29, 2016

Wiring – Doing Homework For Wiring Instillation & Modifications

A fair amount of time was spent the last couple of days prepping for the final push to put a big dent in the wiring chore. A punch list has been prepared by creating a list of action items that involve removing or installing connector pins and wiring for modifications such as additional switches for the fuel pump and left landing light, not to mention the Tosten grip switches.

One item I wanted to verify for myself was that all the grounds on the AV-50000A Control Module are common. The reason for this is because I want to ground the AV-50000A Control Module directly to the grounding block. Why? Because it will offer a good solid ground for the electrical system and should allow the Control Module to be unscrewed and tilted sideways to gain easier access for making adjustments to the trim motor speed and the multitude of audio level controls on the side of the case. However, Van’s warns about powering the system up with the Control Module unscrewed because it obtains it’s grounding though the mounting screws … but with a 14 gauge wire connected directly to the case of the Control Module, this will no longer be an issue if all the grounds are common to the case.

The electrical diagram was studied and all the grounds for every connector was identified. An Ohm meter and a couple of connector testing pins were used to first verify that the designated ground pins on ALL the connectors are common to one another. Glad to report, they are! Next a check was made to verify that without the mounting screws installed and the Control Module sitting on an insulated surface that the case of the Control Module is connected to the internal common ground. Glad to report, it is! … meaning, a 14 gauge ground wire connected directly to the case will allow the Control Module to be powered while unscrewed without damaging the unit or other components in the electrical system. So a 14 gauge ground wire was crimped onto a #6 ring connector and installed onto the case of the AV-50000A Control Module.
AV-50000A Control Module mounted along with the #14 ground wire that will be connected to the ground block on the firewall. This will offer solid grounding of the Control Module and allow the Control Module to be unscrewed and tilted to allow easier access to the adjustment potentiometers (that can be seen on the side and aft) with power applied to the unit.

A dilemma to solve is where to pick up the power for the left landing light. Those following the Blog on a regular basis know an additional left landing light was installed so the DOG Aviation RV-12 could have wig-wag lighting with no additional current penalty (since only one landing light is on at a time). However, because of the limited available power, felt it best to add a separate switch to control the left landing light’s steady on power … and only use it on short final so not to overtax the electrical system for extended periods of time. The steady on function of the landing light will draw between 2.4 to 2.8 amps depending on the battery’s voltage. Unfortunately, there are no spare fuse positions built into the RV-12’s electrical system. There is an unused “Extra” position on the AV-50001 Switch & Fuse Module that connects pin 14 of the connector on the back of the AV-50001 Switch & Fuse Module directly to the main power buss (without a fuse). An Ohm meter was used to verify pin 14 on the connector is connected internally to the main power buss ... it is. So at this point, I’m leaning towards using this location to obtain power for the left landing light’s steady on function. The current plan is to add a wire to pin 14 of the WH-00031 wire harness and run it directly to an inline fuse then over to the left landing light’s switch. This will insure there is fuse protection as close as possible to the AV-50001 Switch & Fuse Module.
A wire will be added to pin 14 of the connector on the WH-00031 wire harness that interfaces with the connector on the back of the AV-50001 Switch & Fuse Module to connect to the “Extra” circuit. A 3 or 4 amp inline fuse will be installed on the “Extra” power wire coming from pin 14 because there is NO internal fuse for this circuit inside the AV-50001 Switch & Fuse Module.

A wrench in the gears. After purchasing the inline fuse block, the electrical drawings were given closer scrutiny … noticed what I hope is a miss-print. The Van’s electrical schematic drawings show the builder the maximum amperage connector pins or circuit traces can handle. I did not notice it at first, but every place the “extra” lead is designated it is rated for 5 amps … that is except at one location inside the AV-50001 Switch & Fuse Module. There are two circuit boards inside the AV-50001 Switch & Fuse Module and the designation for the one that has the fuses on it shows a 2 amp limit for the trace named “Extra”. Yet from that point on, everything else shows 5 amps, so I’m hoping this is a misprint. To get a better visual, the back plate was removed from the AV-50001 Switch & Fuse Module and examination of the circuit board reveled the width of the “Extra” trace on the circuit board going to the connector is seemingly approximately the same as the other 5 amp circuits. At this point in time, based on what I saw, I’m feeling the 2 amp limit is a misprint … unless Van's has reduced the current rating arbitrarily because the circuit is unfused. Will place a call to Vans for clarification. I could not see all of the trace, but based on what I saw, I feel I can safely fuse this circuit to 3 amps and move on.

Return from the future: See the edit at the end of this post regarding the current rating of the Extra circuit.

If another arrangement for the left landing light steady on power needs to be made, the next easiest power source is the power for the 12 volt plug that looks like a cigarette lighter socket. It is a dedicated and fused 5 amp source for power. The most power likely to be used from the power socket would be to charge a notepad (which would be roughly a max of 2.5 amps if using a high output USB charger) so the left landing light could be powered from this available source of power … but if a notepad were drawing a full 2.5 amps, the 5 amp fuse would be at or near its limit for the duration the left landing light is on. Of course, the notepad charger could easily be unplugged by reaching down between the seats and unplugging it from the 12 volt socket so this power source is doable.

It appears I opened up a can of worms in Van’s engineering department when asking about the current capability of the extra circuit in the AV-50001 Fuse & Switch module (which appeared to be incorrectly marked on the drawing, along with other circuits). The good news … the “Extra” circuit can be used as a power source for the left landing light because it IS indeed rated for 5 amps! The bad news, I created some extra work for Van's engineering department which now needs to correct that misprint and a couple of others ... they said an updated drawing will be posted on Van’s WEB site when the corrections are made.