Power Side Clip

The power side clip houses the power PCB, which deals with charging and powering the overall device and also holds the four 18650 back-up batteries.

The design for the side clips was rather challenging because two different current transformers were chosen. The 1000:5 power transformer, SB series, was thinner at the sides, while the 400:5, SA series, current sensing transformer was thicker at the sides. The following dimensions of both current transformers can be seen below in Figure 3.27 [9].

Figure 3.27: Dimensions Of Series A And Series B AcuAmp Current Transformers The need for easy assembly and troubleshooting was also accounted for. While the device should not have to be serviced often once connected to the distribution line, the need for eventually having to service it was accounted for in the design. The clip design would allow for the side clips to snap in place by grabbing the sides of the current transformers and allow for the ease to remove and install the chassis assembly. As seen in Figures 3.28 and 3.29 below, the power side clip and sensor side clip were both designed to have a clip mechanism, which allows for them to snap on and off with ease to the sides of the current transformers.

Figure 3.28: Bare Top View Of Power Side Clip Figure 3.29: Bare Side View Of Power Side Clip The compartment that holds the power PCB and batteries dictated the actual size of the storage compartment. By taking the measurements of the PCB dimensions and the case for the four 18650 batteries, the x and y lengths of the storage compartment were determined, see Figures 3.30 - 3.32 below.

Figure 3.32: Dimensions Of Power Side Clip (Side)

One design constraint that was considered and designed around was to avoid having the storage compartment encroach into the actual transformer window especially since the distribution conductor was to be running parallel to the both clips. Since the distribution conductors can get fairly warm and the electronics inside the actual device can be sensitive to electromagnetic fields, the storage compartment was limited on how far it extended into the current transformer’s window, see Figures 3.33 and 3.34 below. Please see the 3.1 EMF Shielding Module for more information on electronic sensitivity and shielding design.

Figure 3.35: Power Side Clip With CT’s Attached (Top) Figure 3.36: Power Side Clip With CT’s Attached (Side) The height of the side clip was extended to match the height of the smaller current sensing

transformer, see Figures 3.33 and 3.36 above. In order to maximize the vertical height real estate available to house the power components, a shelf was designed to separate the battery and power PCB, see Figures 3.35 and 3.36 The battery storage and the PCB were placed in their respective locations for two primary reasons. Since the device is suspended in the air and is exposed to the sun’s radiation and temperatures, the batteries are to have a cooler location underneath the PCB and are less prone to degrade more quickly. Secondly, the power PCB powers the sensor

electronics located on the opposite clip, which requires interconnections. Please see Section 3.4.4 for more details on this.

To ensure the ability to snap open the current transformer from its tabs, notches were made to allow either fingers or a flat head screwdriver to open the current transformer tabs when installing the device, see Figure 3.37 below.

To secure the power PCB, six standoffs were implemented, where three #4-40 x ⅜ ” _machine screws are needed to restrain the board from movement, see Figure 3.38 below.

Figure 3.38: Standoffs On Power Clip (Back) Figure 3.39: Screw Holes Power Clip (Angle) For easy battery access, the bottom cover of the storage compartment was made removable,

allowing it to slide on and off once the four #6-32 x ¾ ” _{machine screws are removed, see Figure} 3.39 above. With the power transformer powering the sensor electronics and charging the batteries, a cable needed to be run to the power PCB. As seen in Figures 3.38 and 3.39, the bottom cover has a 10mm hole allowing cable from the transformer terminals underneath the clip to be run into the storage compartment. Two additional 10mm holes were made on the shelving piece to allow for interconnections to be made. The left shelf hole allows for cable from the current transformer to be fed and connected to the terminal heads on the PCB. The right shelf hole allows for the battery cables and therm-resistor connections to be fed to the power PCB and connected.

Figure 3.40: Power C-Cover (Angle) Figure 3.41: Power Side Clip With C-Cover And Bottom Cover On

Figure 3.42: Labeled C-Cover (Top)

To enclose the storage compartment from the sides and the top, a c-cover was designed, see Figures 3.40 - 3.42. The c-cover is tightened down with four #6-32 x ¾ ” _{. Also, the c-cover has a} 10mm hole , allowing for the 5V interconnection to exit from the power side clip and run along the top clip and eventually to the sensor side clip. See Section 3.4.4 for more details.

Figure 3.43: Cable Grommet Dimensions Figure 3.44: Physical Cable Grommet (Angle) For the 10mm holes found on the top of the c-cover and the bottom of the side cover, IP68 cable grommets were placed, to create a weatherproof seal for the cable, see Figures 3.43 and 3.44 above [36]. The threading needed for the grommets was done with a tap and die kit. The #6-32 x ¾ ” _{and #4-40 x ⅜} ” _{holes were threaded in CAD and 3D printed as such.}