I haven't really found any practical use of the Harbor Freight 45W solar panel system in the last few months. Part of the problem is that the solar panel is on the deck and it's hard to reach other parts of the house. I was going to buy some wire to extend it to the garage, where I could charge my power robot, and put a LED light in the nearby laundry room which is dark all the time. I was convinced that the garage is the right place for lead acid batteries, and solar charger, not the deck because of the large temperature swings. Besides, I don't want the large battery to be inside the house due to concerns with potential outgassing. One day, I was thinking whether I could use the coax cable system which is now obsolete but there is still plenty wired around the house. I googled and was surprised to find that indeed there is a guru in this who has been using the coax cable system for solar panel for many years (http://ecorenovator.org/forum/solar-power/2881-using-rf-coax-cable-dc-solar-pv-cable.html). I contacted him to confirm that what I was going to do is not crazy or hazardous. I was convinced that it should be safe for low power solar panels such as 45W or below (don't try to do what this guru is doing with high power solar panels unless you are really good at it!)
But be warned that there is some risk in using the coax cable system and make sure you know what you are doing. For example, the coax cables have different kinds and the wire has limits in carrying electricity. In my house I have two kinds: RG6 and RG59. RG6 is 18 AWG which can carry 2.3 Amps, which is low for the 45W solar panel but on the other hand, the 45W panel isn't really generating 45W all the time. Alternatively, I can wire the solar panels in series to increase the voltage and reduce the AMP. RG59 is even thinner and can carry 1.5AMP. I only use RG59 for my 1.8W solar panel to trickle charge a small battery (see figure1).
Step 1: Connecting the Coax Cable.
For my small solar panel (1.8W), I use the RG59 coax cable which goes from the deck to the living room using the existing cables. The connection is easily made. A slight complication is the connector. There are two ways to solve this. One is to modify a "matching transformer" (the kind that hooks up to your old TV). You will have to crack open the transformer and cut out the transformer part. Re-solder the wire to connect directly. The advantage of this approach is that you have a clean and easy connection with the coax cable. The other way is to simply cut off the connector at the end of the coax cable, exposing the wires and connect them. In either case some soldering work would help. And using shrinking tube to finish the job would be a plus. If you don't want to mess with soldering, the later approach probably works better.
For the 45W solar panel, I use the RG6 which is a thicker wire. I actually re-routed the cable around the house from outside to the garage, berried it under the ground. I cut off the connectors at both ends and used soldering to make the connection at the end.
Step 2: Step 2: Operational
Now I put my 33Ahr battery inside my power robot, and use solar panel to charge it in the garage. When I need to use the Power Robot, I disconnect it and go. When I park the robot, I charge it and power the LED lamp inside the laundry room. The power robot has a very low duty cycle (only used to clean the yard, pull the lawn mower, or remove snow, see: https://www.instructables.com/id/DIY-RC-Robot-with-your-Android-Phone-Tutorial-Part/), so this arrangement works well. On the other hand, I still have doubts about the HF solar charge controller despite adding the blocking diode (https://www.instructables.com/id/Make-the-Harbor-Freight-45W-Solar-Panel-Charger-Co/ ), so I am building a simple PWM charger as an add-on to it. We will see how that goes. Later.