Fin MacDonald

The solar thermal monitoring project is moving along despite a couple of setbacks. We received the wireless equipment in the mail and were able to set up the wireless bridge to the schools wireless network. We used a directional antenna to improve the reception because the school’s wireless signal on the roof is weak.

We put a 12V deep cycle battery on the roof and we did a test run. It was able to power both the router and the Web Energy Logger (WEL). The battery is rated at 90 amp hours and the load for both the WEL and router is 0.4 amps combined. This means we are able to get over 3 months of power off the battery before we will need to swap it out for charging. This is good news because the battery is very heavy!

Testing with the pyranometer hit a bit of a wall initially. As I mentioned in my previous post the pyranometer measures the solar intensity in watts per meter squared. Since we are converting the 0-5V signal on the pyranometer to a 4-20 mA (milliamp) signal for the WEL we needed to scale the results. We did the math calculation and did a test run. We weren’t getting to the proper numbers in the upper ranges. Once we were confident the math was correct we tried numerous 4-20 mA devices with the WEL and had the same result. It really pays to have an electrical engineering student around when you are trying to troubleshoot electrical problems. Travis Keeping is our electrical expert at the lab and he a bunch of tests for us. In the end a call to Phil Malone from OurCoolHouse.com who designed the WEL was all it took to discover our problem. Turns out that the WEL has a defect and there are two zener diodes that we will need to snip out of the circuit and it should work fine after that. Phil also told us that new versions of the WEL will have a voltage port so we won’t need to convert the signal in the future. We have another WEL on order and it will have the voltage connection on it.

The wire we chose for the sensor wire run was cheap wire and it started giving us grief. We used a 75m run and it had too much resistance because it wasn’t twisted pair wire. Twisted pair wire helps to reduce the electrical noise on the signal. We started getting “shorted bus” errors on the WEL. I took the wire run down and we will be replacing it with CAT 5 wire, which is what is used for computer network cables. Once the new wire is installed we should be able to go live.