A shocking experience
by, 11-11-2011 at 05:24 PM (366 Views)
Recently I resolved some stray current issues and I wanted to share my experiences so others might benefit from my mistakes and learn some good techniques for current hunting.
About a month ago, I was working in my fish room with my shoes off and went to grab something out of the frag tank and got a fair "zap". The tone of the message wasn't "your life is in danger" - more of the "this might sting a bit" variety. I wasn't afraid to continue working, but it was a bit annoying. At this point, I decided on Bryan's fish room rule #1:
Rule #1: ALWAYS work with your shoes on when in Bryan's fish room.
Shoes will insulate you if stray current finds its way into your tank, through your fingers and into your body. If it can't get back to ground, it will not continue to flow. I continued on with life, reading about stray current and the possibility that it may harm your fish. I decided that if I wasn't creating a path to ground that the risk was lessened, but it still bothered me that the current was present.
After a little while, I noticed that my pH probe was starting to register funny numbers. I came to find out through experimentation that pH probes can be calibrated to cancel out stray current. That is to say, a probe calibrated in test solution not electrically connected to the tank will appear to work fine until you place it back in the tank with stray current in which case it will go bonkers to some degree. Generally, I've found that the pH reading shifts based on the amount of stray current present.
Rule #2: ALWAYS eliminate stray current from your system if you are using a pH probe. (It's probably a good idea anyway because of potential harmful effects on fish, but if your pH is wacked, your reef has bigger problems)
Since my pH probe was controlling my Ca reactor, I decided to get serious about finding the source of my excitement. I figured it would be simple. Stick my finger in the water and ask the g/f to toggle all of the circuits running. In practice, it was not so simple because she needed help reaching some of the plugs. Enter the multimeter.
Rule #3: An inexpensive multimeter is invaluable in the hunt for stray current. Measure between the 'ground' in your wall circuit and the tank water. (DISCLAIMER:: if you don't know what I'm talking about - get someone to help you )
So I set it up on DC and started turning things on and off. I had a guess as to what the culprit was, but didn't want to be rash to jump to judgement. It turns out that before I was done hunting, I could manually "ground" my reef angel controller and watch half a string of my LEDs turn off. Sure enough, when I unplugged the corresponding driver, the voltage between the tank and ground went from 20VDC down to .12VDC. At this point, I learned two new rules:
Rule #4: If you do a DIY LED build, make sure to check that you don't inadvertently solder part of a lead onto the aluminum heat sink.
Rule #5: Your DIY LED build may work without it, but you should not cut corners and neglect to ground the heat sink.
As it turns out, some of the current from the driver was dumping into the heat sink and charging my tank in the process. At this point, I decided to cut another corner. I ran a grounding wire from all three of my heat sinks to a central wiring bus and grounded them to the wall ground. What could be wrong with that, you ask? Well, what I didn't tell you was that my drivers were divided among two different circuits in the house. I intentionally did that to make sure I wasn't tripping any breakers with my power sucking reef. The next time I had my fingers in the water and touched the frag tank heat sink - ZAP! A healthier zap than the first time around. No idea what the problem was. Out came the multimeter. 60Hz A/C 20V between water and ground. I figured a pump went bad. No. Unplugged everything one at a time. Nothing. Finally, I unplugged ALL of my LED lights at the same time and went to plug them in again one at a time. BINGO! This was a different problem than the first time around, however. Eventually, I figured out if I disconnected the heatsink grounding wires for the drivers on circuit 1, everything was fine.
Rule #6: Make sure to ground your equipment on the proper circuit. Failure to do so can result in a ground loop.
Well, that's all I've got for this episode of "a shocking experience". I hope someone else can benefit from my mistakes.