I'm looking to setup a basic demo of backfeeding AC and how it effects some AV equipment. My idea was to wire up an extension cord with a three prong if on one end and a simple single gang outlet on the other. This is US equipment. Then wire an AC transformer to the circuit. Plugin the piece of equipment and slowly increase the voltage coming from the transformer to demonstrate how it effects the equipment. Max voltage would be about 70 volts. Is this even a proper demonstration of what backfed AC is? Would this just not do anything? Will I burn my house down? Or explode?
Why?
I work for a cable company. In this area we have a lot of old houses. Old people. And old TVs. When we have a customer who is experiencing tiling or other abnormal behavior and all RF issues have been addressed, we check each outlet (inhouse cable line) for AC or foreign vtage before it hits the splitter. To test we take the (-) lead from our meters, ground it out and test the center conductor of the coax. There isn't supposed to be any AC. Some trace energy is fine. But we find lines with anywhere from 2 – 70 VAC. We ground out the line in question and no more issues.
The sitters seem to act as a weak capacitor building up stray AC until it causes an issue.
If we have time we check all outlets with an outlet bug to make sure they're properly grounded and wired. Its usually either a broken ground wire, a two wire circuit with three prong outlets, or older TVs and VCRs that are backfeeding.
What I want to demonstrate is how it looks with various amounts of VAC. I have the test board with the coax all setup that's easy. Originally I was going to take a variable AC transformer and wire it to a coax line Hooke up to a splitter and thus the test RF network. Thinking about it again I still feel like that is my best option. But it'd be hard to get real-time readings of VAC POST splitter. So then I wondered about my above question. Why not just wire up a single circuit I can plug in, and send vtage to the outlet itself. I guess that wouldn't be the same though….
Basically I don't know enough about VAC to know if I plug something into an active outlet and somehow send energy back in the other direction if I'd cause a glitch in the Matrix or worse! 🙂
Best Answer
It seems like you are trying to simulate 60 Hz voltage that is induced or otherwise appearing in troublesome levels in cable television coax wiring. You should definitely not use something that is connected directly to a wall outlet. If you have a small variable transformer available, you could feed that with a 1:1 isolation transformer. Put a resistor in series with the output of that so that you have a high impedance source. You probably shouldn't use anything less than 25K ohms. See if that give the effect that you want to simulate.