good Wiggy? - bad Wiggy?
Yo, everyone,
I’m short on time so my traditional overkill approach isn’t possible today - but something in Vetteboy’s post #11 prompts me to point out some interesting facts about the type of tester he mentioned. These things are commonly called “Wiggins” or “Wiggy” testers.
... show 120v due to leakage current, even when an output is off, so now we carry Voltage and continuity testers in our pockets that have solenoids in them to draw down the leakage.
The “Wiggy” is often used - just as Vetteboy said - to “load” a triac-type output circuit to overcome the false “on” test results which can be caused by leakage current through the solid-state output circuit.
Now I KNOW that many technicians use these things day-in and day-out with no noticeable problems - so I’m not going to debate their use - but I am at least going to offer a little food for thought on the subject.
Here are a few simple questions to get us started. First question: “How many volts does your car battery provide?” Simple answer: “About 12.” Next question: “How many volts does it take to fire your spark plugs?” Answer: “At least 20,000 volts.” Final question: “Where do you think all of that HIGH voltage comes from?” Answer: “From the car’s ignition coil.”
And that’s the problem with the “solenoid-type” of tester that a lot of technicians use. It is essentially the same thing as the ignition coil in your car. All of this goes back to the same phenomenon which many technicians call the “fly-back” effect. In simplest terms, the magnetic force existing in a coil doesn't just simply dissipate (or “go away”) when the service power supply is removed. Instead, the lines of magnetic flux actually COLLAPSE back through the conductors (of the coil) and the resulting system suddenly meets the basic definition of a generator - one capable of generating enough voltage to fry the electronic components of any manufacturer's control system.
Now a lot of guys are thinking, “But I’ve used these things for years with no problems.” Well, maybe so - there are a few people who smoke while they gas up their cars - with no problems. Still ... you might just want to think about this.
So what are the highest acceptable voltages for your AC input and output modules? Most are in the range of 140 volts. Now how many volts could you possibly get out of one of these “solenoid-type” testers? A WHOLE LOT MORE than 140 volts!
And the problem could be extremely intermittent in nature. Consider that the 60Hz sine wave of the service power may be at ANY point in its cycle at the instant that the test probes are removed from the module’s terminals (which causes the field to collapse). It's a totally random thing. If the voltage is at, or near, the zero point in its cycle, you may not see a problem. On the other hand, if the voltage is up near its maximum, the “fly-back” voltage which is generated may be enough to qualify as a "lightning strike" type event. I’ve heard of one plant who (under new management) actually outlawed the “Wiggy” testers that their technicians swore by - and then saw a significantly lower number of output modules “go bad”. The consensus of opinion: “Testing the modules was actually damaging them.” - but the issues were still being debated the last I heard. Some technicians just refuse to believe that their faithful old “Wiggies” had a darker side to their nature and were actually burning out a module from time-to-time.
So, once again, I’m not entering into any debate - just offering some food for thought.
Finally, this “fly-back” effect was once traditionally used in the past to indoctrinate apprentices in electrical repair shops. The apprentice was told to use a Simpson meter to “ohm-out” a transformer coil. Now the young lad KNOWS that the only power in the circuit is the 1.5 volt battery in the meter. So he squeezes one meter probe against one primary lead from the transformer - and squeezes the other meter probe against the other primary lead. Notice that his fingers are in real good contact with what he considers to be a “safe” circuit. And while he’s taking a look at the meter reading, the shop foreman reaches down and pulls one of the test leads out of the meter. The field in the transformer winding collapses - and the apprentice gets a serious jolt to help him remember a valuable lesson. “I TOLD you to ALWAYS keep your fingers off those leads!” says the foreman.
Finally, no offense, Vetteboy - I can assure you that you are not alone in using these things - and I'm not going to try to talk you out of it. But still - just food for thought -