Wednesday, March 23, 2011

How to Thoroughly Vaporize a Multimeter

Sorry it's been awhile since I've posted. I've been busy getting engaged (almost married!) and trying to get through school. Here's my latest adventure:
1950s Vacuum Tube Tesla Coil (vacuum tube not pictured)
A 1950s vacuum tube tesla coil based around a Hartley radio frequency oscillator. My uncle gave it to me over thanksgiving. He got his hands on it from the scientific instrument shop of the Los Angeles County School District. Apparently, they gave it to him because he asked nicely and it didn't work (it's ancient).

The last week or so I've been trying to get it working, with limited success. So far I've got the smaller transformer working - providing 6.3 VAC to the base of the vacuum tube so that it lights up nicely.

This evening I was testing the large transformer, which is supposed to convert 120 VAC to +/- 600 VAC (I think). It supposedly puts out -600 volts on one lead and +600 on the other, for a total of 1200 volts. My multimeter says it can handle 600 V, so I decided to try each lead individually.

I disconnected the leads from the large red capacitor shown in front of the large transformer (you can see the leads detached in the picture) and tested each individually with reference to ground. The first (attached to the right side of the cap) came out at about 40 VAC. The second came out as 340 VAC.

Puzzled and assuming I had found the problem, I decided to test both transformer leads at once. I hooked up each lead from the transformer to a cable from my multimeter and turned the thing on. There was a flash of light and a loud buzzing sound as the insides of my multimeter vaporized under what definitely was not 380 VAC. I quickly hit the switch on my power strip and opened up my multimeter to examine the damage. Here's what I found:
Back side of the board of my vaporized multimeter
Front side of the board and underside of the dial of my vaporized multimeter
So, I'm down one multimeter. This was after last week vaporizing my oscilloscope probe by touching it to the large red capacitor while charged.

Tesla coil:   2     Nick:   0