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I figured out that it took around 75 volts to light up a neon bulb I had. I want to make a high-voltage meter with a few bulbs specifying certain amount of volts. So as a first test, I just hooked up two 22 mega ohm resistors in series to create a random voltage divider. The divider burned up and the resistors got damaged. How can I create a divider to display different voltages for different neon bulbs and how can I prevent high-ohm resistor damage?

The high-voltage power source that I supplied was a ZVS flyback driver with a 12 volt battery and I estimate the voltage of about 2K.

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  • \$\begingroup\$ What sort of resistor did you use? A regular ¼W resistor can only handle about 200V max. Check the datasheet for the resistor you use and at least use one that is able to withstand the supplied voltage. \$\endgroup\$ – jippie Jun 16 '13 at 18:34
  • \$\begingroup\$ I don't know. It was out of electronic goldmine surprise box and a got a bunch of 22M. The size is about the size of a piece of rice if that helps at all. I'm at a piano camp for a week so I can't just go home and check :) \$\endgroup\$ – skyler Jun 17 '13 at 3:44
  • \$\begingroup\$ Rice-sized resistors are very likely not rated for 2kV+, more like 200V. \$\endgroup\$ – jippie Jun 17 '13 at 6:12
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Use the same technique used to increase the voltage rating of capacitors: put them in series. 1 watt metal film resistors usually have a voltage rating of 350 volts, so do the calculations to cascade as many as you need for the required total resistance value, but so that any given resistor only "sees" a voltage across its terminals that is within its rating.

Also keep in mind that with neon bulbs, the "striking" voltage is usually higher than the "keep alive" voltage, and a minimum current is required to keep the bulb illuminated before it shuts off and the voltage must again be raised above the striking voltage. The voltage divider will need to be designed to provide enough current to the bulb at the keep alive voltage to prevent it from extinguishing, but still allow the voltage to rise high enough to strike the discharge.

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  • \$\begingroup\$ since my source is pulsating DC, could I use capacitors to divide? \$\endgroup\$ – skyler Jun 16 '13 at 12:37

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