I often have to measure the difference of two 392V sources. Unfortunately, sometimes it become the sum, using a one-time fused muti-meter.
I am thinking about using a rectifier diode (for direction) , 6V zener (for voltage), 6V 5W light bulb (for current) and 10 ohms resistor.
Will it work? Perhaps 22 or 33 ohms resistor?
This will measure high voltage, but my goal is really measuring low voltage (+/- 6V to 12V), with protection from high voltage. Blowing the light bulb is fine.
Or maybe a 220k ohm resistor and a neon lamp? Real electricians needing safety-check support use (used to, anyway) gizmos just that simple.
Did it light up well between 3V and 12V? I can tell when there is around 3V across the 6V light bulb.
-12V to -9V: - 10R -|< - BULB - V6Z -
-9V to -6V: - 10R - |< - BULB - V3Z -
-6V to -3V: - 10R - |< - BULB -
3V to 6V: - 10R - >| - BULB - 6V to 9V: - 10R - >| - BULB - Z3V - 9V to 12V: - 10R - >| - BULB - Z6V -
There's some crude multilamp variants that can tell 120VAC from 240 from 480... it gives enough info to rethink what meter (or meter setting) to use for the real measurement thereafter. Neon doesn't glow at under 50V or so.
That relatively high strike voltage is how it can give a good glow indication off high voltages without drawing much current, using no battery.
But what I want is to tell the difference between two 392V sources, usually +/- 12V floating on top of 392V. However, sometimes it get mis-wired into sum, or 784V. In that case, it's OK to blow the bulb like a fuse.
My Greenlee GT-11 non contact detector is a capacitive pickup and lights an LED; it only senses AC.
a 6V lamp on 700V will probably blow like a 12V fuse does in the same circumstance (explosively), I suspect you would say not ok.
Just buy a 1000V auto-ranging multimeter, with whatever measurement catergory is suited to traction batteries (I'm guessing probably Cat.IV )
I blew one at around 10V, the filament vaporized but the glass container is OK. There was a bright flash, but no explosion.
I got one, but how do we know that it's really safe for 784V.
F35/F16/ATACMS for UA.
How about a neon lamp, a resistor and a capacitor ?
It will flash faster at higher voltage. Double the voltage should be easy-ish to distinguish from 1/2 that voltage.
boB
Yep, but you can also use multiple neon lamps and just hang each on a resistor divider instead of current-limit resistor.
The divider ratio determines whether the AC peak crosses the strike threshold of the (presumed identical) lamps. Just scribble an AC calibration next to each light...
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