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?
HV indicator
Started by ●September 23, 2023
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 8:33:01 AM UTC-4, Eddy Lee wrote:> 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?You can use a standard difference amplifier with very large resistor values, which then produces a reading for the VOM. Amplifier circuit is battery powered. You need to pay careful attention to the voltage rating of the resistors, maybe save some money using series strings of cheaper ones.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 8:33:01 AM UTC-4, Eddy Lee wrote:> 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 would be fun, and quick to build: https://www.homemade-circuits.com/high-voltage-meter-circuit-for-measuring-10kv/ The CA3140 is widely available and costs just a buck: https://www.renesas.com/us/en/document/dst/ca3140-ca3140a-datasheet You don't need to mess with those rheostats shown on the diagram, those are for calibrating that ancient 100uA FS meter.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 8:33:01 AM UTC-4, Eddy Lee wrote:> 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?Put a 1k between the circuit output and your VOM reading point to eliminate possibility of OA going berserk from lead capacitance.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 8:33:01 AM UTC-4, Eddy Lee wrote:> 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?Take that string of HV resistors and split it between the series connection to both HV leads, that will 'symmetricize' the circuit and make it safer. Leave the core OA circuit otherwise unchanged from schematic.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 6:00:58 AM UTC-7, Fred Bloggs wrote:> On Saturday, September 23, 2023 at 8:33:01 AM UTC-4, Eddy Lee wrote: > > 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 would be fun, and quick to build: > > https://www.homemade-circuits.com/high-voltage-meter-circuit-for-measuring-10kv/ > > The CA3140 is widely available and costs just a buck: > > https://www.renesas.com/us/en/document/dst/ca3140-ca3140a-datasheet > > You don't need to mess with those rheostats shown on the diagram, those are for calibrating that ancient 100uA FS meter.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.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 5:33:01 AM UTC-7, Eddy Lee wrote:> 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?Or maybe a 220k ohm resistor and a neon lamp? Real electricians needing safety-check support use (used to, anyway) gizmos just that simple.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 10:49:20 AM UTC-7, whit3rd wrote:> On Saturday, September 23, 2023 at 5:33:01 AM UTC-7, Eddy Lee wrote: > > I often have to measure the difference of two 392V sources. Unfortunately, sometimes it becomes the sum, using 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? > Or maybe a 220k ohm resistor and a neon lamp?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 -
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 11:37:49 AM UTC-7, Eddy Lee wrote:> On Saturday, September 23, 2023 at 10:49:20 AM UTC-7, whit3rd wrote: > > On Saturday, September 23, 2023 at 5:33:01 AM UTC-7, Eddy Lee wrote: > > > I often have to measure the difference of two 392V sources. Unfortunately, sometimes it becomes the sum, using 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? > > Or maybe a 220k ohm resistor and a neon lamp? > Did it light up well between 3V and 12V? I can tell when there is around 3V across the 6V light bulb.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.
Reply by ●September 23, 20232023-09-23
On Saturday, September 23, 2023 at 3:59:57 PM UTC-7, whit3rd wrote:> On Saturday, September 23, 2023 at 11:37:49 AM UTC-7, Eddy Lee wrote: > > On Saturday, September 23, 2023 at 10:49:20 AM UTC-7, whit3rd wrote: > > > On Saturday, September 23, 2023 at 5:33:01 AM UTC-7, Eddy Lee wrote: > > > > I often have to measure the difference of two 392V sources. Unfortunately, sometimes it becomes the sum, using 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? > > > Or maybe a 220k ohm resistor and a neon lamp? > > Did it light up well between 3V and 12V? I can tell when there is around 3V across the 6V light bulb. > 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.
