# HV indicator...

E

#### Eddy Lee

##### Guest
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?

On Saturday, September 23, 2023 at 8:33:01â¯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.

On Saturday, September 23, 2023 at 8:33:01â¯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:

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.

On Saturday, September 23, 2023 at 8:33:01â¯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.

On Saturday, September 23, 2023 at 8:33:01â¯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.

On Saturday, September 23, 2023 at 6:00:58â¯AM UTC-7, Fred Bloggs wrote:
On Saturday, September 23, 2023 at 8:33:01â¯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:

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.

On Saturday, September 23, 2023 at 5:33:01â¯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.

On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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 -

On Saturday, September 23, 2023 at 11:37:49â¯AM UTC-7, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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.

On Saturday, September 23, 2023 at 3:59:57â¯PM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 11:37:49â¯AM UTC-7, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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.

On a sunny day (Sat, 23 Sep 2023 05:32:55 -0700 (PDT)) it happened Eddy Lee
<eddy711lee@gmail.com> wrote in

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?

Specially for HV I bought a few dollar (5 USD or so) little analog multimeter after I blew up a digital one measuring a few kV in a PMT supply
https://panteltje.nl/pub/cheap_meter.jpg

On Saturday, September 23, 2023 at 9:36:10â¯AM UTC-4, Eddy Lee wrote:
On Saturday, September 23, 2023 at 6:00:58â¯AM UTC-7, Fred Bloggs wrote:
On Saturday, September 23, 2023 at 8:33:01â¯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:

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.

The CA3140 circuit, which is copied from a 1960s RCA app not I\'m sure, when modified as I suggested will measure the difference in your small voltage range quite accurately. You don\'t like circuit complexity, so a zero output reading will have to be confirmed by interchanging the HV leads.

The underlying principle is two voltage sources V1 and V2 at either side of a resistance V1--R--V2 results in a current |V1-V2|/R through the resistance. That looks a lot like an opportunity to measure a difference in voltages to me.

But if you like using 1000s times more power than necessary to make a simple measurement, lots of incandescent bulbs, HV diodes, and high power components, to end up with a system producing an indication with 50% accuracy or less, have at it.

On Saturday, September 23, 2023 at 6:59:57â¯PM UTC-4, whit3rd wrote:
On Saturday, September 23, 2023 at 11:37:49â¯AM UTC-7, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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.

Some multimeters, in particular EXTECH, have a Non-Contact Voltage (NCV) Detector in the form of an ionizing gas bulb that lights for VAC in the range 100-600 Volts AC.

These are available in the big box stores off the shelf / display hook.

https://www.flir.com/products/ex330/

On Saturday, September 23, 2023 at 10:55:34â¯PM UTC-7, Jan Panteltje wrote:
On a sunny day (Sat, 23 Sep 2023 05:32:55 -0700 (PDT)) it happened Eddy Lee
eddy7...@gmail.com> wrote in
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?
Specially for HV I bought a few dollar (5 USD or so) little analog multimeter after I blew up a digital one measuring a few kV in a PMT supply
https://panteltje.nl/pub/cheap_meter.jpg

I blew up a few of these, even for the older version with HV of 1000V. The newer one is 200V. Sometimes, the damage is not immediate. After a while, i got strange voltage readings.

https://www.harborfreight.com/7-function-digital-multimeter-63759.html

On Sunday, September 24, 2023 at 5:40:16â¯AM UTC-7, Fred Bloggs wrote:

Some multimeters, in particular EXTECH, have a Non-Contact Voltage (NCV) Detector in the form of an ionizing gas bulb that lights for VAC in the range 100-600 Volts AC.

These are available in the big box stores off the shelf / display hook.

https://www.flir.com/products/ex330/

My Greenlee GT-11 non contact detector is a capacitive pickup and lights an LED; it
only senses AC.

On Sunday, September 24, 2023 at 4:17:02â¯PM UTC-4, whit3rd wrote:
On Sunday, September 24, 2023 at 5:40:16â¯AM UTC-7, Fred Bloggs wrote:

Some multimeters, in particular EXTECH, have a Non-Contact Voltage (NCV) Detector in the form of an ionizing gas bulb that lights for VAC in the range 100-600 Volts AC.

These are available in the big box stores off the shelf / display hook.

https://www.flir.com/products/ex330/
My Greenlee GT-11 non contact detector is a capacitive pickup and lights an LED; it
only senses AC.

Greenlee? You don\'t mess around, that\'s one of the best out there.

On 2023-09-23, Eddy Lee <eddy711lee@gmail.com> wrote:
On Saturday, September 23, 2023 at 3:59:57â¯PM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 11:37:49â¯AM UTC-7, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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.

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 )

--
Jasen.
ðºð¦ Ð¡Ð»Ð°Ð²Ð° Ð£ÐºÑÐ°ÑÐ½Ñ

On Sunday, September 24, 2023 at 7:00:48â¯PM UTC-7, Jasen Betts wrote:
On 2023-09-23, Eddy Lee <eddy7...@gmail.com> wrote:
On Saturday, September 23, 2023 at 3:59:57â¯PM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 11:37:49â¯AM UTC-7, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:49:20â¯AM UTC-7, whit3rd wrote:
On Saturday, September 23, 2023 at 5:33:01â¯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.
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.

I blew one at around 10V, the filament vaporized but the glass container is OK. There was a bright flash, but no explosion.

Just buy a 1000V auto-ranging multimeter, with whatever measurement
catergory is suited to traction batteries (I\'m guessing probably
Cat.IV )

I got one, but how do we know that it\'s really safe for 784V.

--
Jasen.
ðºð¦ Ð¡Ð»Ð°Ð²Ð° Ð£ÐºÑÐ°ÑÐ½Ñ

F35/F16/ATACMS for UA.

On a sunny day (Sun, 24 Sep 2023 10:14:04 -0700 (PDT)) it happened Eddy Lee
<eddy711lee@gmail.com> wrote in

On Saturday, September 23, 2023 at 10:55:34â¯PM UTC-7, Jan Panteltje=
wrote:
On a sunny day (Sat, 23 Sep 2023 05:32:55 -0700 (PDT)) it happened Eddy L=
ee
eddy7...@gmail.com> wrote in
I often have to measure the difference of two 392V sources. Unfortunatel=
y, 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?
Specially for HV I bought a few dollar (5 USD or so) little analog multim=
eter after I blew up a digital one measuring a few kV in a PMT supply
https://panteltje.nl/pub/cheap_meter.jpg

I blew up a few of these, even for the older version with HV of 1000V. The=
newer one is 200V. Sometimes, the damage is not immediate. After a while=
, i got strange voltage readings.

https://www.harborfreight.com/7-function-digital-multimeter-63759.html

Yea, I do not keep it connected for any length of time though...
And PMT circuits do not have a high current capability.
I blew up a nice digital one that was accidently on the Ohms range a few weeks ago
I expected the chip was dead, but investigation found just a 900 Ohm SMD resistor open circuit.
I replaced it by 680 and 220 Ohm in series... Reading is perfect again...
How I found out it should be 900 Ohm? divider circuit measured (with an other meter of course)
90 ? 9000 etc, so that in-between range had to be be 900.

Actually have an other analog one from ebay now:
https://www.ebay.com/itm/250977645828

But with 4 digital ones from ebay that I payed just a few dollars for (model was recommended by somebody here) I have
more meters than I need, some still in the box as spare.
https://panteltje.nl/pub/chinese_multimeter_img_3159.jpg
that was the one I fixed the 900 Ohm in...
Used every day, but does not like HV.
[

On 24/09/2023 6:14 pm, Eddy Lee wrote:
On Saturday, September 23, 2023 at 10:55:34â¯PM UTC-7, Jan Panteltje wrote:
On a sunny day (Sat, 23 Sep 2023 05:32:55 -0700 (PDT)) it happened Eddy Lee
eddy7...@gmail.com> wrote in
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?
Specially for HV I bought a few dollar (5 USD or so) little analog multimeter after I blew up a digital one measuring a few kV in a PMT supply
https://panteltje.nl/pub/cheap_meter.jpg

I blew up a few of these, even for the older version with HV of 1000V. The newer one is 200V. Sometimes, the damage is not immediate. After a while, i got strange voltage readings.

https://www.harborfreight.com/7-function-digital-multimeter-63759.html

So you can either buy a better meter rated to 1000V or build a resistor
10:1 attentuator and keep using cheap meters. Minimally use the meter
input impedance and just enough series resistance to get 10:1

piglet