Another Nixie resistor question

[Nigel]

Hi

I've got a IN-12A hooked up to a boost convertor which is showing to be putting out exactly 180 volts.

I have an anode series resistor in the loop measuring 20.14K Ohms.

The '1' digit cathode is connected up and lights up ok.  It doesn't seem to be too bright.  The voltage measured across the Nixie settles at 140.3 volts.

However, I've measured a current of 15.56mA which seems far too high.

I would have thought that 180 volts - 140 volts / 20.14K Ohms should have given me a current limit of ~2mA.

What am I missing here ?

Thanks

[gregebert]

Where, exactly, did you measure the current ? Best if you can post the exact schematic and where your meter was located.

[Nigel]

Thanks for the prompt reply.

I guess I shouldn't have rushed things.  As I'm typing up my response, I noticed that my positive probe lead was still plugged into the voltage, resistance, etc. socket on the meter.  Plugging into the current socket gives me 1.99 mA.  So, the calculations were correct.  Not so with the initial measuring though :)  I thought that I'd be honest in case it helps someone else in the future.

[Nicholas Stock]

We’ve all been there Nigel! :)

Sent from my iPhone

On Apr 19, 2020, at 07:44, Nigel <nige....@gmail.com> wrote:



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[Mac Doktor]

> On Apr 19, 2020, at 10:44 AM, Nigel <nige....@gmail.com> wrote:
>
> I guess I shouldn't have rushed things. As I'm typing up my response, I noticed that my positive probe lead was still plugged into the voltage, resistance, etc. socket on the meter. Plugging into the current socket gives me 1.99 mA. So, the calculations were correct. Not so with the initial measuring though :) I thought that I'd be honest in case it helps someone else in the future.

We've all been there. Well, everyone but me of course.


Terry Bowman, KA4HJH
"The Mac Doctor"

"Nothing is a cliché when it's happening to you."—Max Payne

[gregebert]

Let's suppose the meter WAS connected properly......then what ?

Since this has a dc-dc converter, it's possible the output was pulsating, rather than smooth DC. In which case the meter might be attempting to measure peak or  RMS current.

In that case, the higher-than-expected reading might actually be correct. All kinds of weird things happen in switched circuits, that's why your oscilloscope will be the most important tool you have.

=====================================================================================================

BTW, I just discovered two back-to-back mistakes on my own that have had me running in circles for months now.

Two PCB sets (6-tube NIMO clock) . Both board sets "working", except board-set #1 was heating more than the other, and board-set #2 would randomly fail after several hours where the A/D converter "hung". and could not be reset despite all sorts of diagnose-and-repair software I had to write.

Board #1 had a damaged NMOS transistor in the HV section, and board #2 had a weak solder joint that eventually failed. I did all of the "shake/wiggle/jiggle" testing more than a year ago and never saw anything go wrong.