Tesing a 50M ohm 65KV resistor

S

sinebar

Guest
So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.
 
On Wed, 23 Feb 2011 18:12:01 -0800 (PST), sinebar
<sinebar3770@gmail.com> wrote:

So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.
Click to expand...
Try a power supply, 10 volts maybe, in series with the resistor and a
DVM set to its voltage range. Most DVMs have a 10M input impedance on
DC ranges, easy to verify.

The Rx and the DVM form a voltage divider. You can easily measure
gigohms this way.

John
 
"sinebar" <sinebar3770@gmail.com> wrote in message
news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...
So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.
Click to expand...
You might need to clean the resistor with some Isopropyl alcohol and let it
dry well, you could scrub it with a swab that is soaked in 99% alcohol.

5KV / 65Mohms only gives 77 microamps , pretty small

shaun
 
"sinebar" <sinebar3770@gmail.com> wrote in message
news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...
So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.
Click to expand...

Oops my goof. 5Kv / 50Mohms = 100 uAmps

shaun
 
On Feb 23, 9:17 pm, "Shaun" <r...@nomail.com> wrote:
"sinebar" <sinebar3...@gmail.com> wrote in message

news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...

So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test.  My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad?  I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor?  The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange.  The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob.  Does that mean the
resistor is bad or is my power supply of too low power.  It came out
of a bug zapper so it's pretty small.

Oops my goof.   5Kv / 50Mohms =  100 uAmps

shaun
Click to expand...
Still small though and I think meters don't measure that small.
 
On Wed, 23 Feb 2011 21:16:18 -0600, "Shaun" <rowl@nomail.com> wrote:

"sinebar" <sinebar3770@gmail.com> wrote in message
news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...
So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.


You might need to clean the resistor with some Isopropyl alcohol and let it
dry well, you could scrub it with a swab that is soaked in 99% alcohol.
Click to expand...
50M is not very high. It would have to be caked with mud to change its
resistance much.

Here's a Keithley electrometer measuring a 1 Gohm resistor. Pawing the
resistor with greasy fingerprints didn't make any difference.

ftp://jjlarkin.lmi.net/Keithley_1gig.JPG

Incidentally, this meter will measure up to 1e14 ohms, and you can get
used ones for a few hundred dollars, a good deal if you intend to do a
lot of hi-Z work.

Or make your own gohm test box.

But as I noted, a cheap DVM and a 9-volt battery is all you need to
measure gigohms.


John
 
John Larkin <jjlarkin@highnotlandthistechnologypart.com> wrote:
On Wed, 23 Feb 2011 21:16:18 -0600, "Shaun" <rowl@nomail.com> wrote:


"sinebar" <sinebar3770@gmail.com> wrote in message
news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...
So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.


You might need to clean the resistor with some Isopropyl alcohol and let it
dry well, you could scrub it with a swab that is soaked in 99% alcohol.


50M is not very high. It would have to be caked with mud to change its
resistance much.

Here's a Keithley electrometer measuring a 1 Gohm resistor. Pawing the
resistor with greasy fingerprints didn't make any difference.

ftp://jjlarkin.lmi.net/Keithley_1gig.JPG

Incidentally, this meter will measure up to 1e14 ohms, and you can get
used ones for a few hundred dollars, a good deal if you intend to do a
lot of hi-Z work.

Or make your own gohm test box.

But as I noted, a cheap DVM and a 9-volt battery is all you need to
measure gigohms.


John
Click to expand...
Do you know how these meters actually work? I can't think of a need to get
one, but they look like they'd be fun to play with for a week or so.
 
On 02/24/2011 04:22 AM, sinebar wrote:
On Feb 23, 9:17 pm, "Shaun" <r...@nomail.com> wrote:
"sinebar" <sinebar3...@gmail.com> wrote in message

news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...

So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.

Oops my goof. 5Kv / 50Mohms = 100 uAmps

shaun

Still small though and I think meters don't measure that small.
Click to expand...
The lowest range on my Metex M-3800 is 200 uA. It's not a high end
model, but also not one of these pocket units.

Bernhard
 
"sinebar" wrote in message
news:cb9ea319-0bd8-4089-855c-2d9d79d6ac94@u24g2000prn.googlegroups.com...

So I have this monster 50M ohm 65KV resistor I got off ebay that I am
trying to test. My fluke multimeter has max rating of 50M ohm and
when I test the resistor it shows an open circuit. Do I need a meter
with a higher rating or is the resistor bad? I conneted it in series
with a 1ma panel meter and hooked to a 5KV rectified power supply
variaced. I figure it should be enough to test the resistor? The
resistor should rescale the panel meter so that 1ma = 50KV so 1KV
should move the needle one increment but the meter acts strange. The
needle goes backwards when I apply a little voltage then back to zero.
It does this each time I move the variac knob. Does that mean the
resistor is bad or is my power supply of too low power. It came out
of a bug zapper so it's pretty small.

-----------------------------

You have an AC panel ammeter with a DC supply hooked to it.

Every time you increase the voltage the AC component of the voltage
registers on the meter backwards due to it's cheap internal construction.

mike
 
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