Can you identify this mystery component?

[Paul Burridge]

Posted to abse. I bought 500 of these last summer. They're unmarked
and appear to be open circuit to a DVM. Could they be some sort of
flash arrestor? Can't honestly say I've seen this component before.
Size is about one inch across.

 

[Tim Wescott]

Posted to abse. I bought 500 of these last summer. They're unmarked
and appear to be open circuit to a DVM. Could they be some sort of
flash arrestor? Can't honestly say I've seen this component before.
Size is about one inch across.

It is a combination varistor and Ankh, to be used in circuits that
mysteriously blow components when connected to the mains, even though
all the proper protections are in place.

The reason that they were so cheap surplus is because the manufacturer
misread the print, making it with two loops instead of one and putting
the crossbar on top.

 

[Genome]

| On Tue, 4 May 2004 14:51:46 -0700, "Terry Given"
<[email protected]> posted
| this:
|
| >| >> Posted to abse. I bought 500 of these last summer. They're unmarked
| >> and appear to be open circuit to a DVM. Could they be some sort of
| >> flash arrestor? Can't honestly say I've seen this component before.
| >> Size is about one inch across.
| >> --
| >>
| >
| >clearly its a MOV with integral fuse (see earlier thread on MOV as
snubber).
| >If it tests as open-circuit the fuse might be blown. measure its
| >capacitance - very little = blown fuse. If you have 500 of them,
dismantle
| >one, the fuse will be obvious. test it with a variac + 25W lamp +
step-up
| >xfmr + rectifier & ammeter, ie wind up the volts slowly and watch it
clamp.
| >
| >cheers
| >Terry
| >
|
| Clearly, the lump on top of the disk is in *parallel* with the disk.
| Not very likely to be a fuse. Fuses usually go in series with things.
|
| Paul, carefully crush the coating on the device with a pair of pliers
to
| remove it. Then give us another picture.
|
| Jim
|
|

Excellent diagnosis, in parallel ay........ my sentiments exactly. Nuff
said, ho ho ho.

RC contact snubber???

DNA

 

[Spehro Pefhany]

| On Tue, 4 May 2004 14:51:46 -0700, "Terry Given"
<[email protected]> posted
| this:
|
| >| >> Posted to abse. I bought 500 of these last summer. They're unmarked
| >> and appear to be open circuit to a DVM. Could they be some sort of
| >> flash arrestor? Can't honestly say I've seen this component before.
| >> Size is about one inch across.
| >> --
| >>
| >
| >clearly its a MOV with integral fuse (see earlier thread on MOV as
snubber).
| >If it tests as open-circuit the fuse might be blown. measure its
| >capacitance - very little = blown fuse. If you have 500 of them,
dismantle
| >one, the fuse will be obvious. test it with a variac + 25W lamp +
step-up
| >xfmr + rectifier & ammeter, ie wind up the volts slowly and watch it
clamp.
| >
| >cheers
| >Terry
| >
|
| Clearly, the lump on top of the disk is in *parallel* with the disk.
| Not very likely to be a fuse. Fuses usually go in series with things.
|
| Paul, carefully crush the coating on the device with a pair of pliers
to
| remove it. Then give us another picture.
|
| Jim
|
|

Excellent diagnosis, in parallel ay........ my sentiments exactly. Nuff
said, ho ho ho.

RC contact snubber???

That would be R in series with C too..

Hey, maybe it's a spark gap in parallel with a MOV.

Best regards,
Spehro Pefhany

 

[legg]

snip

Hey, maybe it's a spark gap in parallel with a MOV.

I also seem to see the parallel connection.

Across-the-line safety cap with built-in discharge resistor?

It wouldn't make much sense to stick an mov and a semiconductor TVS in
parallel, but it might make sense to stick a TVS or resistor across a
cap.

Wrong shape for a PTC.

RL

 

[Paul Burridge]

I also seem to see the parallel connection.

Across-the-line safety cap with built-in discharge resistor?

It wouldn't make much sense to stick an mov and a semiconductor TVS in
parallel, but it might make sense to stick a TVS or resistor across a
cap.

Wrong shape for a PTC.

No idea what all these abbreviations mean, but have just established
2night that it's an EHT capacitor, and *identical* to one a ham friend
of mine (who makes his own toob linears) has marked up as 4KV and
4.7nF! Mystery solved. I'd still like to know what the cylindrical
thingie on the top is, though. :-|

 

[[email protected]]

If that's a cap, the 'thingy' is probably a high value resistor, 470k to 2.2M.
This device may be used in parallel with diodes in a high voltage rectifier
stack where the resistor helps equalize voltages across each diode during the
reverse bias condition and the capacitor absorbs any spikes during that time
when a high voltage diode is most vulnerable.

It's also possible the 'thingy' may be a silicon power diode and the cap is
there to help couple any RF signal around the diode. I've seen powerline
connected RF/wireless intercoms use this as well.

A simple test would be to ohm it out in both polarities.

I think if you look at some of the ARRL handbook's linear power supply
schematics, you'll see discrete parts used for that purpose.

 

[R.Legg]

No idea what all these abbreviations mean, but have just established
2night that it's an EHT capacitor, and *identical* to one a ham friend
of mine (who makes his own toob linears) has marked up as 4KV and
4.7nF! Mystery solved. I'd still like to know what the cylindrical
thingie on the top is, though. :-|

Could you at least stick an ohmeter across the thing, in the 10M
range, and tell us what it says?

If it is a safety discharge resistor, you ought to know how small(or
large) it is, before you use it in a high voltage circuit. A single
resistor with this body size isn't likely to be used in HT, and a 10M
part in this body size will overheat above 1600V if it doesn't arc
over, first.

RL

 

[Paul Burridge]

Could you at least stick an ohmeter across the thing, in the 10M
range, and tell us what it says?

Well I did at the outset but not in that higher range. However, it
appears you're right: 2.8M both ways, so I guess the thing's a bleed
resistor - but is that really necessary on a 4n7 (glorified disk
ceramic) cap?? They don't exactly hold a charge like an electrolytic,
do they? And 4.7n is a pretty small capacitance.

If it is a safety discharge resistor, you ought to know how small(or
large) it is, before you use it in a high voltage circuit. A single
resistor with this body size isn't likely to be used in HT, and a 10M
part in this body size will overheat above 1600V if it doesn't arc
over, first.

Well, apparently it's good for several hundred volts...

 

[Terry Given]

Could you at least stick an ohmeter across the thing, in the 10M
range, and tell us what it says?

If it is a safety discharge resistor, you ought to know how small(or
large) it is, before you use it in a high voltage circuit. A single
resistor with this body size isn't likely to be used in HT, and a 10M
part in this body size will overheat above 1600V if it doesn't arc
over, first.

RL

Oops. Having looked harder, I now sit corrected. parallel it is. I like
Spehro's suggestion of a spark gap, which might make sense in parallel with
an HV cap. Paul, carefully chip the coating away, and take a few pictures...

Terry

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Well I did at the outset but not in that higher range. However, it
appears you're right: 2.8M both ways, so I guess the thing's a bleed
resistor - but is that really necessary on a 4n7 (glorified disk
ceramic) cap?? They don't exactly hold a charge like an electrolytic,
do they? And 4.7n is a pretty small capacitance.

I was poking around with my screwdriver in a box of electrolytics the
other day, looking for a certain value. I got a nice spark off one when
I shorted the leads, even tho it had been in there for weeks or more.
So, yeah, they hold a charge. :-/

[snip]

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[Spehro Pefhany]

I was poking around with my screwdriver in a box of electrolytics the
other day, looking for a certain value. I got a nice spark off one when
I shorted the leads, even tho it had been in there for weeks or more.
So, yeah, they hold a charge. :-/

Or a cow-orker is fooling around when you're out having lunch.. ;-)


Best regards,
Spehro Pefhany