Ceramic disc caps

[Dave Plowman (News)]

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Is there anything better to use for this?

--
*If you think this van is dirty, you should try having sex with the driver*

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[N_Cook]

Dave Plowman (News) <dave@davenoise.co.uk> wrote in message
news:51871e39f0dave@davenoise.co.uk...

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Is there anything better to use for this?

--
*If you think this van is dirty, you should try having sex with the
driver*

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

Wax covered?

 

[Meat Plow]

On Fri, 17 Dec 2010 16:36:00 +0000, Dave Plowman (News) wrote:

I've had a few failures of these recently. Used round a bridge rectifier
- for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Is there anything better to use for this?

Move them away from any heat source? I've not known them to be a trouble
child. If you choose MLCC replacements be sure to choose the correct
class of dielectric. Class COG/NPO contain neodymium, samarium and other
rare earth oxides and have a negligible aging rate.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[Dave Plowman (News)]

In article <pan.2010.12.17.17.52.19@lmao.lol.lol>,
Meat Plow <mhywatt@yahoo.com> wrote:

I've had a few failures of these recently. Used round a bridge rectifier
- for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Is there anything better to use for this?

Move them away from any heat source?

In these cases they were pretty low powered supplies - 100 mA or so and
quite open so heat shouldn't have been a problem. Although they were
mounted close to the diodes.

I've not known them to be a trouble child.

Not exactly that as they'd lasted quite a time. But like all these things
if slightly more expensive ones last even better it makes sense.

If you choose MLCC replacements be sure to choose the correct class of
dielectric. Class COG/NPO contain neodymium, samarium and other rare
earth oxides and have a negligible aging rate.

Thanks.

--
*He has no enemies, but is intensely disliked by his friends

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Jeff Liebermann]

On Fri, 17 Dec 2010 16:36:00 +0000 (GMT), "Dave Plowman (News)"
<dave@davenoise.co.uk> wrote:

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Any chance it was an MOV (metal oxide varistor) instead of a disc cap?
Kinda difficult to tell from your description. "Normal"? "Wax"?

Is there anything better to use for this?

If the bridge has several diodes in series for each leg, you'll need
equalizing caps and resistors to make sure that the voltage is equally
distributed among the series connected diodes. That means they should
all be equal value.

If not, just get a higher voltage rating. Shorted disc ceramic
usually means that some high voltage punched through the dielectric or
that the plating has exploded and sprayed conductive crud around the
insides.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[tm]

"Jeff Liebermann" <jeffl@cruzio.com> wrote in message
news:19gng6lbl31lq6m06beis24imffpa4vlar@4ax.com...

On Fri, 17 Dec 2010 16:36:00 +0000 (GMT), "Dave Plowman (News)"
dave@davenoise.co.uk> wrote:

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Any chance it was an MOV (metal oxide varistor) instead of a disc cap?
Kinda difficult to tell from your description. "Normal"? "Wax"?

Is there anything better to use for this?

If the bridge has several diodes in series for each leg, you'll need
equalizing caps and resistors to make sure that the voltage is equally
distributed among the series connected diodes. That means they should
all be equal value.

If not, just get a higher voltage rating. Shorted disc ceramic
usually means that some high voltage punched through the dielectric or
that the plating has exploded and sprayed conductive crud around the
insides.

Or it might be a NTC surge limiter. If these are in series with the AC line,
it
limits the initial charging current of the DC input capacitors. They protect
the
line fuse.

 

[Meat Plow]

On Fri, 17 Dec 2010 12:03:37 -0800, Jeff Liebermann wrote:

On Fri, 17 Dec 2010 16:36:00 +0000 (GMT), "Dave Plowman (News)"
dave@davenoise.co.uk> wrote:

I've had a few failures of these recently. Used round a bridge rectifier
- for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Any chance it was an MOV (metal oxide varistor) instead of a disc cap?
Kinda difficult to tell from your description. "Normal"? "Wax"?

I havn't seen too many MLCC's that have been waxed or potted but if they
vibrate in a audio detector or IF stage and introduce noise. Waxing them
would be one way to dampen vibration. Plus I think Dave
knows the difference between an MOV and a MLCC dontcha think?


<snip for brevity>

--
Live Fast, Die Young and Leave a Pretty Corpse

 

[nesesu]

On Dec 17, 8:36 am, "Dave Plowman (News)" <d...@davenoise.co.uk>
wrote:

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess. They were the normal sort of wax covered
types. In all three cases, one had shorted.

Is there anything better to use for this?

--
*If you think this van is dirty, you should try having sex with the driver*

    Dave Plowman        d...@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Replace with known good quality parts. Total length of leads including
capacitor disc diameter should be kept as small as possible--1cm is
very desireable. They work even better with about 22ohms 1/4 or 1/10W
in series if there is room.

Neil S.

 

[whit3rd]

On Dec 17, 8:36 am, "Dave Plowman (News)" <d...@davenoise.co.uk>
wrote:

I've had a few failures of these recently. Used round a bridge rectifier -
for RFI purposes, I'd guess.

The usual RF bypass disk capacitor for AC would be
a 1kV rating (just in case of surges) and they last nearly
forever in my experience. What value are they?
If it's high capacitance (like, over .001 uF) it might
be a multilayer type, and THEY can short out.