Dave, Thanks for the notes! I'll see if I can find any information on how they're supposed to fail. It looks like replacement X2 rated components from Mouser are mostly polyester and dipped instead of potted, so I suspect they're less likely to absorb moisture and short out. Thanks, Jonathan On Mon, 14 Dec 2015 13:26:14 -0500 Dave McGuire via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
On 12/14/2015 01:07 PM, Systems Glitch via vcf-midatlantic wrote:
Just had one blow in an old ECL monitor, releasing tons of stinky capacitor smoke. Had to take the monitor outside to let it finish smoking.
Yuck.
I know these are "X2 safety rated" devices, but what does that really mean? "Keep two handy cos they fail a lot?" Seems to me that not blowing up would be a great safety feature, something you wouldn't relegate to cheap rice paper in epoxy.
These are called "safety capacitors". The important part is that they're designed to fail only in very specific failure modes. An X2 capacitor is designed to be placed across the line ("X") and is impulse rated to 2.5kV in most cases. Here is my entire set of notes on safety capacitor types and ratings:
-------------------------------------------------------- Type X: across the line (X1, X2 and X3) Type Y: line to ground (Y1, Y2, Y3 and Y4)
impulse test V peak service V ------------------------------------ X1: 4.0kV[1] 2.5kV - 4.0kV X2: 2.5kV[2] <= 2.5kV X3: - <= 1.2kV
Notes: [1]: If C<=1.0uF. For C>1.0uF, V(kV)=4/sqrt(C). [2]: If C<=1.0uF. For C>1.0uF, V(kV)=2.5/sqrt(C).
impulse test V rated V ---------------------------------- Y1: 8.0kV <= 500V Y2: 5.0kV 150V - 300V Y3: - <= 250V Y4: 2.5kV <= 150V --------------------------------------------------------
-Dave
-- Dave McGuire, AK4HZ New Kensington, PA