fire at ceramic caps

pra3718 · 22nd January 2011, 02:51 PM

I have used many times ceramic cap 0.1uf across the +- rails for opamps & power amps. Today it burns with fire. What must be the reason ? I am using 15-0-15 90VA transformer with split power supply.

Regards.

Jacques Merde · 22nd January 2011, 03:09 PM

Excessive power dissipation

Check ripple current and ESR.

pacificblue · 22nd January 2011, 06:33 PM

Check the voltage rating. 15-0-15 AC leads to 42 V DC from rail to rail. Add 15 % transformer regulation to that -> 48,3 V. Then add 10 % mains fluctuation -> 53,13 V. The caps should have a 63 V DC rating or higher.

theAnonymous1 · 22nd January 2011, 08:05 PM

Are you sure it wasn't a tantalum cap?

johnr66 · 23rd January 2011, 07:53 PM

Quote:

Originally Posted by theAnonymous1

Are you sure it wasn't a tantalum cap?

Took the words right out of my mouth. Unless it is a PWM PSU with a problem of LOTS of HF ripple on the output.

sasmit · 24th January 2011, 04:52 AM

If you're using a disc type ceramic , which what you'll get if you're asking for 0.1uf in India they aren't suitable for bypassing at high voltages. They are rated at something like 63VDC. Ask for 0.1uf poly caps and you'll get a polyester cap with 100VDC rating which should work fine. If you get a box type cap the voltage will be clearly marked on the box itself, these can be used easily for bypassing . If you've not measured your trafo output, I'm sure it's putting out a lot more than it says i.e it might be actually like 18-0-18.

pra3718 · 24th January 2011, 10:28 AM

Thank you,

Quote:

Are you sure it wasn't a tantalum cap?

No, its ceramic type.

ohnoezitasploded · 24th January 2011, 11:31 PM

Quote:

Originally Posted by pra3718

I have used many times ceramic cap 0.1uf across the +- rails for opamps & power amps. Today it burns with fire. What must be the reason ? I am using 15-0-15 90VA transformer with split power supply.

Regards.

Capacitors block DC and pass AC, so assuming it was rated for that DC voltage, the heat must be from ripple current or some other source of AC. You could also just have had the bad luck to have a bad capacitor, I suppose.

ohnoezitasploded · 25th January 2011, 04:38 AM

Wait, tantalum capacitors should not be used for decoupling? Why not?

AndrewT · 25th January 2011, 11:19 AM

Hi,
tantalum caps make good decoupling caps.
That's why they were recommended and used extensively.
But continued build experience has shown them to become unreliable and usually by going short circuit.

As far as I am aware, reliability alone is the only reason for avoiding tantalum caps.

22nd January 2011, 02:51 PM	#1
pra3718 diyAudio Member Join Date: Jan 2009	fire at ceramic caps I have used many times ceramic cap 0.1uf across the +- rails for opamps & power amps. Today it burns with fire. What must be the reason ? I am using 15-0-15 90VA transformer with split power supply. Regards.

22nd January 2011, 03:09 PM	#2
Jacques Merde diyAudio Member Join Date: Oct 2009	Excessive power dissipation Check ripple current and ESR. __________________ "For every complex problem, there is a solution that is simple, neat, and wrong." -- H.L. Mencken

22nd January 2011, 06:33 PM	#3
pacificblue diyAudio Member Join Date: May 2008	Check the voltage rating. 15-0-15 AC leads to 42 V DC from rail to rail. Add 15 % transformer regulation to that -> 48,3 V. Then add 10 % mains fluctuation -> 53,13 V. The caps should have a 63 V DC rating or higher. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

22nd January 2011, 08:05 PM	#4
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	Are you sure it wasn't a tantalum cap? __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

25th January 2011, 11:19 AM	#10
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, tantalum caps make good decoupling caps. That's why they were recommended and used extensively. But continued build experience has shown them to become unreliable and usually by going short circuit. As far as I am aware, reliability alone is the only reason for avoiding tantalum caps. __________________ regards Andrew T.


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24th January 2011, 04:52 AM	#6
sasmit diyAudio Member Join Date: May 2006	If you're using a disc type ceramic , which what you'll get if you're asking for 0.1uf in India they aren't suitable for bypassing at high voltages. They are rated at something like 63VDC. Ask for 0.1uf poly caps and you'll get a polyester cap with 100VDC rating which should work fine. If you get a box type cap the voltage will be clearly marked on the box itself, these can be used easily for bypassing . If you've not measured your trafo output, I'm sure it's putting out a lot more than it says i.e it might be actually like 18-0-18.

25th January 2011, 04:38 AM	#9
ohnoezitasploded diyAudio Member Join Date: Jan 2011 Location: San Francisco, CA	Wait, tantalum capacitors should not be used for decoupling? Why not?

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