Capacitors blowing

[george1]

Hi,
  I had finished putting together a panel for demo for my customers.  Everytime I turn on the power to the PLC within 5 seconds the capacitor would blow.  I hooked upthe capacitor and diode prior to the input as recommended in the manual.  What I did also, I disconnected the panel all together and just hooked up the power supply only to the PLC. IT still blew the capacitor.  I wonder is it the Battery source.  I am using a 24 volt and 3.5 amp power supply.  So, far I have blown 4 capacitors and i am very baffled.
thank you so much
john

[support]

1) Which PLC model are you using?

2) Which capacitor? Is it the one on the PLC or the capacitor that you have added? What is the voltage rating of the capacitor?  The voltage rating must be higher than the actual voltage applied on the cap.

3) If it is the one on the PLC and you have replaced the capacitor with correct rating and it still blow,then you should send the board back to the supplier or to us for checking to find out the cause of the problem.

[george1]

Hi,
  Thank you for the response.  The capacitor that  I added.  The PLC is fine.  The capacitor that  I added is a 50volt  and 470 uF.  I was monitoring the PLC and I had found out as the PLC is warming up its fine.  Once it comes up to 24 volts then Pow the capacitor blows.  I added the capacitor as a safety as the manufacturer recommended.   Do you think I need a bigger capacitor and what kind?  Or I might be using the wrong capacitor.  I think it is the voltage spikes causing it.  I rather the capacitor take care of any spikes then the PLC.  But so far the plc is working fine.  
thank you so much
john

[support]

If the capacitor is rated at 50V then it should be able to withstand 24VDc power. Do check the polarity of connection. Connecting an E-cap in reverse polarity to the applied power almost always result in a blown capacitor as the electrolyte conducts current and the self heating of the electrolyte will eventually blows itself apart.

One other possibility may be the authenticity of the ratings on the capacitors. There are some unscrupulous traders in some third world areas that routinely export knock off of brand name capacitors (i.e. counterfeit goods) and what is wrapped under the label may not be a capacitor that can withstand the actual voltage rating.