stressing a capacitor and measuring the ripple current from oscilloscope

[sri5496]

hi,


i want to perform a test where i can stress an electrolytic capacitor (450V/5A)... i think if ripple current is high ...i can stress it but i want to know how can i increase the ripple current...

i want to know how to measure ripple current from an oscilloscope...(other than measuring RMS voltage ripple and calculating from it)

Thanks

 

[FvM]

You can use a current transformer or shunt.

The purpose of the measurement isn't quite clear. Ripple current will cause heating of the capacitor according to it's ESR which can be well predicted. The most important effect is lifetime reduction due to elevated temperature,

 

[sri5496]

Thanks for replying.. i want to predict the life time and failure mode of the capacitor based on temperature rise.. so am thinking is there any way i can increase the ripple current , so that it would increase the temperature in the cap...

 

[schmitt trigger]

I'm assuming that you are talking about ripple in large, aluminum electrolytic caps.

If you have access to a current probe, you can solder a small ~2cm wire to one of its terminals. Then clip the current probe to the wire, and read with a RMS multimeter or an oscilloscope.

 

[mrinalmani]

To generate a variable frequency up to 20kHz, use a free sound-card oscilloscope. (download is readily available) It will generate the output through the head-phone jack in your laptop. Feed this to a MOSFET and you are done!
Or alternatively use a 555 timer with a variable resistor to adjust frequency. Again feed the output to the MOSFET. Perhaps, these are the fastest and cheapest ways to get started at once.

 

[BradtheRad]

is there any way i can increase the ripple current , so that it would increase the temperature in the cap

To increase the current going through the capacitor...

For every burst of 5A you put in, you need to get 5A out.

To do this, attach a 5A load across it.