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-   -   Filter Cap AC Ripple Questions (https://www.badcaps.net/forum/showthread.php?t=106586)

Crystaleyes 05-20-2022 08:13 AM

Filter Cap AC Ripple Questions
 
Hi all.

Is there any other other cause of AC ripple other than a failing cap?

I say this as I have a new 18000F 15v cap which is showing about 1.5v of ripple when measured on a scope.

Is it ever the case that a failing bridge rectifier causes ripple?

Per Hansson 05-20-2022 01:16 PM

Re: Filter Cap AC Ripple Questions
 
It is completely normal if there is no more active filtering.
I.e. if you just have a bridge rectifier and a cap you will have ripple.
The amount depends on the size of the cap and the connected load.

keeney123 05-21-2022 10:22 AM

Re: Filter Cap AC Ripple Questions
 
Quote:

Originally Posted by Crystaleyes (Post 1134784)
Hi all.

Is there any other other cause of AC ripple other than a failing cap?

I say this as I have a new 18000F 15v cap which is showing about 1.5v of ripple when measured on a scope.

Is it ever the case that a failing bridge rectifier causes ripple?

Maybe, it would be good if you show a drawing of the circuit or a picture of what you have connected.

Crystaleyes 07-05-2022 06:28 PM

Re: Filter Cap AC Ripple Questions
 
As an update, the cap in question ended up exploding out of it's base the other week and covering the main board with a goo which shorted other things out.

I suppose that at least answers my question

keeney123 07-05-2022 08:58 PM

Re: Filter Cap AC Ripple Questions
 
Quote:

Originally Posted by Crystaleyes (Post 1146677)
As an update, the cap in question ended up exploding out of it's base the other week and covering the main board with a goo which shorted other things out.

I suppose that at least answers my question

Seems that ripple was too great for that capacitor. It would be interesting to look up the specifications on the capacitor.
Usually when a diode goes in the bridge rectifier 1/2 of the wave form is missing and the DC voltage will be drop at least in 1/2 and you will also see more ripple. That is because the AC voltage/current going through the bridge rectified in one direction has no path for conduction. This then lowers the positive voltage going to the filter capacitor in your case the 18000uF cap.
I suppose one could have a shorted diode in the bridge rectifier. To tell you the truth I do not ever remember a diode in the bridge rectifier that was shorted that stayed shorted for any amount of long time. They usually just popped, and they were open.
My knowledge is old but, the feedback circuit say in a linear supply goes to a transistor/FET that helps smooth out the ripple. The other term that is use is it is called regulated voltage. That is why I had asked for some type of schematic on this circuit.
Electrolytic capacitors do not like to conduct in the wrong direction. When there is a lot of ripple such as a 1.5 Volt in a 15 Volt DC capacitor it most likely will fail sooner than later. That is why the electronic technician has to understand how the circuit is functioning. In school we learn about the sequence of the circuits. What drives what and what feedback there is. In linear circuits it is easy to break the feedback loop to determine where the problem is. In power circuit with a pulse width modulator, I guess one has to be very careful in breaking the feedback loop because the circuits are not made for static supplies. One then would have to calculate the maximum static load the circuit can take. Here it would be useful if the design engineer would give those figures in the specifications so the technician would know how far he can push the circuit.


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