TRC-99C and cap replacement

[Critter98]

Hi all. I'm replacing caps on this handheld. Some of the older caps in the radio are quite large but the new ones are 1/4 of the size. For example one is labeled Marcom CE04W 100uf 16V. The replacement is labeled United 100uf 16V. Now I have one that is larger but has 50V. Would it matter if I put the larger 50V one in?

Tks in adv.

 

[brandon7861]

I asked that very question here a while back and didn't get an answer.

In that post, I though that with a higher voltage rating, the ESR would be higher, but I now know that its the other way around. Higher voltage caps have a lower ESR. From what I found on EEVBlog, it sounds like some situations require a certain minimum ESR for stability (they use certain voltage regulators as an example). The other difference is obviously in size, higher voltage are sometimes bigger.

The only other thing I have found is occasional mention that higher voltage caps may need to be operated near their design voltage to prevent degradation of the oxide dielectric, but I am not sure how important this is if you keep it at the lower value. When I think of my experiments with anodizing titanium (all you need is a variable voltage supply and citric acid electrolyte, no dye), I recall how I could form a new color by going higher in voltage, but not go back to a lower voltage color (the color coming from diffraction in the oxide layer), so it stands to reason the oxide layer is voltage dependent. I would expect that your 50v capacitor will be just fine in a 12v environment, just don't take it out and expect it to work in a 50v setting later on (without reforming at 50v that is).

 

[brandon7861]

And that just made me realize something....

Being the thickness of the oxide layer IS voltage dependent, and it is that thickness which sets the capacitance, you might find that after a while, when the dielectric deteriorates to the thickness of the voltage you are operating it at, the capacitance will rise. Therefore, I would have to correct my above post and say that, yes, it will work fine, at least for a couple years. After that, I would anticipate an increase in capacitance value as that 50v thickness wears down to a 12v thickness.

Edit: but it probably won't hurt anything if it's just used as a stabilizing or decoupling cap. If it is used for a time constant type circuit (as in audio filters, NB's and ACG circuits), then you may have an issue later down the road. This is just me making what I think is a logical guess, but I honestly cannot tell you how much that value will change.