RB & the Red green caps can be handy. An RB can actually, very neatly be put on a cathode pin leaving the wire fairly long to restrict heat transfer.

Photos uploaded to Post 1.

Thanks Brad.

Wow these caps are selling like hot cakes. I am now down to very few of the 22UFs. I will be posting pictures of the other electrolytics plus the new Big Order In about a weeks time.

Ron, I concur.

Only thing is, where an electro comes just after the rectifier (i.e. input to filter) and especially where higher HT currents are involved (e.g. TVs) size REALLY DOES matter. All other things being equal, a physically larger cap will last longer in this class of service, a small part will heat due to ripple current and may fail prematurely.

Of course, if an electro is rated at 105 degrees C it stands a better chance of lasting longer with the higher self-heating that will occur in a high ripple current location. I just don't like the idea of an electro running warm!

If you can get a full data sheet for the cap., look for the ripple current rating. The higher the better.

Physically smaller caps will have an easier life as the 2nd filter (i.e. after the filter choke of field coil) of a typical radio.

Only thing is, where an electro comes just after the rectifier (i.e. input to filter) and especially where higher HT currents are involved (e.g. TVs) size REALLY DOES matter.

True, and in many old sets that capacitor was part of a multi-section can which, in format, is essentially radial.

" I just don't like the idea of an electro running warm!"

Neither do I, and they are not supposed to. A crusty old navy tech. once taught me, and I quote---;

"If a capacitor runs warm it is passing current."

"So what?" I asked. He did not explain, just shook his head. I felt like I should have known why, and failed somehow, somewhere in my
training.

I thought about this for many years, and still do. I But my theoretical training tells me they do pass current, AC current (let's call it signal)
and the amount of current is determined by signal frequency V the capacitance of the cap. Yes or No?

Sometimes I wish I was smart enough to have gone through Uni and majored in Radio Physics and EE etc. But back to the practical world
of a simple Electronics Tech. (Radio Mechanic when I was an apprentice) capacitors passing current do get warm and don't last long.

Every tech knows this, it is stamped in rock. (That's why when we replace electros we make sure they do not contact power resistors)

Now, my only grace here is Voltage V Current (Watts) Are caps actually manipulating E rather than I, and we wrongly believe they are
passing I when in fact the heating is the product of something gone wrong with the E x I ? Hmm. The old guys would tell me I have
not taken L into account. OK. I'll buy that. We now have inductors working with capacitors smoothing out ripple current.

Just rambling, no need for replies----

they do pass current, AC current (let's call it signal) and the amount of current is determined by signal frequency V the capacitance of the cap. Yes or No?

Strictly speaking they do not pass AC. They store DC because DC cannot flow through the dielectric (unless it breaks down) but they charge and discharge when AC is across them -- thereby effectively blocking DC but not AC.

As for capacitive reactance, this description sums its effect up succinctly:

"Capacitive reactance of a capacitor decreases as the frequency across its plates increases. Therefore, capacitive reactance is inversely proportional to frequency. Capacitive reactance opposes current flow but the electrostatic charge on the plates (its AC capacitance value) remains constant. This means it becomes easier for the capacitor to fully absorb the change in charge on its plates during each half cycle. Also as the frequency increases the current flowing into the capacitor increases in value because the rate of voltage change across its plates increases."

Thanks GTC,

I would say you have answered my evening's ramble quite well. Also, while reading your summary several times over, and in the
clear sober light of day, I now see the 'heating' problem with caps may indicate diminishing capacitance due to aged dielectric separation between plates.

Perhaps leakage also contributes to heating (charge carrier friction)

All in all, a great discussion, and what a grand forum this this for such topics.

Perhaps leakage also contributes to heating

All capacitors have some dielectric losses, which are dissipated as heat. Heat is bad news for capacitors, especially electrolytics. Heating by nearby components such as valves shortens their life. A cap that runs hot in use is suspect. Heat is considered the biggest killer of caps, then there's dielectric breakdown due to over voltage, and the ravages of old age.

Yes, but when high ripple currents in power supply electros are involved, leakage and dielectric losses are not the main issues, provided of course that the working voltage of the cap is not exceeded.

The main cause of heating in this class of service is ESR - Effective Series Resistance. All capacitors, because they are imperfect, are effectively a capacitor and a resistor in series.

To make an electro smaller for the same capacitance, the thickness of the aluminium foil is reduced and the foil is etched, thus increasing its surface area. Doing this generally increases ESR. The AC ripple component of the voltage applied to the electro appears across this series resistor and heats it up. The higher the ESR the more watts need to be be dissipated as heat.

That's why a tiny 10μF 600V cap will suffer when used as Input to Filter in a typical radio. A physically bigger electro with the same voltage and capacitance generally has a lower ESR and more bulk to dissipate the heat. So don't shotgun-change those old electros if you don't need to - they may well outlast the new part you would fit! Check them first! See if they will re-form.

By the way, have you noticed that your typical low voltage switched mode plugpack or laptop power supply these days rarely lasts more than a few years? That's usually because the typical input to filter electro that comes after the mains bridge on the input is too small.

When I am designing an electrolytic capacitor into a product and it's in a critical location I always look long and hard at the data sheets to ensure I have an adequate safety margin against the maximum ratings. Electrolytics have a finite lifetime which approaches their typical rating of only 2500 hours if you run them at their maximum ripple current ratings. Under-running an electro will cause it to last a lot longer.

"Heating by nearby components such as valves shortens their life."

I once purchased a powered USB hub, the switch mode power supply of which ran warm even though it did not often have high current demands made of it. About a year after purchase the supply expired with a bang, under low load. The bang was a small (6mm diameter) electrolytic firing itself like a bullet through the side of the case. The markings were destroyed so I could not determine its temperature rating.
Presumably the cap was hotter than the case of the power supply since there was no ventilation incorporated in the case. This would also apply to caps stuffed into old components. This could be sorted if some temperature measurements could be made of stuffed caps if they are carrying high ripple currents. Would require a thermocouple embedded - not fun to organise. So experience of forum members with stuffed filter caps might be the best guide.

So experience of forum members with stuffed filter caps might be the best guide.

I have re-stuffed numerous can capacitors and have had no trouble to date. That said, I do take into consideration conditions such as proximity to a hot rectifier valve when deciding whether to re-stuff or go under chassis and I use high quality 105 degree electros for such purposes.

One of the things that causes failures is to overlook what happens on start-up.

Rarely do you see a "Surge" (SV) or "Peak Voltage" (PV) on a modern cap. The first cap always runs in the order of 50V in some cases, above the second one. What is not realised by many, is the start-up of Silicon diodes & filament valves with no cathode sleeve like #80 /5Y3. With these they normally feed heater valves: They heat fast & generate voltage fast; This then, due to lack of current draw, creates what is virtually an EMF voltage close to twice the running voltage.

Where there is nothing like a divider, all of the components on "B" cop it: The caps have to be able to withstand that. Many of the old & commonest filter caps had a working voltage & 525 PV written on them. Which is why I will not use below 500V on a 5Y3 etc. where the running voltage after the choke is 250V.

My greatest number of new cap fails were 450V types, that is another reason why I now, will not use them. Long term 600V I think a better choice for a 5Y3 / #80 with the most common "B" voltage of 250V after choke.

Long term 600V I think a better choice

I use 630V regardless for the usual power supplies. So far, so good. And on an inrush current related matter, when dealing with rectifier valves that are followed by capacitor input filters, it's also important not to exceed the rectifier's recommended capacitance.