Nice summary of capacitors

Nicely done.  I had to learn about capacitors the hard way when my very expensive built in refrigerator died and there were no replacement parts for it.  After a lot of diagnosis I tracked the problem down to one capacitor and with a bit of solder work it has run ever since.  I wish i had read your article first as I would have saved days in my diagnosis and repairs.

Keep up the great work.

Capacitors

Very nice Bruce. Well needed article.

I started using caps in the 1950's in tuned circuits.

The two inductors, the green ones also, are 4.7 uhnry and a moot point with no caps I have found. Some think the green ones are resistors.

Rich

Polarity swapped in photo 5 caption

A word of caution here. An error crept into the caption of figure 5.

For surface mount capacitors in this style of molded package, the positive not the negative end is indicated by the marked band. So polarity is swapped in the caption. The marked band on round electrolytic capacitors indicates negative, but it marks positive on these parts! This is a frequent trap for new players and and an occasional trip-up even for experienced engineers.

Although some capacitors in this molded package are electrolytic, most are tantalum capacitors, which have the advantage of a lot more capacitance in a smaller size. However, tantalum capacitors do not tolerate being connected backwards, or voltages that exceed their ratings. They can short out or, if sufficient energy is available, literally catch fire (over my career I watched a few erupt into flames.)

Some modelers connect tantalum capacitors directly across the power supply of their decoders, without the usual resistor/diode network to limit charging current. They do this to save space, but it is not a recommended practice. Should the capacitor be connected backwards and full track power applied, the decoder's bridge rectifier may be destroyed, or the capacitor may spectacularly fail, or both!

Please mind the polarity on the molded surface mount capacitors and remember that it is the opposite of round aluminum can electrolytics.

Bob

Thank you, Bob ...

for pointing out this SERIOUS error. Sorry for the poor proofreading. Nothing like making a point of the WRONG thing.

Here is the correct polarity. Failure to heed can result in a spectacularly messy situation.

+ -

Thanks Bruce

Good refresher, especially pertaining to using them with DCC.

I'm switching...

After buying several LokSound Select Direct boards, I've switched to the Tsunami2. One reason is that I think DDE probably works better with my style of running, but the primary reason is because they made a plug and socket connnection for their Current Keeper capacitor solution.

Anything that keeps me from having to solder on expensive electronics wtihout a significant loss in reliability is a significant gain in my book.

All manufacturers should follow their example as far as I am concerned. - and make the blasted things interchangable too!

Caps

Been quite a while since I did a decoder install but the only place I remember seeing tantalums is for filtering the output of the full wave bridge though The color makes them stand out.

I have done electronics for many years and do remember seiing tantalums used quite a lot. I just missed the diagram.

Rich