questions about tantalum caps

[loosecannon]

hi all,
why are tantalum caps used in some sections of CB radios instead of electrolytics?

is it because they are cheaper?
do they have some characteristic that electrolytics dont have?

whats the deal?

also, can an electroytic replace a tantalum cap in any CB radio application?
which cap is superior?

thanks for any insight anyone can lend,
loosecannon

 

[Captain Kilowatt]

Tantalum caps are better at RF filtering. Electrolytics do not like to act as RF filters and bypass caps very well. Tantalums also generally can pack more capacitance in a smaller package up to a limit although electrolytics are becoming smaller in the low value range.Tantalums are very good caps but silver mica still make better RF bypass caps.

 

[Beetle]

Electrolytics really ARE shrinking in size, largely due, as QRN said, to the lower voltage ratings. Back when I was in high school, we asked the electronics teacher, Mr. Delzer, just why capacitors were rated in MICRO and MICRO-MICRO farads, forcing us students to have to wrestle with "ten to the minus sixth" and "ten to the minus twelfth" so early on a school morning.

He replied that a one-farad capacitor "would be as large as this whole building!" --- which it would, at 450 working volts which used to be a very common voltage rating. We asked why they didn't make capacitors with lower voltage ratings. He asked what they'd be used for. And he was right again. In those days there was no practical use for a one-farad capacitor rated at 1.5 volts....like the ones I pass out like candy to people who still think a 1F capacitor has to be HUGE.

by the way, "micro-micro" is the same as "pico". In the 50s and 60s, we didn't have the "nano", "pico", "atto", "femto" and so forth. Nor "giga", "tera" and such on the other end.

 

[loosecannon]

thank you so much for the replies.

so, do tantalums have the same fail rate as electrolytics, as far as life span goes?
what i mean is do they last the same amount of time in general as electrolytic caps do?
thanks again,
loosecannon

 

[Captain Kilowatt]

thank you so much for the replies.

so, do tantalums have the same fail rate as electrolytics, as far as life span goes?
what i mean is do they last the same amount of time in general as electrolytic caps do?
thanks again,
loosecannon

Good question. Since electrolytics are far more common in circuits you would expect to see far more failures. In my 22 years of electronic service at a commercial radio station I have seen exactly two,that's TWO, tantalum caps fail. I have seen a wheelbarrow full of electrolytics that have failed however.

Here is a bit of info about capacitor types

 

[loosecannon]

QRN i could not have hoped for a more appropriate answer to my questions.

thank you so much.

i am always re-capping radios from the late 70's, and i was wondering if i should start doing the tantalums too.

your experience has shown me that i can save my time and money.

thanks so much.
loosecannon

 

[Captain Kilowatt]

We had a lot of audio gear from the late 70's/early 80's that was loaded with capacitors.There were several tantalums types as well as many regular electrolytics.The electrolytics were the ones that always failed. Of the two tantalum caps I had go bad,one was in a McCurdy on air audio console from the early 80's and the other was in a motor drive circuit in a Studer B67 reel-reel tape machine from the mid 70's. I would not bother to replace the tantalums unless they were known to be bad. they have a very good life span I think.

 

[johnecashflo]

injector noise

im a newbie to the electronics world..i have been trying to solve a noise problem..i have seen a couple mentions about using CAPs to catch the noise.. will this work on the injectors of a diesel engine?? :?:

 

[Beetle]

It might, if the noise you're experiencing is in fact coming from the injectors. It can never hurt to do a little experimenting.

Well, it can only RARELY hurt. Be careful and methodical.

Actually, for bypassing and such, I'd recommend disc ceramic capacitors over tantalums. Capacitance value isn't particularly critical; start around 0.05 microfarad. As far as voltage rating, most disc ceramics are rated around 200 volts, and many are rated higher than that, which is fine. Nothing lower than 50 volts to allow for starting transients and other potential problems.

 

[johnecashflo]

IM not scared :shock: ill try anything at this point..now how do i hook them up and can i get em at the local ratshack

 

[loosecannon]

beetle has steered you in a great direction.

yes, you can get the caps at radio shack, sort of.
catalog #272-134 is very close to what you want, but the voltage rating is only 50 volts. that should be fine for a vehicle.

its a .047uF disc cap which is as close as you will usually find to .05uF (beetle your age is showing. J/K!)

these caps have no polarity, so you can hook them up either direction.
find the hot wire going into the fuel injector, remove some insulation right before the wire goes into the injector, and solder one end of the cap to the wire. insulate the connection with something very heat resistant.
attatch the other end of the cap to vehicle ground IF its within 2" or less of the capacitor. (no long leads here!)
if there is no convenient spot to connect the cap to chassis ground, then connect it to the negative wire going into the injector in the same manner as you did the positive wire.

best to do this right at the injector if possible.
do this to each injector.
good luck,
loosecannon

 

[johnecashflo]

wow thanks for all the help..i cant wait to try this..the inj. are not to hard to get to so hopefully they will have the caps at the shack thanks again CANNON and all the others who helped thanks!!!!!i will let you all know how it turns out....