I need 10mkf capicitor for a HPF(it will be a part of portable magnetometer). Better to use polypropylene but 10mkF polyprop. cap. is bulky- what about tantalum or ceramic?

 

Hi,

Tantalum is polar and has wierd characteristics when exposed to AC. They tend to short, for instance. Ceramic is hard to use. The specs are usually the value +80% to - 20%. Not too accurate, which is critical for filtering. And they tend to be microphonic, and contribute noise when shaken or vibrated.

You have to choose components based on application and not necessarily on size.

 

I would go with the ceramic or silver-mica. I would not worry about noise contributed by microphonics unless your application is going to be subjected to shocks/vibrations as part of the application itself. Ceramics are typically used in high speed applications; e.g., DSP's.

 

The system is working with frequencies from dc to 1KHz and with a voltage ranges 30mkV-2V

 

10mkf and 30mkV (?!)

Weird units, at least to me...

What do they mean? NEVER seen them.

 

10mkf and 30mkV (?!)

Weird units, at least to me...

What do they mean? NEVER seen them.

Interpreting this literally:

10mkf = 10f

30mkV = 30V

Some clarity is needed.

Dave

 

mkF means usually microfarads (mikrofarads) or uF.

 

mkF means usually microfarads (mikrofarads) or uF.

As a terminology this is very confusing, I could understand mcF, but mkF implies milli-kilo-Farad which (interpreted literally) means Farad. Thankfully I haven't come across this terminology before.

Thanks for the clarification anyway.

Dave

 

I'm Russian that's why I have posted mkF istead of uF

 

If you're using a 10uF cap, electrolytics are the only ones that large [at least, that I know of, that are commonly available]. Also, the cap needs to be a non-polarized type since it will have AC applied to it.

 

If you're using a 10uF cap, electrolytics are the only ones that large [at least, that I know of, that are commonly available]. Also, the cap needs to be a non-polarized type since it will have AC applied to it.

That is not necessarily true. As long as both sides of the cap are DC biased then AC squiggles are ok. You see this in video apps with TV's from time to time.

 

Yes, a DC/polarized electrolytic will work fine provided the AC voltage never exceeds the DC in the wrong direction; however Crowbar never said that there would be DC with superimposed AC on this cap. Not knowing the voltage on this cap I suggested using a N/P type. Regards.

 

go with the ceramic or silver-mica. I would not worry about noise contributed by microphonics unless your application is going to be subjected to shocks/vibrations as part of the application itself. Ceramics are typically used in high speed applications; e.g., DSP's.

 

But does the capacitance of ceramic or silver mica caps go that high [10uF] [and at a reasonable price]? If so, I agree, either would be a better choice than electrolytics here.

 

When applied to AC voltage with unknown bias, two back-to-back series electrolytic capacitors can be a cheap solution.

Hasan Murod.