Which one?

[redboat219]

I recently acquired some Graupner Speed 280s from Ghost 2501. These were unsuppressed. So I went to our local electronic center to get some caps. Unfortunately, they were out of those 0.1 microfarad caps. My question is, Can I substitute another cap of different value ? How come some recommend using 0.01 uF or 0.047 uF caps?

[mfr02]

Anything between 470 picofarad and .1 microfarad will work as long as it is RF rated. Paper, ceramic, polymer, all will work. The important thing is to have the capacitor(s) to soak upthe broad interference generated by the motor(s).
When tuning a circuit, you usually need a carefully calculated value - when soaking up interference (re-shaping the waveform, really) which is generated over a wide spectrum, and doing it as near to the source as possible, actual values are less critical.

[timo2]

Hi Redboat 219

RF parts kit at http://www.action-electronics.co.uk/stuff2.php

£ 1.00 plus post

Timo2

[LtDoc]

The 'biggy' with capacitors is the voltage rating. Needs to be much larger than what will typically be put to it. The capacitance value is frequency related, but in general, larger is better, sort of. A 0.1 capacitor is/was probably the most common size, can be used about anywhere, sort of, and since it's so 'common', usually the reason it's the value specified. Larger values typically mean larger physical size. Nothing really wrong with that until it gets too ridiculous to fit. Capacitors also come in polarized and non-polarized types. Means which way the current flows inside them. The non-polarized type is the one to find, less chance of making a mistake in how they are installed, especially if you can reverse the motors ;). A mistake in polarity means destroying the capacitor. Not all that much of a 'much', but they tend to take out things around them when they go, possible huge problem, not to mention the noise. Look for some ceramic disk capacitors. Common as dirt, cheap, withstands heat sort of well. (If they appear discolored or start to 'sweat', get ready for that noise thingy.)
Whole bunch of stuff here you just couldn't live without knowing, right? Maybe, sort of?
- 'Doc

[redboat219]

OK. Bought some caps yesterday. Both 0.1 and 0.047 mF. They seem to be the polarized type as one lead is longer. Will these work? I'm using a reversible ESC.

[mfr02]

Forget lead length. Look at the capacitor body. If there is no marking to indicate + and -, they are not polarised, and therefore OK to connect across a reversible motor. If they look like a miniature can, either with both wires coming out the same end, or one each end, that is a sign of a polarised (electrolytic) type. The other polarised type commonly found looks like an M&M with legs, proper name is "tantalum bead". Both are to be avoided for this job.
The values you have quoted are smaller than I would expect in an electrolytic type, so, again, hook them up.
Keep the leads as short as possible - while the capacitor is soaking up RF energy, the leads act as small transmitting aerials, so the shorter the better. I tend to poke the capacitor leads through the holes in the motor tags as far as possible and solder them down, then fix the motor leads to the wire poking out. Saves trying to solder two wires to the same tag which often results in the first wire coming un-soldered.

[redboat219]

mfrO2,
I forgot to mention my caps are ceramic type. I checked, they're unmarked. I was nearly swayed into getting those Tantalum beads! They were smaller and better looking that the ceramic type. It's a good thing I didn't. Thanks for the info.