LC Filter

[electrotor]

ehehe... thanks for the reply... but I move fast :)

I wouldnt have known what +/-ve means anyways! best to keep leccy terms as basic as poss for us no leccy chaps... thats simply positive and negative yeah?

Yes +ve means positive and -ve means negative. However if you are going to get into making up small items for yourself you must make yourself aware of the industry conventions. You've learned that today and will be unlikely to forget it.

Moving on from this, sometimes -ve is called common. For example with a servo lead which has three wires. One is +ve, one is signal and one is -ve. The reason for this is that the +ve and signal wire need a "return" wire to complete their curcuits. They share this by both using the -ve or common as it is called. It would not be called the common when you have only two wires as in the case of the battery lead you are making up the filter for.

[Devonian]

There you go, it's long been known that electronic circuits really run on smoke and all works fine, unless you make a mistake and let the smoke out, then the circuit doesn't work any more.
Worse still, you cannot put the smoke back in.


Nigel.

[Coyote]

Ian,

Great article - BUT, I'd say that it DOES matter where the cap is for this simple filter.
The inductor should be nearest the input (battery/supply) and then the capacitor nearest the output.

There is a good explanation on RCG (and a long argument) regarding ideal components and placement in LC circuits...

Nigel.

Thats right there is an argument for both, so far from what ive seen theres no difinitive answer so far, thats why i sat on the fence lol :)

[Devonian]

I know which way I make my LC choke input filters ;)

There is sound reasoning to have the inductor first in a single inductor, single capacitor LC circuit
http://www.tpub.com/neets/book7/27f.htm

Nigel.

[Coyote]

Thats a case, ok then lets say it would be better coil first then ill ammend :)

[Pasty]

I find that out now AFTER I've wired it in the other way around :D

ok, a plea to all leccy bods, if you're going to use indutry standard speak for guys who arent and never will be in the industry please explain wtf you're on about when using abbreviations and terms non leccy people wont understand :D

[Coyote]

Hee hee :) Well you can do it both ways Steve, but to have the inductor ( coil ) first does make sense :)

[Devonian]

Another good post (and reasoning why it's inductor nearest the input voltage)...

http://www.rcgroups.com/forums/showthread.php?t=1055252

Both Sander and Thomas Scherrer know how it should be done.

No need for a diode in this circuit, as it would also drop the output voltage by ~0.6 volts as well ;)

Pasty,
Sorry, but 'twas a 50/50 chance weren't it ?!

Nigel.

[Pasty]

hey ho Nigel... its all part of the journey :)

I'm pleased to report my LC filter (with WAY over sized capacitor  :-[) is working a treat, from what I can tell its removed all the interference I had previously.

Thanks to Ian for sharing the knowledge and thanks to the rest of you for the bits of help and sympathy :D

[electrotor]

I find that out now AFTER I've wired it in the other way around :D

ok, a plea to all leccy bods, if you're going to use indutry standard speak for guys who arent and never will be in the industry please explain wtf you're on about when using abbreviations and terms non leccy people wont understand :D

To be fair to Coyote +ve & -ve are in common use and not really confined to the electrical/electronics industry. Surely you have seen + & - on battery terminals.

BTW you might be interested to know the following :

L means inductor, in this case the ferrite ring
C means capacitor

Inductors allow passage of low frequency signals but supress high frequency signals.
Capacitors allow passage of high frequency signals but supress low frequency signal.
That is how audio crossover networks, referred to earlier by Coyote, work. Combinations of these components are also used to create resonant circuits which is where my earlier reference to transmitters and receivers comes in as well as filtering circuits in our r/c gear.

[Coyote]

Super mate, amazing how something that electronically simple can be so effective :) Not you the filter ;) :)

[Badlands]

Following Ian's excellent LC filter build up - i made a few of my own.
They work really well.


Old PC motherboards contain all the parts you need.


Removed the torroids & high value capacitors.


I have a few now...


I cut away the old copper wire & wrap my cable around as many times as i can.


Solder the capacitor onto the cable (black to negative) - done!


Here's one i made - heatshrunk & tidy.

[electrotor]

Neat job Badlands.  :)

When I was an impoverished schoolboy (60s/70s) we used to strip components off any circuit boards we could lay our hands on. Nowadays there just isn't as much you can remove what with multi pinned or surface mounted devices. However there appear to be more ferrite rings and crystals these days, not to mention any amount or surplus computer equipment. My company IT dept is always chucking out perfectly good but slightly old gear. I rescued the 19" flat screen monitor I am now using quite literally from the bin along with another that only had cosmetic damage. Power supplies seem to be popular for home charging of flight packs and some people have even converted the brushess motors from CD/DVD drives to power models. Mind you brushless is pretty cheap now so hardly worth the hassle.

[Badlands]

I agree.
Ive rescued many old laptop mains adapters from the scap @ work, some are 12v @ 6amps, they are perfect for powering 12v lipo charges. Most of the time the cables have failed thru wear & tear - an ez fix for a nice PSU.


:-)

[Coyote]

Cool Martin looks spot on bud ! :)

Never thought of recycling :)