help me, i dont understand

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annoyin_kid

Member
well like a lot of u guys suggested me to do i've been doin some reading about electronics to get a grasp for the basics. when i got to the capacitors i kinda got stuck. i understood the formulas for capacitors in series and parallel fine but not what are they used for and how i wire them into a circuit. i've read the capacitors unit twice and i've understood how they are made but i still dont see what good they would do in a circuit unless you want to give something to get a little boost or you want to turn ac into dc.

can u guys please help me, ive been googling for a whole evening to try to find how to use them in a circuit and what they do in the circuit but i couldnt find anything useful.

do u guys know any useful websites that have information on what ceramic, electrolytic and plastic box capacitors do in a circuit (other than store energy) and why this is useful in a circuit and how to use them in my own circuit.

ak
 
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Dippy

Moderator
Yes, they store charge/energy. Thats about it really at the basic level, but its how you USE the capacitor that is important.
The charge/discharge rates can be controlled and therefore used in numerous ways.

Once you've got the idea about how they can be used then you can look into the construction - ceramic/tantalum etc. and other characteristics. Walk before running.

Search on oscillators, filters, 555 circuits or even loudspeaker crossovers - all these will use capacitors. Then you will see how useful/important they are.
Start here:
<A href='http://www.kpsec.freeuk.com/components/capac.htm' Target=_Blank>External Web Link</a>
and here:-
<A href='http://www.kpsec.freeuk.com/capacit.htm' Target=_Blank>External Web Link</a>

But it sounds like a bit of human tutoring would be better. Do you have a human electronics teacher/lecturer that can go through these things with you? It'll be a darn sight easier than the dozens of text-only responses you will get to your post.

And I mean no disrespect when I say that I will predict that many descriptions in well-meaning responses will go over your head.
... in a few days you'll probably wonder what all the fuss is about... it'll start to 'click'.

But, a little tip, you will have to be prepared to absorb a little bit of maths. It's quite easy to start with before it gets complex (what a pun!)

Edited by - Dippy on 09/01/2007 00:00:20
 
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Fowkc

Senior Member
Here's a site (one everyone should bookmark) which explains the maths and physics behind capacitors (and other electronic components):

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capcon.html#c1
 
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moxhamj

New Member
A few examples -
1) 0.1 caps across chip power supply pins to smooth out spikes in power supply.
2) bigger caps eg 470uF on power supplies to smooth rectified AC into DC.
3) In timers - eg if you charge a capacitor via a resistor it will take a certain amount of time to charge. Make the cap bigger, and it takes longer. Make the resistor bigger and it takes longer. Useful for making pulses of a certain length. Discharge the cap with another resitor and you can make a waveform - eg a tone.
4) For 'blocking' in AC circuits. Eg you can convert a waveform going 0 to 1V to one going 5V to 6V with just one capacitor, and not any DC volts get through.
5) In filters. Eg a low pass filter with one resistor and one capacitor lets through only low frequencies. A high pass filter only lets through high frequencies. Telephones have a low pass filter at 3000Hz and a high pass one at 300Hz. There are also band pass and notch filters. The capacitor sets the frequency.

That is a few examples. You don't really need to know how they work - just where to use them in practice and which ones to use. And don't connect tantalums the wrong way round - they blow up!

Edited by - Dr_Acula on 09/01/2007 01:27:24
 
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annoyin_kid

Member
thanks for the input everyone.

dippy yes i do have electronics teacher but next time i see her is when school starts again and that is 7th of feburary and i really want to know this capacitor stuff or it is gonna keep bugging me for ages, hope you can understand and yes i think im ready for the maths.

dr_acula ill try to make sure i connect the tantalums the right way but i just might be tempted to put it the wrong way on purpose.

anyway thanks again everyone i really appreciate it, ill look over the sites in the morning.

ak
 
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MPep

Senior Member
Hi All,

Just a reminder regarding the tantalums, and not inserting them the wrong way around, that also goes for ALL polarised capacitors, electrolytics etc.

If the body of the capacitor has a + sign, or a - sign for that matter, then that is the way to insert them.
 
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Fowkc

Senior Member
Yes, I never noticed that. Electrolytics will indeed pop if connected the wrong way. I found this out the hard way (getting the innards of a 47000uF capacitor in my face) after testing a power supply I was building.

I recommend it to everyone. Explode an electrolytic at least once, but make sure you're at least a few feet away when doing it.
 
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manuka

Senior Member
<b>Make that WAY more than a few feet ! </b> I've long used this exploding electro. party trick as a class enlivener,&amp; some go off like a gun shot -shooting debris the length of the room.

Re original request however. STRONGLY suggest you learn by doing, perhaps by running a small 12V lamp off a low voltage electro. &amp; recording falling voltages over time etc. PSU smoothing action can be seen well on a CRO of course.

Have you checked the likes of Crocodile Clips simulations? Stan
 
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annoyin_kid

Member
alrite ive done more reading and i got a question. ya know those supression capacitors you put across a motor. are they for smoothing? and what happens if i put a 100 uf capacitor instead of the suggested 0.1nf capacitor. (the 100 uf cap is just a random example)
 
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manuka

Senior Member
The Queen's English appreciated in this esteemed forum please, else regulars may wonder about NZ schooling standards.

Ahem. I think you mean 100nF, as 0.1nF = just a near trivial 100pF. A larger cap. than is really sufficient for the job will usually still work OK (although supression spikes may be AC rather than DC), but will be a waste of money &amp; circuit space. Guess it's rather like fitting your car with a 1000 litre fuel tank.

NB- C values are of course more critical with RC timing &amp; filter circuits, but in plain supression/smoothing use caps. can be MUCH larger than specified. Hence classic 12V plug paks typically use 2200 &#181;F smoothing electros, but you can use MUCH higher values if they're the only ones to hand.

<b>BUT HOW HAS LEARN BY DOING SHAPED UP ? </b> At your age ( mid teens?)I nutted out many of these cap. basics with a crappy old moving coil meter that'd cost me a weeks farming wages. Given today's ultra cheap hi tech you could do wonders with a NZ$10 DMM from DSE. Roll up your sleves &amp; go to it! Stan




Edited by - manuka on 11/01/2007 00:26:27
 
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moxhamj

New Member
After reading many books you will know that the small value caps on motors are used to filter very high frequencies - up into the radio frequencies. Turn on an old kitchen mixer near an AM radio and you will hear this interference. Bigger caps won't filter high enough frequencies.
I like the 'learn by experience' method. Pull stuff to bits. Scrounge broken things. After you have pulled apart several radio controlled toys, or pretty much any commercial product with a motor in it, you will notice they all have these suppression caps on the motor. They must be there for a reason, because everyone puts them there. Who knows or even cares what the reason is - it must be a good one so put them on your own projects as well.
Another thing about scrounging is you end up with lots of virtually free stuff. All my 0.1uF chip caps, 22uF tantalums and motor caps have come out of old equipment. Dead computer monitors are being given away by the computer stores as everyone moves to LCDs, and they have all the big caps and small caps you will ever need, plus heaps of hookup wire.
I have literally a lifetime's supply of wirewrap wire from an old DEC10 http://www.cray-cyber.org/pictures/dec10.php which I scored some bits out of when I was 12.
So start pulling things to pieces and you will learn a lot about how things work. Then the theory will make a lot more sense.

Edited by - Dr_Acula on 11/01/2007 00:57:12
 
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annoyin_kid

Member
alright i understand. i also came across a transistor switch circuit and i realised it saved me a long bike ride to the local electronics store to get myself a relay. i got a little question about the circuit though. is it possible for me to make a h-bridge circuit for a motor using the transistor switch?

and dr_acula i would go scavenging through parts of old monitors, etc left on the street but it is just my mum wont let me. if i could i would have motor which is the size of my fist and possibly a rechargable battrey pack to go with that from a broken motorised scooter which was left across the road from my house.

Edited by - annoyin_kid on 11/01/2007 04:49:20
 
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moxhamj

New Member
Dude, that is bad news re your mother. You are going to need a shed and a bench and some shelving to collect stuff and some parts drawers etc. I think Manuka has already said this, but this little hobby can lead to jobs and a career. Cutting code is useful too - in my medical practice I save several thousand dollars a year in subscriptions for software because I wrote my own. And my house would not function without handmade electronics as we are off mains water and I don't have time to run it all manually. (Picaxes run the entire irrigation system).

All the people I know from school who were interested in electronics have gone on to have successful careers. How can we help explain this to your mum in a diplomatic way?

Re the transistor switch, is it an H bridge or a single transistor? If it is a single transistor, see my posting a few days ago re the RC car. How many pins does it have and do you have any specs?


Edited by - Dr_Acula on 11/01/2007 05:26:58
 
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steirny

Member
I'd like a dollar for every time my wife has said &quot;What have you brought home now.&quot;

I suggest you let your mother read selected parts of this thread.

Try to convince her that she could be limitting your potential.
 
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steirny

Member
By the way, re tanatalun caps.

Generally they are pretty reliable, if their ratings are respected. But has anyone noticed that when they fail, they fail spectacularly - like a magnesium flare.

I have a conspiracy theory here. Where most components just go open or short circuit and often do little damage, tantalums must be designed to fail such that their resistance exactly matches the source impedance of the power supply.

This results in maximum power transfer and maximum damage to the pcb and nearby components. Murphy's law dictates that the failure will expensive.

Just an observation.

Try to abuse one and see the light show. Make sure to use protective measures.
 
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Fowkc

Senior Member
Further to the exploding capacitors, here's one I made tonight:

http://www.fowkc.com/elec/PICAXEforum/ExplodedCap.JPG

Was formerly a 100uF 25v electrolytic. I was only using 12V, so I guess I connected it in reverse. Due to the rather disintegrated state, there's no way to know for sure :)

My ninth sense kicked in and told me to stand back when I plugged the battery in. Went off with a mighty bang, I'd forgotten just how much smoke is inside one!
 
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manuka

Senior Member
I've even had electros. go off like this <A href='http://www.chm.bris.ac.uk/motm/ni3/ni3_detonation.gif' Target=_Blank>External Web Link</a> (Celebrated Nitrogen Triiodide animated .gif)
 
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demonicpicaxeguy

Senior Member
when i was at tafe we got a small ball bearing a large pen shaft shoved a suitable sized capacitor up one end bearing up the other and fed it a rediculsy high voltage spike which preceeded to make the capacitor explode we kept it up for several weeks firing bearings down the hall 50 metres away into another class room untill we had to explain a broken window... but it's amazing how much of a kick they can give off inside a pen shaft
 
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