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 Electrolytic Capacitors

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smyers10



Join date : 2012-06-06

PostSubject: Electrolytic Capacitors   2015-11-25, 1:50 pm

I just fixed a computer speaker set. I know it is not in the realm of Antique, but the question does transverse (?) Antique and also New.

My wife gave them to me to fix as they had a hum. I could not find a scamatic for the set (BOKA 35 watt Model SW-2000). She liked the sound out of them when she listened to her CD's on the Computer. I thought I would open them and see (visually) a bad cap. No such luck! I then got on Duck Duck GO (alternative to Google) and I found where a guy had the same problem. He replaced two Caps (220 micro Farad at 16v) with 1000 micro Farad at 16 volts, His hum went away. I got my stash out and I had 1000 micro Farad at 25 volts. I replaced the two with the larger, and my wife thinks I can now fix anything!

Can anyone explain to me what upgrading the micro Farads from 220 to 1000, what I did? Also, what is the diff. from 16 volts to 25 volts. It is hard to argue with success, but I was wanting some info. Thanks for the Bandwith.

Steve
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Electrolytic Capacitors   2015-11-25, 2:12 pm

You have to understand that capacitors store a voltage, the 16 volts is designed to withstand voltages up to 16 volts without breaking down, replacing it with a 25 volt one just means that now it would take up to 25 volts before malfunctioning. The capacity of the capacitor tells us, with out going into math and such, that it will take a longer time to discharge the stored voltage. 

Capacitors are used in power supplies, to fill in the voltage swings, by adding the stored voltage when the voltage in the power supply drops. The power supplies a changing voltage that needs to be smoothed out, because the supplied voltage itself actually goes from 0 then up to 12 volts then back down to 0 volts, this is repeated 60 times a second. The capacitor sees the voltage starting to go down and like water seeking its own level discharges its stored voltage to fill in the gaps of lower voltages.

So when the capacitor goes bad the the voltage is no longer smooth, but has ripples. That then sneaks into the audio circuit, causing hum.

Hope this helps you understand the reason for filter caps and one of the functions it is used for.

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smyers10



Join date : 2012-06-06

PostSubject: Re: Electrolytic Capacitors   2015-11-26, 5:46 am

Yes it does! Thanks for the reply, very informative.
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smyers10



Join date : 2012-06-06

PostSubject: Re: Electrolytic Capacitors   2015-11-28, 10:46 am

Additional thought. When I found the 220 MFD caps and replaced them with the 1000 MFD, how did the designer come up with the need of 220, and why did the 1000 work? Was the 220 bear min. and the 1000 overkill?

Steve
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Electrolytic Capacitors   2015-11-28, 3:50 pm

Designers are not always in a position to design efficient and quality in each circuit, a lot of designs are based on a compromise between costs and quality demanded by the manufacture.

The size of the capacitor has to be taken into consideration as far as recovery time to charge fully up to the voltage used. A larger capacitance takes more current and could be a strain on the power source. So a heftier power source would cost more, larger transformers, heavier duty solid state devices, heavier wires or thicker traces on a circuit card. Yet the design can be to use the least parts and still be functional. There are two main thoughts by manufacturers either fast turnover of cheap products or quality to prevent failure thereby enhancing reputation.

Look at my experience with two manufacturers, GE AND MOTOROLA. I have worked on both Mobile two way transceivers and pagers, GE had a rats nest of wiring causing a lot of repairs, on the MOTOROLAs very seldom were there repairs, mostly just cleaning. The circuit cards had no modifications and were clean of after the fact mods. If MOTOROLA HAD mods a new designed circuit card would be made.

By substituting the capacitor for a larger capacity you may have the power supply put under stress during startup. Higher voltage rating is better for less failures, but you can also look for quality in capacitor manufacturers and by their reputation. 
But that's another type of discussion.
If you were talking about other than power supplies, then capacity values are critical, in A.F., I.F., and R.F. and even trace layouts can be critical.

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smyers10



Join date : 2012-06-06

PostSubject: Re: Electrolytic Capacitors   2015-11-28, 5:48 pm

This was in (I feel) each of the channels (L & R), but I could not find the scamatic for the amp. I don't think that these were in the power portion of the amp. I was just trying to get an understanding of how they came to the 220 mf and how come the 1000 mf worked.

Thanks,
Steve
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Cliff Jones
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Join date : 2010-11-22

PostSubject: Re: Electrolytic Capacitors   2015-11-28, 7:05 pm

O
Unless I can see a Schematic there is no way I can tell what they were used for. 
If it's made in China, the chances are finding a schematic will almost be fruitless.
If made even here recently, it would be difficult.

If you think they were in the audio portion of the amp, then they could be used as filters because the power supply still has to provide all the voltages to make the rest of the system work.

Capacitors can also be in the audio system, and provide additional smoothing of what is called the B+ or rail voltage. Also they can be used to stop D.C. Voltage from entering another part of the circuit. There can be an audio signal present on a D.C. Voltage, the capacitor can allow just the audio portion through.

Capacitors have many functions, smoothing, blocking, passing, shorting, oscillation, all depending what part of the circuit it's designed for, and that's just capacitors. 
Unless you start to understand the basics of electronics, you will have a difficult time comprehending electronics design.

I started in electronics at the tender age of 12, and that was just to understand how a simple crystal radio worked. I ended up studying electronics to get my ham license, and having buddies in school that helped. I built my first 1 tube radio after hours at High school evening class. It wasn't easy, because I was lacking in math skills, yes geometry, algebra, calculus, and trigonometry are require just to prove concepts and show how the electricity is manipulated in a circuit.
One formula is R = E / I, then there's other math formulas on how to find out what values of reactance, resistance, current, voltage, impeadance, conductance, phase, capacitance, inductance, wire sizes needed, insulation thickness, schematic reading, tube, transistor, I.C.s functions, and then construction of the same. There are physics involved, and the list goes on.

It has taken Me almost 50 years, of working in electronics, to understand just the Basic, I don't think I would be able to get into Engineering design, and carry on any type of discussion, when you don't understand the very basics,
If you want to learn, there are many books, and college courses that you may take if you have a serious penchant for learning. 

You can get a lot of information even in forums, and there are free PDF FILES RELATING TO THE BASICS OF Electricity and Electronics.
A rule of thumb is any size of capacitance greater than say 0.1 mfd is probably used in the power supply side, anything less is frequency control. Thats not a fact but my own interpetation.

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