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 Polarized vs. non-polarized caps...

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Aaron

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PostSubject: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:02 am

I'm sure this question has been asked and answered before, but here goes. I'm fixing a set that uses a 2uF (50V) polarized e-cap. Is it okay to use a regular non-polarized film cap instead?

Thanks!

Aaron
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:05 am

Aaron wrote:
I'm sure this question has been asked and answered before, but here goes. I'm fixing a set that uses a 2uF (50V) polarized e-cap. Is it okay to use a regular non-polarized film cap instead?

Thanks!

Aaron
Yes, it will last longer too.
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Johnnysan



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:14 am

I sometimes wonder where Smeeze gets his technical expertise.

Just how does he know it will last longer?

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Aaron

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:16 am

Johnnysan wrote:
I sometimes wonder where Smeeze gets his technical expertise.

Just how does he know it will last longer?


Well, John, leaving that issue aside, what's your opinion? It is an acceptable substitution or not? Smile

Aaron
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Johnnysan



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:21 am

Yes, a mylar or film cap will work just fine in place of a regular electrolytic, if the voltage is correct or above the original.
Smeeze just seems to get off on making off the wall comments that have no basis in fact.

PS: I've been a tech for 2/3 of my life, and I'm getting old.
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:23 am

Electrolytic caps fail even when off, polyfilm will not.
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Johnnysan



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 12:57 am

I feel like such a fool, replacing all those poly and mylar caps just because my $200 cap testers said they were bad.

I should have checked with Smeezekitty first; would have saved me so much trouble.
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 1:07 am

Johnnysan wrote:
I feel like such a fool, replacing all those poly and mylar caps just because my $200 cap testers said they were bad.

I should have checked with Smeezekitty first; would have saved me so much trouble.
If you spent $200 on a cap tester, then...theirs your problem.
I am going to discontinue this conversation.
BTW The only way it could be bad was the max voltage was exceeded.
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burnt fingers



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 8:12 am

Smeeze has to start his post count all over again so expect more gems.
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Alan Douglas



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 10:35 am

Well, they DO last longer. He didn't say "forever".

Just an observation: if you choose a screen name that looks, shall we say, less than professional, some other people are apt to take you at your word.
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 11:00 am

[quote]
This has been my username for ~7 years on various websites.
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w8who

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PostSubject: Need additional info on capacitors   Tue Oct 19, 2010 7:16 pm

Hello all, Being new on this restoration of vintage radios I have a question on capacitors.
I always thought you had to watch the polarity on electrolytics . Are these mylars a different deal. Maybe this is a special type of cap. Ok guys please get me straight on this polarity issue
Sorry if I am not seeing the light here. Really enjoy this forum.
Cliff
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burnt fingers



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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 7:46 pm

A polarized electrolytic is just that and has to be used that way. A non polarized electrolytic is just what it says.

Paper caps are non polarized altho the outer foil end was often used as a shield and grounded.

Mylar and film caps are just a modern extension of the old paper caps using improved components and manufacturing. They are non polarized and can be used anywhere, anyhow their ratings and size permit.

Are they better? Ask me in 60-70 years Rolling Eyes No one expected mica caps to ever go bad.

Ive also tested 50-60 year old well used electrolytics that show no more leakage than a brand new one of similar ratings that were installed in high end equipment such as HP. The same goes for paper caps, not all Black Beauties are created equal...you paid more you got better quality.

Carl

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glasdave

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 8:11 pm

So the answer is, yes it is fine to do so.
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Radiosmoker

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PostSubject: Re: Polarized vs. non-polarized caps...   Tue Oct 19, 2010 11:33 pm

Embarassed Don't put down any member that makes a comment, we are supposedly ALL adults, not girls having a cat fight.
---------------------------------------

Just another verification online

Click Here to see

If you use a non-polarized cap in a power-supply filter, and by chance it is removed and then put in backwards (because of no polarity markings) will it have disastrous results. Will it reform or is the polarity set once it's installed? Just curious.
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OZ132HOME



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 10:06 am

Smeeze is right about the caps.
Electrolytics have failure mechanisms that paper and mylar don't.
Odds are they will not last as long.
What's your problem?
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Dave Wise



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 1:22 pm

I wouldn't use a non-polarized (a polarized cap is Right Out) electrolytic cap as a heater string reducer unless it was rated for "motor run" applications, where it's expected that it will carry current day-in, day-out. I don't know off the top of my head if any are; I've only heard of motor-start electrolytics.
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thetexan



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 3:28 pm

I have often wondered about this myself....'why does that cap have to be polarized?'

This goes to a previous question I had before which is....

Isnt capacitance is capacitance is capacitance? Does it really matter how you get it as long as you get how much you need. Unlike diodes, where polarity actually performs some function...there is no CAPACITANCE reason for one particular lead of a capacitor to be attached to either positive or negative other than because of the requirement of its design? In other words, the polarity requirement of an electrolytic or other polarized cap is because it is necessary in order for the cap to operate functionally IN ORDER TO GIVE YOU THE CAPACITANCE. Im probably not making good sense.

So, if you have a 30 uf electrolytic that means you need 30 uf of capacitance any way you can get it.....correct? Even if you can find a ceramic disk cap big enough to give it to you. Only if the capacitor needs polarity (physically) to give you the capacitance do you need to use a polarized cap.

Which brings up another point....using the previous theory (if Im correct) lets say you used a electrolytic cap to replace a ceramic (bear with me here). Since the electrolytic needs to be hooked up correctly how do you determine which is the negative and positive at that point in the circuit?

Of course you need to observe the other parameters such as tolerance, voltage rating, leakage in the process of finding a cap suitable for the job. And each type may be better at one thing than another. But in the end I could solder wire to two pieces of aluminum foil if it would give me the correct capacitance and parameters I need for the job.......right?

I used to struggle to find a particular cap. Now I just look for capacitance...or at least that's what I got from my previous thread.

Ill probably just end up blowing something up!

Please remember, for me and any other newbies, this is a good learning topic where we depend on the experience of you experienced techs to guide us. And thanks for all of your teaching.

tex

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Dave Wise



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 3:35 pm

Polarized electrolytic caps are polarized only because that construction is cheaper and smaller. (This also makes them the vast majority, to the point where it's befuddling to run into one that's not polarized.) Reversal damages polarized caps; there's no circuit application for it.

Now, there was such a thing as an "electrolytic rectifier" at one time, and it so happens that it is built similar to the early electrolytic caps. I am getting the cart before the horse, as actually, electrolytic rectifiers came first. I think that someone realized that, provided you didn't reverse it, you could use it as a cap, and that's how electrolytic capacitors came about. I could be wrong about this history, if anyone has it better, speak up.

Dave Wise


Last edited by Dave Wise on Wed Oct 20, 2010 4:34 pm; edited 1 time in total
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Johnnysan



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 3:56 pm

Smeezekitty wrote:

'Electrolytic caps fail even when off, polyfilm will not.'

This is simply not true, and this is certainly not the first time that Smeezekitty has made incorrect and misleading statements. How does Smeeze know that mylar and poly will last longer? And how much longer?
It's not as if electrolytics blow up like firecrackers. I have equipment that has plenty of electrolytics that are now over 50 years old. Will they last another 50 years? No. Should they all be replaced with polyfims caps? No.
Some people should get a little experience under their belts before they start making blanket statements.
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Alan Douglas



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 8:27 pm

The anode film in an electrolytic is created at manufacture, and the polarity can't be reversed later.

There are no motor-run electrolytics.

Ralph Mershon had the original patents on electrolytics. I believe they were for overvoltage protectors on power lines, not capacitors per se, but I haven't looked at the patents. I suspect he got lucky. His biography was published in 1956 by Ohio State University, 2 elaborate volumes, I'm almost certain as a condition of their receiving his estate since the author was a former registrar of the university and not a technical author.
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radiotechnician



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PostSubject: Re: Polarized vs. non-polarized caps...   Wed Oct 20, 2010 10:00 pm

If you use a non-polarized capacitor it cannot form anything. Both plates are the same and need no forming, ever. (that said, everyone in here knows an example or many a capacitor developing polar leakage. Hell some turn into batteries!) (after 20 years--)
If you use a non-polarized (np) electrolytic it is known as a double layer electrolytic, acts like two polarized electrolytics back to back in series. These are designed for AC use so each layer gets exercised. The layers alternativley offer a low impedance and then act as capacitors.
That creates heat. Motor starting capacitors are rated for duty, ie passing 7 amps AC (150ufd)
for 30 seconds (17 ohms reactance 120 V 60 Hz,) and resting for 4 minutes.

On forming, Ive seen caps increase their rated capacity by 25 % after years of being used on voltages lower than what they were rated at.

Old electronics need to be brought up slowly because an electrolytic dormant for 10 years
may show hugh conductance (blow uo) but if coaxed back to life with a current limited power pack, will be servicable again. Make up your own chemistry.

.

de

VE7ASO

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Dave Wise



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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 10:31 am

Quote :
There are no motor-run electrolytics.

Thanks for nailing that down, Alan. So electrolytics
are NOT in the picture for heater string reduction.
The only parts one should consider are film/foil and paper/foil.

Dave Wise
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smeezekitty

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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 11:13 am

Johnnysan wrote:
Smeezekitty wrote:

'Electrolytic caps fail even when off, polyfilm will not.'

This is simply not true, and this is certainly not the first time that Smeezekitty has made incorrect and misleading statements. How does Smeeze know that mylar and poly will last longer? And how much longer?
It's not as if electrolytics blow up like firecrackers. I have equipment that has plenty of electrolytics that are now over 50 years old. Will they last another 50 years? No. Should they all be replaced with polyfims caps? No.
Some people should get a little experience under their belts before they start making blanket statements.
Electrolytics dry out and the paper drys out and when you turn them on, you have leakage and zero capacitance.
If the dielectric in a polyfilm does not have a hole in it and the plates are good then its good to go.
No paste or paper to worry about.
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Lou deGonzague



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PostSubject: Re: Polarized vs. non-polarized caps...   Thu Oct 21, 2010 2:39 pm

There is no doubt that a mylar film cap will outlast any electrolytic under normal conditions used in a radio. I have nos electrolytics from the 30's and they are all bad. Also electrolytics do explode sometimes when they go bad. Using a mylar in place of a small electrolytic is a good idea especially in the old AK's and others that used 1 or 2 mfd in their powerpacks.
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