Capacitor hook up question

ajm · Post by **ajm** » 29 Nov 2004 6:08 pm

Let's say that I have two electrolytic polarized caps of equal value and voltage rating. For any math that might come up, let's say that they are 100 uF 50 volt caps.

I hook them up in series so the two "-" leads are connected together.

I can then take the two "+" leads and connect them across a circuit (for example, one + lead to a power supply lead and the other to ground.

What does hooking these caps up this way accomplish? Is this a way of making a large value NON-polarized cap?

What is the value of this component now? Is it 2 x 100 uF in series = 50 uF? What is the DC rating of this component? Is it the rating of the cap with the lowest value? (In this case they are both 50V caps so it would be 50v.)

Thanks in advance.

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Artie McEwan

Dave Grafe · Post by **Dave Grafe** » 30 Nov 2004 12:52 am

Bingo - you just have created a 100uF 50v non-polar capacitor.
dg

Jay Fagerlie · Post by **Jay Fagerlie** » 30 Nov 2004 6:17 am

That would be 50 uf, caps in parallel add up, in series you have to do the one over math.
I would be wary of connecting an electrolytic across reverse voltages. They are designed to be connected + to plus voltage, and - to minus voltage. Connected the other way around usualy ends up in a loud pop and one ruined cap, not to mention spraying the electrolytic fluid and the guts of the cap all over the place.
If you want a non-polarized cap, buy one.
Jay

John Daugherty · Post by **John Daugherty** » 1 Dec 2004 5:10 am

I have used this method when I needed a non-polorized cap in a hurry. When connected in series (minus to minus) you will have a non-polorized,50 mfd, 100volt cap.
I recently repaired an antenna rotor by making a cap by this method........JD

Dave Grafe · Post by **Dave Grafe** » 1 Dec 2004 10:43 am

My bad on the math.
Sometimes one cannot get the desired value in a NP cap.
dg[This message was edited by Dave Grafe on 01 December 2004 at 10:46 AM.]

ajm · Post by **ajm** » 2 Dec 2004 7:45 pm

That's what I thought: a non-polarized cap.

However, if you have two each 100 uf 50v caps and hook them up like this, I believe that the new non-polarized cap will have a value of 50 uf and 50v. The voltage rating will be the lowest rating of the two caps.

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Artie McEwan

Blake Hawkins · Post by **Blake Hawkins** » 3 Dec 2004 2:56 am

Nope, Artie...when caps are in series,
the voltage divides across them.
In your example, you have 50 mfd at 100 volts. (As John stated.)

A reference to check this is any edition of the "Radio Amateur's Handbook" published annually by the ARRL.
I happen to have a 1968 edition handy and it is on page 25 in that one.
Blake[This message was edited by Blake Hawkins on 03 December 2004 at 02:58 AM.]

Ray Minich · Post by **Ray Minich** » 3 Dec 2004 4:37 am

1968 edition, Red Cover? I built the regenerative receiver from about a 1956 edition. Long Live 12SQ7's !

Blake Hawkins · Post by **Blake Hawkins** » 3 Dec 2004 7:12 am

Ah...yes, Ray..
The Red Cover is correct. It's a bit worn and dog eared.
Those "first" radios were fun to build and to use.

73

Blake
N4YCQ

Keith Hilton · Post by **Keith Hilton** » 3 Dec 2004 12:27 pm

The way I remember it is like this: Capacitors do the opposite from resistors in parallel, and the opposite from resistors in series. I mean if the capacitance is increased or decreased. Of course polarized capacitors must be put in with the correct polarity. They must also have the correct voltage rating.

John Daugherty · Post by **John Daugherty** » 3 Dec 2004 12:38 pm

Keith, You are sure getting smart in your old age.......hahaha. Absolutely correct information. Good to see you are still kicking, my friend. Have a great day.
As soon as I recover from my atv rollover,(messed up my rib cage) I will resume trying to wear out my Hilton Pedal and leave the stunts to Evil Kneivel...........JD

ajm · Post by **ajm** » 4 Dec 2004 12:16 pm

Blake wrote: "Nope, Artie...when caps are in series, the voltage divides across them.
In your example, you have 50 mfd at 100 volts."

This is true if they are hooked up + - + - (or - + - +). That is how one normally finds caps hooked up in series.

But remember that one of them is hooked up "backwards" in our case here. If they are hooked up in series with the + leads tied together (or the - leads tied together) as we are talking here, is this still true? My source tells me it is not, and my suspicions are the same. The rating of the non-polarized cap that we have made is equal to the lowest rating of the two caps used.

If you have a 100uf 50v cap, and a 100uf 30v cap, and you hook them up like this, your new cap will be a non-polarized 50uf 30v cap.

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Artie McEwan

Blake Hawkins · Post by **Blake Hawkins** » 4 Dec 2004 5:03 pm

Artie, perhaps I was too hasty in my reply.
I have looked through my library and am unable to find anything in my electronic textbooks about hooking the electrolytics up backwards.
I do have some information in "Hi-Fi" construction articles but they fail to consider the voltage.
On an audio forum, I've seen a discussion which says that the voltage adds either way.
But having no information on the poster's background, I cannot cite that as being of any value.
So, lacking any reliable reference, I will defer to your source.
Blake
[This message was edited by Blake Hawkins on 04 December 2004 at 05:04 PM.]

Ken Fox · Post by **Ken Fox** » 5 Dec 2004 7:00 am

Well, I set up a test scenario on my work bench with 2-25ufd@50WVDC and my old trusty B and K cap tester. It was the same backward in series or in series with polarities aiding, 1/2 the capacitance.[This message was edited by Ken Fox on 05 December 2004 at 07:03 AM.]

Bill Crook · Post by **Bill Crook** » 5 Dec 2004 7:42 am

Ken.....

You should also add that it doubles the voltage capabilities.......

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ajm · Post by **ajm** » 5 Dec 2004 8:15 am

Bill;

If you connect them (+ -) (+ -) then the VOLTAGE capabilities will add.

If you connect them (+ -) (- +) then the jury is still out, but I'm betting that they do not.

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Artie McEwan

Bill Crook · Post by **Bill Crook** » 5 Dec 2004 9:39 am

AMJ.............

You are right !!

It is an imformed Electronics tech that understands the miride of elctronics formulars that make up the working stuff that we do and use (after we do the physical stuff) that we know just how ever the real world works when we attempt to do the physicial stuff.

Work on it....... thats the best way !!

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http://f1.pg.photos.yahoo.com/ph/crookwf/my_photos