non-polarised electrolytics - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th September 2010, 12:52 AM   #1
diyAudio Member
 
Join Date: Mar 2002
Default non-polarised electrolytics

When putting 2 electrolytics in series to
make a non-polarised cap .......
Is it preferable to put + to + or - to - ?
  Reply With Quote
Old 11th September 2010, 02:07 AM   #2
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
I usually put (+) to (+) but in reality it should not make any difference......but.........


For small capacitors - say, 1 uF or less - a non-electrolytic type will very
likely be satisfactory if its size - these are usually much larger - is not a
problem.

There are several approaches to using normal polarized electrolytic capacitors
to construct a non-polarized type.

None of these is really great and obtaining a proper replacement would
be best. In the discussion below, it is assumed that a 1000 uF, 25 V
non-polarized capacitor is needed.

Here are three simple approaches:

* Connect two electrolytic capacitors of twice the uF rating and at least
equal voltage rating back-back in series:

- + + -
o----------)|-----------|(-----------o
2,000 uF 2,000 uF
25 V 25 V

It doesn't matter which sign (+ or -) is together as long as they match.

The increased leakage in the reverse direction will tend to charge up the
center node so that the caps will be biased with the proper polarity.
However, some reverse voltage will still be unavoidable at times. For
signal circuits, this is probably acceptable but use with caution in
power supply and high power applications.

* Connect two electrolytic capacitors of twice the uF rating and at least
equal voltage rating back-back in series. To minimize any significant
reverse voltage on the capacitors, add a pair of diodes:

+---|>|----+----|<|----+
| - + | + - |
o-----+----)|----+-----|(----+------o
2,000 uF 2,000 uF
25 V 25 V

Note that initially, the source will see a capacitance equal to the full
capacitance (not half). However, the diodes will cause the center node
to charge to a positive voltage (in this example) at which point the diodes
will not conduct in the steady state.

However, there will be some non-linearity into the circuit under transient
conditions (and due to leakage which will tend to discharge the capacitors)
so use with care. The diodes must be capable of passing the peak current
without damage.

* Connect two capacitors of twice the uF rating in series and bias the center
point from a positive or negative DC source greater than the maximum signal
expected for the circuit:

+12 V
o
|
/
\ 1K
/
- + | + -
o----------)|-----+-----|(-----------o
2,000 uF 2,000 uF
35 V 35 V

The resistor value should be high compared to the impedance of the driving
circuit but low compared to the leakage of the capacitors. Of course, the
voltage ratings of the capacitors need to be greater than the bias plus the
peak value of the signal in the opposite direction.

Last edited by jam; 11th September 2010 at 02:13 AM.
  Reply With Quote
Old 11th September 2010, 02:12 AM   #3
jcx is offline jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
no its really better to buy a nonpolar/bipolar electrolytic with a full thickness oxide grown on both electrode foils

according to Bateman's "Capacitor Sound" series the 2 back-to-back electros gives much more distortion
  Reply With Quote
Old 11th September 2010, 02:16 AM   #4
jam is offline jam  United States
diyAudio Member
 
jam's Avatar
 
Join Date: May 2001
Location: Auburn, CA, USA
........yes, but only if it is available.

Jam
  Reply With Quote
Old 11th September 2010, 03:15 AM   #5
Fedess is offline Fedess  Argentina
diyAudio Member
 
Join Date: Jul 2010
Location: Buenos Aires - Capital Federal
Depending what do you need it for, maybe it's better to buy few (or lots!) of polyester, (or MKT, etc) caps and put them in parallel to get the value you need. I understand this way you get better sound quality...

Anyway I used two electros in series for a 1st order filter and they just worked well...

I have read on internet that using at least one polyester (or other kind of non polarized caps) in parallel with the resultant of the in-series electrolytics gives better sound quality... but I'm not sure of that...
  Reply With Quote
Old 11th September 2010, 08:46 AM   #6
pjp is offline pjp  India
diyAudio Member
 
pjp's Avatar
 
Join Date: Nov 2006
Location: under the rainclouds
Back to back electrolytics are sooo 1990's.

When you can buy 100F Ceramic caps, I don't see any reason to use electrolytics.
  Reply With Quote
Old 24th April 2015, 05:53 AM   #7
diyAudio Member
 
Join Date: Jan 2008
I'am recapping a old dbx160 compressor, and I need a 4.7uF/25V non polarized cap.
I could use 4x 4.7uF polarized caps and arrange them in 2 parallel pairs + to +.
What if I put 2x 10uF + to +, in order to safe space? Would the 0.6uF on each side in excess make a difference or is it neglectable?
I don't have any 4.7uF caps on hand but tons of 10uF/50V...
  Reply With Quote
Old 24th April 2015, 06:31 AM   #8
chip_mk is offline chip_mk  Macedonia
diyAudio Member
 
Join Date: Jul 2005
Location: Skopje, Macedonia
Quote:
Originally Posted by PhantomBox View Post
I'am recapping a old dbx160 compressor, and I need a 4.7uF/25V non polarized cap.
I could use 4x 4.7uF polarized caps and arrange them in 2 parallel pairs + to +.
What if I put 2x 10uF + to +, in order to safe space? Would the 0.6uF on each side in excess make a difference or is it neglectable?
I don't have any 4.7uF caps on hand but tons of 10uF/50V...
2x10uF should be OK, elcos tolerance is typically +-20% anyway. However, if space is not critical it's even better to go for 4.7uF MKT cap.
  Reply With Quote
Old 25th April 2015, 02:14 AM   #9
diyAudio Member
 
Join Date: Dec 2005
Location: Kuala Lumpur
Quote:
Originally Posted by pjp View Post
Back to back electrolytics are sooo 1990's.

When you can buy 100F Ceramic caps, I don't see any reason to use electrolytics.
100 uF ceramic is going to be using X5R dielectric. This is very voltage dependent, see http://www.niccomp.com/help/VoltageC...-032012-R1.pdf

Not a good idea for a crossover
  Reply With Quote
Old 25th April 2015, 04:44 AM   #10
benb is offline benb  United States
diyAudio Member
 
Join Date: Apr 2010
Quote:
Originally Posted by jam View Post
...
* Connect two capacitors of twice the uF rating in series and bias the center
point from a positive or negative DC source greater than the maximum signal
expected for the circuit:

+12 V
o
|
/
\ 1K
/
- + | + -
o----------)|-----+-----|(-----------o
2,000 uF 2,000 uF
35 V 35 V

The resistor value should be high compared to the impedance of the driving
circuit but low compared to the leakage of the capacitors. Of course, the
voltage ratings of the capacitors need to be greater than the bias plus the
peak value of the signal in the opposite direction.
I've read about this very thing, "biasing" capacitors in crossovers, being done before with both electrolytics and other types.
Charge Coupled Crossovers Article By Jeff Poth
Pre-bias capacitors in crossover

Quote:
Originally Posted by pjp View Post
Back to back electrolytics are sooo 1990's.

When you can buy 100F Ceramic caps, I don't see any reason to use electrolytics.
For better or worse, I haven't seen a 100uF ceramic. I can imagine it used to drive a stylus in a record cutter.

Do they make ceramic capacitors big enough to be woofers?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Coupling Capacitors - Bipolar or Polarised? Narks Parts 5 12th August 2011 12:02 PM
Replacing electroytics in signal path with non-polarised - which type of caps to use? jpcoetzee Solid State 13 15th May 2008 01:12 PM
non polarised cap replacement lt cdr data Parts 13 26th November 2006 10:31 PM
Polarised SMD Caps? Lostcause Parts 10 23rd March 2006 07:28 PM
Doubt on plarised cap vs non polarised rs1026 Chip Amps 4 17th September 2004 06:15 PM


New To Site? Need Help?

All times are GMT. The time now is 09:28 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2