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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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29th May 2020, 7:21 pm | #1 |
Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 595
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Capacitor Polarity
Good evening all, which is positive/negative on the attached caps.
Why would they not make things easier and just put + and - on the caps? |
29th May 2020, 7:23 pm | #2 |
Dekatron
Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,127
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Re: Capacitor Polarity
+ve on the left, -ve on the right in the upper one. N.B. apart from any other clues, the minus signs in the circles have an arrow pointing to the right.
On the same basis, the -ve in the lower one is toward the viewer.
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29th May 2020, 7:25 pm | #3 |
Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 595
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Re: Capacitor Polarity
Thanks Dave; just checking with you all.
Brian |
29th May 2020, 7:35 pm | #4 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,713
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Re: Capacitor Polarity
Does someone know what prompted the change from highlighting the +ve end to the -ve end?
The current scheme always seems a bit contra-intuitive to me
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29th May 2020, 8:31 pm | #5 |
Heptode
Join Date: Jun 2017
Location: Southport, Merseyside, UK.
Posts: 646
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Re: Capacitor Polarity
I agree Graham. Back in the day the +ve often had a red spot on the tag.
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29th May 2020, 8:47 pm | #6 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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Re: Capacitor Polarity
Isn't the body/case always negative on an electrolytic?
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29th May 2020, 8:57 pm | #7 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,871
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Re: Capacitor Polarity
Case doesn't always have to be negative on aluminium electrolytics, also some get formed the wrong way round. They are symmetrical before forming.
Convention is to mark the -ve pin on aluminium parts, but the +ve pin on tantalums. God only knows why. David
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29th May 2020, 9:13 pm | #8 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
Posts: 2,172
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Re: Capacitor Polarity
Sorry I meant on an axial leaded one
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29th May 2020, 10:14 pm | #9 |
Dekatron
Join Date: Jun 2013
Location: East Sussex, UK.
Posts: 3,326
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Re: Capacitor Polarity
I heard it was to do with component insertion machines and they optically recognise the stripe and most PCB's are marked with a shaded area for the negative terminal.
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30th May 2020, 12:14 am | #10 |
Banned
Join Date: Jun 2015
Location: Mareeba, North Queensland, Australia
Posts: 2,704
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Re: Capacitor Polarity
Those Illinois Capacitors are not very good at high voltage !! Yes thats off topic but I change them regularly. They blow the end seals out, AND with very much lower voltage than written on the can.
Joe |
30th May 2020, 7:31 am | #11 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,982
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Re: Capacitor Polarity
I saw this problem with a brand new-old-stock Tektronix FET probe I picked up for not very much. I opened the power supply to change the mains transformer tapping, and the main (axial) smoothing cap seal had failed.
Turned out that over a period of time Tek had that problem as a result of the de-fluxing agent they used on the boards. It compromised the rubber seal on the + end of board-mounted electrolytics. Perhaps that was what saw off those Illinois caps, Joe. Craig |
30th May 2020, 11:30 am | #12 |
Heptode
Join Date: Nov 2018
Location: Staffordshire Moorlands, UK.
Posts: 595
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Re: Capacitor Polarity
Thanks Joe, will keep an eye on that one; luckily I only needed to purchase one of them.
Brian |
30th May 2020, 2:29 pm | #13 | |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,129
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Re: Capacitor Polarity
Quote:
Printing the details on the heat shrink sleeve adds no cost, it must be printed and applied in any case. This pre-dated the general use of machine vision and automatic assembly. |
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31st May 2020, 7:38 pm | #14 |
Dekatron
Join Date: Oct 2003
Location: Southport Lancashire, UK.
Posts: 3,233
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Re: Capacitor Polarity
I find that a good double check is that the positive lead is usually the longer one on radial caps
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Paul |
31st May 2020, 8:04 pm | #15 |
Nonode
Join Date: Jan 2016
Location: Stafford, Staffs. UK.
Posts: 2,532
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Re: Capacitor Polarity
Apparently some years ago RS sent out a batch of capacitors, where the sleeve had been put on the wrong way round. Allegedly amongst other things there were a few gnnnnnn bang incidents at the army school of electronics. As told to me by my first boss who had been an instructor there. In case anyone doesn't recognise it gnnnnnn is the sound of amps (as described by him). I recognise that sound.
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31st May 2020, 8:29 pm | #16 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
Posts: 4,395
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Re: Capacitor Polarity
There was a thread here a while back where someone queried the polarity indication on an RS-supplied Sprague HV electrolytic, and it turned out to be from another reversed-sleeve batch.
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