Electrolytic capacitor symbols on circuit diagrams – point to watch out for ! - Page 1
Forum section: electronics / general

author: Chris56000
author_rank: Frequent Contributor
timestamp: August 07, 2021, 02:02:33 pm
content: Hi!Can I take the opportunity to advise Members to be careful of electrolytic capacitor symbol polarities on some of the less well–known maker's circuit diagrams please?Amber, who manufacture a range of audio testing equipment, use the conventional symbol of a black plate and an open plate, but for reasons known only to themselves, they've used the black plate as positive !Some E. European makers that use the horrible i.e.c. symbol have used the "open box" plate as negative as well !Admittedly these makers do clarify the polarity with a plus sign, but what's the point of having a "standard" when maker's invent their own variations on a theme?The circuit symbols on my drawings (see my most recent posts on page 2 of this thread:–https://www.eevblog.com/forum/testgear/soviet-oscilloscopes/. . . here on the Soviet C1-112A Oscilloscope for an example) are based on those specified by BS3939 (1975 edition) which have been standardized by UK Electronic Magazine publishers since the last world war, and are almost identical to the symbols used in "Elektor" magazine.(I have added the Russian system of coding resistor wattage ratings on my C1-112A drawings as it saves adding endless extra part wattage references) – if a clear table is provided on the diagram there's no problems with this!)The other reason I've not adopted the ghastly single–line '60617 representation is that my drawing software uses the older 1975 type symbols in it's libraries and I'm not going to spend hours redrawing them all just to please the Germans, etc., who dreamed up '60617 in the first place – they can keep them along with their horrible i.s.o./i.e.c. lettering !Chris Williams

author: bob91343
author_rank: Super Contributor
timestamp: August 07, 2021, 11:15:05 pm
content: I still use the older symbology, a curved line for the negative and, just to be sure as well as redundant, a + symbol in case polarity is very important.

author: cortex_m0
author_rank: Regular Contributor
timestamp: August 08, 2021, 12:02:13 am
content: The standard is the IEC 60617 symbol - two parallel plates, with a + symbol on the positive plate for polarized capacitors.If you're going to complain about deviating from standards, complain about deviating from an actual standard.

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 01:49:34 am
content: The nice thing about standards is that there are so many to choose from.Quote from: bob91343 on August 07, 2021, 11:15:05 pmThat is what I do also, but I always include the + symbol.

author: rdl
author_rank: Super Contributor
timestamp: August 08, 2021, 04:02:15 am
content: What I've read is that the curved line was to represent the outer can of polarized (electrolytic) capacitors, which is almost always the negative. Non-polarized capacitors used parallel lines (both sides straight). Having all types use parallel seems like a loss of obvious clarity.

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2021, 05:15:18 pm
content: In practice I take the curved line to mean electrolytic capacitor which includes the various tantalum parts, although not all electrolytic capacitors are polar.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2021, 06:40:00 pm
content: I still like the old British symbol. Less susceptible to misinterpretation on sloppy back of a fag packet schematics and poor scans, even if it is a bit harder to draw.EDIT:Quote from: Chris56000 on August 07, 2021, 02:02:33 pm... even if you do get idiots who draw it upside down.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 08, 2021, 06:45:04 pm
content: If there is no plus symbol, I assume whoever draw that symbol is either just clueless, or a total sadistic dickhead if they omitted that on purpose. In either case, I reverse-engineer the circuit enough to deduce the correct polarity, this usually is trivial. It's good to check that anyway.

author: floobydust
author_rank: Super Contributor
timestamp: August 09, 2021, 05:57:52 am
content: Most important is to be able to see the polarity on a PCB-with the cap installed.I use a silkscreen arc and (+)outsidethe part body (although Altium is stupid still and thinks the part is a square giving false clearance violations).I've always used the electrolytic capacitor symbol with a curved plate, it was used in American and Asian schematics back to the 1980's and that's what I learned and stay with. Europe has their own versions.I use straight plates for ceramic caps and very rarely curved plate (with no polarity) for film caps where the outside foil end is critical.

author: Chris56000
author_rank: Frequent Contributor
timestamp: August 09, 2021, 09:56:56 am
content: Hi!There is also the "non–polarised" electrolytic capacitor, manufactured with a double layer oxide film internally so that it is effectively two polarised capacitors of twice the value, internally connected "back–to–back", commonly found in speaker crossover networks, op–amp audio circuits where a large value is needed in a small size where the polarization voltage is low and subject to reversal, and very occasionally in some old CRT monitors for the "pincushion distortion" correction circuit.The conventional symbol for this is two open plates – physically they look exactly like a standard polarised capacitor but without a polarity marking (you did find "BP" on some older types), altho' large axial lead ones occasionally turn up.Chris Williams