Will 220uf electrolytic capacitors rated at 6v work in a 9v pedal?

[jimitrader]

Will 220uf electrolytic capacitors rated at 6v work in a 9v pedal?
here is the build:
https://effectslayouts.blogspot.com/2016/03/wampler-faux-spring-reverb.html
thanks!

[Steben]

Will 220uf electrolytic capacitors rated at 6v work in a 9v pedal?
here is the build:
https://effectslayouts.blogspot.com/2016/03/wampler-faux-spring-reverb.html
thanks!

It is the main power cap, it really connects to 9V. Bad idea.

[Mark Hammer]

Generally advisable to use caps rated at 1.5-2x the voltage they expect to encounter.  So one probably want to use a 16V cap in the power part of a 9V pedal.  In view of how many players are likely to experiment with higher supply voltages that their power bricks can provide (e.g., 12V or 18V), and the negligible price and size difference between 16V and 25V-rated caps, manufacturers are more likely to use 25V or even higher ratings just so they don't get returns or burden authorized repair folks with problems that could be easily avoided.

The interesting sort-of almost-exception is caps used to provide Vref (artificial ground).  The power supply may be 9V, but get divided down to half of that, or thereabouts, with a resistive pair, or perhaps a zener diode.  Of course, even there, a 6V-rated cap doesn't really provide a sufficient margin of error for a 4.5V Vref that might conceivably go higher if the source powering the pedal goes higher.

I'm curious about, and will defer to the real EEs here, regarding what an appropriate voltage rating is for LFOs.  For instance, some LFOs will use a back-to-back pair of electrolytics (e.g., 10uf + 10uf) to achieve a large non-polarized capacitance value.  If such an LFO were embedded within, say, a synth or similarly complex system, powered by +/-15V or +/-12V, what would be an appropriate minimum voltage rating?

[jimitrader]

Quote from: Steben on Today at 11:48:40 AM<blockquote>Quote from: jimitrader on Today at 11:34:32 AM<blockquote>Will 220uf electrolytic capacitors rated at 6v work in a 9v pedal?
here is the build:
https://effectslayouts.blogspot.com/2016/03/wampler-faux-spring-reverb.html
thanks!
</blockquote>
It is the main power cap, it really connects to 9V. Bad idea.
</blockquote>
Thanks thats what i thought...

I am trying to find some 220uf with higher v rating..this town has no electronics stores at all..
what about 2 100 uf 25v caps in parallel ??

on my cap meter says 220 uf seems like would work?

would be around 220uf 50v?( doubles the voltage)

[willienillie]

what about 2 100 uf 25v caps in parallel ??

That would be perfectly fine.

would be around 220uf 50v?( doubles the voltage)

No, still 25v.

[antonis]

Voltage is doubled when caps are placed in series (like batteries..) but capacitance is halved (in case of equal value caps)..
(e.g. 2 X 100μF at 25V set is series result into 50μF at 50V..)

About over-voltage rating, it should be wise to take into account what Mark said but, IMHO, only in case of reservoir caps (right after rectification configuration) 'cause it has to count for mains over-voltage variations..

[willienillie]

Voltage [rating] is doubled when caps are placed in series

Are you sure about that?  Wouldn't the "first" cap have the full DC voltage across it?

[bluebunny]

The full DC voltage is across the two capacitors in series.

[davent]

Voltage [rating] is doubled when caps are placed in series

Are you sure about that?  Wouldn't the "first" cap have the full DC voltage across it?

Formula for voltage across caps in series.



https://www.electronics-tutorials.ws/capacitor/cap_7.html
dave

[Marcos - Munky]

what about 2 100 uf 25v caps in parallel ??

This cap is for power supply noise filtering. You'll see values between 22uF and 220uF for this cap, depending on a few things like the circuit itself and what the creator of the circuit had on stock when they created it. Using a big cap doesn't hurt, so often this cap is oversized.

In short. Since you have 100uF 25V caps, try a single one and check how it goes. It may be enough. If it's not, then add another one in parallel, but I think it won't be necessary.

[Harry Muff]

get yourself the right part or work alike , dont work hard on something then compromise. place a parts order is my recommendation  - mouser has free programs for projects and bom you can store them on their website or print off

[Rob Strand]

In short. Since you have 100uF 25V caps, try a single one and check how it goes. It may be enough. If it's not, then add another one in parallel, but I think it won't be necessary.

Far more sensible.

Don't use series caps for Electrolytics unless you use parallel resistors to force the sharing of the voltages.  It's undesireable for low voltage circuits.   Paralleling smaller values is far more preferred.

C8 (220uF) should be at 16V or more.
C10 (100uF) and C11 (100uF)  should be 10V or more;   6.3V is *just* OK.
All the others would work with 6.3V or more.

[willienillie]

Voltage [rating] is doubled when caps are placed in series

Are you sure about that?  Wouldn't the "first" cap have the full DC voltage across it?

Formula for voltage across caps in series.



https://www.electronics-tutorials.ws/capacitor/cap_7.html
dave

Thanks for the link.  Obviously I don't know what I'm talking about.  I think of capacitors as blocking DC, not dividing it like series resistors, and I wouldn't have guessed that capacitance even factored in.  But I have zero electronics education, I just like building guitar stuff.  I'll read up.

Question though, why did Fender (and others) add this resistor voltage divider to their amps?  I thought it was necessary to divide the B+ evenly between the two series filter caps (each rated for only 350VDC), allowing them to use lower voltage caps there.



Edit:  Rob's simul-posting this:

Don't use series caps for Electrolytics unless you use parallel resistors to force the sharing of the voltages.

So something electrolytic specific?

[Rob Strand]

So something electrolytic specific?

Electrolytics have large and varying leakage.  Leakage can cause the voltage across series capacitors to be quite different.  Just like a voltage divider but with one resistor must smaller than the other.   When you add a voltage sharing divider, like you see in some tube amps, the current down the divider is chosen to be somewhat larger than the expected leakage. 

Strictly you need sharing dividers on all series cap but often that defeats the purpose of the cap providing isolation.

(There's one special case where you *never* use voltage sharing resistors:  in some parts of switch-mode power supplies there are caps which connect between the primary and secondary  These caps should never have sharing resistors.  The whole point of the cap is to provide isolation.   Adding resistors is forbidden for safety reasons.   In fact, the safety standard says *each* cap must handle full voltage,  Adding a second series cap is not about increasing voltage ratings or about part values.   The reason for adding the second cap is about increasing safety if one of the caps gets shorted.    The motive for series caps is *much* different here.)


EDIT:
You don't have to believe me, here's a paper from a cap manufacturer,
https://www.illinoiscapacitor.com/pdf/Papers/Voltage%20balancing%20resistors.pdf

[Rob Strand]

Question though, why did Fender (and others) add this resistor voltage divider to their amps?  I thought it was necessary to divide the B+ evenly between the two series filter caps (each rated for only 350VDC), allowing them to use lower voltage caps there.

That was to increase the voltage rating.   I guess maybe the size or availability drove them to use 350V caps.

On the higher power tube amps with 600V to 800V rails the series caps are very common.

[davent]

Thanks for the link.  Obviously I don't know what I'm talking about.  I think of capacitors as blocking DC, not dividing it like series resistors, and I wouldn't have guessed that capacitance even factored in.  But I have zero electronics education, I just like building guitar stuff.  I'll read up.

Was a lesson for me as well.
dave

[PRR]

> I think of capacitors as blocking DC, not dividing it like series resistors, and I wouldn't have guessed that capacitance even factored in.

The initial turn-on surge, voltage splits about like 1/C.

Long term (after a part-second) the voltage splits AS RESISTANCES. What resistance? EVERYthing has a resistance, or a similar DC current flow from DC voltage pressure. A 100uFd cap may leak 100uA, which at 10V is a lot like 100,000 ohms. VERY variable with time, age, temp, abuse, and etc. But two same-spec same-lot caps in series are fairly sure to split like 40:60 or 60:40 or even near 50:50.

[amptramp]

The NAVSEA derating spec is useful for what we do and aluminum electrolytic capacitors are derated to 70% meaning in a 9 volt circuit, the capacitor must be rated at 12.85 volts (70% of that is 9 volts).  I am not a fan of such thin dielectrics, so 16 volt would be an absolute minimum and I would be much more comfortable with 25 volts.  The document is here:

https://www.navsea.navy.mil/Home/Warfare-Centers/NSWC-Crane/Resources/SD-18/Products/Capacitors/Derating/

Some NAVSEA derating specs are more stringent than NASA specs but the NASA specs seem to have deleted aluminum electrolytics entirely.

The very thin aluminum oxide layer on a low-voltage aluminum electrolytic is subject to high leakage currents and local faults that could be ignored at higher voltage ratings, so I prefer to stay at 25 volts as a design minimum.