Author Topic: Upper cap voltage. Any limits to this?  (Read 3822 times)

chumbox

Upper cap voltage. Any limits to this?
« on: June 30, 2013, 08:04:22 PM »
Hey all

Just read the great thread here:

http://www.diystompboxes.com/smfforum/index.php?topic=43546.0

And have always understood not using a low voltage cap (eg below 16v or 25v).  However from what I can gather from the thread is that there is no upper limit at all? So one could use a 1000v cap (ridiculous I know) and a circuit would still work fine?  Just wanted to clarify this in my own head.

Thanks
David

mistahead

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Re: Upper cap voltage. Any limits to this?
« Reply #1 on: June 30, 2013, 08:09:55 PM »
Novice musings before RG tells us the score  :icon_razz:
I suspect a lossy-ness somewhere there, the maximum rating also has an impact on physical size...

No there isn't an issue using 35v instead of 16v in a 9v circuit, but I suspect again diminishing return of some form (physics says more mass, same energy, different outcome, probably higher at an undesirable output and lower at the desirable one) if only you need to pump more in to reach/maintain charge across a greater surface area of capacitor material.

Guru's?

PRR

Re: Upper cap voltage. Any limits to this?
« Reply #2 on: July 01, 2013, 02:01:19 AM »
My porch needs a 6-inch beam for strength. I can use a 12" or 18" beam if I want. Though cost and weight (to lift an 18" beam) may be unattractive.

I have a 3/4-ton (1500 pounds) rated truck, but I can carry one 5-pound six-pack in it. I can't buy a vehicle with a 5-pound rating, my beer-runs are always "under-loaded".

HIGH-voltage caps cost more. However in small values, there may be no difference. (Thicker insulator may be easier to handle than super-thin film.) (Traditional Silver Mica couldn't be shaved any thinner than 500V stuff, and was often used in "zero" volt work, though today you can find 50V micas.)

There is an old-old-old thought that in *electrolytic* caps you should not send a 450V man to do a 5V boy's job. Usually cost makes this a poor idea, but sometimes it just gets too convenient (like when you have a 450V 3-section can-cap, need 2 sections for 400V duty, and have a 5V cathode to bypass.) There are stories of such caps decaying in a year. I suspect this relates more to old-old-old cap technology, and today's caps are far better. We often use 100V electrolytics in 2V work, no problem.
« Last Edit: July 01, 2013, 02:04:52 AM by PRR »
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chumbox

Re: Upper cap voltage. Any limits to this?
« Reply #3 on: July 01, 2013, 05:16:43 AM »
Thanks PRR, that is easily the best bunch of analogies that could have been used. I totally understand now.

Thanks again all.


mistahead

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Re: Upper cap voltage. Any limits to this?
« Reply #4 on: July 01, 2013, 05:20:54 AM »
Also thanks PRR - but wouldn't, with electro's which need to be charged and discharged to maintain their capacitance, still have some indication of those "old-old-old" problems that would be magnified as you scale up the substrate mass?

greaser_au

Re: Upper cap voltage. Any limits to this?
« Reply #5 on: July 01, 2013, 07:10:54 AM »
Beware low-value (<10uF), high voltage (50V) electrolytics. the bane of the serviceman's life (and were a good source of income - shotgunning all the lowC-HighV caps was usually a good start to a repair of a monitor or TV!!)

david

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Re: Upper cap voltage. Any limits to this?
« Reply #6 on: July 01, 2013, 08:02:15 PM »
Unless its a Sony TV with overheating power MOSFETs in the wake-up circuit, so common an issue and just needs a better heatsink...

Some of the reasons that make those caps the "likely suspect" in those fix jobs are why I asked about the life-span of high V electros in low V application.

Bad cheap electro caps were a plague for a while in the dark days (remember I was a network tech then) - entire devices bursting into smoke due to popping caps in dense power supply cases was not uncommon, but is also not the norm now.

Kesh

Re: Upper cap voltage. Any limits to this?
« Reply #7 on: July 02, 2013, 02:45:08 AM »
i remember some vague factoid that 63V to 100V electrolytics had the least non-linearity. possibly over generalised nonsense.

duck_arse

Re: Upper cap voltage. Any limits to this?
« Reply #8 on: July 02, 2013, 09:22:37 AM »
there is a lot of good junk in this thread ....

http://www.diystompboxes.com/smfforum/index.php?topic=102952.0

which answered some questions from this thread .....

http://www.diystompboxes.com/smfforum/index.php?topic=102766.0
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