audio-talk

I've seen various references to super capacitors recently, and now Stan Berisford is offering updates for the SEG DAC with them, and latest news a 15v power supply with them.

Early indications are that they sound very good.

Given their low voltage (2.7v & 5.5v seem common) are they useful in our hobby ?

I've seen them used in memory circuits but never in audio so far.

So, what would be the effect of putting a 16v 1.6F capacitor on the output of a 15v power supply ?

https://www.ebay.com/itm/282714456859?s ... Track=true

Bear in mind the value is enormous, so will take a long time to charge and discharge. I imagine will put a huge strain on the DC source, be like a virtual short circuit.

Mike H wrote: ↑Tue Apr 24, 2018 3:35 pm Bear in mind the value is enormous, so will take a long time to charge and discharge.

I understand that bit. But not the virtual short circuit bit.

Would the held charge respond more quickly (to transients etc) than the PSU on it's own ?

Bear in mind I'm guessing. But I'm thinking about the power supply charging up the super cap, which may be for several seconds starting from zero.

And whatever is taken out of the cap, has to be put back in after by the PSU. But I see what you mean.

As often the case, only one way to find out.

Are you volunteering?

A capacitor is simply a store of charge, Q, which is the capacitance (in Farads) times the voltage across the device.

This is all common knowledge.

With a "super capacitor", there is simply more charge there.

What controls the capacitor's ability to provide "top up" quickly is mainly its ESR - low ESR means very responsive, high ESR means slow to deliver charge. The series inductance, ESL, tends to be small.

Good supercapacitors have ESRs in the range of 50mohms to 500mohms. The unit you refer to has 6 in series, plus a voltage spreading network.

The best case ESR of that 16V package is therefore about 0R3 and the worst is 3R or so, assuming that they are top class capacitors, e.g. Murata etc. At the price quoted, I suspect that they are using cheap-n-cheerful capacitors, i.e. the ESR of each cap may be significantly worse.

You can do the sums!

I suspect they'd sound a bit crap, because when you want to force a lot of capacitance into a small volume, the electrolytes tend to be high-distortion.
Mike I suspect the demand/recharging thing is a red herring, since if you have a very big cap value on the end of a PS, the voltage drop induced in it by a given circuit demand is much lower than on a small value cap. So hence I don't believe the current-inrush (recharging) is any worse. Could be checked pretty easily on PSUD.
It will have the advantage of being lower Zout to a lower frequency than a normal cap.

Edit : I see Nick has explained things more rigorously then me !

The reports from the audio standard forum are very positive so I wouldn’t dismiss them too quickly.

I would be very careful handling them though and would treat them like a LiPo battery cell. Huge discharge capability and require careful charging IE: current limited or constant current charging and absolutely no over charging.

The way Stan (Berisford) reports things It sounded like he had sourced a 16v 1F capacitor but I'm not sure it's like the one I linked to.

None of the major component suppliers seem to do a single 16v 1F capacitor.

He’s using these Phil afaik. To get 15v you need to stack them, like a battery.

https://www.mouser.co.uk/ds/2/212/KEM_S ... 776376.pdf

1farad caps became highly desirable for 'in car's systems didn't they?

All supercars are low voltage and will need to be stacked in series to operate at higher voltages.

Due to their chemistry and physical construction, they also need voltage spreading to ensure they are managed correctly and operate safely.

They were never designed for this type of operation. As noted, just the stored energy is quite dangerous.

A 2F capacitor at 16V stores 256 Joules - if there is a short and the ESR is low, there can be damage to all sorts of things, including the capacitors - remember these are not designed for pulse operation.

Neal wrote: ↑Tue Apr 24, 2018 8:58 pm He’s using these Phil afaik. To get 15v you need to stack them, like a battery.

https://www.mouser.co.uk/ds/2/212/KEM_S ... 776376.pdf

They seem very low current ?

pre65 wrote: ↑Tue Apr 24, 2018 9:21 pm

Neal wrote: ↑Tue Apr 24, 2018 8:58 pm He’s using these Phil afaik. To get 15v you need to stack them, like a battery.

https://www.mouser.co.uk/ds/2/212/KEM_S ... 776376.pdf

They seem very low current ?

Indeed - they are designed for battery backup for microprocessors and ram, i.e. milli Amps.

Not only that, their ESR is in the 100s of ohms and they're only rated for 1000 cycles.

Round peg, square hole.