Hi all,
I got questions per private messages which I think I can better answer here so everybody can read this and profit from it.
Considerations before designing ultracap psu's
1- Doesn't draw the consumer circuit too much current for this kind of psu?
2- If not, investigate the upper and lower voltage threshold of the circuitry
3- Use this tool to calculate the needed capacity
https://tools.eatonelectronics.com/tools/supercapcalculator
4- Build psu's, set voltage of dc-dc converters accordingly and set timer for switch time accordingly
5- Last but definitely not least, don't use more then 3 cells in series without balancing boards or balancing resistors to avoid over voltage
The basics:
Ultracaps and supercaps can deliver a constant current but do drop in voltage immediately after delivering current.
Depending on the capacity of the ultracap and the needed amperage of the consumer it does drop in voltage slower or faster.
Most ultracaps can be used at 2.7V max. Keep this in mind. Lifespan DRASTICALLY decreases when over voltage is applied, and if voltage is too high they will EXPLODE.
If you want the best of the best out of ultracaps within audio designs it is best NOT using regulators behind them, thus let them delivering directly without regulating them.
The drawback of this is that you need a big capacitance so voltage drop keeps within the margins of your consumer.
How to handle voltage drop:
Measure the current flowing thru your circuitry and note it. Investigate it's voltage thresholds (upper and lower). Some circuitry use on board regulators, thus having a very wide voltage threshold.
For example, my first ultracap psu I build was for feeding a Kali reclocker from Allo.com This Kali reclocker has regulators on board and regulates voltage down to 3.3V.
Knowing this we can feed the Kali with much higher voltages, lets say the max of 2 ultracaps in series, 5.4V The lower threshold at which the regulators still work normally would be around 4V
I tested this and Kali stil worked perfectly at 3.6 V. So, when feeding Kali reclocker with ultracap psu, starting at 5.3V (to be sure the ultracaps don't get overloaded) and let voltage drop to
3.6V, this took about 15 minutes. To be on the (very) safe side I set switching time at 10 minutes and did set starting voltage of 5.3V a little lower, at 5,1V to spare the ultracaps and extend their lifespan.
The above story shows and tells us that every ultracap psu is specific made and set for a certain consumer.
Second example:
Directly feeding voltage rails of a dac. This is a little more crucial and more difficult to manage.
The first time I created ultracap psu's for a dac was for the AKM AK4495SEQ. Since I used this dac with LT3042 psu's first, it was easy to measure their current so I could calculate needed ultracaps in relation to runtime.
This dac had 6 voltage rails consisting of 4 Analog 5V rails (which do perform best at 7V), one digital 3.3V rail and a 3.3V analog rail. To create 7V I had to put 3 ultracaps in series, thus every 7V psu consisted of 6 ultracaps.
The 3.3V rails had 2 ultracaps in series, thus 4 ultracaps per psu.
To define the voltage thresholds I consulted the AK4495SEQ whitepapers which lead me to minimum and maximum voltages. I kept all voltages between those thresholds and managed to keep runtime at 15 minutes.
Finally I did set it to 10 minutes so runtime was same as Kali reclocker and I could switch the psu's at the same time.
The second time creating ultracap psu's was with the DA-M1 modules. Since Kingwa provided me with different mA draw ratings, I wasn't sure how the end result would be and I calculated worst case scenario.
Looking at the Xilinx whitepapers, I thought this was the chip used in the DA-M1 modules which consumed the most amperage. I created ultracap psu's of 400F for these, so 4 ultracaps in parallel.
In the end this seems to result in HUGELY overkilled 1.8V psu's. I can run them at least for half an hour without seeing any voltage drop.....
The 3.3V Analog and Digital rails are fed with 100F psu's, 2 parallel sets of 2 ultrcaps in series. The 3.3V rails I start at 3.45V and saw them NEVER drop below 3.4V even after half an hour runtime.
Final word.
Why do ultracap based power supplies perform that well in audio applications? Well, it definitely is related to the absence of mains influences such as HF EMI/RFI. Further, ultracaps can deliver PURE DC,
and last but not least, they do deliver WITHOUT NOISE. Even a battery has noise because of chemical reaction, ultracaps do not have this attribute and do NOT suffering from creating a noise level when charging or discharging.
About keeping output impedance as low as possible: Many ultracaps have very low ESR figures nowadays. It is possible to create psu stages with the lowest possible ESR values, but keep in mind, if using relays or other devices
like mosfets to switch between the capacitor banks, they all inherit some sort of resistance. You have to add that resistance to your ESR values of the ultracaps. Keep this in mind when designing this kind of psu's.
To keep impedance low I did choose for dedicated relays for each voltage line, and also for each ground line. Further, I did take use of bifurcated double throw relays, and paralleled the contact pairs to half the resistance of the contacts.
Please keep in mind that relay contacts have a max current. If designing this kind of psu's, be aware of the destructive force these ultracaps have. For example, the 100F powerstor ultracaps we use have a shorting current of 225A.
No, this isn't a typo, they can deliver 225 AMPS shortly. Their pulse current performance exceeds 60 Amps!!!
That said, can you imagine what happens when i short an output or input cable at one of my four 1.8V ultracap psu's? Those are 400F, 4 cells in parallel. They can deliver a pulse current around 250 Amps and have a shorting current of 900 Amperes!!!!!!!
When tweaking my psu's inside my
ΛΓienStreamer I made mistakes, several times. At the beginning I wasn't aware of the BIG danger soldering and screwing around in those while the ultracaps were charged.
Well, this did cost me about 20 relays ($4,50 each.....). While screwing around and shorting some cables, as be it VERY short, those relay contacts some sort of incinerated immediately.... they weren't there anymore, hahahaha
Keep that in mind if soldering and modifying while they are charged!
What I learned of this is: When designing ultracap psu's, and when working with relays, DO take use of DIL sockets to put those relays in (I GLADLY DID, pfew, hahaha). This makes it VERY convenient to replace defective relays.
What I forgot to keep in mind when designing ultracap psu's was: DO PLACE ALL RELAYS AT PLACES WHERE YOU CAN EASILY REPLACE THEM....... My psu's ALSO have relays INSIDE the psu's and not only on top.
Hmm, you get the point, hahahahaha
Having any questions? Please feel free to ask them.
Cheers,
Alex