@b0bb,
I can understand your concerns about relay reliability, but you know as I know that there are very reliable relays which can do the job perfectly, like the Takamisawa NA12W-K or others.
The gold contacts really do not oxidate that much as you mentioned, and, they are bifurcated, and, those are DPDT, so you can parallel those and reduce resistance to 25 mOhms.
Those Chinese relays, used at the boards I bought, are far from reliable, and this isn't related to relay reliability in common, they just are very cheapo and crappy.....
To prevent oxidation within relays, they often use a so called "WET circuit", which simply is a bypass film cap across switching contacts, in this case 100nF to 1uF should do the trick.
Quote from
http://control.com/thread/963420679 :
"> What is Oxidation of relay contacts and what can be done to prevent it ??
For both relay and metallic switch contacts for low current level (e.g. logic) You have two choices.
1) use Au plated contacts
2) Use a film capacitor which has low ESR to "wet" the contacts. Unless the contact is specifically designed for dry contact switching (eg telephony sealed switches) you MUST use a cap to make it a "WET" circuit. This means the current during switching is high enough to burn through a partial oxidation layer to lower the contact resistance ESR using the low ESR and stored charge of a capacitor to dump the current across the contacts. The capacitor must be close to the switch. Suitable values of Film caps start at 10nF and for say 30Amp relays use 10uF tantalum or low ESR alum. This will keep the contacts clean when used enough. Normally current must be 10% of rated current to prevent oxidation. Although the transient from a low ESR cap will be much higher than this, the duration will be so short that there is not thermal rise except at the surface oxidation layer enough to burn off the ofxide.
Tony Stewart EE '75 (retired PEng)"
When looking at the Takamisawa specs, Electrical lifespan is about 500.000 operations at 1A-30VDC
It's mechanical lifespan is about 100.000.000 operations.
In my case, switching every 10 minutes, relays should exactly last as much as long as the 100F ultracaps which, if used 24/7, would last for 18 years of continuous playing.........
For my new design I will use those Takamisawa's, and put them in simple DIP-14 IC-sockets, which is very handy to replace a relay in case of troubles.
There are some people who are designing charge controllers, which just makes it easier to use (no runtime calcultaion because of voltage sensing), but still would need relays, mechanical or SolidState, or mosfets to switch.
You know as much as I know, voltage drop of SSR's or mosfets ruins ESR of ultracaps, which makes all those upcoming "better" designs worse sounding.
And, using voltage regulators also ruins the perfect audio characteristics of those ultracaps.
I can understand if you wanted to use utracap psu's for your LKS, it wouldn't be a practical design, but, since we are no commercial guys, and want the best of the best available SQ,
this should be of some interest to you.
Just try to power a simple USB-I2S interface with ultracaps, I am very sure you'll get interested................
Cheers,
Alex
