Soekris Dam Dac

[randytsuch]

Hey John
Yeah, they definitely have their drawbacks, just wanted to bring this up for attention.

Maybe for two for 5 volts. I don't like running two lifepo4s at 2.5v each to get 5v. They don't have much capacity left at 2.5v.
And then its cost of two caps vs two batteries, so not as much difference as 3.3V.

Randy

[jkeny]

Hey John
Yeah, they definitely have their drawbacks, just wanted to bring this up for attention.

Maybe for two for 5 volts. I don't like running two lifepo4s at 2.5v each to get 5v. They don't have much capacity left at 2.5v.
And then its cost of two caps vs two batteries, so not as much difference as 3.3V.

Randy

Yea, for 5V they make sense but are there critical 5V supplies? (or are they regulated down to 3.3V)?
I agree running 2 LifePO4 batteries @ 2.5V each is something I wouldn't do either - it's right on the edge of their min recommended voltage & couldn't have much stored current at this voltage so we are losing some of the battery benefits, I believe

[nige2000]

interesting caps, i tried 5f 5v supercaps on soekris vref i found the lifepo4 cell an awful lot better
these ones look quite a bit more interesting

wonder if we had a bunch of lt3045's in parallel with these supercaps what could be accomplished ?

[randytsuch]

Forgot to mention that I would add a small value, current limiting resistor between the output of the vreg and the super cap, for the reason John mentioned. Sometimes I add them on my lifepo4 circuits, to make sure my vreg's don't get too hot.

EDIT:
Heres the solution
https://www.mouser.com/ProductDetail/Ma ... q48phMw%3d

For the bargain price of only $500

[jkeny]

There are 3.8V supercapacitors in existence - Lithium Ion capacitors but they are no longer available outside Japan, I believe?
https://www.mouser.ie/new/Taiyo-Yuden/t ... apacitors/

They are half-way between batteries & capacitors - quick charging but like batteries require voltage to stay above 2.2V or they will eventually fail

[nige2000]

There are 3.8V supercapacitors in existence - Lithium Ion capacitors but they are no longer available outside Japan, I believe?
https://www.mouser.ie/new/Taiyo-Yuden/t ... apacitors/

They are half-way between batteries & capacitors - quick charging but like batteries require voltage to stay above 2.2V or they will eventually fail

ive a couple of them somewhere, havent tried them though

[jkeny]

There are 3.8V supercapacitors in existence - Lithium Ion capacitors but they are no longer available outside Japan, I believe?
https://www.mouser.ie/new/Taiyo-Yuden/t ... apacitors/

They are half-way between batteries & capacitors - quick charging but like batteries require voltage to stay above 2.2V or they will eventually fail

ive a couple of them somewhere, havent tried them though

I tried them - couldn't really justify them on any grounds.

[nige2000]

Well they don't seem to have any advantages over batteries
So.. yeah no point
The 2.7v variety at least can be powered down

[jkeny]

Forgot to mention that I would add a small value, current limiting resistor between the output of the vreg and the super cap, for the reason John mentioned. Sometimes I add them on my lifepo4 circuits, to make sure my vreg's don't get too hot.

EDIT:
Heres the solution
https://www.mouser.com/ProductDetail/Ma ... q48phMw%3d

For the bargain price of only $500

Randy,
I saw you mention before about using tl431 as a voltage regulator on each lifePO4 battery in series - do you use some sort of isolation - if not how do you overcome connecting the ground of the 2nd battery Vreg to what is effectively the + pole of battery 1.

Here's what I mean for 2 batteries in series giving 6.6V
+battery2-+battery1-
One 3.3V vreg connects to +battery1-
next 3.3V vreg connects to +battery2- (but battery2 neg pole is connected to battery1 pos pole so vreg will see 3.3V on it's ground output & the ground output is usually connected straight through to ground input i.e we are shorting battery 1 by using the second vreg without isolation.

if you are doing it like Nige does using a transformer with multiple secondaries then you are isolating each battery ground from one another so no problem but I didn't gather that was what you were using?

[nige2000]

if i remember right it uses mosfets and ref voltage and a single ps
kinda charges like a voltage divider would