Super-Supercaps

[toms]

This is really quite fascinating.
For a layman like me - not quite in terms of electronics, I understand capacitance and Farads - would there be a way to... equate, not quite convert, hundreds of Farads (hey, huge numbers, if you're used to micro and milli at best) to Ah?

I mean (just curious mind you) if you had a big enough supercap, or a bunch of them, maybe with a shunt on the "output" to limit current, could it replace a battery?
And would it have "infinite" cycles - for its lifespan, which could be considerable if properly sized?

You don’t need to limit output current from the supercap, the issue is with LiFePO4 cells exceeding their discharge rate when charging the supercap.

Load sources will only use the current they require.

You definitely could make a supercap only battery, it is just not cost effective. For me it’s only cost effective to use them like i do as i’m using second hand units. If i had to buy new ones i would just buy more LiFePO4 instead.

 

[Don B. Cilly]

You definitely could make a supercap only battery, it is just not cost effective.

Right, this is basically what I was curious about.
So, would there be a way to... equate, not quite convert, hundreds of Farads to Ah?

And, what would the life expectancy of a supercap be?
Because, as I understand it, there would be no "cycles" to worry about, no BMS, no voltage drops. (well, I don't know about that, another factor to consider)... if they have "near infinite" life expectancy - and you can get enough of them used from trains...

 

[Hedges]

one Farad delivers 1 ampere for 1 second per volt of discharge.
Energy stored in a capacitor (Joules) = 1/2 V^2 x C
One Joule = 1 watt second, one amp at one volt for one second.
Two capacitors in parallel doubles capacitance, same voltage.
Two capacitors in series halves capacitance and doubles voltage.

So 3600 farads delivers one Ah while discharging one volt.
If you got 7 of those 500 F 16V caps, that's 3500F.
Charged to 15V, it could deliver 1 Ah while discharging to just under 14V.

 

[wattmatters]

Because, as I understand it, there would be no "cycles" to worry about, no BMS, no voltage drops. (well, I don't know about that, another factor to consider)... if they have "near infinite" life expectancy - and you can get enough of them used from trains...

They also have a pretty high self discharge rates meaning they add leakage current to a system.

 

[eXodus]

They also have a pretty high self discharge rates meaning they add leakage current to a system.

yes they leak out over a week or so - but since the total energy contained is not that much - it's really not that bad in total terms.
But still something you want to consider - nothing you want a in high efficiency system.

You don’t need to limit output current from the supercap, the issue is with LiFePO4 cells exceeding their discharge rate when charging the supercap.

Load sources will only use the current they require.

You definitely could make a supercap only battery, it is just not cost effective. For me it’s only cost effective to use them like i do as i’m using second hand units. If i had to buy new ones i would just buy more LiFePO4 instead.

That's why people are building Hybrid batteries - Supercaps and LFP

Usually for Cranking an Engine - the BMS limits how much a battery can deliver - and engines usually need a ton of energy to get the starter going. Supercaps are great for that - and since the process is only a second or two.

 

[Scph9002]

Keep in mind that a lot of the announcements have the sole purpose of raising funding... as such the authors are incentivized to make it sound like a sure bet.

Exactly!

To me it feels like unless it has a "buy now" button it is just a waste of time to even read.

 

[toms]

The used Maxwell Supercaps work as i have described, and are readily available.

I also have no interest in unobtainable technology.