Super Caps Better Than Lithium?

[noelex 77]

Super capacitors development is increasing rapidly, but there seems little discussion about using them in sailboat applications.

A little like lithium, I think the best value is going to come from people who are prepared to design there own system, but there are already some promising commercial systems on the market.

Avrio has released a 3.55 kilowatt-hour super capacitor “battery” (this is about 270 AHr @12v) for about $4000. That sounds expensive, but 100% of the capacity is usable. The “battery” can be left at any SOC without any effect on cycle life. 0% or 100%, it makes no difference to the life. The cycle life is virtually unlimited. The Super capacitors do deteriorate slightly with age, but they are predicting a 45 year life. They have very high efficiency. They can be charged or discharged at any rate that could be generated by a yacht.

There is a lot to like, undoubtably there is some marketing hype in the claims, but the fundamental properties of super capacitors are very different to conventional batteries of any chemistry.

Tech Pack | ARVIO | The Home of Innovation

Problems include more self discharge if you are leaving the boat for weeks without a charging source, but of course they can be run completely flat and left there for extended periods without any effect. Finally, the only model on offer currently is 48v, but you can make your own Super Capacity battery, given their robust nature, system design is arguably easier than lithium.

Personally I am happy with simple, proven lead acid batteries, but I admire those on the bleeding edge. Super capacitors offer all the advantages of lithium without any concerns of destroying (or even effecting) the battery with over or undercharging.

As well as a stand alone system, the super capacitors can be combined with conventional batteries to create a hybrid system.

Thoughts?

[CatNewBee]

Well, not really. There are current limitations too. But seems they are much higher voltage range that can be challenging to the electronics around.

If you discharge a capacitor from 100% to 0% SOC that means the voltage goes from Vmax down to zero. So if 100% SOC is 48V, 50% SOC would translate to 24V and 0% SOC will be at 0V. This is not what electronics usually deal with. So I doubt the claim of usable 100%.

The maximum current is also limited to 120A / 200A depending on size, so the claim of faster charging / discharging is questionable too.

On one side there is the marketing blabla and then there are the technical specs, just read both. Also internal resistance and resulting current during discharge / charge play a significant role. That said, a usable capacitor current will drop with dropping voltage / SOC too, so that besides internal wiring limitations may be a reason too why the current is so limited by specs.



Capacitors do not behave like batteries. If you use the capacitor on high voltage only (upper 30%) then charge current is very limited, and discharge voltage drop very significant with high discharge current.

[gmakhs]

I am happy with my lead acid , but if I had to change I would use lead crystal batteries , I consider them better than lithium.

[CatNewBee]

Originally Posted by gmakhs

I am happy with my lead acid , but if I had to change I would use lead crystal batteries , I consider them better than lithium.

LC-Batteries - another can of worms...

At the moment LFP is the best bet if you want performance and FLA if you want it cheap. AGM/GEL/Lead-Calcium deep cycle somewhere in the middle.

Some like the lead crystal, some consider them scam. I personally think they are in the range of FLA/AGM for special purposes - like maintenance free telecom UPS battery banks.

[NPCampbell]

Originally Posted by CatNewBee

Well, not really. There are current limitations too. But seems they are much higher voltage range that can be challenging to the electronics around.

The internal characteristics of a supercapacitor are shielded from the user by the BMS just like they are in lithium batteries. Lithium cell-to-cell balancing complexities, DoD cutoff and max charge and discharge currents are regulated with a good BMS and the same applies to a supercapacitor. It has to use a wide range input voltage regulator but other than that the end user wouldn't know the difference.

[NPCampbell]

I am still critical of the spec sheet but if true, to summarize:

Compared to lithium and lead acid the pros of super caps are:
Near infinite cycles
Considerably faster charge times without affecting cycles (1.7C - less than 45 minutes)
Safely reach 100% depth of discharge, vs 80% for lithium and 50% for lead acid.
99%+ charge/discharge efficiency - so no heat

The cons are:
60% more expensive per KWh than even lithium
Twice as heavy per KWh as lithium (on par with lead acid)
Twice the size of lithium per KWh (on par with lead acid)

[CatNewBee]

i am still not convinced, to transform 52V...0V to something constant stable output 120A at 48V you need massive electronics that create a lot of heat, so 99% efficiency is a marketing tale. I would like to see this and measure it before believing. It may work if you use 10..20% of the capacity on the top end, but down to 0 SOC - no way. Assume a SOC 20% with a Voltage of 10V, you must draw over 600A to output 120A at 48V and the current will increase infinite the lower the SOC is.

It is simple physics.

[NPCampbell]

Originally Posted by CatNewBee

i am still not convinced, to transform 52V...0V to something constant stable output 120A at 48V you need massive electronics that create a lot of heat, so 99% efficiency is a marketing tale. I would like to see this and measure it before believing. It may work if you use 10..20% of the capacity on the top end, but down to 0 SOC - no way. Assume a SOC 20% with a Voltage of 10V, you must draw over 600A to output 120A at 48V and the current will increase infinite the lower the SOC is.

It is simple physics.

/agree. The 99% efficiency may apply to the cap itself but power regulators are never that efficient.

[44'cruisingcat]

Better still?:

https://www.slashgear.com/honda-reveals-fluoride-battery-breakthrough-for-next-gen-power-storage-06557121/

[rgleason]

All I know is that supercaps decline fast, but there might be a hybrid use in connection with longer term storage.

[hzcruiser]

Yes, super-caps have quite different characteristics to any type of chemical cell and it would be difficult to compare them.
I do wonder why these specific ones are so heavy though..

[kudukuguam]

I wonder why only a 10 year warranty (if I read that correctly)?

[CatNewBee]

Originally Posted by kudukuguam

I wonder why only a 10 year warranty (if I read that correctly)?

because capacitors can dry out their dielectricum fluids over time and lose capacity.

[skipmac]

Maybe they've solved the problem but I know regular capacitors self discharge rather quickly and would be terrible for power storage. Last time I researched this technology that was still a big issue.

[Paul L]

Originally Posted by skipmac

Maybe they've solved the problem but I know regular capacitors self discharge rather quickly and would be terrible for power storage. Last time I researched this technology that was still a big issue.

Spec says 2% per month.