Abs. Max. voltage of supercaps?

[Flyback]

Hi,
What is the voltage derating required for supercaps?

The following one is rated 3V, but it says the lifetime rating needs it to be at 2.4V....do you know what this means for operation to 3V?

Vinatech 3V, 100F (2245) supercapacitor...

https://www.vinatech.com/winko/data/product/VEC_3R0_107_QG_2245_data_sheet_%5B%C7%A5%C1%D8%5D_Ver.9.3%28R0%2C210201%29.pdf

 

[Papabravo]

You need to learn to read the datasheet CAREFULLY.
For temperatures less than 65°C, 3V is specified, but at a temperature of 85°C you should limit the voltage to 2.4V. I'm assuming they are talking about ambient temperature, but it pays to read everything, especially footnotes, with EXTREME care.

 

[shortbus=]

You need to learn to read the datasheet CAREFULLY

Why? so far he'd rather ask the forum. Then when people that know things tell him he won't believe anyhow. I've come to the conclusion he's either a Chatbot or just old fashion troll.

 

[Papabravo]

Why? so far he'd rather ask the forum. Then when people that know things tell him he won't believe anyhow. I've come to the conclusion he's either a Chatbot or just old fashion troll.

Well, I'm not losing any sleep over whatever he is jonesing about today.

 

[Flyback]

Thanks, wow, i never heard of a capacitor that had different max voltages for different temperatures.
Does this occur with all Supercaps?
But it looks like we can use it for 3V at 85degC, but it will just have "reduced life"...where "reduced life" appears to mean doubling of ESR.

In fact, the datasheet doesnt say what happens if you run it at 85degc with 3V.
May anyone advise on this?

 

[Nigel Goodwin]

Thanks, wow, i never heard of a capacitor that had different max voltages for different temperatures.
Does this occur with all Supercaps?
But it looks like we can use it for 3V at 85degC, but it will just have "reduced life"...where "reduced life" appears to mean doubling of ESR.

In fact, the datasheet doesnt say what happens if you run it at 85degc with 3V.
May anyone advise on this?

What are you trying to do?, supercaps are VERY poorly named, and aren't at all 'super' - they are a very poor imitation of a battery, and unreliable as well.

 

[Flyback]

Thanks , doing a Battery powered LED flashlamp.....120w when on for 5 secs, off for 5 seconds, then repeat.

 

[alec_t]

Why does a battery-powered flashlamp need supercaps?

 

[Papabravo]

Elevated temperatures cause the insulating material between the metal layers to degrade at an accelerated rate. Once it gets to a certain point you no longer have a capacitor, it becomes a paperweight. the following is from the Wikipedia article:

Since supercapacitors do not rely on chemical changes in the electrodes (except for those with polymer electrodes), lifetimes depend mostly on the rate of evaporation of the liquid electrolyte. This evaporation is generally a function of temperature, current load, current cycle frequency and voltage. Current load and cycle frequency generate internal heat, so that the evaporation-determining temperature is the sum of ambient and internal heat. This temperature is measurable as core temperature in the center of a capacitor body. The higher the core temperature, the faster the evaporation, and the shorter the lifetime.​

 

[Nigel Goodwin]

Thanks , doing a Battery powered LED flashlamp.....120w when on for 5 secs, off for 5 seconds, then repeat.

Use a battery - FAR better than 'so called' super caps.

 

[Flyback]

Why does a battery-powered flashlamp need supercaps?

Because the high capacity batterys cant manage the high pulse current...so need the supercaps to buffer it.

 

[Nigel Goodwin]

Because the high capacity batterys cant manage the high pulse current...so need the supercaps to buffer it.

Use better batteries then?.

 

[Flyback]

supercaps are much cheaper and lighter

 

[Tony Stewart]

Because the high capacity batterys cant manage the high pulse current...so need the supercaps to buffer it.

If Leds are in parallel then ESR = k/Pmax for K<1 then your LED ESR is 1/120W or < 8 mohm which is about the ESR of a single 26650 cell. For series operation then ESR is the sum. To maximize brightness for some duration like 0.5s both the equivalent ESR and C of each cell remains constant for T=RC regardless if in series or parallel strings as well as Wh in energy time constant. for a fixed qty.

If you need 10T to reduce the 64% sag for 1T in say 0.5 second then you need a Supercap of C=Tau/R= 0.5s*10/8 mohm = 625 Farads rated >= 4.5V for safety. during rapid charge. This is not feasible. If you think you can make a better flashlight than XTAR who makes the batteries, think again and expect that they sort batteries for ESR for their flashlights.

https://v4.cecdn.yun300.cn/100001_1903115277/XTAR%20Catalog-2021%20V9.pdf

Lithium batteries have more than 10k Farads when not dead

 

[Papabravo]

The TS is obviously smarter than we are so maybe we should just let him discover the facts of life on his own. He wouldn't be the first one that had to do that. The process is not necessarily efficient, but it does have a level of dramatic finality.

 

[Nigel Goodwin]

supercaps are much cheaper and lighter

But are MUCH poorer. Similarly low capacity Li-Ion cells are cheaper and lighter as well

Suitable super caps aren't particularly cheap anyway - we use them to supply the current peaks for GSM modems, powered by non-rechargeable Li-Ion batteries, with 5+ year battery life. These batteries are unable to supply large currents, so the super caps provide that.

The cheap little super caps are likely to be much too poor to do what you want, they certainly won't cope with GSM modems, and their estimated life is only 1000 hours.