I want to use a supercapacitor ( Lithium Ion 3.8V 30F) to be charged only by a small solar panel. And the circuit will only do something between between 2.7 and 3.3 V. In standby mode the circuit will use some micro amperes. So in the winter the voltage can slowly drop below the minimum working voltage. In the spring the voltage will go up again and the capacitor will only be loaded between 2.7-3.3V. Will the capacitor be damaged if the voltage drops below the minimum voltage or is it not allowed to discharge the capacitor significantly below the minimum voltage?
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\$\begingroup\$ Which brand/make/model capacitor? Is there a data sheet you can link to? \$\endgroup\$– JustmeCommented Mar 10 at 21:35
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\$\begingroup\$ For example: eaton.com/content/dam/eaton/products/electronic-components/… \$\endgroup\$– trema1305Commented Mar 11 at 15:43
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\$\begingroup\$ If there is ANY chance of discharge below 2.2 volts, consider using a conventional gold foil supercapacitor. You can discharge it to zero volts as often as needed. You live with the lower capacitance. \$\endgroup\$– Sparky256Commented Mar 11 at 17:42
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3 Answers
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The question doesn't contain a link to a specific datasheet for a Lithium Ion supercapacitor, but looking at the example for the CAP-XX LY13R8 RADIAL LEAD LITHIUM-ION CAPACITOR datasheet contains the warning:
Rated voltage range: 2.5V ~ 3.8V (DO NOT discharge below 2.5V)
The answer in Is draining a Li-Ion to 2.5 V harmful to a Li-ion cell? contains:
Yes, lithium-ion cells undergo unwanted chemical reactions when discharged below 3 V, causing their internal resistance to be permanently and significantly raised. Their capacity will suffer as well, meaning that they won't accept the same amount of charge anymore. When such an over-discharged cell is "brought back to life", it will likely become chemically unstable, creating a risk of a short circuit developing inside the cell. jms
Unless the datasheet for the specific Lithium Ion supercapacitor says otherwise, discharging below the minimum voltage could lead to an internal short circuit and therefore fire risk when the Lithium Ion supercapacitor is next attempted to be re-charged.
See also Is it okay to charge a deeply discharged Li ion cell below 1V?
answered Mar 10 at 21:45
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The data sheet of your example capacitor is clear on this.
Minimum working voltage is 2.2V.
It also says "Do not discharge supercapacitors below minimum working voltage.".
They are litium based hybrid supercaps. They are not allowed to discharge below rated limits or they degrade in performance or damage.
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Discharge down to 2.5V is most likely safe. The "minimum working voltage" is usually more like 2.2V for these capacitors, so you have still margin.
But to have a guarantee, this should of course be specified in the data sheet of your capacitor, so you should look it up (or if you still have to order the capacitor you can select one that is clear about this!)
