# Can you safely exceed the nominal voltage of a supercapacitor?

From what I found the data sheets usually only specify the nominal voltage, not Absolute Maximum Value or similar.

I need to use supercapacitors for a project where they will run for a total of ~20 2s discharges. Can I charge them to a higher voltage than the 2.7V recommended? What are the risks?

• "Can you safely exceed the maximum voltage of ..." - No. – marcelm Oct 31 '17 at 12:19
• No one here nor the manufacturer will tell you (and take responsibility for) that what you want to do is safe / OK. So while you can charge your caps to something higher than 2.7 V there is no one who will tell you at what voltage you can still do your 20 runs. It could be 2.8 V but also 2.9 V but maybe at 2.9 V one of the caps break after the 18th run. How would you like that ? Only with 2.7 V can you expect to do your 20 runs. Anything above 2.7 V and you're on your own. – Bimpelrekkie Oct 31 '17 at 12:34
• Thank you for the answer. I was expecting some experience-based predictions on how likely it is to work, now I know that I can't get that and I either need to use them as designed or do my own testing. I don't, on the other hand, understand why am I getting downvoted. – Chumanista Oct 31 '17 at 12:40
• Even then no one will tell you to run stuff out of spec. without specifying anything about the context. Your mileage may vary a lot. A cap from a good manufacturer may tolerate a lot of abuse while I wouldn't run a cheap one even near nominal limits. – Wesley Lee Oct 31 '17 at 12:52
• The reason you are getting downvoted is because this to many reads as "Can I do this thing that all the documents say I shouldn't do". If the manufacturer says it's 2.7V, there is going to be some reason for that, because if it worked at a higher voltage, they would have sold it as a higher voltage capacitor and had an edge on the competition. It's a behaviourism that I've noticed in a lot of people with little experience, where they seem to think that the maximum ratings are just for beginners, and that experience means you can exceed them. This is however not the case... – Joren Vaes Oct 31 '17 at 12:59

## 2 Answers

From Cooper Bussmann on supercapacitors:

Voltage

Supercapacitors are rated with a nominal recommended working or applied voltage. The values provided are set for long life at their maximum rated temperature. If the applied voltage exceeds this recommended voltage, the result will be reduced lifetime. If the voltage is excessive for a prolonged time period, gas generation will occur inside the supercapacitor and may result in leakage or rupture of the safety vent. Short-term overvoltage can usually be tolerated by the supercapacitor.

Nominal means rated. Break the rules and behavior is undefined.

It does say overvoltage can be tolerated for a short time, but this does not imply using overvoltage in designs.

Extracted from Cooper Bussmann HB Supercapacitors data sheet:

Maximum working voltage 2.5 V

Surge voltage 2.8 V

Life (1000 hours @ +70 °C @ 2.5 Vdc)

Warnings Do not overvoltage, do not reverse polarity

Edit - acual part number posted in comments.

Data sheet for MAL222091003E3 (20F) clearly states the rated voltage at a case temperature of 65°C is 2.7V (peak current 25A), but if the case temperature increases to 85°C, the rated voltage is derated to 2.3V (peak current 20A). Measured at Tamb = 20 °C, P = 86 kPa to 106 kPa and RH = 45 % to 75 %.

The data sheet says:

Maximum operating voltage (refer to derating table) must not be exceeded.

To get the true application rated voltage, you will have to factor in ambient temperature, peak current, charge/discharge rates, cooling, case, moon phase, etc.

The supercapacitor does allow a surge voltage of 2.85V, but this is for less than 1s.

In Aluminum Capacitors, Vishay define surge voltage. I doubt it's meaning is different for supercapacitors.

Surge Voltage US

The surge voltage is defined as the maximum voltage which may be applied to the capacitor for a short time only .... The surge voltage may not be used for periodic charge and discharge.

To answer the question, no, a supercapacitor rated at 2.7V should not be charged above 2.7V.

Will it work for your "non-standard application" (which I read as railgun), since you appear not to be concerned about useful life? A high rate of discharge will probably raise the case temperature to 85°C, which will affect the rated voltage, so I think probably not. This supercapacitor is not super-enough.

The nominal voltage specified in the datasheet is for a specific reason. It is the safe limit at which the super capacitor can be used. Maybe it could take a small value of increase but the manufacturers always tend to give slightly lower values for longevity of the device/component and safety.

Also why would you want to use a 2.7V super capacitor and over-volt it? What voltage do you plan to charge it upto? Choose one that is above your range for safety reasons.

• I have a strict limitation on budget, and thus am limited to a handful of reasonable solutions. Getting 2.8V would help and I wanted to know if I can count on getting it beforehand. Now I know there isn't enough information and I need to do my own testing before going down that route. – Chumanista Oct 31 '17 at 13:30
• The price for a 2.7V 10F can be from $5 to a 2pcs 5.5V 4F coin supercapacitor has$2-\$3. what is the voltage value you intent to charge it to? – The_Vintage_Collector Oct 31 '17 at 13:36
• I was going to use MAL222091003E3s, was thinking about 2.8V – Chumanista Oct 31 '17 at 13:43
• As per the data sheet the nominal voltage is 2.7V, but it don't think the 0.1V increase is gonna make much difference.Assuming that you strictly limit it to 2.8V, then its okay. – The_Vintage_Collector Oct 31 '17 at 15:07