Supercapacitor charging and discharging

Question

Hi,

Due to space constraints we have a very small battery (capacity around 20 mAh) which can provide max currents around 10 mA. However we would need short pulses (1 ms) of peak current (about 300mA) for about 1s. The only option that came to mind is to use supercapacitor as a secondary storage and drive the peak pulsed current from there. Would it be practical to use supercap for this kind of peaked discharging? Are there any dangers that we should consider?

michaelkellett · Answer

That's an average of 150mA for 1s. A 1F cap will drop 150mV, you need to decide how much drop you can stand and that will set the size of cap you need. Suppose you go for 0.5F and accept a 300mV drop in voltage, If the effective ESR of the cap is 0.3R you lose 0.75V at the end of the one second. AN AVX SCMR14C474PRBA0, Farnell 2696625 will do this. Watch out for short life, huge size, large leakage current and other factors (like efficiency of cap charging circuit, need to charge to above battery voltage to allow for drop during 1s interval etc) You don't say how big your battery is or what type. You'll get better answers if you explain what you are doing in more detail Like, why can't you have a shorter pulse burst more often ? MK

genebren · Answer

I see a lot of talk about the discharge of the supercap, but what about the charging? Do you have an external source to charge the supercap, or are you pulling charge out of your Li-ion cell?

There have been a couple of recent articles on super capacitors on this site that might be of interest to you, here is a link to one of those:

https://www.element14.com/community/people/nikhilstephen/blog/2018/08/27/supercap-to-the-rescue#comment-138547

Good luck on your project.

Gene

jc2048 · Answer

I'd guess that the supercap you've found is intended to replace a back-up battery (for keeping a RTC or memory alive in the absence of power). It doesn't seem very suitable for what you want to do here.

Supercapacitor charging and discharging

Top Replies