Some time ago I received mail from an employee of NuinTEK, Korea. The reason was my mini article concerning the Condensor Plane. As described, this plane is powered by an so called GoldCap which has 3.3 F at 2.5 V.
NuinTEK manufactures such ultra capacitors, also known as EDLC (Electric Double Layer Capacitor) or Ultra Capacitors. The technical data of their Ultra Capacitors are superior to the originally supplied GoldCap.
Lets look at the dimensions of the original GoldCap. 23 by 13 mm (length x diameter). The closest resemblence in NuinTEKs portfolio is an Ultra Capacitor with 3 F at 2.7 V, beeing substantially smaller having 21 x 8 mm.
A NuinTEK EDLC with similar mechanical dimensions has as much as 20 F at 2.5 V or even 25 F at 2.3 V.
There are other EUltra Capacitors with different sizes and values available at NuinTEK.
According to speech of NuinTEK, they are one of the biggest manufacturers of motor running capacitors and metallized film capacitors in Korea and also newly developed Ultra Capacitors for mass production as an extension of business.
NuinTEK provided me with samples of their Ultra Capacitor production, so I could do some investigation. I used the Condensor Plane as test vehicle since it was the reason for NuinTEK to get in touch with me.
In the picture you see (from left to rigth)
GoldCap 3,3 F @ 2,5 V (Original)
Ultra Capacitor 3 F @ 2,7 V
Ultra Capacitor 10 F @ 2,3 V
Ultra Capacitor 20 F @ 2,5 V
Ultra Capacitor 25 F @ 2,3 V
just to give an impression of the different sizes.
At the moment we have harsh weather which is likely to smash the little Condensor Plane, so I have to take my measures on the workbench and perhaps deliver values under real flight conditions next summer.
I fixed the model in a vice and took the motor running times with a stopwatch. As comparison I first evaluated the original GoldCap, afterwards the Ultra Capacitor samples from NuinTEK.
1) the 20 F and 25 F types were charged only until the charge current reaches 50 mA since they did not reach the expected 30 mA cutoff current even after several minutes.
2) approximate value (balance with 2 grams resolution, weighed several samples for each type).
The capacitors were charged with a laboratory power supply at 2.5 V until charge current ceases and reached 30 mA cutoff current. Right afterwards the motor was started and the time until stop of the airscrew was taken. In stationary operation at 2.5 V the motor consumes 0.6 A so that can be taken as the starting current for the discharge cycle.
The reason for all charging currents staying beneath 1.3 A is the current limiting circuitry of the power supply. Without limitation the maximum currents may reach 30 to 150 A respectively (depending on the type of EDLC) according to the data sheet of the capacitors. With the given setup the supply voltage broke down to 0.6 V at the beginning and slowly rose with progression of the charge process.
The times resulted from the described measuring procedure are not to be taken as values for the time the plane will be airborne. To get an idea on that we can take the 30 seconds the Condensor Plane made with the original GoldCap. Since the 10 F Ultra Capacitor has a similar weight one can expect around 1.5 minutes of flight time taking into account the values from the table above.
Whether the bigger types of Ultra Capacitors will result in even longer flight times may be in doubt since they are at least 60% heavier than the original GoldCap. This is of some significance since the mass of the plane alone without energy storage facilities is only 12 grams.
One remarkable fact is that the 25 F capacitor yields shorter motor on times than the smaller 20 F type.
Here has to be stated that the charge times become shorter for every charge-discharge cycle, while the motor on times remain unchanged. E.g. the 20 F type in three
sucessive cycles first needed 180, then 120 and 112 seconds, respectively, to reach the cutoff current of 50 mA. In all three cycles the motor ran exactly 382 seconds.
There seems to take place a forming process affecting the storable energy per time.
The shorter motor run times find their explanation in less energy stored in the capacitor, caused by the smaller resistance of the 25 F type in conjunction with the fold back characteristic of my lab power supply.
Other ideas are: