00:00:01.220 [Music] 00:00:03.57900:00:03.589 hello today I will show you a method to 00:00:07.51900:00:07.529 measure the capacitance of super 00:00:10.04000:00:10.050 capacitors normal electrolytic capacitor 00:00:13.50900:00:13.519 such as these ones have capacitance in 00:00:17.77900:00:17.789 the order of micro farad's that is one 00:00:21.85900:00:21.869 millionth of a farad this for example 00:00:24.89000:00:24.900 which is a large one is of ten thousand 00:00:28.97000:00:28.980 microfarads by contrast this smaller 00:00:33.08000:00:33.090 super capacitor is of ten pallets so you 00:00:37.54900:00:37.559 will need to put in parallel one 00:00:40.16000:00:40.170 thousand of these to have the 00:00:42.13900:00:42.149 capacitance of this one and this order 00:00:46.10000:00:46.110 is of 100 watts and this of five hundred 00:00:50.27000:00:50.280 files most multimeters can measure 00:00:54.61900:00:54.629 capacitance what they range goals 00:00:58.45900:00:58.469 typically to a maximum of two thousand 00:01:01.88000:01:01.890 microfarads so it will be impossible to 00:01:05.06000:01:05.070 use your multimeter to measure the 00:01:08.30000:01:08.310 capacitance of a super capacitor we need 00:01:13.25000:01:13.260 a little bit of mathematics 00:01:15.73000:01:15.740 remember that current equals capacitance 00:01:20.63000:01:20.640 times the derivative of the voltage with 00:01:23.87000:01:23.880 with respect to time 00:01:26.71000:01:26.720 but if the current is constant we can 00:01:32.09000:01:32.100 write this formula as capacitance times 00:01:37.12000:01:37.130 voltage interval divided by time 00:01:41.30000:01:41.310 interval okay so we can write this as 00:01:50.31900:01:50.329 capacitance equals current times time 00:01:55.94000:01:55.950 interval divided by voltage interval 00:01:59.64900:01:59.659 okay suppose now that we use a current 00:02:03.10900:02:03.119 of 1 amp and a voltage interval of 1 00:02:09.35000:02:09.360 volt for example we can charge the Kappa 00:02:13.30900:02:13.319 little from one world to two volts so 00:02:17.30000:02:17.310 the interval is one volt 00:02:20.31900:02:20.329 so the formula becomes capacitance 00:02:23.72000:02:23.730 equals one times delta time divided by 00:02:30.45900:02:30.469 delta v which is 1 volt so capacitance 00:02:35.69000:02:35.700 equals time interval what is the meaning 00:02:40.87900:02:40.889 of this ok if we charge of super 00:02:46.49000:02:46.500 capacitor from a voltage of 1 volt to 2 00:02:51.31900:02:51.329 volts with a constant current of 1 amp 00:02:55.39900:02:55.409 then the capacitance will be equal to 00:02:59.08900:02:59.099 the time in which we charge the 00:03:03.67900:03:03.689 capacitor let's see a practical example 00:03:06.37900:03:06.389 I will test the 100 farad capacitor if 00:03:12.61900:03:12.629 your capacitor is new or it has not been 00:03:14.72000:03:14.730 used for some time you need to charge 00:03:16.55000:03:16.560 and discharge the capacitor a couple 00:03:18.77000:03:18.780 times before making the test 00:03:21.14000:03:21.150 the cap is connected to the power supply 00:03:23.67900:03:23.689 which is set at a constant current of 1 00:03:27.83000:03:27.840 amp and is also connected to the 00:03:31.12900:03:31.139 multimeter to check the voltage and we 00:03:33.67900:03:33.689 will measure the time with the timer so 00:03:38.83900:03:38.849 I'm going to start the power supply and 00:03:44.05900:03:44.069 the voltage in the cup is starting to 00:03:47.59900:03:47.609 raise we will wait until the voltage 00:03:52.39000:03:52.400 reaches 1 volt and then I will start the 00:03:58.03900:03:58.049 timer and the timer has to be stopped 00:04:01.78900:04:01.799 when we reach two bolts in the capacitor 00:04:14.58000:04:14.590 [Applause] 00:04:24.33000:04:24.340 so the timer is running and we will stop 00:04:27.39000:04:27.400 it when we reach a voltage of two bolts 00:04:31.49000:04:31.500 remember that the capacitance will be 00:04:34.08000:04:34.090 equal to the time interval when we 00:04:37.98000:04:37.990 charge the capacitor from one to two 00:04:40.11000:04:40.120 volts 00:04:55.73000:04:55.740 so we get a time of 1 minute and 56 00:04:59.88000:04:59.890 seconds all time was of one minute and 00:05:08.34000:05:08.350 56 seconds or 96 seconds so that means 00:05:13.56000:05:13.570 that the capacitance is of 96 balance 00:05:16.74000:05:16.750 however this method overestimates the 00:05:20.40000:05:20.410 capacitance of the super capacitor why 00:05:24.18000:05:24.190 is that because capacitors have an 00:05:27.69000:05:27.700 internal resistance that consumes a part 00:05:30.72000:05:30.730 of the current used to charge it 00:05:33.54000:05:33.550 this overestimation is on the order of 00:05:36.27000:05:36.280 25 percent of the value that we get so 00:05:40.65000:05:40.660 of these 96 pallets 00:05:44.21000:05:44.220 approximately 24 is lost in the internal 00:05:48.87000:05:48.880 resistance 25 percent of 96 00:05:52.47000:05:52.480 so the real capacitance must be closer 00:05:55.50000:05:55.510 to 96 minus 24 equals 72 farad's okay 00:06:05.18000:06:05.190 now what happens if we are testing a 00:06:09.33000:06:09.340 very large super capacitor for example 00:06:11.85000:06:11.860 at 3000 for a super capacitor we will 00:06:14.49000:06:14.500 need a lot of time to do that however 00:06:17.06000:06:17.070 remember that or formula says that 00:06:20.69000:06:20.70000:06:24.90000:06:24.910 interval over or divided by the voltage 00:06:28.59000:06:28.600 interval if we still use a voltage 00:06:32.88000:06:32.890 interval of 1 volt but we use a larger 00:06:36.72000:06:36.730 current to charge the super capacitor 00:06:38.73000:06:38.740 for example we set current equal to 2 00:06:41.52000:06:41.530 amps then capacitance will be 2 times 00:06:46.16000:06:46.170 delta T for example if we get a time 00:06:52.92000:06:52.930 interval of 200 seconds then the 00:06:57.72000:06:57.730 capacitance will be double that quantity 00:07:02.08000:07:02.090 or 400 pallets and of course we can use 00:07:06.97000:07:06.980 a larger current to reduce the charging 00:07:10.51000:07:10.520 time
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