now to measure 500F - Page 1
Forum section: electronics / beginners

author: GigaJoe
author_rank: Frequent Contributor
timestamp: June 21, 2023, 02:48:26 am
content: i have supercap 500F 2.7Vhow to measure a real capacity?

author: srb1954
author_rank: Super Contributor
timestamp: June 21, 2023, 03:05:24 am
content: Quote from: GigaJoe on June 21, 2023, 02:48:26 amEnsure that the capacitor is fully discharged and then connect it to a 2.7V PSU (3A minimum rating) via a 1resistor and start charging up the capacitor. Monitor the voltage while charging and record the time taken to reach 63.2% of 2.7V i.e. 1.706V.The capacitance in Farads is equal to the time in seconds since this time represents one time constant.

author: tggzzz
author_rank: Super Contributor
timestamp: June 21, 2023, 07:51:43 am
content: Quote from: srb1954 on June 21, 2023, 03:05:24 amThen try it with 1000ohm and 0.1ohm resistors, and see if you get the same calculated value.

author: Picuino
author_rank: Super Contributor
timestamp: June 21, 2023, 11:27:53 am
content: 1. Do not fully discharge your supercapacitor, you may damage it.2. Try connecting your capacitor to a constant current source (e.g. 0.1 Amps) and measure the rate of change of the voltage with a multimeter and a stopwatch.Apply the formula to calculate the capacitance:C = I · dt / dvC = 0.1 · 500 seconds / 0.1 V = 500 Farads

author: GigaJoe
author_rank: Frequent Contributor
timestamp: June 21, 2023, 08:01:27 pm
content: so ...(0.01 * (45 * 60 +12) ) / ( 0.190 - 0.078) = 242 Fhmmm ... it can be right as it non trusted cap ...

author: golden_labels
author_rank: Super Contributor
timestamp: June 21, 2023, 08:24:15 pm
content: Energy storage capacitors are having poor tolerance to start with. And then capacitance is not a constant. Seesupercapacitors measurementon Wikipedia for discussion.

author: tggzzz
author_rank: Super Contributor
timestamp: June 21, 2023, 08:27:43 pm
content: Quote from: GigaJoe on June 21, 2023, 08:01:27 pmSee the datasheet for the specification of how the capacitance is specified and measured by the manufacturer. Other techniques can be expected to give different results.Capacitors are not simple, and cannot be represented solely by a single parameter. A couple of extreme examples...MLCC's capacitance infamously depends on the DC voltage. Many "lose" 80% of their capacitance at the rated voltage.Other capacitors exhibit "soakage". After being charged for a long time, then discharged, anddisconnected, the voltage on the terminals will rise until it is similar to the voltage before it was discharged.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: June 21, 2023, 09:49:23 pm
content: about 2,5H:(0.008*(20*60+7200))/(0.33250-0.078) = 264quite interestin another thingimy current source dropping current when cap charging ....the current sense resistor around 50 ohm ( it 10 , 10ppm 500ohm 0.25W thruhole thermal glued on massive aluminum platewell , i didnt expect it. it def. not a sense resistor culprit.cap are this onehttps://www.aliexpress.com/item/1005004298279921.html

author: BillyO
author_rank: Super Contributor
timestamp: June 21, 2023, 11:58:00 pm
content: Quote from: GigaJoe on June 21, 2023, 02:48:26 amWith a measuring tape.Charge it up to maximum voltage.Then connect it to a constant current load (1A) and after 500 seconds it should be be down to 1.7V

author: EPAIII
author_rank: Super Contributor
timestamp: June 22, 2023, 03:14:21 am
content: Tape?NO! You count the electrons going in or out......No, really, that is exactly what you do!Quote from: BillyO on June 21, 2023, 11:58:00 pm

author: GigaJoe
author_rank: Frequent Contributor
timestamp: June 22, 2023, 03:17:50 am
content: thanks palbut you guys too late at show, rubber duckie ate cap.

author: BillyO
author_rank: Super Contributor
timestamp: June 22, 2023, 04:44:32 am
content: Quote from: GigaJoe on June 22, 2023, 03:17:50 amBetter late than fish scales, .. or such..

author: Siwastaja
author_rank: Super Contributor
timestamp: June 22, 2023, 06:30:53 am
content: Quote from: srb1954 on June 21, 2023, 03:05:24 amOr, if one has a usual CC-CV lab power supply, as they probably do (or should) if they have a 500F cap, just set CV=2.7V and CC=1A and measure the time it takes to reach 2.7V, and calculate C = A*s / V = 1A * time / 2.7V.The advantage is that the lab supply is regulating the current to the accuracy specified in the manual, regarless of wire/connector resistances, and one can use a separate multimeter (or 4-wire measurement of the lab supply, if available) to monitor the capacitor terminal voltage. If separate multimeter is used, a slightly lower stopping voltage than the CV setpoint should be chosen so that the supply does not inadvertently go into CV mode during measurement - e.g. 2.5V. This lower voltage needs to be used in calculation. One also doesn't need to sit and carefully stop at any certain point. You can just stop at 2.345V if it is convenient to you and record time taken.