super capacitor meter - Page 1
Forum section: electronics / general

author: maxamp
author_rank: Contributor
timestamp: April 11, 2021, 04:42:27 am
content: Is there a meter to measure the capacitance of super capacitors (+1F)? If some one does know of a super capacitor meter, what is the cheapest one? And which one has the highest capacitance range for any price?The fluke 289 can measure 100mF.I have maxwell 3000F 2.7V capacitor. I've been using a constant current power supply with a scope to measure the capacitance.capacitance=Coulombs/Volt=(time in seconds)*(content current)/(voltage change)I want to know the capacitance of the super capacitors to make sure they are balanced when put in series.I'm guessing multi-meters/LCR meters don't measuring high capacitance because it would involve high currents and be power intensive to give an accurate reading in a short time.

author: bob91343
author_rank: Super Contributor
timestamp: April 11, 2021, 04:51:04 am
content: I think your method of measuring is probably the way to go. Assume it's a capacitor, then apply a step function via a resistance and watch the rate of voltage climb. If you want to match capacitors you can test two at once and measure the voltage difference between them.

author: MiDi
author_rank: Frequent Contributor
timestamp: April 11, 2021, 07:06:50 am
content: Quote from: maxamp on April 11, 2021, 04:42:27 amKeep in mind that the capacitance changes individually with charge/discharge cycles, over time and temperature.The self-discharge may be even more important.It needs some sort of balancing e.g. with parallel resistors.

author: dietert1
author_rank: Super Contributor
timestamp: April 11, 2021, 09:19:36 am
content: The usual balancer board applies small currents, like 2.7 V / 10R = 0.27 A max. If capacitors agree within +/- 20 % the maximum allowable charge current would be about 1 A. Also depends on total voltage margin left in the end. During high current discharge there won't be any problem with balancing, i mean if you combine supercaps of the same make/lot.A precision capacitance measurement doesn't make sense with those parts as they are electrolytical capacitors. For example you will notice that it takes hours or days for self discharge to settle after reaching final voltage.Regards, Dieter

author: RoGeorge
author_rank: Super Contributor
timestamp: April 11, 2021, 11:12:49 am
content: Quote from: maxamp on April 11, 2021, 04:42:27 amBeware that having the same capacitance is not enough, they need to have the same initial voltage, too. For example, if one is already charged to 2V while the other series capacitor is only at 1V you'll still have an unbalance.Different voltage on two series capacitors of the same size can appear, for example when one capacitor has bigger leakage and self discharges faster.

author: Picuino
author_rank: Super Contributor
timestamp: April 11, 2021, 11:38:09 am
content: It is also very important to measure the equivalent series resistance (ESR) because in these capacitors it is usually very high (it can be 100 Ohms for 1 Farad capacitor)

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: April 11, 2021, 12:15:42 pm
content: Quote from: maxamp on April 11, 2021, 04:42:27 amif you already have a Fluke 289, you can try this (make sure that the cap in question doesn't have more than a couple of 100 mV residual voltage accross its terminals):1. make a [Lo Ohms] measurement on the capacitor and  a .2. press the  button, and  the recording after exactly 60 sec.3. look at the trend record and find two points on the linear portion of the Ohms vs. time plot that are 60 sec apart.4. find the slope of the plot by calculating D = (Ohms2 - Ohms1) / 60. [Ohms/sec].5. calculate the capacitance of your cap as C = 1/D .albeit a bit lengthy to perform, this method gives quite decent results on the Fluke 289. you probably can shorten the measurement [i.e., recording] time to just a couple of seconds and sacrifice some accuracy, but i didn't try that.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 11, 2021, 12:36:45 pm
content: Quote from: Le_Bassiste on April 11, 2021, 12:15:42 pmBeware some supercapacitors have aminimalvoltage, same as some rechargeable battery have. If they are discharged under their minimal voltage, they get damaged.https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-supercapacitor-hybrid-cylindrical-cells-data-sheet.pdf

author: coromonadalix
author_rank: Super Contributor
timestamp: April 14, 2021, 06:28:09 am
content: Sencore Lc102 and Lc103 can go up to 20 Farad ....