I want to determine if a couple of capacitors from a TV power supply are still good. My DC tests below suggest they're fine. Do I need to do anything more?
Both caps are rated at 1,000µF and 25v.
1) Do they hold a charge? Both were touched across a laptop power brick, ie. 20v. They were both over 14v more than a week later. Normally I would take use this test alone to judge them "good". Negligible parallel resistance.
2) Do they have rated capacitance? For this I set up my LabJack to follow the voltage on the cap as it discharged through a resistor. The LabJack itself has about 1.3M impedance and this was in parallel with 3 tests with added resistors; none, 100K and 220K. (The latter were measured on my DMM at 100.5K and 223K Ω.) The starting voltage was again set with the power brick to ~20V.
After fitting the data, I was surprised that the caps came in at 1,132µF and 1,174µF or slightly above spec.
3) Do they allow DC to pass? I hooked the caps up to the DMM as an ammeter and the power brick, all in series. After charging the cap, the current eventually fell to well under 1µA, for instance 0.2µA. Near infinite series resistance.
Both caps are rated at 1,000µF and 25v.
1) Do they hold a charge? Both were touched across a laptop power brick, ie. 20v. They were both over 14v more than a week later. Normally I would take use this test alone to judge them "good". Negligible parallel resistance.
2) Do they have rated capacitance? For this I set up my LabJack to follow the voltage on the cap as it discharged through a resistor. The LabJack itself has about 1.3M impedance and this was in parallel with 3 tests with added resistors; none, 100K and 220K. (The latter were measured on my DMM at 100.5K and 223K Ω.) The starting voltage was again set with the power brick to ~20V.
After fitting the data, I was surprised that the caps came in at 1,132µF and 1,174µF or slightly above spec.
3) Do they allow DC to pass? I hooked the caps up to the DMM as an ammeter and the power brick, all in series. After charging the cap, the current eventually fell to well under 1µA, for instance 0.2µA. Near infinite series resistance.