.... but when diagnosing caps in a malfunctioning circuit with a lot of caps you will need a ballpark numbers for ESR because desoldering all those caps would be a problem....
Resistors are very unlikely to be burnt in a 1W SMPS (12v, 120mA max), but you are right, i will chech them.
Sorry for the members of the holy ESR church but this it the way it should be done. And yes, in cheap TV's and other consumer crap 99% of the times so much caps are bad that the chance of shunting a good one with a bad one is small. That lonely not completely shot cap that on its own tries co keep thing running will not influence much.
I've a lot of old vintage computer power supplies from the 60's 70's and 80's. Stuff like IBM, Digital, DEC. I just don't run into very many computer grade electrolytic caps that need replacement. When I do, I replace them with the same exact capacitor that is also 40+ years old. I believe these old caps will likely work flawlessly another 40 years. To me, blindly replacing them just because of their age is irresponsible.
I've a lot of old vintage computer power supplies from the 60's 70's and 80's. Stuff like IBM, Digital, DEC. I just don't run into very many computer grade electrolytic caps that need replacement. When I do, I replace them with the same exact capacitor that is also 40+ years old. I believe these old caps will likely work flawlessly another 40 years. To me, blindly replacing them just because of their age is irresponsible.Electrolytic capacitors do have a shelf life. If a piece of vintage equipment was unpowered for decades, it may need a reforming of some caps before it can be used again. Blind replacement of caps is quick solution for this problem, if maintaing of original state is not required.
The datasheet gives tan d = 0.20 at 120Hz
The capacitor value is 3.3E-6
ESR = 0.02 / (2 x Pi x 120 x 3.3E-6) = 8 Ohms
Hi,
Sorry I made a typo
The ESR should be
ESR = 0.20 /(2 x Pi x 120 x 3.3E6) = 80.3
This is the maximum value allowed by the datasheet.
I used LTspice for the simulation.
I would expect new capacitors to be better than this.
Regards,
Jay_Diddy_B
Since the max DF is specified at 120 Hz, 80.3 ohms is the max ESR also at 120 Hz. At the lower left corner of the first page of the data sheet is a chart labeled "Multiplier for ripple current". The different allowable ripple currents at different frequencies tells us that ESR is varying with frequency. The allowable ripple current at 100 kHz is 5 times what it is at 120 Hz. Since the dissipation in the ESR is proportional to the square of the ripple current, the max ESR at 100 kHz is apparently 1/25 of the value at 120 Hz, namely 3.2 ohms.
WindWalker made his measurement at 100 kHz, so the max ESR at 100 kHz of 3.2 ohms is what he should be comparing his measurement to.
Try reforming them. Apply a variable voltage (through a protective resistor, maybe 100k) increasing gradually to rated 400 VDC. Leave the cap on the voltage supply for an hour or so. Then discharge the cap with a 10k resistor connected to the cap for several minutes. Disconnect the cap from the 10k resistor, wait several minutes and measure the cap voltage, which will recover somewhat. Make sure the recovered voltage won't hurt your ESR meter before you measure it. If the recovered voltage is more than a few tenths of a volt, reconnect the 10k bleeder resistor and wait several more minutes, and try again.
If you can't apply 400 VDC, use the highest DC voltage you can come up with.
I've occasionally had NOS capacitors end up with much inproved ESR after this treatment.
Try reforming them.
I read that proper ESR values should be less than 1Ω, eventually down to 0.1Ω, so I guess this applies only to lower rated voltage capacitors.