[TenTec] ESR vs Leakage

[Jim Brown]

On 7/9/2014 7:28 PM, Kim Elmore wrote:
> Can ESR be related to DC leakage? 

ESR is "equivalent series resistance" to an AC current. ESR will vary 
with frequency. Here's are a couple of tutorials.  fairly good 
discussion of it. I think the second one is better.

http://www.low-esr.com/QT_LowESR.pdf

http://www.avnet-abacus.eu/news/technical-news/details/?tx_ttnews[tt_news]=1731&tx_ttnews[backPid]=2338&cHash=3ddf3975f083fbff1eadd89fd708e6f9

In terms of practical meaning, ESR is the component in the equivalent 
circuit that tells us how much heat will be dissipated as a result of RF 
current through the capacitor. If, for example, the capacitor is simply 
bypassing a component to circuit common, it carries very little AC 
current. But capacitors in the resonant parts of a power amplifier's 
tank circuit, or in a bandpass filter in a contest station, are likely 
to carry a lot of RF current.

When I first moved to CA in 2006, one of my first antennas was a 
vertical for 160M that I loaded so that it was much longer than a 
quarter wave. This made it inductive and with a series resistance of 50 
ohms, so I used a series capacitor to tune out the inductance. I run 
legal limit, so if the ESR is high, it's gonna fry. Here near Silicon 
Valley, we are still blessed with a good electronics surplus warehouse, 
so I grabbed a half dozen pieces each of 20-30 different capacitors that 
looked like candidates. Prices are discounted to 5-10% of standard 
costs, so I could afford to stock my junkbox.

I then took those caps, combined them to get the computed value for the 
matching, and fired up the rig. Some of those caps got hot (and would 
have smoked if I'd run them very long), others did not and are still 
running fine 8 years later. The difference was ESR.

73, Jim K9YC