Acceptable ESR for large PS filter caps?

Mojodog333

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I'm going over 2 Midway power supplies and the ESR of the filter caps (1000-18,000 uF) are all in the 300-400 mohm. I've seen more than once in threads not to worry about replacing the large caps, but was wondering if there was a threshold where they should be replaced.
 
What are you measuring them with? And are you zeroing out the resistance of the test leads? My ESR meter has 400mOhms of resistance in the leads alone. So when you want to test a low ESR (like in larger filter caps), you have to zero it out.

There are empirical charts out there that give guidelines for what 'typical' ESR values are for various caps. The value will depend on both the size of the caps, as well as the voltage rating. However even these charts should be taken with a grain of salt. They are just guidelines.

When in doubt, compare against another similar PS, and/or a new cap of the same value. But in general, when caps really go bad, the ESR shoots up into the ohms or tens of ohms range (or even more in some cases, it depends on the cap).

Personally, I keep large filter caps unless they are leaking, or so verifiably bad the game won't boot. Generally speaking, the larger the cap, the less likely it is to go bad. (And vice versa for small caps.)
 
I use a $50 ESR meter i bought on Amazon. The leads are short and only 40mohm, but I zeroed them out.

I compared the caps to my Sea Wolf and they are maybe 100mohm higher except a 1000uf that is more than double than the BIG caps. I change that with something I pulled off another board and take your advice on the rest. Thanks!
 
Remember, the bigger the cap, the lower the ESR.

(Though it's a factor of both the capacitance AND the voltage rating. So you can't compare apples to apples if they are different voltage ratings.)

My experience with caps is they're typically ok, or they are REALLY not. (Like either leaking, or the ESR will be 10/20/50x what you expect, if not more.) And/or they just won't be filtering, in which case you get very high ripple. But for anything except the smallest caps (<10uF), if I throw the ESR meter on there and get something under an ohm, they're fine.

And the larger the cap, the less likely it is to be bad. So I really only take notice on small caps, if you get measurements of 10 ohms or more. When you do find bad ones, it's usually the small ones that are also lower-tier or unknown brands. It's really not that common to find 470uF or bigger caps with high ESR. Not impossible, but not anywhere as common as bad 1/4.7/10uF's.
 
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