Re: Grinder that makes the hummmmmmmmm sound

I would expect that huge bug up your ass would cause you enough discomfort that you would want to have it removed, but I guess you've grown fond of it instead.

You seem to know it all, have done it all, from building space craft to transmitters.. OH, and a dd form 214.
But, you're clearly misinformed about capacitor ESR.

Heat isn't the major circuit problem with borderline ESR readings in caps. High ESR caps essentially appear as open-circuit/reduced capacitance, failing to filter the ripple.
In SMPS electrolytic caps, internally generated heat is a result of high frequency, high ripple currents by design.

The ripple currents create internal heat in the caps, accelerating drying out of the electrolyte, and then the cap's ESR begins to increase.
There is going to be internal heating before high ESR even contributes to circuit problems, not the other way around.

The cap being discussed is operating at 60Hz, not tens of kHz.

The primary B+ filter caps in SMPSs, operating at 120Hz don't commonly have high ESR readings, even after many of the secondary-side caps have become ineffective as filters, and the SMPS shuts down (or melts down).

Replacing the start cap in the grinder motor that's been showing signs of difficult starting, is being thorough.
To not replace it would be ineffective, lazy, and hoping for the best outcome.

The OP should halt the simple, inexpensive repair and buy an ESR meter that he might find a use for about 10 time per year, because you insist that the repair isn't done properly because he doesn't know the ESR of the already stressed cap, that costs $4 (he stated).

What he won't know is the leakage current, value change or dielectric absorption characteristics.

So genius.. what ESR do you have in your lookup data for a motor start cap marked 435-580uF 125VAC, or a 125-270uF 377VAC cap, or one that's just marked 136uF -10/+20% 120VAC?
You're not going to find any ESR numbers that are published by the manufacturer, such as 3 ohms max, or any other specific ESR reading.
What you may find is a vague statement such as less than 20 ohms, even if 2 ohms would be ideal for any particular value and series of their caps.
The value and voltage markings don't offer a clue as to what materials the motor start cap is made of.

Caps operating at 60Hz aren't especially susceptible to high ESR.

Maybe next time you can insist that the ESL be checked.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Michael A. Terrell" <mike.terrell@xxxxxxxxxxxxx> wrote in message news:kISdnYOKj-_ioEnXnZ2dnUVZ_o6dnZ2d@xxxxxxxxxxxxxxxx

Assorted ramblings that everyone could learn from:


In other words, replace everything and hope for the best. Gotcha.
Take the lazy way out and never learn anything.

How many companies do you think make motor start and motor run
capacitors? Especially the ones in the molded plastic cases? How much
variation in ESR do you expect between those brands? If any, then you
would have to use the exact same capacitor as the OEM for every repair.
A house number is meaningless, if you know the capacitance and operating
voltage. All the house number does is make it easier in house for the
assembly drones to put in the right parts. also, the capacitance can be
dead nuts on spec, yet a high ESR will cause the capacitor to heat.
Even new capacitors can be defective.


The acceptable ESR for an AC cap that was possibly manufactured with a
20-30% tolerance on the cap's value, isn't likely to be very specific.


Really? How much variation in ESR do you calculate for a 30% change
in capacitance?


You're not the unique special snowflake that grandma said you were (altered
movie reference).


Neither grandmother said any such thing. One said to work hard and
do your best at whatever you do. The other grandmother rarely said
anything, but then she was an old grouch, like you.


.

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