A new set of bearings, a $4-$7 capacitor, and with a little effort the
grinder should be good for maybe 5-10+ years of maintenance-free operation.
Whether repairing/servicing equipment for myself or for a friend, I'd put
more value in reliability than saving a few bucks and waiting for an already
stressed, used capacitor to fail.
I wouldn't want to hear that the friend had scrapped the potentially very
good grinder, and replaced it with a POS from HF/sears/other.
In the OP's instance, the new cap is good for him as a fixer-type guy and
seller, good for the buyer, and good for the economy.. so I can't see the
captastrophy here.
FWIW, ESR meters are an indispensable troubleshooting aid for switchmode
power supplies and various other types of electronic gear, but they don't
provide a complete evaluation of caps.
They're especially useful in that they can be used to check caps in-circuit
for a basic, quick "likely good" or "questionable-test further to determine"
checks.
Out-of-circuit readings are much more reliable, and can indicate "definitely
bad" on the excessive readings. I'm aware of the stresses that caps are
subjected to in SMPSs.
The typical low voltage circuit of an ESR meter can't apply the rated
working voltage to the cap, as a Leakage tester does.
It' not as though the grinder repair would include $70 worth of caps, or a
repair kit, to replace "shotgun" all the caps in a piece of video equipment,
furchristsake.
Good luck finding specs for the cap in an aged machine motor, or a cap
that's only marked with an in-house stock number.. but the point in looking
escapes me.
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.
Currently produced components products' specs are readily available, and
I've referred to Panasonic, Nichicon and others literature from time to
time.. not the same as looking for a missing cap's specs when all I've had
is a GE motor's stock number for a fairly new motor.
An ESR meter reading of 3.2 or 7 ohms for an AC cap doesn't mean anything if
the person interpreting the reading doesn't have experience with AC caps for
that particular application.
I've worked from the EIA charts regarding capacitor test parameters. They're
essentially basic guidelines.
You're not the only one that's kept lists of test results of new components
and marked packages of incoming new stock, and rechecked parts before
installing them.
You're not the unique special snowflake that grandma said you were (altered
movie reference).
--
WB
.........
metalworking projects
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