On Tue, 04 Dec 2018 00:44:44 -0500, Clare Snyder wrote:
On Mon, 3 Dec 2018 13:53:29 -0600, Terry Coombs ... wrote:
Â* Well , Mr. Compressor has a case of the humms . That is , when I try
to start it , it just humms (until the O/L cuts it off if I let it go
that long). This is the original motor on an old Speedaire 60 gallon
tank , 220 volts and 3450 RPM's . Specs call for 15 amps full load ,
rated output is 2.98Kw , about 6 hp . This is an Emerson/Doerr
compressor duty motor .Â* Tested both caps , one is good and the other
isn't according to the tests with my DMM . Problem is that the bad cap
has rubbed the capacitance and voltage ratings off the label . Got a
couple of calls in , looked around on the internet , can't find a
definite answer . I'm pretty sure it needs to be around 250uf and at
least 250 volts - though maybe higher voltage to account for spikes . I
have the motor type/classification numbers , just can't find a reference
to check ... anybody got a lead on that type of info ?

That will be the start cap - 275 volt and 80-100 uf

Don't take my word for it - take a look where I got the info:

https://inspectapedia.com/electric/M..._Selection.php

The tables at that link appear to only go up to about 1 HP (.746 kW)
and it looks like 80-110 uf is the .373 kW entry in the 220V table,
instead of corresponding to the 6 HP (2.98 kW) Terry mentioned.

A formula at http://homeenergypros.org/profiles/b...ctly-sizing-a-
capacitor
suggests about 164 uF for 3 kW. [2652*amps/volts, ie, 2652*13.6/220].
A rule of thumb in www.elcomp.net/conis.pdf suggests 30-50 uF per kW
(for a 220V 50Hz motor) ie 90 to 150 uF for a 3 kW motor. A formula at
https://www.electricneutron.com/elec...ase-capacitor-
sizing/ calls for a power factor number; I didn't calculate that one.

--
jiw