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[email protected] etpm@whidbey.com is offline
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Default Compressors - kinda on topic !

On Mon, 3 Dec 2018 16:08:31 -0600, Terry Coombs
wrote:

On 12/3/2018 3:54 PM, wrote:
On Mon, 3 Dec 2018 13:53:29 -0600, Terry Coombs
wrote:

* 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 .* 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 ?

I think Speedair was sold by Grainger. If so they should be able to
tell you which caps yiou need. I just went through this with an old
compressor sold by Grainger. It blew a couple caps and the problem
turned out to be the centrifugal strting switch. I replaced the switch
with and electronic one that sits outside the motor, which makes for
easy change down the road if need be.
Eric


* I did some more poking around , found a formula that gave a
believable result . The suggestions they make (a chart) for smaller
motors is in line with my result - looks like I need about 250-270 mfd
with a voltage rating of 250 or higher . I do remember from my days in
electrical type work that a little more is better than a little not
enough ... Compressors are known to need plenty of start torque , so I'm
looking at the top of that range . I'll probably scoot into town
tomorrow before my wife has to go to work and pick one up .

The values my compressor uses are quite high, this is because the
motor was made for running a compressor. The high torque demand. If it
still hums after the new cap suspect that start switch.
Eric