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Old December 5th 18, 08:49 PM posted to rec.crafts.metalworking
Gunner Asch[_6_] Gunner Asch[_6_] is offline
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Default Compressors - kinda on topic !

On Wed, 5 Dec 2018 06:30:16 -0600, Terry Coombs

On 12/4/2018 2:16 PM, Gunner Asch wrote:
On Tue, 4 Dec 2018 07:07:25 -0600, Terry Coombs

On 12/4/2018 2:03 AM, James Waldby wrote:
On Tue, 04 Dec 2018 00:44:44 -0500, Clare Snyder 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 ?
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:
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
suggests about 164 uF for 3 kW. [2652*amps/volts, ie, 2652*13.6/220].
A rule of thumb in suggests 30-50 uF per kW
(for a 220V 50Hz motor) ie 90 to 150 uF for a 3 kW motor. A formula at
sizing/ calls for a power factor number; I didn't calculate that one.

* I visited the same site as Clare and I think his number is low too .
I don't recall which website I visited that had this formula : current x
10-6th divided by 2 x pi x frequency x voltage , the result of that
formula was 180 mfd ... I'm going over to my blacksmith neighbor's this
morning , he has a compressor very similar to mine . I'll check his
start cap to be sure but I believe the value needed is going to be a
little higher than that due to the high start torque needed for this
application . This is an Emerson/Doerr motor , but I can't find any info
on this specific motor ... it's at least 20 years old and the Emerson
site just burps and says "not found" when I enter the info from the tag
. I believe it's going to be somewhere in the 270-330 mfd range . I may
borrow the cap from the neighbor's compressor to see if it works on mine
since they're very similar . If I can't get it going I'm probably going
to order a new motor , they can be had for around 200 bucks and this one
is pretty old . At this point I've got less than that tied up in this
unit including the original (very used) purchase and parts to rebuild
the pump . Nowhere I know of to get a unit of this size and qualityfor
anywhere near that cheap , including a new motor .

Ive got a 6hp Harbor Freight motor on my old Dvillbiss compressor. Has
worked well for..humm...10+ yrs so far. Its mounted outdoors and it
gets rained on (when we get rain) and its held up quite well. I did
have to replace the start cap last year.

I think I paid somewhere around $100 or less for it then...rack up 10%
for inflation....


* And your point is ? This is/was a Speedaire , had a cast iron pump on
it but - it was used in a large cabinet shop , way beyond it's duty
rating and the pump fried . I paid a c-note for the tank and motor , put
an Ingersoll-Rand pump I had on it . Aside from having to replace the
con rods because I got stupid , this is the first repair it's ever
needed . It is sheltered , I have more respect for my tools than to
leave them out in the rain .

I was simply saying you can find a cheap decent motor for very little
money. I pick up used ones for $25. Anything single phase over 5hp
will be harder to find and will often be $50-75..simply because of
their scarcity. I was not trying to bust your bubble or insult you

My "outside" motors tend to be TEFC or OCP type motors. That being
said..we get so little rain here..4-5" a year...that putting a
compressor outdoors with only a small "roof" over them works well
enough. My compressor and tank was built in June, 1964. Its spent
nearly all of its life outdoors and doesn't appear to be harmed in the
slightest. Still has most of the original paint as well.

Your area of course is much different.



"Poor widdle Wudy...mentally ill, lies constantly, doesnt know who he is, or even what gender "he" is.

No more pathetic creature has ever walked the earth. But...he is locked into a mental hospital for the safety of the public.

Which is a very good thing."

Asun rauhassa, valmistaudun sotaan.

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