Compressors - kinda on topic !

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
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 ?
Reply to
Terry Coombs
Loading thread data ...
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
Reply to
etpm
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 .
Reply to
Terry Coombs
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
Reply to
etpm
Does this one look like yours?
formatting link
$mdmain$
formatting link
$mdmain$
Or look at all the photos and see which one is yours:
formatting link

Reply to
gSbxn⚛← ╬ 𝑴𝒊𝒈𝒉𝒕𝒚 𝑾 𝒂𝒏𝒏𝒂𝒃𝒆 ╬ →⚛YghJK
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:
formatting link
Reply to
Clare Snyder
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 calls for a power factor number; I didn't calculate that one.
Reply to
James Waldby
ry
I had a similar problem a few years ago with my Speedaire 20 gallon 2hp. My caps checked out. Ended up cleaning the contacts on the starting/centrifugal switch. Has been okay since. Take a look at this pdf file and see it it lists your motor:
formatting link

It had mine in it plus quite a few more...
Reply to
Leon Fisk
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 .
Reply to
Terry Coombs
is on my tag - it calls for a 704 mfd at 110 volts . Hmmm , that doesn't seem right since this is a 220 volt motor . If doubling the voltage halves the capacitance needed , a 330-380 mfd cap would seem about right ... I just found a contact link for Emerson , messaged them . We'll see what they say . I never really thought about how much I use that compressed air until I don't have it ... and since my ne'er-do-well son has apparently burned up my small portable for me , I'm kinda in a pinch .
Reply to
Terry Coombs
t
Mine is wired for 110 but can be switched to 220v by moving wires in the motor. The start cap is 649MFD and 110VAC with a plastic case. The run cap is in a metal case. So that 110 value maybe okay (shrug). A picture here:
formatting link
Reply to
Leon Fisk
The cap in your motor is only connected across one line and neutral, that's why the 110 volt rating. The very high capacitance is because the motor is a compressor rated motor and needs the extra torque. I just went through all this a couple months ago. You really need to check the starting switch. I guarantee it is easier and cheaper to replace it with a motor starter if it is the problem. The phenolic support for the switch in my motor warped which is why I opted the replace it completely. Electric motors don't usually wear out unless the windings are really stressed by high current, high voltage, high temp operating conditions, moisture, etc. Bearings and starter switches are what usually dies in a single phase electric motor. If you do decide to replace the motor make sure it is rated for high torque loads and check the shaft size. Ther is a good chance your motor has a 25mm shaft, not 1 inch. Eric
Reply to
etpm
Doerr motor so I borrowed his 189-230something start cap to test . My motor spun up just fine with the belt off but wouldn't quite go with a load . So I went to town and bought 2 , one at 243-292 and one at 340-408 . It will start under load with the smaller one , but starts much better with the big one . It has always been a bit slower to start when it's really cold out , so I'm going to leave the big one in for now , try the smaller this summer and see what it does . Total cost to get 'er done was 31 bucks and change , much cheaper than a new motor !
Reply to
Terry Coombs
If you can wait , I can probably come up with suitable motor or cap.
A few week- ago the scrap yard had 6 or maybe 12 swimming pool motors brand new in original boxes. And 3 phase motor are sometime available in the 50 or 100 hp sises, Smaller are most always available-
Dan
Reply to
dcaster
At one time - pre 1950 +/-, some areas used 25Hz., Voltage was refered as 120/240 or 110/220 with 208 as common 3Ph.
Reply to
Gerry
At least the start cap should do at 110 VAC even if the motor is wired for 220 VAC. In that case, the start winding is connected between the center tap of the two run windings and one end, so it only sees 110 VAC (or 120 VAC depending on local power voltage).
Enjoy, DoN.
Reply to
DoN. Nichols
I may have a similar problem with my small lathe. It quit yesterday. Had a couple slow starts where I pushed it with the collet closer handle to get it going, and now nothing. The fact that its nothing "not even a hum" mkes me wonder of the on/direction switch is bad. Fortunately I had radiused just enough alignment pins for the projects that were finishing yesterday.
Reply to
Bob La Londe
I made a short 12 AWG type SO extension cord with some of the outer insulation removed to diagnose motor problems with a clamp-on ammeter. It helps to measure how much they draw before they break.
Reply to
Jim Wilkins
I made a short 12 AWG type SO extension cord with some of the outer insulation removed to diagnose motor problems with a clamp-on ammeter. It helps to measure how much they draw before they break.
****************
All fixed. There was a terminal block on the motor that looked like white ceramic. When I unscrewed it from the motor case it just disintegrated. There were two wires that were broken at that point. Its seems that the terminal block may have been holding them in contact without a good mechanical connection for some time. I put it back together with (yuck) butt splices. The wire stubs coming out of the motor were so short nothing else would work. They were so short I had to use one tool for stripping with forward strippers and another tool for crimping with forward crimpers. It works again.
Reply to
Bob La Londe

Site Timeline

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.