Motor Start Capacitor

[VinceMash]

I have a motor that requires a 108 MDF - 110v start capacitor, I found two choices online at grainger:

http://www.grainger.com/Grainger/items/2MDN9

http://www.grainger.com/Grainger/items/2MDR1

The question I have is should I be buying the 88-108 MDF or the 108-130 MDF capacitor.

What do the ranges mean? the motor specs out only 108 MDF

Thanks !

Vince

 

[waross]

Either one. Start caps are pretty forgiving. The higher capacitance will give a higher starting torque. I solved a severe breakaway torque challenge years ago by going 200% on the starting caps. One set of caps has been replaced but the motors are still in service.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VinceMash]

Thanks

does anyone know where I can get a (reasonably priced) delay relay to work with this setup?

The motor I am using is to power a grain mill, so i would assume I would only need the start cap to fire for a few seconds to get the thing going with the mill full of grain

I also need some sort of wiring diagram if anyone knows how to wire this up, the motor is reversible and has a red, blue, white black and green wires

thanks

 

[VinceMash]

now that I am thinking perhaps a 3 way switch (off-on-momentary on) would be cheaper and easier to wire... like this

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=120538703361&fromMakeTrack=true

 

[amptramp]

VinceMash:

Whether or not the "starting" cap can be removed from the motor circuit after starting depends on the type of motor, i.e., capacitor start versus split-phase. If the cap is removed from the circuit after starting, then there should already be a device in the circuit to do so, i.e., a centrifugal switch.

I agree with waross that either cap value will start the motor. For example, a typical hermetic compressor found in your home a/c unit is sometimes repaired when it will not start by adding a "hard start" kit. The hard start kit is nothing more than a replacement starting cap of a higher value.

 

[waross]

Find out if the motor is capacitor start or permanent split phase. If the capacitors are intended by the mnufacturer to be permanently connected you can't use starting capacitors.
If the capacitors are for starting only, fix the centrifugal switch.
There are after market relays designed specifically for replacing a centrifugal switch. They should be roughly matched to the motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ccjersey]

You need to match the voltage rating of the capacitor as well as the capacitance value.

The "hard start kit" mentioned above is a start relay with a start capacitor and sometimes an overload device connected.

http://www.supco.com/eclass.htm

These work best and are intended primarily for a PSC(permanent splitphase capacitor) motor with no starting switch or relay, only a run capacitor permanently in the circuit between the auxillary or "start" winding and the line. The added capacitance of the start capacitor increases torque while it is in the circuit.

These units are sometimes used as a replacment for the starting relay or centrifugal switch of a capacitor start motor as well, though the switch leads of the centrifugal switch would have to be brought out of the motor enclosure.

On refrigeration compressors, the leads for the start winding are externally accessable since the capacitor(s) and or start relays cannot be inside the compressor case.

On a PSC motor, the leads are already brought to the run capacitor and can usually be accessed pretty easily.

 

[gpedens]

Typically T1 - Blue run1,T2 - White run2, T3 - Orange run3, T4 - Yellow run4, T5 - Black start1,T8 - Red start2, P1 - unknown color from thermal device, P2 - Brown from thermal device. You swap the T5 black and T8 red lead to reverse direction. Your blue and white leads should be the run winding. Green should be the motor frame ground. I cant promise this is always the case but is typical NEMA single phase motor lead markings.

Thank You,Radar. Duke Power

 

[jraef]

Don't do it with a timer even if you can. It's typically done with what's called a "Potential Relay" that looks at what is actually going on in the motor rather than guessing. Since you are already shopping at Grainger, they can sell you a potential relay.

http://www.grainger.com/Grainger/co...hvacr-controls/hvacr/ecatalog/N-cds?op=search

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