New elec motor

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jkwidener
Posts: 5
Joined: Sun Nov 01, 2009 12:45 pm
Location: Central Indiana

New elec motor

Post by jkwidener » Sun Nov 01, 2009 1:43 pm

My electric motor on my 3 in 1 machine let go today. Was wondering if anyone else has replaced there, ind if they have, where did you get it at? Below is a picture of the 3 in 1.
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lathe mill.gif

sch
Posts: 276
Joined: Wed Jan 15, 2003 7:51 pm

Post by sch » Tue Nov 03, 2009 10:48 pm

Chinese motors (1Ph) tend to have lousy capacitors and suspect
starter switches. Before giving up on the motor check the caps
first, replacement caps are $3-5 each. The start winding switch
is the clik you here as the motor rpm winds down below 2-300
rpm. Chinese switch contacts can be pretty marginal and a burned
or stuck together switch will bugger the motor. You have to pop the
endbells off the motor to get at the switch. Finally Chinese motors
don't conform closely to western standard motor bases, nor to
shaft sizes. Chinese shafts likely to be metric and larger by 2-4mm
than an equivalent sized US made motor. So the motor pulley
may need to be replaced. www.surpluscenter.com has fractional
HP motors for cheap that can be adapted. Might consider this an
opportunity to get a 3ph motor and VFD, allows you to run the
lathe at 30-60rpm for threading and increase top end speed by
500-1000 rpm, depending on the bearings.

Doc Hoy
Posts: 39
Joined: Wed Nov 18, 2009 4:22 pm
Location: Chesapeake, VA

Capacitors

Post by Doc Hoy » Wed Nov 25, 2009 10:51 am

Replacing the caps on a machine is easy but you have to take two things into consideration.

On some of the machines you will find that it is difficult for a western person to figure out the polarity of the cap that is being replace. Polarity of caps is important.

I would also want to see a photo of replacement cap to make sure it will fit in the housing. This is most often not a problem since advances in cap technology have resulted in smaller size caps.

sch is right about the caps in foreign motors. I just replaced mine (G4015z) and I felt like it failed too quickly.

I can not swear to this but I believe a secondary action of the caps in the motor is to keep the inductive kick (A high voltage spike which occurs when a motor is turned off) from being fed back to the input circuit. To the on/off switch this is not generally a problem but if you have a machine with a fwd/rvs switch or worse yet a solid state speed control a leaky cap can cause additional problems.

Others with more experience, correct me on this if I am wrong.
Tnx,

Doc

I don't think much of a man who is not wiser today than he was yesterday. ~Abraham Lincoln

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heavy_groover
Posts: 37
Joined: Fri Jan 21, 2005 2:18 am
Location: western PA
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Re: Capacitors

Post by heavy_groover » Sun Dec 20, 2009 10:04 pm

[quote="Doc Hoy"]Replacing the caps on a machine is easy but you have to take two things into consideration.

On some of the machines you will find that it is difficult for a western person to figure out the polarity of the cap that is being replace. Polarity of caps is important.


It should be noted that capacitors for AC induction motors are not polarized.

If a capacitor has + and/or - minus symbols (or black or red dots) it's for DC circuits, and should not be used for an AC motor capacitor.

The important marking on an AC motor capacitor is the voltage rating, which is nearly always printed as xxxVAC (or xxxV AC), indicating that it is an AC motor capacitor.

The value of the capacitor will generally indicate what type of capacitor it is.
A value is typically shown as xxxmfd, MFD or uF (all versions of microfarad).
High values (over 100uF) are Start capacitors, and low values (under 70 most often) are Run capacitors for fractional horsepower split-phase motors and sizes up to about 2 horsepower.

Many small or medium sized machines utilize capacitor Start split-phase motors.
Heavy duty applications such as air compressors often utilize capacitor Start and Run split-phase motors (2 capacitor covers on the motor case).

A rule of thumb for the value of Start capacitor value is 500uF per HP, with a value of about 130uF for a 1/4 to 1/3 HP motor.

Motor start capacitors marked values can vary by 20% from the actual measured value, so locating a replacement capacitor with exactly the same marked value isn't necessary.

New AC motor capacitors can be found online, but check your local suppliers such as HVAC or appliance supply or motor repair shops, for replacements.

Testing motor capacitors with a DMM or VOM isn't a reliable method of determining if a capacitor is good or bad. Capacitor testers will often check he capacitor at or near it's working voltage, which a typical meter can't do.
A meter can help determine if the capacitor is shorted, but otherwise not very useful.

Each time a capacitor Start motor is started, the capacitor is stressed. Many restarts in an hour's time is fairly severe duty for the capacitor. Good quality capacitors can withstand starting stress much better than low quality capacitors.
Replacing low quality Start capacitors is usually fairly easy, and having a quality capacitor installed is worthwhile.

With nearly anything electrical from China, I always take the covers and parts off to check that all the electrical connections are fully secure.
Many of the factory connections are often loose and improperly terminated.

HTH

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