Cap question.

[BiggyJ]

Can you tell if you have a start or run cap by it's specs?

I have a Black and Decker 6" bench grinder with a prob. (the older blue one - 9407)
https://www.partswarehouse.com/Black-Decker-9407-Bench-Grinder-Type-2-s/157403.htm

The OEM cap is Black and Decker part number DWB-284450-00.

Little confused, if you assist the start up spin, it runs. BUT also has a problem while running. It doesn't seem to have much power and kind of bogs down a little when using it. and will slow it's RPM down. Like it has a start AND run cap, but it doesn't. Could the cap serve both purposes?

Would appreciate you guys/gals input.

Thank you,
John

 

[BiggyJ]

Wow... 58 reads and no responses? Come on guys

 

[joel63]

Try this.

https://www.ereplacementparts.com/capacitor-p-96314.html

 

[BiggyJ]

Yes... that will work. Thank you very much for your time and effort Joel63, however, that was not one of the two questions in my post. Actually that is the same exact cap already
in my post above.

Thank you again...

 

[Lassen Forge]

Could be a starting cap, without which you will get the symptoms you describe - for 10 bucks it's not that much of an investment...

It could also be worn bushings, depending on how hard a life your machine has. My C'Man block grinder (from the 1960's) was dirty and pretty rough and was getting weak, tore it down, cleaned it out, lightly emery clothed, polished, and lubed the "permanent lubed" (ha ha ha) bearings, and it now does duty as my wire bush motor. But yeah, the first thing I'd try is swapping the cap - they can go bad without letting their smoke escape. If that isn't it you may beed a megger to check the windings in your motor - one could be bad or shorted, which WILL cause your machine to run like a turtle instead of a jackrabbit.

BTW - sometimes it takes DAYS to get an answer here, sometimes no one really knows... that you got 2 answers in 8 hours is pretty good, ESPECIALLY for someone with 9 posts. That's OK, once you've been here a while, you'll understand that this is our playground, not our jobs!

 

[jl4c]

Can you tell if you have a start or run cap by it's specs?

Usually a start capacitor has a uF rating that is larger than a run cap by several multiples (i.e. 7.5uF vs 55uF). If you have a cap that has single- or low double-digits for its uF rating, odds are that it's a run cap.

Usually in a high starting torque application (such as a compressor), the start cap is switched out of the circuit by a centrifugal switch that activates when the motor reaches a certain speed, indicating that the load has been started and the extra torque provided by the start capacitor is no longer needed.

Some motors do not have separate start capacitors, particularly those with low starting torque loads (like a fan or a small bench grinder). I've had bench grinders both with and without a separate start capacitor. But they ALWAYS had a run cap.

From the symptoms you're describing, my bet is that your motor only has a run cap and it's bad. Low running torque is a symptom of a bad run cap. Inability to start (but good torque once started by hand) is generally a bad start cap.

Of course it's possible to have a motor with both caps and they are both bad, as happened with the last air compressor I bought. Two new caps and it ran great.

Better quality multimeters can measure capacitance. Buy or borrow one.

 

[Lightning rod]

well said jl4c

Biggy J
your grinder is a fractional HP motor typically 1/4 to 1/3 HP
Your motor is what is called a split phase motor requiring only 1 cap permanently connected in the circuit
These caps are typically less than 15uF at 250v
Your part number on amazon states a 6uF, 250v cap
This is in the typical cap range
You need a new cap
I didn't understand your last post; did you purchase a new cap and it still doesn't"t run ?

 

[jl4c]

well said jl4c
Your part number on amazon states a 6uF, 250v cap
This is in the typical cap range

Typical run cap is what my esteemed colleague Lightning rod is trying to say.

 

[Lightning rod]

Typical run cap is what my esteemed colleague Lightning rod is trying to say.

thank you and yes as my honoured fellow jl4c has stated