Posted on 02/12/2019 8:01:16 AM PST by Paul R.
Smother Brothers routine:
“I fell into a vat of chocolate and nearly drowned.”
“Wow. How did you get out?”
“I yelled, “Fire, fire!”
“What? Why did you yell ‘fire?’”
“Well, nobody was gonna come if I yelled, “Chocolate!”
Agreed...to my knowledge the large cap is only used to ramp up voltage/current to start the motor. It’s better to replace it then fret over the capacitance reading!
Ooops wrong thread
My conspiracy theory about this is that the mfrs use substandard caps so when they give it up, likely from heat over long periods of time, most people will have to buy a new motor/alternator/etc.
Interesting. I'll have to look into that. However, I do know polyester and PP are often spec'd as "run caps". I'd think if the ESR (internal resistance) is low enough, reasonable current should not be a problem. Of course, some of the tradeoffs are capacity, working voltage, ESR, and size. If capacity and voltage are set, then you have ESR vs. size (essentially)...
Like the maintenance supervisor I had who had to make a run for an emergency part. He called ahead to be sure it was ready. When he went to the counter, it was the wrong part.
The clerk checked the part’s number and said, “Well it was only off by one.”
Just go to Tractor Service Center and they will match your old sump pump for half what Lowes, HD or other big box stores will sell it to you for. It costs about $75-150 for an electrician to wire it you are still lost.
The cap is used to shift the phase of the current to create (IIRC) a rotating magnetic field.
I’m definitely not “lost”. But I am very curious about “oil filled poly caps” (never heard of them B4), certain failure mechanisms, and maybe dodging typical mfgr skimping.
I’m not so sure that’s only a theory!!!
Except they are almost all too big (dimensions).
A true start cap would be in the 200 mfd range (177-217 for instance) depending on the HP of the motor.
That's what I figured. But then this 47 uF 200v cap in the chipper motor makes no sense, unless it's a case of serious skimping.
Do you mean “Tractor Supply Company”? A search for “Tractor Service Center” turned up nothing useful - unless I need a tractor fixed.
TSC’s prices look “comparable”. House brands suspect until proven. Lowes & Home Depot often cheaper for same model of brand name pumps.
Thanks for all the replies! Will check back in a couple days: duty (elderly Mom care) calls...
By the way I did bookmark All About Circuits. Thanks
Generally +/-10% of the rating is considered ok, otherwise replace. Residential HVAC industry commonly uses 370VAC caps on blower motors, these are oil-filled and usually oval in shape. I’ve seen motors start well outside of the 10% range but they usually don’t get to full RPM. Zero Uf=no start.
This similar to what you have?
https://www.homedepot.com/p/Packard-370-Volt-7-5-MFD-Motor-Run-Oval-Capacitor-TOC7-5/204417183
I recommend the Flux Capacitor in the 1.2 gigahertz range.
Also, I am not an electrical engineer, but I did stay in a Holiday Inn Express and watched Back to the Future on Cinemax.
Checking back in 1 more time...
That’s close but physically too big.
Closest I’ve found so far:
It is a little bigger than the orig, and polyester vs. oil filled “something” for the orig cap, but I think it’ll squeeze in.
I may break apart the old one when I get back home.
Best answer is switch over to three phase.;-)
If by ‘almost too big’ it will fit, do it.
I have no idea what a chipper motor looks like, voltage, horsepower or anything else.
My experience is with HVAC, household items, pump motors, etc.
We often used what is called a ‘hard start kit’ on stiff single phase AC compressors. Basically a start cap and electronic relay that is hooked up in parallel with the run cap.
Check Graingers for your capacitor?
TSC or whatever store is cheaper. In my area, TSC is definitely lower.
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