Author Topic: electric motor capacitor  (Read 6960 times)

rpg52

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electric motor capacitor
« on: April 10, 2007, 08:05:19 PM »
Not exactly listeroid related, but I will be driving it with my listeroid.  I have a 1 phase 1 hp. motor made by Century that wont spin when power is applied.  It makes moaning sounds and wiggles but will not spin until started by the sole of a shoe.  (Then it seems fine.)  I was told it was because the capacitor was blown.  Makes sense to me, does it make sense to anyone else?

Next question, (assuming this is correct), where do I find a replacement?  Writing on capacitor:
Aerovo
100280-37
378-420 MFD
125 VAC

Any insight from those who know about such things?
Thanks,
Ray
PS Listeroid 6/1, 5 kW ST, Detroit Diesel 3-71, Belsaw sawmill, 12 kW ST head, '71 GMC 3/4 T, '79 GMC 1T, '59 IH T-340

mobile_bob

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Re: electric motor capacitor
« Reply #1 on: April 10, 2007, 08:15:50 PM »
Ray

you might try grainger,,, they usually have caps
if you wanna try surplus then
www.surpluscenter.com

bob g
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rpg52

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Re: electric motor capacitor
« Reply #2 on: April 10, 2007, 08:23:36 PM »
Thanks Bob,
Grainger has one with a MFD rating of 378-454
The original is 378-420
Is this what I want?  It's all greek to me.  I seems like it would physically fit, but I've no idea of what MFD is.
Ray
PS Listeroid 6/1, 5 kW ST, Detroit Diesel 3-71, Belsaw sawmill, 12 kW ST head, '71 GMC 3/4 T, '79 GMC 1T, '59 IH T-340

rcavictim

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Re: electric motor capacitor
« Reply #3 on: April 10, 2007, 08:43:27 PM »
That one will work fine as long as the voltage rating is 125 or higher.  Higher makes the capacitor physically larger but also gives you a safety window.  This sounds like a motor starting capacitor  as opposed to a motor run capacitor.  A motor start cap is made cheaper with series wired electrolytic capacitors wired backwards towards each inside to allow momentary use on AC current.  For the reason of containing electrolytic elements I would not go too much higher than say 2X the voltage rating.  On a totally non-polar motor run cap going way above the voltage rating on a replacement would not be a concern except larger physical size.

It would be fine to use a motor run cap on your application, but they are physically larger than motor start caps of similar electrical properties.  They are available in the MFD rating and voltage you need as well.  The MFD rating will be stamped on the cap as a single number, not a range.  Choose one that is within the range you need.
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rpg52

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Re: electric motor capacitor
« Reply #4 on: April 10, 2007, 10:11:59 PM »
Thanks rca,

So, am I right that MFD = microfarad (also written as (funny u with long tail) farad? (Named after Michael Farad I assume?  I sort of remember his name from a physics class many years ago.)   McMaster-Carr has them for even less$ than Grainger, the MFD is 340 - 552, VAC  is 110-125.

Sound ok?
Thanks again guys,
Ray
PS Listeroid 6/1, 5 kW ST, Detroit Diesel 3-71, Belsaw sawmill, 12 kW ST head, '71 GMC 3/4 T, '79 GMC 1T, '59 IH T-340

dkwflight

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Re: electric motor capacitor
« Reply #5 on: April 10, 2007, 10:34:39 PM »
Hi The start capaciter is in the circut for a short time during the start up. There maybe a switch opertated by fly weights on the motor shaft. if the contacts are not clean, this would cause the same symptoms.

Depending on what you are running with the motor a hand start may not bother much, like a bench grinder.
Dennis
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tymbo

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Re: electric motor capacitor
« Reply #6 on: April 10, 2007, 11:08:45 PM »
Michael Faraday ;D

rpg52

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Re: electric motor capacitor
« Reply #7 on: April 10, 2007, 11:30:06 PM »
Thanks Dennis, I'll check to see if I can find the switch without completely taking it apart.  In this case, I hope to use it for running a sawdust drag chain - not easy to start by hand.

Tymbo - yeah! That's the guy.

Ray
PS Listeroid 6/1, 5 kW ST, Detroit Diesel 3-71, Belsaw sawmill, 12 kW ST head, '71 GMC 3/4 T, '79 GMC 1T, '59 IH T-340

Doug

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Re: electric motor capacitor
« Reply #8 on: April 13, 2007, 02:10:34 AM »
Century also made a line of motors called the switchless Centurians....

Your motor should be marked if its one of these. The reason I'm bringing this up is these motors were a capacitor run and need the apropriat cap. A local rewind shop or pump service ect should be able to sell you a new or used one depending on the need.

The switchless Centurian had less starting torque than a split phase and in all honesty I can't rememebr what the designed aplication was ( possibly furnace motors ). But they were quite runners and scarce....

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rpg52

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Re: electric motor capacitor
« Reply #9 on: April 13, 2007, 03:40:58 AM »
Thanks Doug,

This motor will run, if you start it spinning, so I assume it is just the starting cap.
Ray
PS Listeroid 6/1, 5 kW ST, Detroit Diesel 3-71, Belsaw sawmill, 12 kW ST head, '71 GMC 3/4 T, '79 GMC 1T, '59 IH T-340