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Old 02-23-2012, 07:27 AM   #1
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How can I determine the size of a starter capacitor?


My Lathe has a bad starter cap. The cap is unmarked. The machine has been out of production for a few years now, and replacement parts are unavailable. Can any one here give me a reliable way to determine the size(uf, and voltage) of the capacitor using a multimeter? It's on a 1/2 horse Delta lathe, and is not a variable speed motor. Delta has not been forthcoming with the specs.
Thanks in advance...

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Old 02-23-2012, 11:07 AM   #2
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How can I determine the size of a starter capacitor?


You're not going to find out what you need to know using a multimeter. They measure voltage, current, and resistance. Capacitance is a whole different thing.

Delta probably did not manufacture the motor. Does it have a nameplate (most do). With the information on that, the manufacturer or perhaps a motor rebuild shop could probably fix you up.

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Old 02-23-2012, 11:41 AM   #3
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How can I determine the size of a starter capacitor?


Here's some generic information that may help you....good luck Single phase capacitor sizing
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Old 02-23-2012, 12:58 PM   #4
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How can I determine the size of a starter capacitor?


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Originally Posted by md2lgyk View Post
You're not going to find out what you need to know using a multimeter. They measure voltage, current, and resistance. Capacitance is a whole different thing.

Delta probably did not manufacture the motor. Does it have a nameplate (most do). With the information on that, the manufacturer or perhaps a motor rebuild shop could probably fix you up.
You're right, Delta didn't make the motor....it was sourced from China. Delta has a really bad habit of removing identifying marks and data...I guess it's to keep selling their over priced repair parts( I should know....I worked for them for a long time), but in my case it's discontinued.I was trying to avoid the motor shops, I'm pretty cheap, but if the tools I have won't get the answers I need, I might have to go for it. I do have a tester that will tell me(go/no go) the status of a cap, but it doesn't read out any data...just a red or green light.
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Old 02-23-2012, 02:05 PM   #5
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How can I determine the size of a starter capacitor?


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Here's some generic information that may help you....good luck Single phase capacitor sizing
Wow...good stuff there...it'll likely come in handy someday( I do like to tinker and have built a few simple machines.
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Old 02-23-2012, 02:08 PM   #6
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How can I determine the size of a starter capacitor?


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Wow...good stuff there...it'll likely come in handy someday( I do like to tinker and have built a few simple machines.
Glad to help.............
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Old 02-23-2012, 03:27 PM   #7
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How can I determine the size of a starter capacitor?


Another way is to measure the volume of your capacitor in cubic inches (for complex shapes use mensuration formulas) and compare this volume to similar capacitor dimensions for 1/2 hp motors from catalogs.

You are converting volume to capacitance and working voltage. Probably a 2x increase in volume equals a ~2x increase in capacitance or a ~2x increase in working voltage.

First figure out your minimum working voltage. AFAIK this is way less critical than the capacitance value.

The correct value can probably be approximated pretty well by using the link and this method.

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Old 02-24-2012, 08:50 PM   #8
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How can I determine the size of a starter capacitor?


Okay...I found the specs on the capacitor...It's a 30 mfd, 300volt cap, the configuration is 'CBB60SH' I cannot find this combination. Now comes the next question...what is the most important match, the capacitance value, or the voltage. Physical size is irrelevant, I can make a new cover. The closest match I can find is a 30 mfd, 370VAC. Will this work without fryin' my motor?
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Old 02-24-2012, 08:57 PM   #9
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How can I determine the size of a starter capacitor?


Yup, the capacitance value is the important thing. Voltage rating can be higher than the old one. In the case of the replacement being 370 V, that is perfectly OK. All it means is the new capacitor is capable of being exposed to higher voltage. The capacitor will probably not see voltages above 120 volts anyway.
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Old 02-24-2012, 09:00 PM   #10
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How can I determine the size of a starter capacitor?


Cool....the part I found has a capacitance of 30-36 mfd...will that variable mess with me?
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Old 02-24-2012, 09:03 PM   #11
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How can I determine the size of a starter capacitor?


Nope, that should work fine.
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Old 02-25-2012, 11:35 AM   #12
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How can I determine the size of a starter capacitor?


The old capacitor may show a tolerance marked on the case, like 30 uF, +10%, - 50%.

You are less likely to have problems if your new cap has a value, including the tolerance, within this range.

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Old 02-25-2012, 12:16 PM   #13
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How can I determine the size of a starter capacitor?


Quote:
Originally Posted by Yoyizit View Post
The old capacitor may show a tolerance marked on the case, like 30 uF, +10%, - 50%.

You are less likely to have problems if your new cap has a value, including the tolerance, within this range.
The old cap has no markings whatsoever...a common ploy by Delta to keep end users strung out on their high priced replacement parts.My new cap should be here in a few days....we shal see what happens.

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