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Electrical Capacitor ??

Old 07-11-2012, 12:56 PM
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nsh
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Default Electrical Capacitor ??

What is a resistor's purpose on some capacitors? Such as a capacitor on a electric motor? Some have them, some don't. Just curious and trying to learn.
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Old 07-11-2012, 12:59 PM
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an RC circuit? if so it is to filter a signal
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Old 07-11-2012, 01:08 PM
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No, this would be on a electric motor such as for a pressure washer. A start cap.
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Old 07-11-2012, 01:11 PM
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Probably to adjust the discharge time constant.
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Old 07-11-2012, 01:46 PM
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I was going to give you one of my long winded explanations, but it was easier to copy and paste. The reason a pressure washer needs a start capacitor is the motor is starting against the water pressure in the system and needs more torque.


Start and run capacitors are normally used in AC motors to aid in starting and running efficiency.
Both capacitors are wired in series with the start winding of the motor.
The reason they are not both called start capacitors is that the start capacitor gives the motor more torque to overcome the fact that it is at standstill, and then automatically disconnects itself from the circuit. The run capacitor gives the motor better running efficiency and remains part of the circuit, it is therefore called the run capacitor.


Read more: http://wiki.answers.com/Q/What_is_th...#ixzz20Lgp657H
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Old 07-11-2012, 01:49 PM
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Is the value of the resistor at least several hundred ohms? It would bleed the charge held in the capacitor, when power is removed.
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Old 07-11-2012, 01:55 PM
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Originally Posted by CaptWill View Post
Is the value of the resistor at least several hundred ohms? It would bleed the charge held in the capacitor, when power is removed.
Ding ding ding we have a winner.
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Old 07-11-2012, 02:03 PM
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the capacitor creates a phase difference, which is applied to the motor windings to get it running. Then, after up to speed the phase differencebecomes near 0 and doen't matter anymore. The resistor is usually across the capacitor to intentionally introduce a 0 phase small current to aid in running. This is how the start capacitor becomes dormant at high speed. (an discharges the start capacitor for safety reasons.
Or, this is how I remembered electric motors 101 in the techncal high school I went to in the early 60s.
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Old 07-11-2012, 02:55 PM
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Originally Posted by baker2605 View Post
Ding ding ding we have a winner.
OOPS, I misread the question. That's what happens when they want you in the hospital first thing in the AM. I haven't even been to the bathroom yet.

I think I'll take a nap and try again tomorrow (before my dentist appointment for a broken tooth), does it ever stop?
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Old 07-12-2012, 06:24 AM
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Thanks for the help. I understand what a start and run cap do. I was just curious why some hace res and some dont.
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Old 07-12-2012, 04:22 PM
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bleeder
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