Author Topic: Capacitor  (Read 4498 times)

NoSpark

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Capacitor
« on: December 18, 2008, 06:59:36 AM »
I've seen mentioned a few times about the use of a capacitor on an ST to help with flicker. Is it worth doing? Size? Where does it get wired?
Anand Powerline 6/1 ST5

matt

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Re: Capacitor
« Reply #1 on: December 18, 2008, 02:03:01 PM »
Quote
Where does it get wired?

Across the field coil connections.
Dunno what size though.

Here is the thread where MacGyver posted the results of his hard work with capacitor experiments and STs......

http://listerengine.com/smf/index.php?topic=3710.0

regards,
matt

MacGyver

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Re: Capacitor
« Reply #2 on: December 18, 2008, 07:42:38 PM »
My experience with the capacitor is that it does nothing to help the flicker problem. That's a whole 'nuthur issue...

The capacitor DOES significantly clean up the shape of the waveform, and it also raises the output voltage quit a bit. You may need to insert a resistor in series with the field to drop the voltage back down unless your unit has very low voltage to begin with.

If you want to tame the flicker problem, you'll need some sort of AVR. Or better still... a set of SOM flywheels.  :)
Steve

JKson (PS) 6/1 'roid & ST 7.5

NoSpark

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Re: Capacitor
« Reply #3 on: December 18, 2008, 10:55:39 PM »
O.K. Thanks. :), Read the thread, nothing about flicker improvement. I was wondering how a capacitor would know when to inject that voltage without some kind of timing circuit.

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12 gauge

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Re: Capacitor
« Reply #4 on: December 19, 2008, 01:26:14 AM »
It's automatic.  When voltage in the circuit is higher, the capacitor charges.  When voltage in the circuit drops, the capacitor discharges back into the circuit.  This how it smooths the voltage ripple.

compig

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Re: Capacitor
« Reply #5 on: December 21, 2008, 01:10:58 PM »
Just to clarify , capacitors can only hold a DC charge not AC. AC voltage just charges and discharges the Cap at the frequency of the AC voltage applied. In AC circuits they are used as filters in conjunction with inductors (chokes) and resistors. They have an impedance (just think resistance) to AC which is dependant on the value of the Cap and frequency applied.
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needenginerunnin

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Re: Capacitor
« Reply #6 on: January 04, 2009, 04:34:12 PM »
afternoon all

i read with interest, but nobody as yet seems to have reported back with concrete findings.
if somebody is running a cap on there st head could they report back also with the value of said cap?

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MacGyver

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Re: Capacitor
« Reply #7 on: January 04, 2009, 05:07:31 PM »
I'm using 270 uF.

I tried larger values (as high as 30,000uF)
 Larger values did NOT improve the quality of the waveform significantly, but they did result in severe voltage overshoot on the output when a large load was suddenly removed.

Around 200- 300uF seemed to give good results without the voltage overshoot on my ST7.5
Steve

JKson (PS) 6/1 'roid & ST 7.5