psu power rating suggestion for 1.2F car capacitor - diyAudio
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Old 9th March 2009, 06:59 AM   #1
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Default psu power rating suggestion for 1.2F car capacitor

hi guys

i got a car amplifier and subwofer that i would like to use in my audio systems. i also have 1.2Farad car capacitor. yes 1.2F 24v

i am going to build a psu. i am just wondering whats the rated current that my psu need to handle if i want to use the 1.2F capacitor?

how do i wire the cap? after the regulator or before the regulator? i am planning to use lm317 with 3 or 4 pcs of 2n3055 paralleled to get the boosted current.

TIA

Erwin
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Old 13th March 2009, 03:16 AM   #2
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btt
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Old 13th March 2009, 05:40 PM   #3
AndrewT is offline AndrewT  Scotland
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try charging it with an lm317 based constant current sink/source (CCS).
Set the CCS to 1A and the maximum dissipation of the 317 is ~ 13.8W for the first couple of seconds.

Similarly use a CCS to discharge it.
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Old 14th March 2009, 03:04 AM   #4
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yup, i'll bet that needs a real slow soft start circuit...... with proper wiring, inrush current for that cap isn't a problem in a car. actually a faster method would be an open frame power supply with foldback current limiting, and a standby/operate relay for the amp driven by a comparator that senses when the cap reaches full charge before it applies power to the amp. likewise you could have a 500 ohm 5 watt resistor on the normally closed contacts of the relay, so when you turn the power off, it will bleed the charge off the cap. also you might find it useful to connect an LED and resistor across the cap so when the LED goes out, it's discharged to about 2V. by all means stay below about 20V with this cap, because when you get very close to the cap's rated voltage, the leakage current WILL become an issue. leakage current generates heat, and heat dries caps out. i've seen large electrolytics (30,000uf/ 35V) in a piece of industrial equipment where the nominal voltage of the supply in the equipment was 28V, but actually ran closer to 30V. these caps dried out in a very short time (some of them less than a year)>
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Old 14th March 2009, 03:39 AM   #5
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hmm looks like not that easy to implement

does the use of 1.2F cap on psu worth the trouble of actually implementing it. i mean sound wise?

TIA

erwin
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Old 14th March 2009, 08:13 PM   #6
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with an impedance at 20hz of 6 milliohms, yes it would make a difference.
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