car audio capacitor question

skywhr

Diamond Member
Oct 30, 2000
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For initial charge is a resistor necessary?
Where would I get a resistor from, what am I looking for when I go there?


The capacitor I bought was missing the resistor and I cannot return it.
 

PurdueRy

Lifer
Nov 12, 2004
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What do you mean by "for initial charge"?

I would need much more info to make any suggestions.
 

skywhr

Diamond Member
Oct 30, 2000
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You must first "charge" your power capacitor using a resistor before connecting it directly to +12 volts. This is done with the a 1k ohm resistor and a voltmeter. The exact value of the resistor is not critical but I would keep it in the 500-1k ohm range. I would recommend getting a 1 watt resistor if possible (your capacitor may have come with a resistor for charging). A lower wattage resistor will heat up too quickly. Also, do not hold the resistor with your bare hand. The current flowing through the resistor will cause the resistor to heat up and you could be burned. A good place to put the resistor is in the main power wire fuse holder. Simply substitute the resistor for the fuse. A diagram for the capacitor charging setup is shown below. You will need to place a voltmeter across the capacitor to monitor the voltage. Once the voltmeter reads 12 volts you can remove the voltmeter and replace the resistor with the power fuse.
 

skywhr

Diamond Member
Oct 30, 2000
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can i just hook up the battery to the resistor or is the "charge" necessary?
 

PurdueRy

Lifer
Nov 12, 2004
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this thread is going places.

OP, I still have no idea what you are trying to accomplish. Which is quite impressive considering I am an EE.
 

nboy22

Diamond Member
Jul 18, 2002
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Originally posted by: PurdueRy
this thread is going places.

OP, I still have no idea what you are trying to accomplish. Which is quite impressive considering I am an EE.
With car audio capacitors for amplifiers/subwoofers they come with a small resistor for the initial charge. I can't remember what it is for because high school electronics class was a few years ago. I believe it has to do something with how capacitors can be ruined and/or other safety precautions.

EDIT:

" Charging large capacitors:
When connecting a large capacitor (1/2 farad or larger) to the 12 volt source, you may want to charge it slowly before making the final connection to the power wire. Most capacitors come with a resistor to charge the cap slowly. If you're working on your system, and disconnect the capacitor, the cap may get discharged (something might accidentally touch across the terminals or it may partially self discharge over time). If you can't find the original resistor to recharge the cap, you can recharge it with a standard test light (you know, the one with a light bulb, not one of those fancy pants test lights with LED indicators). There's a somewhat helpful demo near the bottom of the page.

If you don't have a test light and want to use a resistor to charge or discharge your capacitor, use a ceramic encapsulated high power resistor like the one below (I'd recommend using a resistor rated for 10 watts or more and about 20 ohms). If you use a small resistor (i.e. a 1/4 or 1/2 watt) of too low value (less than 100 ohms), it may get hot enough to seriously burn your fingers.

REASON:
The reason you may want to charge a cap slowly is to reduce the arcing involved with fast charging. This arcing won't hurt the cap but it might damage the chrome or gold finish on the connectors."

- Taken from Here
 

PurdueRy

Lifer
Nov 12, 2004
13,837
4
0
Originally posted by: nboy22
Originally posted by: PurdueRy
this thread is going places.

OP, I still have no idea what you are trying to accomplish. Which is quite impressive considering I am an EE.
With car audio capacitors for amplifiers/subwoofers they come with a small resistor for the initial charge. I can't remember what it is for because high school electronics class was a few years ago. I believe it has to do something with how capacitors can be ruined and/or other safety precautions.

EDIT:

" Charging large capacitors:
When connecting a large capacitor (1/2 farad or larger) to the 12 volt source, you may want to charge it slowly before making the final connection to the power wire. Most capacitors come with a resistor to charge the cap slowly. If you're working on your system, and disconnect the capacitor, the cap may get discharged (something might accidentally touch across the terminals or it may partially self discharge over time). If you can't find the original resistor to recharge the cap, you can recharge it with a standard test light (you know, the one with a light bulb, not one of those fancy pants test lights with LED indicators). There's a somewhat helpful demo near the bottom of the page.

If you don't have a test light and want to use a resistor to charge or discharge your capacitor, use a ceramic encapsulated high power resistor like the one below (I'd recommend using a resistor rated for 10 watts or more and about 20 ohms). If you use a small resistor (i.e. a 1/4 or 1/2 watt) of too low value (less than 100 ohms), it may get hot enough to seriously burn your fingers.

REASON:
The reason you may want to charge a cap slowly is to reduce the arcing involved with fast charging. This arcing won't hurt the cap but it might damage the chrome or gold finish on the connectors."

- Taken from Here
If all the OP wants is to charge a 12V cap more slowly to avoid any burn marks on the metal, just use any power resistor as mentioned on that page nboy linked to.

You will have 12V source charging a large cap. Make sure that whatever resistance you pick, it can handle the power.

P = 12^2/R

Provided you pick a power resistor that can handle this, it will work fine at slowing the charge time.

http://physics.bu.edu/~duffy/semester2/c11_RC.html

There is a website that will let you simulate the time domain case. Use this to find out how long, depending on how big a resistor you have, to leave the circuit connected before the capacitor is fully charged.
 

Rubycon

Madame President
Aug 10, 2005
17,768
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A lightbulb acts as a resistor with an attitude. The resistance of a cold filament is extremely low however when heated it will jump to where it allows current to flow (given the same operating voltage) to its wattage rating. This can be used from a plethora of things from protection MF/HF drivers to inrush current protection.

The advantages of large capacitance - a storage device with extremely low terminal impedance - is a double edge sword as it presents a near short briefly if fully discharged but can provide quick bursts of power beyond the capability of the vehicle battery+lead wire length. So a bass amp with a large cap tends to hit harder or sound tighter.

LOL at damaging the appearance of the terminals. :laugh: Arc skidmarks = breaking something in when it comes to high power electrical components. Or as the 'lectric boys put it - if your dikes don't have spark marks and chunks missing from cutting live 450volt circuits, they're still virgin! :laugh:

If the arcing scares you or you're worried about the appearance of the terminals (IASCA whore or whatever they call those competitions now) then you want to use a resistor to get it charged up. Once it's over 12 volts just hook directly to the line.

I've never played around with low voltage high capacity caps like those before but it would be neat to have a 10F+ battery of them charged to 14+ VDC and short it out with a 1" thick magnesium rod. ;)
 

Smoove910

Golden Member
Aug 2, 2006
1,236
6
81
Just pull the fuse in the fuseblock you 'should' have on your power line. Connect your CAP inline as you normally would. Go back and throw fuse back in...

Whala, your CAP is ready to use. No resistor needed when I've done mine.
 

Rubycon

Madame President
Aug 10, 2005
17,768
485
126
Originally posted by: Smoove910
Just pull the fuse in the fuseblock you 'should' have on your power line. Connect your CAP inline as you normally would. Go back and throw fuse back in...

Whala, your CAP is ready to use. No resistor needed when I've done mine.
A knife switch would work nice for this. There's nothing like throwing a knife switch and hearing that POP and seeing a few sparks when things come to life. :)

capacitor fun
 

Billyk77

Junior Member
Jan 8, 2017
5
0
6
Does anyone know if a good replacement for the terminal screws that actually screw into the inside of the position and neg posts on the top of the cap. Or is it safe to just hook to the posts with another but to screw it n pkace
 

Billyk77

Junior Member
Jan 8, 2017
5
0
6
Also having installation issues with remote turn on wire. Not sure if I should run separate wires to cap and amp or just jump the remote turn on. From the cap to the amp. Also does remote turn on need to b wired in order to charge the cap?
 

NutBucket

Lifer
Aug 30, 2000
26,585
310
126
There shouldn't be any connection between the cap and the turn-on wire, period. There's nothing to wire to the cap except power and ground. And like the post from 7 years ago said, that fad died out in the late 90's.

The screws that go into the cap aren't anything special. Just take the cap to the hardware store and find something that fits.

Besides necro-ing a 7 year old thread, perhaps you need the help of a professional?
 

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