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Old 1st June 2005, 05:39 AM   #1
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Lightbulb how do i charge a capacitor?

i just got a 1.2farad stiffening cap, how do i charge it and what with? don't give me internet diagrams, tell me how i can do it at home! thanks!
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Old 1st June 2005, 06:24 AM   #2
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Do you mean reform it?

It charges simply by being in the circuit, be sure to use correct polarity.
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Old 1st June 2005, 12:05 PM   #3
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Default charge

1.2F will draw big current, normally they come with a little charging thing. If you want to charge it in house get a normal 12V adapter(make sure if its unregulated the voltage isnt going past its rating) and you need a series resistor try something about 1.2K ohm to 2.2K and it will probably take a minute or 2. notice it will discharge itself when not in use.
I believe my rockford 1F is 16V and 20V surge
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Old 10th June 2005, 06:05 PM   #4
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i've heard you can us a lightbulb as a resistor, that true? if so, what wattage bulb? do i have to turn my car on to charge it, or should i just put the power wire to it? (after grounding it of course)
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Old 10th June 2005, 06:29 PM   #5
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Quote:
Originally posted by Infinity_Addict
i've heard you can us a lightbulb as a resistor, that true? if so, what wattage bulb? do i have to turn my car on to charge it, or should i just put the power wire to it? (after grounding it of course)
A cold filament has a low resistance. Just the opposite of what you want. No need to fire up the car.
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Old 12th June 2005, 01:31 AM   #6
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actually, i JUST found this little bulb looking thing in my kit, very small single wire surrounded by a glass bulb, i'm guessing this is the resistor?
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Old 12th June 2005, 04:04 AM   #7
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You can't just connect the cap straight to your amplifier/fuse block/ distribution block. these caps normally come discharged (0 volts) and will suck a HUGE amount of amps for a short while when they charge up. this will cause huge sparks (like touching jumper cables together!) and blow a fuse. You need to have a resistor or a car light bulb connected between the positive input of the soundsystem and the battery. I have had luck with connecting the capacitor as usual, and inserting the resistor between the main feed from the battery and the rest of the audio chain (such as removing the main fuse and sticking in the resistor, or connecting the resistor between the battery and the wire to the audio system when i go to connect it to the battey. just be sure not to short anything while in there.)

If you are suing a resistor, you will also need a voltmeter and the resistor needs to be at least several watts. I have used a 8 ohm, 20 watt dummy load/speaker crossover resistor with good luck (just because I had it). the more ohms, the slower it will charge. I wouldn't use anything much smaller than 10 ohms. stuff over 100 ohms might take quite a while. The meter will be used to tell you when it's done. you can either connect it accross the resistor to show how much more voltage you need to go. will start at around 12 and work it's way down to zero. you can also connect it from the cap positive to ground (starts at around 0 and goes up) and see when the voltage on the cap is very close to the battery voltage. Note that the charging is NOT linear, it will asympotically approach full charge, this means that the voltage will change fast at first, and then get slower and slower as it gets closer and closer to being full. Theoretically, it will only get reeely close but never exactly there. I prefer the method of connecting the meter accross the charging resistor. hat way I know it's done when the voltage is very close to 0 (under .1 volt) and changing very slowly. I will usually then measure the voltage from the cap positive to ground to make sure it's 12V and then connect the cap in and call it a day.

use the lightbulb just like the resistor, it will light up bright at first, and then get dimmer. once it goes out, wait a little bit and then you're done. You cna use any kind of 12 volt bulb. small interior lighting and brake light bulbs are popular.

Just be very very careful with the cap once it is charged, you do NOT want to short it out, it can deliver HUGE amounts of current. treat a charged capacitor much like a car battery - DON'T SHORT!
if you remove your main fuse at the battery, your system will still be powered for some time since the capacitor will hol a charge. if you want to "safe" it, you can either turn the system on and let the amps drain the power, or use the lightbulb/resistor accross the capacitor this time (cap positive to ground), with the meter to assure that there is no voltage on the system at this point

Also note that the vehicle's electrical system will still be powered for a while off of the cap when you remove the battery (don't let the car's terminals short to each other when the battery's out, or you'dd short the cap and make sparks/blow fuses). I recommend leving a door open or something when taking out the car bettery with a "capped system" - the car's interior lights should drain the cap to a coupla volts in a little bit, and provide visual feedback in the process. remember to go through the "charging" procedure again when you put a new battery in the car.
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Old 12th June 2005, 06:23 AM   #8
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why do you want to charge this capacitor?
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Old 12th June 2005, 08:04 AM   #9
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if you just connect the capacitor w/o first charging it up, it'll make a huge SPARK and blow a fuse every time, and possibly damage something. tis will happen every time the capacitor is connected to a "live" system, or when you first connect the power to a system that you have just insalled.
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Old 12th June 2005, 08:24 AM   #10
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dr.p, you are full of knowledge, thanks! lemme ask one more thing. once the cap is charged, i will disconnect it and put it in its proper mounting place, what is the procedure for hooking it up to the amp (reconnecting it)? power cable intput first, power output to amp second, and ground last?

and do you think the small bulb that came in my kit is the resistor?
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