Does a Cap Lose Its Charge if Battery Dies?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=37686
Printed Date: May 11, 2024 at 1:10 PM

Topic: Does a Cap Lose Its Charge if Battery Dies?

Posted By: crazykev81
Subject: Does a Cap Lose Its Charge if Battery Dies?
Date Posted: August 18, 2004 at 6:04 PM

hi, I have a cap and i am planning on installing it soon. i have read alot of the forums on the cap installation, etc. my question is.. if my battery goes dead and has to be jumpstarted, or the battery cable has to be disconnected for some reason, does the cap lose its charge? if there are any precautions i should take, as to when to re-charge / discharge the cap.. please let me know so i can have an understanding before i hook this thing up, just so i know what i am up against. thanks!!

ps. is it also true that if i am playing my stereo with the engine off and the cap installed, is it true that my battery will go dead quicker, or will it take just as long to go dead? thanks:)

Replies:

Posted By: stevdart
Date Posted: August 19, 2004 at 12:40 AM

1. No. A capacitor will stay charged until it is discharged. 2. To the ps: Your battery will go dead if you play it too long, but the cap is not the reason, the amp is the reason. If the battery is drained two seconds sooner because the cap is allowing a stronger bass hit, then it is still dead nonetheless. Draining your battery will quickly shorten its life, as you may already know.

Make sure you follow the capacitor instructions for charging/discharging. You will have a resistor to install inline with the cap to allow for proper charging.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: zane9000
Date Posted: August 19, 2004 at 2:07 AM

stevdart, just for clairification: when you take a bare electrolytic cap (or any for that matter) and charge it up, then let just sit unattached form a power supply it will discharge on its own. is this different for caps made specificly for car audio? ive seen some in an enclosure with extra circuitry. is that what keeps it charged or do even the large electrolytics ment for cars hold a charge on their own as well?

~warren

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I had Cheetos and wine for dinenr.

Posted By: crazykev81
Date Posted: August 19, 2004 at 3:29 PM

ok, thanks:) sooo just to clarify... even if the battery goes dead, the cap still has juice... it only loses the charge if i discharge it manually? also, the charging bulb serves the same purpose as a resistor, correct? thanks for the input guys, I have been around car audio and doing my own installs and keeping quite neat the last little while, i just havent worked with capacitors much.. i read alot of forums on here etc, and all the how-to's and directions.. just playing out the "what if's" now i guess. I appreciate the input posted_image

-Kevin from Canada-

Posted By: haemphyst
Date Posted: August 19, 2004 at 10:47 PM

OK, guys... and this is to everybody.

1) If you battery goes dead, your cap will be dead (empty of charge) as well. It CANNOT remain charged if the charging source has no electromotive force to maintain the charge on the plates. What this means is that, if your battery is completely dead, and you try to connect to a good battery, (to jump start your car, for example) you will get the characterisitc BIG spark of charging a (dead) high value capacitor. When jump starting a car with a capacitor installed, it is always a good idea to remove the fuse(s) to the system, and make certain all of the caps are properly recharged using the manufacturers instructions, after the car is started.

2) EVERY capacitor can and will self discharge. There is no such thing as a perfect capacitor, and there is parasitic resistance in EVERY kind of capacitor. If you leave your car sitting for a VERY extended period of time, it might be a good idea to disconnect the power lead to you cap (bank) and amplifier, as this parasitic resistance will have (negligible, true) draining effects on the primary electricity source in your car - the battery. I know the alternator is the primary POWER source (but the secondary electricity source), but without a primary electricity source (the battery), the alternator cannot EVER put out any power. If it could, then you would NEVER need to jump start a car, 'cause the alternator could just "make power" - and we all know that they don't.

3) If you simply disconnect you power cable for some reason, your cap will maintain a charge for quite some time, (unless you short your power cable accidentally to the chassis - good times!!! posted_image

) but if you have it disconnected for more than about 30-45 minutes, it might be a good idea to recharge it using the mfr's recommendations. Most likely, it will not be necessary, but it is better to be safe than sorry. You are playing with/near a lead acid battery, and they DO make explosive hydrogen gas, and it is best to minimize any possibility of sparks.

Thank you for your attention...

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Posted By: stevdart
Date Posted: August 19, 2004 at 11:21 PM

Thank you for sharing your knowledge, hemppist. Consider that bookmarked.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: crazykev81
Date Posted: August 19, 2004 at 11:24 PM

ditto.. thanks!