Replacing an amp connected to a 1F cap
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=34569
Printed Date: July 07, 2025 at 6:06 AM
Topic: Replacing an amp connected to a 1F cap
Posted By: brewtownska
Subject: Replacing an amp connected to a 1F cap
Date Posted: June 25, 2004 at 2:37 PM
About 2 years ago when I worked at Best Buy, I had a system put in (probably nothing near as good as what you all have in your vehicles) because I was able to get things at a good price. At the time, I didn't think I needed a huge sub and lots of amp power for it because I didn't listen to hip-hop/rap. Bad move on my part. The good news is I had them put in a 4-gauge ground wire and a 1 Farad cap in back, so I'm all set for something better. The sub was a RF 10" (don't remember model, but it handled 200W RMS). The amp was a RF small stereo amp that could be bridged to put out about what the sub needed. The installer probably knew this was too little power and sub for the rest of the system, but they didn't bother to inform me otherwise. He turned the gain WAY up (even though the Kenwood deck had 4.5V preouts), and so I found the amp would give out after only 30mins of straight play. Eventually I found I needed to reverse the phase of the sub and then was able to lower the gain on the sub amp...so things got somewhat useable. A friend was getting rid of his RF 12" DVC sub (4 ohm coils, each 200W RMS), already wired into parallel. I know I shouldn't have this connected to my little amp, because it could probably fry the amp up seeing that the amp is bridged and not stable to 2 ohm, but I'm doing it anyway...been that way for about a year now, and no problems. Now I got a new RF 351 Power amp, and that will put out like 400 or 450W RMS (actually, the birth cert says 493W) into 1 channel at 2 ohms. The only problem is that I'm a wuss and not sure what I need to do to take out the existing amp and put the new one in. If there was no capacitor between the battery and amps, I'd have no problem, but with all the talk about the cap being like a bomb waiting to go off if something goes wrong, I'm a little hesitant to do anything unless I have some instructions to follow. I probably know most of what I have to do, I'm just looking for some reassurance and instructions. Can you guys help me out here? My THOUGHT is that I need to disconnect the negative wire from my battery. Do I also need to take off the positive, or remove the fuse on the positive? I then think I need to disconnect the power lead to the amp, the amp-turn-on wire, speaker wires, and LAST the ground wire (all together making sure not to ground the power wire or let the positive/negative touch each other). Am I good so far? Then when putting the new amp in (it's only a slight bit bigger, so it'll go in the same place), I connect the ground FIRST, right. Then what order should I start connecting everything else? Is there anything in the process that will drain the cap if I do it wrong? I think as long as I know what's going on, the process should be like 15-20 mins tops. Any help would be greatly appreciated!!! Mike
Replies:
Posted By: haemphyst
Date Posted: June 25, 2004 at 4:18 PM
good so far...
1) Remove the fuse under the hood.
2) Using a test light across the terminals of the cap, driain the cap, and you'll know it's done when the light goes COMPLETELY out. Leave it on about 30 to 45 extra seconds just to be safe.
3) Disconnect the cables to the amp, they are all dead now, but a little electrical tape around the ends could never hurt.
4) Mount (I mean install  ) the new amp.
5) Reconnect all of the cables in the positions they belong.
6) Listen carefully! Go to the fuse holder under the hood, attach the clip of your test light to the battery positive terminal. Now touch the tip of the testlight to the outgoing side of the fuseholder. The light will come on, then get dimmer, slowly. When the light goes OUT again the cap is charged. Again, wait there 30 to 45 extra seconds, replace the fuse, but do so within about 10 seconds. There MAY be a small spark, but it will not hurt anything. You are done.
Good luck! These instructions will get you there, but it is ALWAYS a good idea to use a bit of extra caution around charged caps. They will not kill you, but they could burn you or cut you IF they were to explode (and they can). Just use common sense, and be extra careful. ------------- 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: mikedawg
Date Posted: June 25, 2004 at 8:53 PM
yeah man,haemphyst knows whats up. only thing to add is a quick way to charge your cap. when your car is running and youve already reinstalled your fuse, and youve got the ground on your cap, slightly tap the power wire to the positive lead on the cap. its gotta be pretty quick. youll see a spark. nothing scary or nothing. then tap it a couple more times and youll see the spark get smaller until there isnt one. then connect the wire and youre ready to go.
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always looking for new info and willing to give it
Posted By: Ravendarat
Date Posted: June 25, 2004 at 11:30 PM
Not a good way to charge a cap up. I try not to be so strait forward but what you are suggesting will really deminish the life of your cap. Caps are shipped with a resistor used to charge them up for a reason. If you charge a cap slow it will retain a charge for far longer and the life of the cap is also increased. Its the same as when you charge a car battery with a charger you should always charge on the lowest setting if time alows it because it is far better for the battery. Just putting strait 12v to it with no resistors is a bad Idea. There is no quick way to charge a cap properly, its one of those things that just takes time. ------------- double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: mikedawg
Date Posted: June 26, 2004 at 11:53 PM
sorry if i gave the wrong advice but i doubt that was the wrong advice.i was told by randy whom is a tweeter installer. not a best buy or circuit city installer but a TWEETER installer. trickle charging a battery is the best way if you have a regular battery. but if you have a cap then i doubt you didnt upgrade to a drycell which is better suited for high strain. jumpstarting your car is the same thing. using a test light is almost as quick as the way i was taught. and i also learned from dyohn that the cap is a transient filter not a power source, so holding a charge is not the job of the cap.
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always looking for new info and willing to give it
Posted By: Ravendarat
Date Posted: June 27, 2004 at 10:17 AM
holding and discharging is not the ONLY job of the cap but if it cannot preform that job properly than everything else doesnt matter. I stand by my previous statement.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: mikedawg
Date Posted: June 28, 2004 at 1:59 PM
well i think ill just wait for the word from dyohn. he seems to know what hes talking about.
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always looking for new info and willing to give it
Posted By: brewtownska
Date Posted: June 28, 2004 at 2:36 PM
Thanks guys for the suggestions. I was hoping there was a safe way for me to swap the amps without having the discharge and recharge the cap, but that doesn't seem to be the case. I'm just taking it to my local car audio specialty shop and having them take care of it. The piece of mind that I won't screw something up is worth the $50 they'll charge. Mike
Posted By: mikedawg
Date Posted: June 29, 2004 at 4:01 PM
yeah thats understandable. caps used to scare the crap out of me. i was installing one with my friend back in the day and he dropped it post down in the trunk and it welded itself to the floor. we had to grind it off.
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always looking for new info and willing to give it
Posted By: Ravendarat
Date Posted: June 29, 2004 at 5:31 PM
thats never a good sign, when the cap welds it self to the floor. That would have sucked. BTW I dont know what your experience level is but I have been doing this for 5 years now and I dont know if it was your intention but it seemed to me that you implied that I didnt know what I was talking about which is kinda insulting. I install a couple of caps a month usually so I'd like to think I "Know what Im talking about". If you ever wanna see for yourself go ahead and check out manufactors directions and I have never seen a single one hat says that you tap the power wire till its discharged. They all say to use the supplied resistor or in RF's case the supplied charging board.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: mikedawg
Date Posted: June 29, 2004 at 10:00 PM
i never said that you dont know what youre talking about. you seem to think that i dont. so ill just let someone that i know, that knows more than you and i prove one of us wrong. if you think that your little car stereo business is above that of Tweeter's and hi fi buys, than i feel sorry for you. but for now you do it your way, and ill do it my way. oh btw, my line of work is that im a certified executive chef with a little mobile electronics hobby/ business on the side.
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always looking for new info and willing to give it
Posted By: archemedes
Date Posted: June 29, 2004 at 10:19 PM
I worked for a distributor, and the cap manufacturers all specified to use the resistor for charging initialy
Posted By: fuseblower
Date Posted: June 30, 2004 at 8:01 AM
I hate to burst anyone's bubble but the guys at those stores are no better than anyone else technically speaking. I have dealt with some of them and they only know what the books showed them and others for the love sound knew what was going on. I've read some of the books and some did not even mention how to create a 4-ohm load using 2 dual voice coil speakers. A cap is not to be charged at a high rate of speed for multi purposes. You could ruing it or even cause it to explode. Yes, a cap holds a charge but not as great of charge as a battery because it is designed for instant bursts of energy not constant power. A charging transistor is best when charging a cap because it helps prolong its life span.
Posted By: metalcorolla
Date Posted: June 30, 2004 at 10:56 PM
speaking of caps, mine is doing some funny things. the digital display always reads 3 volts too low. i have had the thing looked at by someone whos knows what they are doing and they said its fine other than the display. weird huh
Posted By: mikedawg
Date Posted: July 01, 2004 at 12:46 PM
well according to some of the people on here, nobody but them knows what theyre talking about so i wouldnt even mention having someone else looking at it. most of the people that think theyre better than everybody arent even mecp certified. they just read a couple of geocities websites, install a couple of stereos and think they own a business.
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always looking for new info and willing to give it
Posted By: Ravendarat
Date Posted: July 01, 2004 at 12:48 PM
OK mabye over reacted and Im guessing you did as well. First off I never claimed that everyone who worked in electronics stores know what they are talking about. I have asalesman who doesnt know his ass from a hole in the ground. As I said before, my point is that they supply resistors or charging and discharging pads for a reason and that they never intended for people to operate them in any other way. Simple as that. And I dont think that you dont know what you are talking about, all im saying is that what you suggested is not the proper way to do it. May still get the same end result, Im not sure of that but i do know that its not the suggested path. Im done on this subject. Hope theres no hard feelings, Im just guessing that this is a subject we arent ever going to agree on.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: mikedawg
Date Posted: July 01, 2004 at 5:44 PM
no prob, i know that thats not the stated way that are in the instructions. i remember my first cap i bought came with the little .8 ohm resistor. but you can also do it with a test light like some dude on here said earlier and it doesnt say to do it that way. the instructions they provide, im guessing they take the safest route to prevent anyone with no experience from messing it up some how. im sure you have your own tips and tricks to installing to make your job faster and easier that the companies dont offer in their instructions.
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always looking for new info and willing to give it
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