what size cap do I need?
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=35195
Printed Date: July 06, 2025 at 11:56 PM
Topic: what size cap do I need?
Posted By: olingerd
Subject: what size cap do I need?
Date Posted: July 07, 2004 at 2:37 PM
I am pretty new to installation, I know how to do it fairly well for just little experience. Just need some advice I have sony just kinda begginer stuff, I have 2 P5 12's and the XMDS1600P5 amp that has the two subs at 900 watts. I know my amp is going to be pulling 130 amps and my alternator isnt going to be able to handle that. So what size cap do I need? Is 1 farad enough??
Replies:
Posted By: mikedawg
Date Posted: July 07, 2004 at 2:51 PM
one farad would be sufficient. i really doubt youre gonna wanna upgrade your alternator with that setup.
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always looking for new info and willing to give it
Posted By: haemphyst
Date Posted: July 07, 2004 at 2:53 PM
If you are aware that your alternator is too small, then why are you asking what size cap you need? If you read these posts, you will know that it has been stated over and over "A cap will not fix your problem!" Take that 100 bux, save another hundred or so, and do it RIGHT. Get an alternator that will provide the current you need for the amplifier you have. THEN, and only then, consider a cap. A cap will NOT fix an underrated alternator sistuation... It will NOT make it worse (as some people believe) but it will not fix it.
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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: olingerd
Date Posted: July 07, 2004 at 5:59 PM
what will happen if I run this system without a new alternator or cap while I look for either??
Posted By: maglin
Date Posted: July 07, 2004 at 6:06 PM
Ah.. it'll prolly burn it out, or the car won't work quite right. the other components in teh car will go to sh*t... personally, i noticed my ABS went to crap in a handbasket before i upgraded my alternator in my 93 sunbird (had a whole bunch of BS neons and a small amp). I upped the alt, and life returned to normal. The car also had issues with reving up, and there were assorted other issues... like the seatbelts were convinced they were not plugged in, for 5 second random intervals. hehe. ~~Dan Lansing. Upgrade it. save your self a load of crap.
Posted By: godd dan it
Date Posted: July 07, 2004 at 9:10 PM
A good rule of thumb............Use at least .5 farad per 500 watts RMS of power output. You can have as many farads as you wish, just do not use less than what you need.
Posted By: forbidden
Date Posted: July 08, 2004 at 4:25 PM
Bad rule of thumb dude, cut off your thumb and go back to go. Remember that a cap does not create current, it uses and stores it. Just because you have this amp with say a 60 amp fuse, does not mean that it draws this much current all the time. The current draw is proportional to the load the amp sees, the volume it is played at and the duration it is played for. The first thing you should do is upgrade all the ground wiring from the battery to chassis, block, alternator and for gods sake make sure you have a good proper ground at the amp. (this means a resistance of below 1/2 ohm) Make the ground return as efficient as possible to ensure the amp can work to it's full capabilities. Cause the amp to stuggle for power, the vehicle circuits will notice next. After the wiring upgrade save for an alternator if you need one.
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Top Secret, I can tell you but then my wife will kill me.
Posted By: godd dan it
Date Posted: July 08, 2004 at 6:25 PM
Forbidden....that was not my rule of thumb. Thats what they recommend. But that is without having alternator problems and not supplying enough power. I wasnt discussing that at all.
Posted By: mikedawg
Date Posted: July 10, 2004 at 1:50 AM
i dont know where olingerd got the info that a XMDS1600P5 amp is gonna pull 130 amps but thats largely overrated. get a dry cell battery and a one farad cap and youll be fine. dont even think about getting a h.o. amp until you get some real subs. ------------- always looking for new info and willing to give it
Posted By: Ravendarat
Date Posted: July 10, 2004 at 10:14 PM
Ya that amp cant possible pull that much current. If I remember right the fuse rating in the amp is only 60 amps or 80 amps max so there is not way it can pull130 amps. If it did it would be snappin the fuses. I dont think any of the above is probally nessasary for that amp with those subs. I mean, contrary to what people seem to say I DO think that caps can help when you are a little short on power. I mean a little though. Like 15 amps to 20 amps at absolute max draw when all things are considered. It may not make your lights stop flashing but its gonna help avoide problems like those maglin talked about. NOTICE I SAID HELP NOT SOLVE. I really dont feel like getting this thrown back in my face. This is an Issue where I dont agree with a lot of the experts on here and it has become quite clear to me that neither side is gonna budge so I try to stay out of these disscusions if I can.
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double-secret reverse-osmosis speaker-cone-induced high-level interference distortion, Its a killer
Posted By: mikedawg
Date Posted: July 11, 2004 at 2:15 PM
i kinda agree with you ravendarat about the cap in this situation. i mean we are dealing with sony. he'd be better off with a discman and a pair of headphones. but i do think that a dry cell battery will help more than a cap. i got a 10w7 with a one farad cap. i had a regular battery and i had dimming lights and my monitor would even turn off at a stop light. but i got the yellow top optima and i have no dimming lights at all.
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always looking for new info and willing to give it
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