will my stock alternator on my 94' H2.3 prelude be enough to power an Alpine MRV-F345 amp and an Alpine MRP-M850 amp? on the Alpine MRV-F345 amp that i already have the voltage reading on it i get is about 13.9v at idle after a 15 minute drive.
also,Alpine SWR-1542D is the sub i want to run on a 2 ohm load with the MRP-M850.

thanks for the help in advance.

 

What wire gauge are you running?

And how is the ground?

Your lights dim?

Did you upgrade the big 3?

i think most amps will run on 11-14 vdc safely... but i'm a n00b so what do i know?

 

Use Ohm's Law and figure it out yourself...

http://www.the12volt.com/ohm/page2.asp#current

 

i just talked to the guys at Kinetik this week, they said, rule of thumb, youll need about 70 amps per 1000 watts.

http://www.kinetikpower.com

 

Nauc, they were off...The stock alternator in my 1991 Accord is 80A (though it only produces 40A @ 2,000rpms), and the place I got my sonicboomers installed said I could run the two 6.5" and 6x9's on a 60W RMS 4-channel and the two 12" sonicboomers on a 300W RMS mono-block without a problem. The guys there said the rule of thumb is at least 80A for every 500W in RMS power with a 1.2 Farad Cap or 100A for every 500W RMS without a cap. He said that for cars with alternators that make less than 60A, it is highly unlikely they will be able to run anything more than 300W RMS total power (that is the combined wattage between the 4-channel and mono-blocks) without AT LEAST a 2 Farad capacitor or bigger, and if you want to pump out more than 1,000W, you need a MINIMUM 120A alternator with a 1.2 Farad Capacitor or a 200A alternator without a cap, though, as he put it, "I do not see why anyone needs 1,000W...A good 75W RMS 4-channel amp hooked to good Eclipse or Bose speakers and a good 300W RMS mono-block hooked to good Pioneer or Sony Xplod 12" subs is loud enough. Unless you're trying to power a concert, you don't need more than a combined output of 500W RMS...Or, if you want to shatter your eardrums or turn your car into a heart attack on wheels...Those are the only two other reasons why people would need more than 500W RMS. All the car stereo shows around here can be won with a combined wattage of 500W RMS or less, because at these shows, its not the power of the system, but rather the sound quality that matters most, and all of our systems are set up to meet or exceed even the best car stereo systems in sound quality." I agree with the man. My system is loud enough to violate noise ordinances even when my windows are rolled up, but at the same time, the system specs (as rated at a car show just recently) ended up being: 10Hz to 30kHz response, <0.1% THD, and 120dB signal-to-noise ratio at the rated power of the amplifiers.

I am running an MTX Thunder TA 4-channel amp and a Sony Xplod monoblock amp, all hooked to Sony Xplod speakers and subs, with a Sony Xplod head unit. The quality for the price is unmatched. I have a 2 Farad Tsunami capacitor with Tsunami 8-guage amp cables and Tsunami 4-guage power cables, and the 8-guage speaker cables are Tsunami as well. The speakers are Sony Xplod all the way, the subs are Sony Xplod, and the head unit is Sony Xplod. The two 6.5" speakers up front are rated for 60W RMS and the two 6x9's in back are rated for 80W RMS, while each 12" sub is rated for 350W RMS. Unless you're out to wake the dead, settle for sound quality instead of volume. The voltage meter on the cap usually reads about 14.8VDC at idle after 15 minutes of driving (the voltage output of the alternator...Duh).

Also, get yourself hooked up with an Optima Yellowtop battery. That should alleviate some of the problems with running high-power systems on low-power alternators.

The 2-Farad capacitor feeds the entire system, not just the subs, and it really works. At night, I could rain thunder all the way down the street and the lights would never dim.

On most single-battery cars, if you get a reading of 14.8VDC while the car is running (even at idle), the alternator is good, but if the reading is less than 14VDC, you need a new alternator. 12VDC is the MINIMUM needed to maintain a charge on the battery, so if the alternator is reading less than 14VDC, you better swap it out while you still have power coming off it.


Modified by otacon122 at 6:02 PM 10/9/2007

 

then i just killed physics. im running a txa1000d off a stock 80a alt, stock bat and no cap with no problems

but who am i

 

I have a Alpine MRP-M850 running a 2 Ohm load and a MRP-F250 running my Alpine 6.5's front and rear in my 94 EJ stock alt and battery. No cap, 4ga wire, and distribution block down to 8ga. No dimming.

 

You'll be fine. Don't get a cap, unless it is a carbon capacitor. The other ones alot of people are used to need power to work, or in other words put strain on your electrical system. I upgraded "THE BIG 3" which is positive from alt to battery, battery negative to chassis ground and the best way for the third is to ground straight from alt case to chassis. I used 1/0 for everything, and came up with a zero resistance ground in my trunk. I ran a modded Rockford Fosgate 1500bd at 1 ohm on 4 12's in a 95 Civic. So, at a little over 2,000 watts full tilt NO lights flash what so ever. My battery would float at 13.8v

 

nice.... id love to do all 1/0, someday

 

The size of the alt. will depend on how much current is needed, how much current is needed will depend on the RMS power of the amp(s) the amps efficiency, and how much of the amp(s) RMS power you will be using, [how loud you play the system normally and consistently
Keep in mind music is dynamic, under normal use the average current draw is probably less then 50% of max current needed by the amp(s).

In regards to the use of a cap, it is a good way to get current to an amp at the amps peak current requirement times, keep in mind a cap is another current load on the cars charging system, it is very effective when you have more then one amp and only running one power lead and using a splitter box, it will prevent the sub amp from drawing current, at high current demand times, [lots of loud bass] from the high-pass amps power supply.
To avoid that problem run two power leads, one for sub amp and one for the high-pass amp, it's a better way to power your amps anyway. 94

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fcm &raquo;</TD></TR><TR><TD CLASS="quote">In regards to the use of a cap, it is a good way to get current to an amp at the amps peak current requirement times, keep in mind a cap is another current load on the cars charging system, it is very effective when you have more then one amp and only running one power lead and using a splitter box, it will prevent the sub amp from drawing current, at high current demand times, [lots of loud bass] from the high-pass amps power supply.</TD></TR></TABLE>

The way I have my system set up with the cap: The battery is directly connected to the cap (wired in parallel), so that the power feeds directly into the cap, then both amps and all the other components (including the head unit) are connected to the cap and draw power from it, using the cap as a sort of second battery. The only load on the vehicle's charging system is keeping the capacitor charged and powering the rest of the car. This setup drastically reduces the power load on the alternator from the stereo system, and also allows the capacitor to remain charged even when the engine is off. Since the capacitor is wired in parallel with the battery, I get nearly twice the runtime off the battery, and the load on the charging system is a lot less than what it would be had I hooked everything up to the battery itself. The downside to this setup is you need a MINIMUM of a 2-Farad capacitor to get this setup to work, even if your alternator can support the system.

 

Your cap is not installed properly, cap need to be as close to load, [sub amp] as possible.
There is no way a cap will extend play time, it is not a batt., it is in fact another load for the batt. and alt. to supply current to, so it does not lessen the load it increases the load.
A caps use in a car audio system is technically a band aid, if the alt./batt. could supply the current needed by the amp(s) a cap is not needed at all, however, the current requirement of an amp, especially a sub amp, has short durations of very high current demand, this is where a cap can be useful.

I always run a separate power lead for the sub amp, I always mount cap as close to sub amp as possible, cap is wired in parallel with the power lead and amps power terminal, [daisy chained] caps ground is grounded to the same spot as amp is grounded, [never in parallel with ground lead and amps ground terminal].

After 30 years of doing it this way, [long before anybody made "car audio" caps] or car audio amps for that matter, I have found it to be the most effective way of using a cap in a car audio system.

BTW, the above also keeps the cap charged at all times, in fact doing it any other way, [switched power to cap] would be wrong. 94

 

I have a stock civic alternator, 0 gauge wire, 10 farad cap, 2 directed d2400's running at 2 ohms and 2 mtx thunder 9500's for subs. also have compressors for air ride. the stereo will make my lights dim when driving and if i sit at idle it will drop it to 10-11volts. i also have an optima battery. my sugestion would be to run atleast 4 gauge, really 0 and get a 10 farad cap. they usually say 1 farad for every 1,000 watts of power but the more the better.

 

It's 1 farad for every 500W RMS, more is not better, more adds more load to the cars charging system.
Your lights still dim because you do not have enough current, a cap does not increase current, [no matter how big it is] only a bigger alt. will increase current.

Voltage dropping to 10V-11V at idle tells me the alt. is already on it's way out.

Gauge of power and ground cable is determined by current needed and length of cable. 94

 

i know my alternator is going out, running to compressors pulling 60 amps and then having the stereo going plus lights way excedes the output of the alternator for a stock one. but im swapping the motor and putting a high output alternator so i figured id let it go till it stopped.
the more farads will help, yes it will be more strain on the electric system to charge it, but once its charged it doesnt take much to keep it full.
i know the cap does not increase current but it helps level it out and keep it constant.

but for what he is running i would say he is ok with a stock alternator as long as you dont have it blasting all the time.

 

"but once its charged it doesnt take much to keep it full."
It takes as much to "keep it charged" as much as it is drawn down, nothing is free.

but for what he is running i would say he is ok with a stock alternator as long as you dont have it blasting all the time I agree. 94

 

so you suggest i run a separate power lead, from the battery, for each amp with or without a cap,correct? also if you would suggest a cap for the mono amp, should i get a 1-1.2 farad or 2 farad cap? it will be running at 800w RMS but i wont have it running full bast too much.

thanks a lot for all the replies guys.much appreciated.

 

i would run 0 gauge or 4 if u have to from the battery back to a distro block. if the cap has multiple outputs then use that as a distro block.shop around and buy a good brand cap, dont settle for some off brand 1 farad cap cuz its prob only .5 farad or it will crap out on you. my caps a stinger 10 farad and i love it.

i agree with fcm about running a seperate line for the mono amp back but it really depends on your budget.

 

Tsunami is another good cap brand. You can get Tsunami wiring for the cap as well.

 

Yes I would suggest running 2 power leads, as long as the leads are no longer then about 12' use 4ga for the MRP-M850 and 8ga for the MRV-F345, use appropriate ANL fuses.
Run the 8ga directly to the 4ch amp, install a 2 farad cap, [or two 1 farad caps in parallel] on the 4ga for the mono block amp, [as close to the amp as possible].

Ground both amps and the cap to the same point, or at least the cap and mono block amp to the same point if the 4ch has to be grounded at another point, [keep the ground leads as short as possible], use existing bolts/studs that are in the cars floor pan for ground points, [seat and seat belt belt bolts work well].

Another point, if you are using rear speakers, [4ch amp], disable the tweeters, wire the speakers in series and connect them to the bridged rear channels of the amp, [ch3+ch4].

As for the cap, most brand name "car audio" caps are about the same, I have never had any problem with Stinger caps or EFX caps. 94