Power Capacitors...

Does anyone run these in thier boats?

I have a relativley small stereo with 2 amps running 8 speakers and a sub. I also have 2 batteries run through a perko switch. I have noticed a huge drain on the batteries when its played loud. I guess my question is does anyone us a power capacitor in thier boat? I was thinking about getting one like a 6 farad cap to help out and wanted to know if it was going to help.

some do, but they are very arguable as to the effect. Many companies overate the farrad capacity of their capcaitors. All a capacitor is designed to do is act a a type of "battery" but has the ability to charge and recharge in miliseconds. It cna arguably help you if you have short/high current draws on big bass hits (for example) but you need more batteries to solve your power drain, not caps.

what amps speakers are you using....my guess is the amp are proabbly very ineffecient...a quality of low end amps. 2 amps should not be draining that much power. are you batteries fully charged to begin with?

well, im running a rockford p4004 amp (50x4 @4 Ohms RMS) to power 4 MB Quarts in the boat off the front channel and 4 polks on the tower off the rear channel. Also have a Pioneer mono block class D amp powering a JL w3 at 2 Ohms. I have 4 gauge off the batteries for power and ground running into distrubtion blocks then 8 gauge to the amps. The batteries are about 1.5 years old. Maybe I just need to bite the bullet and get some new blue tops.

I would not expect that kind of power draw from thsoe amps. What kind of batteries do you have? Are they deep cycle? Unless you haev to moutn your batteries in an akward position there are just as good/better batteires out there IMO.

To go back to the original question what are you classifing as a "huge drain"? Are you not able to start the boat? how long of a period?

Yes, they are deep cycle marine batteries mounted in the normal position.

I dont run the stereo without the engine running. I have a 2000 maristar with the motorized rear hatch. What I have been noticing is after a period of time with the stereo turned up I can watch my volt gauge drop. Once the motor is off the batteries have a hard time lifting the hatch open and the motor is slow to start.

Cap's can and do work for some system's. Sorry if I’m going to explain something that lots of people all ready know about but here go's.
A battery is like a long distance runner it can run (or provide power) for a long time at a steady pace, But when your system hit a heavy Bass note it can put a large draw on your batterys for a second A cap is designed to provide a burst of power that your system draws because your batterys cant respond fast enough
A cap is like a sprinter it can provide a quick burst of power but just for a few seconds. So a cap and battery can work hand in hand with each other. IMO a cap can make an all ready good system better but in no way is a cap going to fix a power shortage problem. Like what you are talking about.
The way I see it is a extra battery is going to set you back $150-$200 and a cap is going to set you back the same amount of money if not more so if you look at what is going to do your system better a extra battery or a cap? IMO for YOUR specific system and the equipment you have listed I would say an extra battery. Sorry if thats not answering your question but I thought I would just cut to the chase.

one last thing: unless your gonna get a 30 fard cap I wouldnt mess with it.

Grant, thanks for that explination! I guess I was in the minority cause I figured a cap would act as a third battery. So now it looks like I will be picking up a third battery.

My next question would be how to wire it all up. I already have 2 batteries connected through a perko switch, so how would you add a third to it?

A cap may help a poorly designed amp. If the amp is well designed it won't be bothered by a millisecond drop in voltage.

One of the basic formulas for a capacitor is:
i=c*dv/dt
which is the current equals the capacitance (farads) times the change in voltage divided by the change in time. If you wanted the capacitor to provide 100 amps for one second and have the voltage only drop one volt then 100amps=c*(1 volt/1 second), or C would need to be 100 farads.

A 10 farad capacitor would keep the voltage from sagging from those big bass hits, but it won't hold it up while the guitarist goes crazy.

From what Scott describes he needs more alternator output. A capacitor won't do anything for him. Adding another battery will provide him with a little more run time, assuming that he started with the battery fully charged, but if the alternator is not providing more than the boat is using the batteries will go dead, no matter how many you have.

wireing a third to the system is really easy you will have one batt on one side of the perco and two batts on the other. you will want to run the two batts in paralell to maintine your 12vdc. you now have doubled your AH (Amp Hours) or runtime if you will. I would recomend getting two identical batts for that.
JJ

Ok so it looks like im going to be picking up some new blue tops this weekend. Last question and the paralell wiring. Its been a long while and im not sure what paralell is...is it positive to positive then negative to negative? Like this?
Sorry for the bad paint diagram

yup thats it

you got it. except your perco shouldnt have a place to land you -12vdc only your +12vdc will land on the switch
JJ

Scott - Although I'm not running as many speakers as you are my amps are pretty close. I've got the p4004 and a T5002 for the sub running at 2 ohms. I can easily play at a non-conversation volume for over 1/2 hour without running the engine with a single interstate battery. I do have a farad cap but just because I had one laying around.

I'd check your charging system and the battery levels before going for that third.

(Message edited by bull on August 27, 2006)