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Old     (flux)      Join Date: Jun 2003       06-15-2006, 4:02 PM Reply   
So our old 50x4 amp finally bit the farking dust and I am considering upgrading to a JL e6450 6 channel to power the cabin and sub speakers, the bows will stay on the HU, they usually have fatsack over them anyway.

My 02 SANTE has two batteries and a 55 0r 65 amp alternator. We are not loud listeners, but I want a clean amp that powers everything properly instead of wiring the 4 speakers in 2 series like before. All should be 4 ohm loads.

If I keep the gain down on the channels will the amp still draw major power?? Or does it still draw a large amount just by being on??

I am just a bit worried about straining the alternator and causing problems with the electrical system in general. I want clean, not necessarily loud although I like some volume.

input is greatly appreciated.
Old     (flux)      Join Date: Jun 2003       06-15-2006, 4:26 PM Reply   
I found something on Crutchfield:

You take the total RMS wattage and double it, divide that by average alternator output (13.8), then divide that by 3 for the average power sucked up by the Amp.

This number needs to be less than 40% of the alternators amp rating.

Sound alright to you audio guys??
Old     (rodmcinnis)      Join Date: Sep 2002       06-16-2006, 8:42 AM Reply   
Estimating average power draw is pretty much a guess.

The wiring between the amp and the battery needs to be sized large enough to handle the peak power, so essentially the maximum output of the amp. The alternator needs to be sized according to the average power draw which will be a lot lower.

If you don't have the volume cranked up then the amps will draw a lot less power. More volume = more power = more current.

With a 65 amp alternator you will find situations where the output is not enough, but they can be short duration periods that you can handle. For example: If you have the bilge blower on, a heater, cranking the tunes to be heard at wakeboard speeds and you are running three ballast pumps there is no way the alternator will keep up. Turn the bilge blower off, you don't need it while moving. The ballast pumps will only be on for a few minutes, your battery will last that long. Just pay attention to the volt meter on the dash: 13 volts or higher you are fine, below 13 volts and your battery isn't charging, below 12 volts and your battery is being drained.

The biggest drawback of an undersized alternator is that battery recharge time can become an issue. If you sit and listen to the stereo for a couple of hours you may need to put 100 amp-hours back into the batteries. If you only have 10 amps to spare out of the alternator it could take you all weekend to get the battery back to full charge.

Old     (flux)      Join Date: Jun 2003       06-16-2006, 9:30 AM Reply   
So essentially I risk draining the batteries by playing the stereo all day and maybe keep the stereo off while filling and draining the tanks and sacs.

My biggest concern was adding an electrical appliance that is bigger than the system can handle. We are not loud listeners so I don't think it will be a huge issue and we can be careful not to tax the system by turning on everything at the same time.

Thanks for the input Rod. Before I drop the coin and spend the time, I just want to know what I am getting into.
Old     (acurtis_ttu)      Join Date: May 2004       06-16-2006, 10:28 AM Reply   
Flux, yes there is a risk, but it's small. You should be fine, unless you drive around all day with everything electrical on your boat turned on and the volume up. Get in the habit of always puttign yrour batteries on trickle chargers in between outings, this will ensure yoru batteries are fully charged at the start of each outing. Like Rod mentioned keep an eye on yoru voltmeter just to be safe.


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