90 amp alternator enough?

RoughRiverMike · Outlaw Joined: 08 Dec 2005 Posts: 107 City: louisville

Is there a formula to calculate my alternator needs?
My planned accessories are; Clarion head unit, JL 6450 amp for interior speakers(45x6 @ 4ohm), I want to get the NVS tower speakers with the 1000 watt zapco amp. I'll also have 6 tower lights, heater and standard interior and dash lights.Blower of course,but that will not be running simultaneously. The boat will have dual batteries and a 90 amp alternator. Mastercraft does not offer a beefier alternator. I refuse to break down in a new boat. I have simmilar accessories on my malibu now and have never had a problem (even if I just float and listen to the stereo). I have Kicker amps now. One is similar in power to the JL, but the other is not quite as powerful as the Zapco.
Help would be greatly appreciated.

acurtis_ttu · Soul Rider Joined: 16 Aug 2004 Posts: 499 City: Houston

That 90 amp alt will probably produce up to 110-115 amps under full load. You can use ohms law to calculate amps, but it's excluding many variables. the only real way to test accurately is wiht an amp meter. I wouldn't chage anyhting just yet untill you test it on the water. IF you running everyhting at once (stereo on max) ...you could be pulling more than the alt can produce , but how often are you doing that? When ever the alt can't keep up the power is coming straight from your batteries. Running alot of acc. requires the operator to contstantly monitor voltage. I run big enough batteries so if my alt fails I can usually run all day long w/o any issue. (had this happen 2 weeks ago). You can tell alot about what your alt is producing based on your batteries voltage.....assuming yoru batteries are at a full charge when you test. 12.5-12.6 is normal resting voltage. you should be seeing 14.0-14.5 w/ no accesories on.

acurtis_ttu · Soul Rider Joined: 16 Aug 2004 Posts: 499 City: Houston

As long as your dual battires are setup right you'll never be stranded regardless of how your alt performs.

RoughRiverMike · Outlaw Joined: 08 Dec 2005 Posts: 107 City: louisville

acurtis,
Thanks for the reply. I'll take that advise and wait till I get the new boat to check it out on the water. My MC dealer feels pretty good about the setup using dual batteries. I think your right, when would I be running the stereo full tilt for long periods of time?

mike

RoughRiverMike · Outlaw Joined: 08 Dec 2005 Posts: 107 City: louisville

acurtis,
Thanks for the reply. I'll take that advise and wait till I get the new boat to check it out on the water. My MC dealer feels pretty good about the setup using dual batteries. I think your right, when would I be running the stereo full tilt for long periods of time?

mike

brianw21 · Newbie Joined: 07 Sep 2005 Posts: 35 City: Boise

Add the fuses together for all the devices you plan on having on then multiply that by 75% (.75). Fuses are rated in amps at 12V. Most alternators are rated in amps at 14.4V.

To make it easier... compare watts to watts... Voltage * Amperage = Watts

If you electronics add up to (75%) more then your alternator, then you know that at full tilt you will be draining your battery, and starving your engine electronics. At least this way you know how much of a gap exists.