funkdamonkman

I plan on putting in a system soon with the following parts:

501bd Rocksford Fosgate AMP
551x Rosksford Fosgate AMP
lilliput touchscreen
in-car pc.


Is this going to stress the alternator? I don't plan on using any capacitors, but I don't think that changes the stress on the alternator.

FYI, I will be running the 501bd at 2ohm which is 500w RMS.

The 551x will be run at 4ohms wich is 280w, but I don't plan to push it that hard. Probably something like 150w. The sub, however, may get pushed at 500w a lot of the time.

I think the Z has a 110amp alternator.
both subs have 60amp fuses, and the most the computer could pull is 30amps. I'm worried about running all of this at once with my brights on. I don't think nissan would cover the alternator under warranty if I burnt it out.

Dream2Reality

iTrader: (1)

I'm curious too, but remember; even if you have 2 amps with a combined 120a fuse rating, you will NEVER pull 120a at once unless you're playing full-range sinewaves or something like that. For regular music, there are so many peaks that you won't pull all the power from your amps; otherwise the fuses would blow. I think you're ok, especially since I think the 501bd is class d, which means greater efficiency.

onecoolee

you really don't need to worry about wattage, but total current.

Amps are rated in peak and rms watts, and IMHO wattage is really a poor rating if you are looking at speaker limitations. However, it is valid, if you know how much wattage your amp is actually putting out. Wattage is a rating of power lost or used in a system. This power is used up in 2 ways, heat and output to your speakers. You have to consider something important though, and that is amp ratings are made at clipping which can be considered the max rating before the amp starts to distort the music too badly. You will hardly ever reach this limit at either full gain or full power, since your ears will probably be bleeding if you do...and not many people turn their systems up past halfway for too long. So, you are never really using the full power supplied by your amps--like Dreamtoreality said earlier.

Also keep in mind that a speaker will handle 10x or more wattage than what it is rated for, as long as the power is clean and undistorted. That is why its bad to rate speaker by power handling capability, I think.

Anyways, onto the geeky stuff... providing you know the actual power output of your amps, and you are using them in the conditions described in the amps manual, ie proper load impedance, you can calculate the total current draw on your system. By looking at the total watts, and system voltage. Essentially, Power = Current (squared) x resistance (load impedance) OR Voltage x Current. With a little rearranging of the formula, I (current) = Power (watts) / Voltage (volts). For this to work, you will need to know the exact power being delivered to each speaker and load. Assume 14.4volts too, since your Zs battery probably won't last long without the engine running, I know mine doesn't.

In your case, lets say conservatively that the sub is getting 400 watts and the seperates or whatever are getting 150 watts each. Thats a total of 700 watts. If you plug the numbers back into the formula above, that equates to 48.6 amps. Even at close to full power, with total of 1000 watts, the total current draw is 69.4 amps. That leaves plenty of extra current for battery charging and system draw for your ride.

One great thing to monitor is at night...if your headlights dim, then you are tasking out your alternator and this abuse will cause your alternator to fail earlier than normal. You can do a few things to fix this, get a larger/better battery, or add an extra battery and charge both batteries using a dual battery isolator, or add a large stiffening capacitor, which will act like a battery, and supply your audio system with the power it needs during max draw times, then recharge itself during low draw times. A capacitor will make a huge differnece in bass response in any quality audio system, and I recommend you add one soon.

The bottom line is, if you are not blowing fuses, which typically do not blow unless they are put to 2-3 times their rating for more than a second, then your total current draw is no more than 100A...I would guess its still less than 80A total, even at full power, unless you are driving your subs at a very low impedance which could effectively double or quadruple your current draw. Use the headlight test, and if your headlights dim...get a cap...if they still dim, look into some other options, or turn the volume down !

By the way, our Zs have 115A stock alternators, which is usually plenty to provide our amps with enough current, and still keep the battery charged, and provide enough current for the car, even with a more demanding audio system.

Dream2Reality

iTrader: (1)

"One great thing to monitor is at night...if your headlights dim, then you are tasking out your alternator and this abuse will cause your alternator to fail earlier than normal. You can do a few things to fix this, get a larger/better battery, or add an extra battery and charge both batteries using a dual battery isolator, or add a large stiffening capacitor, which will act like a battery, and supply your audio system with the power it needs during max draw times, then recharge itself during low draw times. A capacitor will make a huge differnece in bass response in any quality audio system, and I recommend you add one soon."

Not exactly true... Adding a second battery will make your alternator die MUCH sooner. It makes your alternator work way harder because it is trying to charge 2 batteries instead of one. Also, capacitors are known as "band-aid" fixes. There's still voltage drop at the alt/batt, so you can still fry your alt pretty quickly. The bass WILL be better because you're maintaining 14.4v @ the amps, but there's a drop before that. The ONLY true fix is a high-output alternator; or just have the stock one rewound.

funkdamonkman

Thanks for your calculations onecoolee. I will be running one amp at 2ohms, which is supposed to make it output 500w. The other will be running at 280w MAX, and there is no way the stock speakers can handle that. So from your calculations, I should be drawing under 60amps even at full load. Thanks!