When do you need to upgrade alternator?

[tige']

Other than waiting until you find out the hard way that you can't keep your battery/batteries charged, how do you know when you need to upgrade to a bigger alternator or add another battery?

I am thinking of adding another amp but don't want to overload my alternator. It is still a stock alternator, 60-65 amps.

There is a formula Amp = Watts/Volts. So, running through my equipment below:


I currently have 1 starting battery and 1 stereo battery (Trojan Deep Cycle) that are connected with a Yandina combiner.

I am currently running (with no problems):

2 Cadence SQA-4 amps in a 4 x 60 watt mode (240 watts each.) 1 is running 4 Polk Audio db651's in-boats, the other is runing 4 Polk Audios db651 tower speakers

1 Cadence SQA-1 amp in a 1 x 500 watt (maybe 700 watt?) Runnig a XS12 Wetsound sub

I am going to upgrade my tower speakers to HLCD speakers. I am adding a Boston Acoustic GT28 amp in a 2 x 350 watt (2ohm mode).

So I will be adding another 700 watts but removing 240 watts (removing the current tower Cadence SQA-4 amp).

BUT, I am considering using the SQA-4 amp and rewiring both the SQA-4 amps in a bridged mode to power the in-boats. This would be a 2 x 200 watt mode (per Cadence spec). With the 4 in-boats, that increases the wattage from 240 to 400 for the in-boats.

Plus the increase on the tower speakers (700 - 240) that is a total increase of 620 watts.

So, my new total watts (assuming the sub is at 700) would be 1800.

Back to the formula: 1800 watts / 12 volts = 150 amps.

If this is all correct, I am OK with one stero battery and a 65 amp alternator?

Thanks

[Joeprunc]

Hopefully I can confuse you more....

That equation seems to look good (thought part of me thinks you need Ohm's Law I=V/R in there for each speaker, but I don't remember much from EE in college ). Also if you look at your volt gauge you should be pulling closer to 14 volts when the motor is running.

You are taking your peak power for each unit, I bet each of those amps uses an average of not even half the peak over a given day on the lake. But on the other side of the coin, we left off all the additional accessories...(ie ballast pumps, lights, head unit, ECU).

Sorry I didn't mean to be a Negative-Nancy, but I thought I could help, but realized there are too many variables for my small brain to handle.

One thing you could do is charge your batteries, test them before you go out on the lake. After a day of playing pull them and test them again.

[chpthril]

Back to the formula: 1800 watts / 12 volts = 150 amps.

If this is all correct, I am OK with one stereo battery and a 65 amp alternator?

Assuming your math is right, I haven't dbl checked it, you are trying to get 10 gals of chit from a 5 gal bucket. You have a 150A load on the battery and a 65A Alt trying to recharge it. The alt will not keep up and will leave the battery drained at the end of the day, unless you have a charger to plug up and recharge at home.

Now, as Joe says, there are many variables, mostly, how will the system be used i.e. mainly for riding with engine running, lots of chill time with engine off, etc. 1st, most peeps dont listen to the system at wide open all day, so most figure the current draw at .5 to .75 of max.

Alternators really aren't meant to "recharge" a battery, but simply to keep up with normal loads (1800 watt stereos aren't normal ). So, to do this, you need a real heavy-duty workhorse of an alt and they cost money and use HP. With what you've got so far, an alt upgrade may be needed, as well as adding a 2nd stereo battery. Even then, the Alt still wont keep up with you possible demand, unless you drop a couple G's for one. Alts dont like to run wide open all the time, so if you want one that will keep up with the load, you'll need one rated at 1.5+ your expected load.

Do you have a means to plug up to A/C at the end of the day? If so, I would consider building a battery bank that will give you the Ah's you need and then recharge the stereo bank by means of an on-board charger.

[tige']

Yes, I do have a Battery Tender charger that the boat is plugged into at home. It is plugged in any time we are not using it, so the batteries are fully charged when we leave.

There are already two batteries, the starting battery and the stereo battery. The stereo battery only runs the stereo equipment. And, the Yandina combiner automatically keeps both batteries charged at home and on the lake.

I agree that the stereo doesn't always run at those wattages (which is a plus) and there is other equipment that the alternator needs to make up for (which is a negative).

We are usually running 80% of the time when we are out. Either wakeboarding, tubing, skiing, whatever...which again is a plus. But when we are doing those things, I am running the stereo at high volumes (which is a negative)

My dilema is this...Our season is basically done. The new amp doesn't get here until Friday so I won't have much time to install it and test how this is going to work.

So I need to decide if I need a new alternator, a third battery, or both if I installed all 4 amps OR, if I could get by with everything as I have it if I left one of the SQA-4's out.

If I need to change anything then I have a nice winter project (I love working on my boat in the winter, it keeps us close) If I wait until until spring to find out that I don't have enough juice then I am working on it instead of using it!!!

I have a Tsunami digital capacitor/dist block and it has a volt and amp meter on it. It bounces around a lot so it is hard to read tha amp draw but maybe I need to start with the SQA-4 left out and see what it reads.

[chpthril]

Good thing is, there is really nothing to get out on the water and test, it's all in the math.

Based on your post, it sounds like most of your listening is done with engine running, so a big, high Ah battery bank is not needed, nor is a huge expensive hi-output alt.

I'll stand by my original thoughts that you would benefit most by adding a 2nd deep-cycle (yes, I understood from your OP that you have 2 batts already, i'm recommending a 2nd dedicated stereo battery wired in parallelto the 1st) as this will, in a sense, double your stereo banks Ah's (play time). Being that you have a means to recharge the battery bank while off the water, if the battery bank has sufficient Ah's, then it wont matter if the alt cant keep up. Down side of this is that the alt will try it's arse off to keep up, that's it's job. If you do the calculations pretty close, and build a battery bank with enough Ah's, I would consider even pulling the stereo bank off the alt and just let the tender recharge it at home. Or consider upgrading the alt to a 90 or 120 amp.