GT-40 100-amp Upgrade - Still not enough???

[pdxCC]

I need your help fellow GT-40 owners. I am finally upgrading my stereo on my 01' Air Nautique. Last year I added two amps. A 4-channel 320w (RMS) JBL for the interior speakers and a 300w RMS Alpine driving a sub. All was fine with the original alternator. Never a problem. Till this year....

this is season I added a MQ Quart amp with 540w RMS. I am only using 4 of the 6 channels giving me 360w of power. When I crank it and the speaks all hit the volt meter jumps down from the 13.5v to around 12-12.5. It doesn't stay low but jumps up and down. Even after I did the 100-amp alternator upgrade. I thought that adding another 50-amps was going to be plenty but no dice. There is definitely a point where if I keep the volume at say 26 and there are no issues. If it take it to 28 or 30, I run out of juice. The MB Quart powers kicker tower speakers and the gain is cranked all the way up.

all amps have AMPLE wiring on the supply and ground sides. Any ideas on if this is 1) an issue I need to worry about and 2) can I solve this problem?

[DW SD]

I speculate that this is a wiring issue vs. alternator issue.
Couple thoughts:
0. The voltmeter samples voltage at the dash not at the battery or engine.

1. How are the amps wired? Do you know the wiring size feeding them? Think of a Hose. Volts are hose pressure. Wire is hose size. Current is water flow. Your amps draw a lot of water and through a small hose the pressure drops.

2. Voltage will drop as current loads increase . The wire is a resistor (like a small diameter hose). Check out a voltage drop calculator to see this effect.

3. To solve this I'm guessing you might need to use much heavier gauge to feed the amps and / or the dash.



Sent from my iPhone using PLT Nautique

[MLA]

So, there would not be a problem if you never looked at the helm volt gauge, correct? In other words, the only thing wrong is what you see in the gauge? Need to verify the issue with a hand held volt meter. After that, take a 2nd look at the gain setting on that MBQ amp.

[pdxCC]

DW - Good thoughts on the amp wiring. I know that I have oversized the amp wires because when the stereo shop originally screwed up my sub/speaker amp install I had to rip it out and redo it correctly. The new MBQ has 4-ga on the feed and ground which should be PLENTY for 360watts. All my amps have a dedicated feed and ground so they should not be drinking through a straw. That said, the MBQ is fused lower on the cable than at the amp. 60 vs 70 but that should not be the issue.

MLA - I unfortunately haven't grabbed my volt meter. I will the next time I am on the water. (Which is Saturday for an 8-day houseboat trip). I have the gain CRANKED on the MBQ. Without it the kicker tower speakers do not get enough power.

The dash power and reference for the gauge is downstream of the main 60-amp breaker and the new alternator is upstream of the breaker so I think the gauge, while not exactly accurate, is a fair representation of what the system is experiencing.

Basically I think my amps are pulling more than the alternator can supply and I get a deficit which is taxing the batteries. Basically this sucks so I am going to need to figure a new solution.....

Any more ideas are appreciated!!

[MLA]

Sounds like the amp may not be bridged correctly.

I bet if you put an amp clamp on each amp feed, you would not see a cumulative draw of more than 45A. I dont see a 100A alternator nto keeping pace.

[pdxCC]

I will admit that getting the amp to run in bridged mode was a major pain. The amp requires y-splitters when bridging it. It is a class a/b amp so I am wondering if going to a 2-channel class d amp would help.

[DW SD]

I wonder if you really have a problem. I think what matters is on average if you are at 12.5V system volts while running, then your batteries won't charge for your next outing. If the batteries back stop your alternator for a bit here and there things should be fine. Note, I did a quick calculation (see attached) and see significant voltage drop, if your amplifiers are drawing 40 amps (and based on RMS watts, it is possibly they are drawing significantly more). I guessed at length of wires, but note you have to use total length of 12V+ and ground, and assumed your batteries are in the back like mine. I'm guessing you are seeking large current draws on your volt meter.

What is your at rest battery voltage, say when you come to use your boat again?

I have a different solution, if the problem is keeping your batteries charged. I have a standalone solar panel and charge controller I plug in to my boat while it is in storage. Even if I run the stereo for an hour while cleaning in the parking lot, after I plug in, the next time I come to use the boat, the batteries are topped off at 12.8V. In fact, I run for four days a small 12V computer cooling fan via a timed relay to allow things to dry inside between uses. The panel and charge controller over come that, too. I think that is a .1 or .2 amp load.

The solar setup cost me about $100. A larger panel would charge faster, but I don't need that. My panel is about 30" x 18".

cheers,

Doug

[MLA]

(and based on RMS watts, it is possibly they are drawing significantly more

Might seem that way. However, the watts rms is in AC and the you are trying to calculate 12DC amp draw.

It is a class a/b amp so I am wondering if going to a 2-channel class d amp would help.

To fix a yet to be verified problem? No. At this point, you are seeing a helm gauge fluctuate. An old timer textile worker could count on one hand, the number of accurate helm volt gauges out there. Most analog gauges are mostly inaccurate and get worst with age. Not uncommon to find a .75+ volt drop by time you get to the helm.

If you switched to a class-D delivering the same wattage, I doubt you would see much of a difference. Maybe 4-5 amp reduction if you clamped it.

[pdxCC]

Awesome thoughts! I am a front (single battery) setup with amps under the helm. 15' of total cable at most. The biggest culprit is likely that I leave my boat on the water and it leaks (rudder needs replacing) so the bilge fires every 3-4 minutes. At rest my battery is 12V flat. But I was running just the 50-amp alternator so there is a chance the battery never had been able to recover. I'll play with it over the next week and report back. My current plan is to separate the interior and tower speakers at the head unit so I can turn down the interior using the front/back fader and then reduce the gain on the tower speakers. Basically crank the tower to 11 with the interior running at a mellow 5 on the volume dial and hopefully cutting 25% off the peak load.

thanks again for the feedback!!!!

[MLA]

12V at rest is a 75% depleted battery. If the bilge is bringing the battery down between trips, then even a 100A alternator will struggle to recharge a low battery unless there is a significant length of ride time. Old battery cables can also lead to voltage drops.

You did also upgrade the alternator supply cable too?

[kend]

Ditto On The Alternator GROUND And Charge cables