alternators and audio systems

[Jmp]

In my relentless pursuit of ironing out the bugs in the boat, my latest project is replacing my alternator. I'm almost positive the alternator has gone bad due to the 12.5 volts seen on the voltmeter gauge when the engine is running. I also notice a big voltage drop when turning on any accessory, ie blower, bilge pump, navigation lights(led), etc. With that being said I'm replacing the alternator with a 105 amp alternator to keep my 3 optima blue tops charged. I have 3 amps with a total of 1800 watts combined. do you guys think that the factory 10 gauge alternator charge wire is big enough to handle the additional current or should I look at upgrading that also?

 

[Ibeplumbing]

When I used to do car audio doing the big 3 was a pretty important first step. For a boat I imagine it would be worthwhile. Run 1/0 from alternator to battery. 1/0 battery ground to engine block.

 

[Big B Hova]

I wouldn't rely on the volt Guage. Most all dashes in boats haveverywhere bad Daisy chained wiring. Throw a volt meter at the alternator and check it. Then check the wires at the dash.

 

[djunkie]

I wouldn't rely on the volt Guage. Most all dashes in boats haveverywhere bad Daisy chained wiring. Throw a volt meter at the alternator and check it. Then check the wires at the dash.

Agreed but I'd put the voltmeter on the batteries while running to see the voltage there.

 

[SBMech]

How about you do both then find out the answer...voltage drop from resistance or bad alternator?

 

[rrrr]

...do you guys think that the factory 10 gauge alternator charge wire is big enough to handle the additional current or should I look at upgrading that also?

It's not big enough. Here's an ampacity chart. The colors correspond to wire sizes in the lower chart.

I would run a #6 or #8 from the alternator. Same for the primary ground. If you discharge the batteries down to 50% you will see about 40-50 amps charge current for a few minutes. I know that's not the wire size the chart recommends for such a short run, but the chart is for accessories, not a primary charging circuit. A few feet of #6 is cheap insurance.

I use Ancor marine wire exclusively for my boat electrical wiring. It has more strands than automotive wire, it's tin plated for corrosion resistance, and the insulation is rated for 105 degrees centigrade. That's 221 degrees Fahrenheit.

Your observation that the voltage is dropping when a load is placed on the electrical system makes me think you have a corroded connection on the primary feed to the dash. With those three batteries acting as a large reserve of power you shouldn't see any voltage drop when an accessory is energized. I'm assuming your stereo equipment is wired directly to the batteries with a #4 or #2.

 

[Ibeplumbing]

Is that 1800 watts rms? Or peak watts?

 

[Jmp]

That's 1800w rms, although the system will never run at 100% capacity.

 

[Jmp]

How about you do both then find out the answer...voltage drop from resistance or bad alternator?

I have verified that voltage with a multimeter at the battery terminals. I know the alternator is not charging

 

[DLow]

Look into running a capacitor on your system also. It takes a lot of load off of the electrical system.

 

[SBMech]

I have verified that voltage with a multimeter at the battery terminals. I know the alternator is not charging

All that tells you is that the amperage is not reaching the batteries, hit the stud on the back of the alt to be sure.

Looks like you have it in hand.

 

[Waffles]

Look into running a capacitor on your system also. It takes a lot of load off of the electrical system.

A capacitor will do nothing more than add more stress to an already stressed electrical system by forcing the alternator to redirect a portion of its limited current supply away from your audio system and charge your EXTRA device. OP, do the big 3 and upgrade to a bigger alternator to support these loads and you'll be golden.

 

[rrrr]

Look into running a capacitor on your system also. It takes a lot of load off of the electrical system.

Adding capacitance to the system causes more problems than it fixes. The OP has the right idea. The larger alternator will provide the power the stereo system needs while the engine is running. When the engine is off and the batteries are providing the power, they are eventually discharged to the point where a large amount of charging current is needed to rejuvenate them. Where does that current come from? The larger alternator!

Remember: Your car audio system is running mainly off your alternator, not your battery because its voltage potential is 12.7 V, whereas your alternator supplies 14.5 V. Since the alternator has the highest potential, it will supply the demanded current up to its point of saturation, whereby the battery takes over to supply the extra spikes of current demand. But in such a saturated scenario, the voltage supplied to your audio system has dropped substantially. The addition of extra batteries is only a limited band-aid fix to the problem. There is only one solution: You?re gonna need a bigger alternator!

https://axleaddict.com/cars/Car-Audio-CAPACITORS-Why-They-DONT-Work

 

[BigSteve]

When I used to do car audio doing the big 3 was a pretty important first step. For a boat I imagine it would be worthwhile. Run 1/0 from alternator to battery. 1/0 battery ground to engine block.

Very good advice
I deal with semi tractors and 53 foot trailers running lift gates with remote batteries having charging trouble

Solved a lot of voltage drop problems by adding additional ground straps and additional alternator output cable

 

[DLow]

A capacitor will do nothing more than add more stress to an already stressed electrical system by forcing the alternator to redirect a portion of its limited current supply away from your audio system and charge your EXTRA device. OP, do the big 3 and upgrade to a bigger alternator to support these loads and you'll be golden.

Adding capacitance to the system causes more problems than it fixes. The OP has the right idea. The larger alternator will provide the power the stereo system needs while the engine is running. When the engine is off and the batteries are providing the power, they are eventually discharged to the point where a large amount of charging current is needed to rejuvenate them. Where does that current come from? The larger alternator!



https://axleaddict.com/cars/Car-Audio-CAPACITORS-Why-They-DONT-Work

Um, no. And no. But Ok.

 

[rrrr]

Um, no. And no. But Ok.

 

[Waffles]

Um, no. And no. But Ok.

How so? Capacitors are nothing more than storage banks that keep power hungry components fluid through transient peaks.

 

[Ibeplumbing]

Honestly you are better off with another battery and a voltage meter than a cap. I'm not a believer in caps, you can get a small agm battery that will do everything that cap will and more

 

[Jmp]

Capacitors are good for cars when dimming of headlights needs to be resolved. My issue is charge current in general. My alternator is not working at all that's why I see such a large voltage drop for the burden the electrical system is experiencing from the stereo, accessories and ignition system.

 

[Ibeplumbing]

The suggestions I had were purely for the stereo. The new alt will fix your charging issues.

 

[was thatguy]

A capacitor will do nothing more than add more stress to an already stressed electrical system by forcing the alternator to redirect a portion of its limited current supply away from your audio system and charge your EXTRA device. OP, do the big 3 and upgrade to a bigger alternator to support these loads and you'll be golden.

Adding capacitance to the system causes more problems than it fixes. The OP has the right idea. The larger alternator will provide the power the stereo system needs while the engine is running. When the engine is off and the batteries are providing the power, they are eventually discharged to the point where a large amount of charging current is needed to rejuvenate them. Where does that current come from? The larger alternator!



https://axleaddict.com/cars/Car-Audio-CAPACITORS-Why-They-DONT-Work

How so? Capacitors are nothing more than storage banks that keep power hungry components fluid through transient peaks.

Honestly you are better off with another battery and a voltage meter than a cap. I'm not a believer in caps, you can get a small agm battery that will do everything that cap will and more

Back in my competitive SPL days I spent quite a bit of time and money trying caps in all sorts of set ups and configurations. My experience is that they absolutely make a marginal voltage supply situation worse. In fact, in SPL as well as SQL set ups with a well designed voltage supply, I never once found a situation where a cap made any measurable improvement.

Big alternator, 0 gauge + - wiring, with SOLID GOOD GROUNDS, is the ticket.

I am curious what the total fuse rating is on the 1800W system?

 

[Jmp]

Back in my competitive SPL days I spent quite a bit of time and money trying caps in all sorts of set ups and configurations. My experience is that they absolutely make a marginal voltage supply situation worse. In fact, in SPL as well as SQL set ups with a well designed voltage supply, I never once found a situation where a cap made any measurable improvement.

Big alternator, 0 gauge + - wiring, with SOLID GOOD GROUNDS, is the ticket.

I am curious what the total fuse rating is on the 1800W system?

Total fuse rating is 150 amps for the 3 amps