[alligatorman]

So I have a new GMC 3500 that came with two batteries...

One battery is tied directly to the alternator with all of the other fuses on it.

The other battery is just wired to the first battery and is charged by the alternator.

So...question is...which battery should I tap for power wire for my amps?

PS the second battery would save me about 4' of power wire length. I am currently getting a bit of dimming on the headlights and would like to remedy that issue, without upgrading alternator, if possible. I have a Bluetop from my boat that I might try to put where the secondary battery is now...not sure if it will fit, though.

 

[evo9]

Is this a diesel truck? If it is, it does not matter where you make the connection. A full size diesel truck runs off both batteries. If it is a gas engine with an isolated secondary battery. You would then connect to this battery.



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[alligatorman]

Thanks evo9.

It is a diesel. I will connect to the battery that allows a shorter cable run.

 

[nick650]

Get rid of the second battery and just run one, the main one. Less strain on your alt.

 

[alligatorman]

Interesting point...but wouldn't the second battery act as a reserve from which the stereo could draw from?

 

[nick650]

No.

Look at like this.

Alt provides 120 amps and stereo draws 110. Then there is a bass drop. The stereo will draw 130 (lets just say) for a few seconds. It goes to the battery. The alt is big enough to charge the battery back to its full potential. If we had a system were he had a 120 amp alt and stereo draws 120, we have an issue and need a new alt and another battery won't fix this.

All in all the alt MUST PROVIDE MORE then what the stereo wants or you will have a dead battery.

Note: Battery's purpose is to give that instantaneous peak that the alt could not handle. The alt is made for a stable steady draw and when you demand more, it can't provide, you take it from the battery. Then when the situation calms down, the alt powers the battery back up. Having more batteries WON'T fix this, just make it worse.

 

[jcollin76]

Interesting point...but wouldn't the second battery act as a reserve from which the stereo could draw from?

I have a 08 gas silverado. In my setup, I have two batteries, one is isolated, and all stereo connections are to the isolated battery.

In key off situations, only the isolated battery is drawn upon. Leaving the stock battery fully charged to start the vehicle, If the auxiliary bat is drained.

Key on situations, the vehicle uses both batteries as needed, as well as charges both. The reason for isolating is to present cross flow draining. If one bat is low, it will draw from the second, draining it... Until both are dead.

Get rid of the second battery and just run one, the main one. Less strain on your alt.

It's a diesel, he needs both.

 

[alligatorman]

Thanks all.

Looks like I need a bigger alternator ( I have the 125amp unit ) or more efficient amps...or just stop bridging the amps.

I am using the ARC KS300.2 bridged to an IDQ12 sub and a KS300.4 bridged to a pair of HAT Clarus speakers. These amps are hungry in bridged mode. KS300.2 draws up to 75 Amps and the KS300.4 draws up to 82 Amps. I am thinking of trying to run the whole works on the 300.4. Bridge rear channels for the sub at 350w RMS and then run the fronts off their two channels at about 100w RMS/channel. It would be a step down in SQL but it would solve my battery issues.

(buyer's remorse....wish I went with an HD900/5.)

 

[nick650]

Opses, your right about Diesel. Just Isolate them >_<.

 

[sqshoestring]

What a confusing thread. If its a diesel it must have the dual batteries to start it, and the attaching cable will be huge. It will not matter what one you hook to. My diesel has a 190A alternator and its not a new truck, you should check on that most have large ones or have them available.

Having more batteries is not a bad thing, it just means you take less from each one on a large draw. The alt will still have to make up the same amount no matter. However more batteries can supply more power at higher voltage if you are really trashing the one battery. You would have to do something like play bass tracks or sine tones at full output in order to get a constant max draw from an amp, music will not do this.

If you want to isolate you should add a third battery to do that with, as I don't think a diesel will be too happy starting on one battery.

Dimming can be two issues; when you pull more than the alt makes you drop to 12v on the battery. This is usually not bad dimming but you can see it. If you take more power yet and drop the battery under 12v then the dimming is worse. You can figure it out as an alt makes more power at more rpm, so it will dim at idle and same output it will stop when the engine runs faster. Anyway, more batteries will help it not go under 12v like with one. They don't stack batteries in SPL vehicles for fun, and if they are not 12v then the alt charging them is still more voltage.

 

[evo9]

Get rid of the second battery and just run one, the main one. Less strain on your alt.

It is a diesel truck! Diesel engines requires two batteries to start due to higher engine compression.

Opses, your right about Diesel. Just Isolate them >_<.

uuuhmmm NO! Read above.

No.

Look at like this.

Alt provides 120 amps and stereo draws 110. Then there is a bass drop. The stereo will draw 130 (lets just say) for a few seconds. It goes to the battery. The alt is big enough to charge the battery back to its full potential. If we had a system were he had a 120 amp alt and stereo draws 120, we have an issue and need a new alt and another battery won't fix this.

All in all the alt MUST PROVIDE MORE then what the stereo wants or you will have a dead battery.

Note: Battery's purpose is to give that instantaneous peak that the alt could not handle. The alt is made for a stable steady draw and when you demand more, it can't provide, you take it from the battery. Then when the situation calms down, the alt powers the battery back up. Having more batteries WON'T fix this, just make it worse.

Unless you you know about diesel engines & its requirements dont be giving this type of advice..

To the OP. Stick to what I have told you based on whats already on your vehicle. Also keep in mind a diesel engine is usually equip with a higher output alternator than a gasoline motor.



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[H2Ocaver]

Get rid of the second battery and just run one, the main one. Less strain on your alt.

Joke right?

 

[evo9]

Thanks all.

Looks like I need a bigger alternator ( I have the 125amp unit ) or more efficient amps...or just stop bridging the amps.

I am using the ARC KS300.2 bridged to an IDQ12 sub and a KS300.4 bridged to a pair of HAT Clarus speakers. These amps are hungry in bridged mode. KS300.2 draws up to 75 Amps and the KS300.4 draws up to 82 Amps. I am thinking of trying to run the whole works on the 300.4. Bridge rear channels for the sub at 350w RMS and then run the fronts off their two channels at about 100w RMS/channel. It would be a step down in SQL but it would solve my battery issues.

(buyer's remorse....wish I went with an HD900/5.)

Unless you are running that setup full tilt all the time, you have nothing to worry about. Best thing to do is test both betteries, and make sure they are in good health. Have them load tested with a carbon pile type tester @ 1/2 the cca rating. I cant remember off the top of my head right now. But if any of them fails to maintain 9.5 volts for 5~10 seconds replace that battery. Also keep in mind because this is diesel engine, the alternator is design & spec for a commercial type operation. What I mean by this; the internals are spec to deal with higher loads at longer periods. So in short HEAVY DUTY.



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