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another amp question

Old 02-19-2012, 05:50 PM
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Question for the experts. I am installing a JL MHD 900/5 amp to drive (4) M 770 speakers and (1) M 10IB5 sub. Head unit is an Alpine CDA 118M.

My thoughts are to install a dedicated battery under the console, mainly to reduce the length of power wiring to the amp but also to be able to easily run other electronics off of this battery. I have (2) multi-purpose batteries on a standard Perko switch. The boat is a 2011 Seahunt BX 22 and my engine is a 2008 F250B (leftover bought brand new a couple of weeks ago) that has the auxiliary isolation charging lead so I would like to connect this third battery to that circuit. I have "heard" that the 8 awg charging lead is too small to do what I am wanting to do and that the voltage drop across that lead is more than one volt so that the battery is only going to see 13 volts. Can anyone confirm this? Does what I want to do sound like a good plan? Any help would be appreciated.
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Old 02-20-2012, 02:49 AM
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My kind of stereo in that little boat. One battery should be conected to the engines main charging wire and the other on the aux wire. To add another one I'd just put it by the other 2 and be done with it. Probably parallel to the main charging lead battery. From there 2 gauge to the console to a 60 amp resettable breaker and then 4 gauge to the amp.
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Old 02-20-2012, 04:42 AM
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You could do it the way you want just use a 4ga instead of an 8ga from the engine to the battery.
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Old 02-20-2012, 05:05 AM
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if he has two batteries wouldnt his aux lead already be in use?
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Old 02-20-2012, 05:14 AM
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Originally Posted by bradv View Post
if he has two batteries wouldnt his aux lead already be in use?

The boat came set up with (2) batteries on a "1-2-All-Off" Perko Switch and the aux lead was not used. In fact they told me that the motor didn't even come with the auxiliary lead and that I'd have to buy it. That doesn't exactly sound right to me but what can I say. It sounds like the wire size would be too small anyway for what I am wanting to do.
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Old 02-20-2012, 05:17 AM
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Originally Posted by MB Marine Electronics View Post
You could do it the way you want just use a 4ga instead of an 8ga from the engine to the battery.

One other question about wiring that up. Does hot and ground both hook up to that aux. circuit or is there a common ground and only the hot lead coming in from there?
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Old 02-20-2012, 11:50 AM
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i would run a dedicated hot and ground for the amp. and the only way your battery is getting charged if its the one being used. the other one even though you paid for the charging lead is apparently not doing anything.
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Old 02-20-2012, 12:27 PM
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Originally Posted by bradv View Post
i would run a dedicated hot and ground for the amp. and the only way your battery is getting charged if its the one being used. the other one even though you paid for the charging lead is apparently not doing anything.

The auxiliary charging lead will charge the battery I am adding whenever the motor is running. It is seperate and isolated from the main charging circuit.
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