1 alternator 2 batteries
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=118780
Printed Date: May 15, 2025 at 12:11 PM
Topic: 1 alternator 2 batteries
Posted By: rfhvhtoo
Subject: 1 alternator 2 batteries
Date Posted: December 24, 2009 at 2:59 AM
I want to run my engine battery for my truck only and my second battery for my system but in a different manner than most I have heard.
I want to run the normal oem connection for my Truck and a 0-Gauge power wire from the Alternator straight to the 2nd Kinetik Battery in the rear to power the system.
What do you think?
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Replies:
Posted By: oldspark
Date Posted: December 24, 2009 at 5:26 AM
Why?
To use & discharge both batteries? (And not have a guaranteed charged battery?)
Or to ensure if one battery fails, it discharges and may wreck the other?
What do you have against whatever method you have heard?
Posted By: haemphyst
Date Posted: December 24, 2009 at 11:56 AM
You can do what you are suggesting, sure... ABSOLUTELY no difference in connecting your secondary battery to the alternator output post than connecting it at any other +12V terminal in the car. Do you think this removes the truck's battery from any responsibility in powering the system? They are both still connected to the system, right?
More work and more wire, with no benefit, it seems to me.
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: rfhvhtoo
Date Posted: December 24, 2009 at 6:10 PM
haemphyst wrote:
You can do what you are suggesting, sure... ABSOLUTELY no difference in connecting your secondary battery to the alternator output post than connecting it at any other +12V terminal in the car. Do you think this removes the truck's battery from any responsibility in powering the system? They are both still connected to the system, right?
More work and more wire, with no benefit, it seems to me.
The problem is my power wire is creating too much resistance to my amps which i think is causing my spikes. I checked the voltage from my alternator to battery during a spike (Spikes only when RPMs are above 1400 and charging at 220+ amps) and it was at 14.5v while the voltage from battery to my amps were 15.5v. The only variable that has changed is the length of wire. 2 feet to 10 feet. So resistance could possibly be the problem unless there is a short in the wire. ------------- I can't hear you!
Posted By: haemphyst
Date Posted: December 24, 2009 at 8:14 PM
Denied...
You said 1/0? For one ohm to be measured in copper 1/0 cable, you need 10175 feet! In 1000 feet there will be .0983 Ohms! In a mere ten feet, we are looking at .000983 Ohms. An immeasurable resistance at "human" levels. Properly crimped and soldered connections MAY double that, if you are lucky. (Or unlucky, as the case would be in such a situation...)
I promise you this right now... It ISN'T resistance in your wire! You would have to be pulling 503A through ten feet of 1/0 for a .5V drop. Your issues lie elsewhere.
The figures above were taken from this page...------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: rfhvhtoo
Date Posted: December 25, 2009 at 12:44 PM
Alright good Because I really didnt want to have to get more wire... Well I crimped my power wire to my amps about a week ago tighter and it stopped doing it for a couple days compeltely then started back up. and like I said the Voltage drop is different between Alt-Bat and Bat-Amps. How could I test for a short in the wire without removing it completely?
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Posted By: i am an idiot
Date Posted: December 25, 2009 at 1:13 PM
If the battery wire were shorted to ground, believe me when I say, you will not have to ask us where the short is.
Posted By: oldspark
Date Posted: December 26, 2009 at 1:02 AM
rfhvhtoo wrote:
I checked the voltage from my alternator to battery during a spike
Describe the spike - what voltage (peak or DMM average, or measured as AC)?
rfhvhtoo wrote:
...while the voltage from battery to my amps were 15.5v
That suggests a poor engine to body earth.
Is the regulator external to the alternator (not inbuilt?)
To clarify my first reply - I usually deal with people whose solution to underpowered alternators is to get a bigger battery (I can hear that some " folks are dumb where I come from" (Dorris Day?) now as I write).
Hence an 80A to 120A isolating relay between the first & second battery is not a problem, and it makes no difference to their amp's operating voltage.
Posted By: rfhvhtoo
Date Posted: January 02, 2010 at 4:19 PM
Sorry it took so long for the reply my laptop went in the shop. The spike is a DMM type of spikes.
I tightened my battery to amp terminal and it fixed the problem for about 3 days which left me to believe that something was loose. I have ring terminals at the Battery so im not sure maybe I need a better Connections at the battery.
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