Dual Battery Setup
Thread Starter
1st Gear Member
Joined: Apr 2005
Posts: 53
From:
Dual Battery Setup
I need to install a second battery into my trunk in order to power some extra stuff I'm putting in (trust me the one battery isn't pumping out enough amps alone). So I just rigged up the two batteries so they'd be running 12V still with some 4guage jumper cable wire (cut off the ends and stuff, nice and cheap at WalMart). It worked like a charm, both batteries seemed to be charging equally and whatnot. I drove from NJ down to Florida (1400+ miles) without a single problem.
When I was down in Florida for about a week, however, I had a problem. I was driving around when I heard popping coming from the firewall. Then sparks. Then flames. Then toehair singed. I pulled over and quickly put the fire out. I had no choice but to disconnect the rear battery (took a few hours in the heat) and went on my way.
I noticed that right by the firewall, the insulation (rubber) around the wires had melted somehow and the + and - had shorted, thus setting the fire. But the wires weren't touching the metal frame, it was touching the rubber plug thru the firewall.
So I dunno if the altanator was effing things up and pumping too many amps for 4 guage.
Basically I'm asking how do I properly set up two batteries to be running at all times (no stupid switch for A or B)...Do I need an isolator? Fuse setup? Help.
When I was down in Florida for about a week, however, I had a problem. I was driving around when I heard popping coming from the firewall. Then sparks. Then flames. Then toehair singed. I pulled over and quickly put the fire out. I had no choice but to disconnect the rear battery (took a few hours in the heat) and went on my way.
I noticed that right by the firewall, the insulation (rubber) around the wires had melted somehow and the + and - had shorted, thus setting the fire. But the wires weren't touching the metal frame, it was touching the rubber plug thru the firewall.
So I dunno if the altanator was effing things up and pumping too many amps for 4 guage.
Basically I'm asking how do I properly set up two batteries to be running at all times (no stupid switch for A or B)...Do I need an isolator? Fuse setup? Help.
3rd Gear Member
Joined: Nov 2004
Posts: 537
From:
RE: Dual Battery Setup
if you drove 1400 miles, i would think that you had it wired correctly. How many amps are drawing on the 4 guage wire and how long is the wire? What size alternator do you have, and are you absolutely sure the positive cable running through the firewall didnt rub through to the frame somewhere? The wires probably didnt short together the + lead might have grounded causing the fire and melted both wires. to many amps, grounded or shorted. should of used a fuse.
Gentleman's Relish
Joined: Feb 2005
Posts: 13,189
From: AZ
RE: Dual Battery Setup
ORIGINAL: Epon
I need to install a second battery into my trunk in order to power some extra stuff I'm putting in (trust me the one battery isn't pumping out enough amps alone). So I just rigged up the two batteries so they'd be running 12V still with some 4guage jumper cable wire (cut off the ends and stuff, nice and cheap at WalMart). It worked like a charm, both batteries seemed to be charging equally and whatnot. I drove from NJ down to Florida (1400+ miles) without a single problem.
When I was down in Florida for about a week, however, I had a problem. I was driving around when I heard popping coming from the firewall. Then sparks. Then flames. Then toehair singed. I pulled over and quickly put the fire out. I had no choice but to disconnect the rear battery (took a few hours in the heat) and went on my way.
I noticed that right by the firewall, the insulation (rubber) around the wires had melted somehow and the + and - had shorted, thus setting the fire. But the wires weren't touching the metal frame, it was touching the rubber plug thru the firewall.
So I dunno if the altanator was effing things up and pumping too many amps for 4 guage.
Basically I'm asking how do I properly set up two batteries to be running at all times (no stupid switch for A or B)...Do I need an isolator? Fuse setup? Help.
I need to install a second battery into my trunk in order to power some extra stuff I'm putting in (trust me the one battery isn't pumping out enough amps alone). So I just rigged up the two batteries so they'd be running 12V still with some 4guage jumper cable wire (cut off the ends and stuff, nice and cheap at WalMart). It worked like a charm, both batteries seemed to be charging equally and whatnot. I drove from NJ down to Florida (1400+ miles) without a single problem.
When I was down in Florida for about a week, however, I had a problem. I was driving around when I heard popping coming from the firewall. Then sparks. Then flames. Then toehair singed. I pulled over and quickly put the fire out. I had no choice but to disconnect the rear battery (took a few hours in the heat) and went on my way.
I noticed that right by the firewall, the insulation (rubber) around the wires had melted somehow and the + and - had shorted, thus setting the fire. But the wires weren't touching the metal frame, it was touching the rubber plug thru the firewall.
So I dunno if the altanator was effing things up and pumping too many amps for 4 guage.
Basically I'm asking how do I properly set up two batteries to be running at all times (no stupid switch for A or B)...Do I need an isolator? Fuse setup? Help.
You can pick one up at Pep Boys for about $30.
Here's better info on how they work.
http://www.bcae1.com/battiso.htm
3rd Gear Member
Joined: Aug 2005
Posts: 984
From:
RE: Dual Battery Setup
What would lead you to believe he overcharged a battery? I seriously doubt that, with two batteries, you are at risk over overcharging. I mean...the alternator didn't overcharge the stock SINGLE battery, let alone both. Secondly, I believe you would see/smell evidence of an overcharge at the site of afflicted battery. I'm shooting towards the short. Especially since the incident occured around the firewall.
Furthermore, how exaclty would a battery isolator prevent overcharging? If a regulator is bad, you would get overcharging reguardless of an isolator. What you are describing is more-so a relay than an isolator.
Furthermore, how exaclty would a battery isolator prevent overcharging? If a regulator is bad, you would get overcharging reguardless of an isolator. What you are describing is more-so a relay than an isolator.
3rd Gear Member
Joined: Aug 2005
Posts: 984
From:
RE: Dual Battery Setup
ORIGINAL: vfast
battery cables have to be a min of a 2 gauge but a "00" is what you need to del good voltage to the starter..if needing 2 batteries maybe a lite wt dry cell might be right 4 you
battery cables have to be a min of a 2 gauge but a "00" is what you need to del good voltage to the starter..if needing 2 batteries maybe a lite wt dry cell might be right 4 you
Gentleman's Relish
Joined: Feb 2005
Posts: 13,189
From: AZ
RE: Dual Battery Setup
ORIGINAL: pj1010
What would lead you to believe he overcharged a battery? I seriously doubt that, with two batteries, you are at risk over overcharging. I mean...the alternator didn't overcharge the stock SINGLE battery, let alone both. Secondly, I believe you would see/smell evidence of an overcharge at the site of afflicted battery. I'm shooting towards the short. Especially since the incident occured around the firewall.
Furthermore, how exaclty would a battery isolator prevent overcharging? If a regulator is bad, you would get overcharging reguardless of an isolator. What you are describing is more-so a relay than an isolator.
What would lead you to believe he overcharged a battery? I seriously doubt that, with two batteries, you are at risk over overcharging. I mean...the alternator didn't overcharge the stock SINGLE battery, let alone both. Secondly, I believe you would see/smell evidence of an overcharge at the site of afflicted battery. I'm shooting towards the short. Especially since the incident occured around the firewall.
Furthermore, how exaclty would a battery isolator prevent overcharging? If a regulator is bad, you would get overcharging reguardless of an isolator. What you are describing is more-so a relay than an isolator.
You didn't read anything on the link I posted previously. Some isolators are relay type. Also, in a dual battery setup, the smaller battery runs the risk of being overcharged. Thus my original response that he probably did overcharge one of the batteries. The alternator does not differentiate between teh batteries, all it does is see that A battery needs charging. If the alternator is always charging whether or not it's needed, the battery would get overcharged.
take a look at sections 7.1.9 and 7.3.2
http://www.uuhome.de/william.darden/carfaq7.htm#wiring
That link is for boats but also applies to ANY type of craft including cars that use dual or mult-battery setups. If you have something that says otherwise from what I've posted and can back it up. Then please do so.