dual batteries w/out isolator

dfoxengr · 02-24-2007, 03:45 PM

first off ill get it out of the way that i hate wiring, and dont uderstand much, which is why im ME, not EE.

ive read a lot of writeups but all of them seem complicated and expensive.

anyways, i want the simplest setup for dual batteries, and im wondering why i cant just wire 2 in parallel with a disconnect for the piggyback so i can run it independantly of the main.

i dont want a starter only battery which is what im reading most people do this for.

ill have one in stock location, and another in my bed box(which will have my converter and compressor and aux outlets wired to it)
i can then leave the disconnect out for normal use, and when i need a recharge on the aux., or a jump-start ill just stick in the disconnect in and go.

also planning on a higher output alternator at the same time.

what would be the downsides of this method?

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4Crawler · 02-24-2007, 04:06 PM

Sure, that will work. No different that using a solenoid like I use on mine. A solenoid is nothing more than an electrically controlled switch.

tc · 02-24-2007, 05:12 PM

When I did the competition car audio thing, we never used isolators due to the voltage drop across them. Wired all the batteries in parallel.

It is CRITICAL to have a fuse on the wire to the back within 18" of the front battery, and I would use BIG wire, like 1/0.

dfoxengr · 02-24-2007, 06:03 PM

so its not looking like there are any downsides. thats great, makes my life tons simpler. and yes ill use some big wire. thanks for the tip.

and what size fuse 100A? i have no idea about lots of this stuff.

ill also probably upgrade the stock alternator wiring as well.

another ?. if i were to just have to use the duals as a stick welder, could i unground them from the chassis and hook up my leads to the aux one, both in parallel and only connected to eachother, and not burn anything up?

thanks again.

tc · 02-24-2007, 08:18 PM

You'll want to connect them in series for welding I think.

And you're looking at a 300 - 500A fuse - whatever the CCA of the battery is and what size wire you use.

4Crawler · 02-26-2007, 09:47 AM

Yep, series for welding, I have both my batteries "floating" so when I unplug them from the vehicle, both + and - terminals are not connected to anything. Then I can plug in some jumper cable extensions and tie the + to - on one set to get 24 volts. I find that it is very hard to strike an arc w/ 24 volts, so usually end up needing another battery (in series) to jump to 36 volts for good welding:
- http://www.4crawler.com/4x4/CheapTri....shtml#Welding

02-24-2007, 04:06 PM	#2 (permalink)
4Crawler Contributing Member Join Date: Jun 2002 Location: SF Bay Area, CA Posts: 7,828	Sure, that will work. No different that using a solenoid like I use on mine. A solenoid is nothing more than an electrically controlled switch. __________________ 1985 Toyota 4Runner SR-5, 22REC engine, dual t-cases, 4.88 gears, dual ARBs, 33x10.50 BFGs or 35x12.50 MTRs r.c.brown@ieee.org TruckEditor@tlca.org Project: 4Crawler 4Crawler OffRoad Gettin'Off 4WD Club

02-24-2007, 05:12 PM	#3 (permalink)
tc Contributing Member Join Date: Nov 2005 Location: Longmont, CO Posts: 8,372	When I did the competition car audio thing, we never used isolators due to the voltage drop across them. Wired all the batteries in parallel. It is CRITICAL to have a fuse on the wire to the back within 18" of the front battery, and I would use BIG wire, like 1/0. __________________ Check out www.coTTORA.org to hook up with great Toyota 'wheelin' folks! Current - 93 4Runner: 3VZ 33"x10.50" no lift ARB F/R 96 Impala SS: My own personal cop car Previous - 89 2WD Pickup 22R, Fabtech "Ivan Dan" lift, 31x10.50, IASCA World Finals 4th Place Stop with the mods and get on the trail! Pix at www.4wheelingoh.shutterfly.com/action

02-24-2007, 06:03 PM	#4 (permalink)
dfoxengr Registered User Join Date: May 2005 Posts: 632	so its not looking like there are any downsides. thats great, makes my life tons simpler. and yes ill use some big wire. thanks for the tip. and what size fuse 100A? i have no idea about lots of this stuff. ill also probably upgrade the stock alternator wiring as well. another ?. if i were to just have to use the duals as a stick welder, could i unground them from the chassis and hook up my leads to the aux one, both in parallel and only connected to eachother, and not burn anything up? thanks again. __________________ Fox Design Works http://www.honda-tekh.com - Owner A better Honda / Acura community forum. Last edited by dfoxengr; 02-24-2007 at 06:06 PM.

02-24-2007, 08:18 PM	#5 (permalink)
tc Contributing Member Join Date: Nov 2005 Location: Longmont, CO Posts: 8,372	You'll want to connect them in series for welding I think. And you're looking at a 300 - 500A fuse - whatever the CCA of the battery is and what size wire you use. __________________ Check out www.coTTORA.org to hook up with great Toyota 'wheelin' folks! Current - 93 4Runner: 3VZ 33"x10.50" no lift ARB F/R 96 Impala SS: My own personal cop car Previous - 89 2WD Pickup 22R, Fabtech "Ivan Dan" lift, 31x10.50, IASCA World Finals 4th Place Stop with the mods and get on the trail! Pix at www.4wheelingoh.shutterfly.com/action

02-26-2007, 09:47 AM	#6 (permalink)
4Crawler Contributing Member Join Date: Jun 2002 Location: SF Bay Area, CA Posts: 7,828	Yep, series for welding, I have both my batteries "floating" so when I unplug them from the vehicle, both + and - terminals are not connected to anything. Then I can plug in some jumper cable extensions and tie the + to - on one set to get 24 volts. I find that it is very hard to strike an arc w/ 24 volts, so usually end up needing another battery (in series) to jump to 36 volts for good welding: - http://www.4crawler.com/4x4/CheapTri....shtml#Welding __________________ 1985 Toyota 4Runner SR-5, 22REC engine, dual t-cases, 4.88 gears, dual ARBs, 33x10.50 BFGs or 35x12.50 MTRs r.c.brown@ieee.org TruckEditor@tlca.org Project: 4Crawler 4Crawler OffRoad Gettin'Off 4WD Club

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