WATRD

NOW I am jealous... I want to do the dual battery thing, but I have not quite finalized the details. Being an automatic tranny guy, a dead battery spells "overnighter"

Yep, I got your mail I am going to try to respond to it tonight if I can find a few minutes.

Tacoma Dude

oooh...
dual batteries....


Now I DEFINITELY smell a write up

Actually, to set up 2 "normal" non-Optima batteries you just need to hook up the 2nd negative terminal to the chassis and the positive to the alternator... right?

Then proceed on to plug whatever to that 2nd battery? Or did I miss a whole bunch of stuff?

I'm guessing by the way - I don't know what the heck I'm talking about

WATRD

You *could* wire them together in parallel for more capacity, but there is a HUGE disadvantage to that. When you leave your dome light on and it drains the battery, it drains *both* batteries. It will take longer, but you are just as stuck.

What most people do is install an "isolator". That device allows one battery, the primary to be used to start your rig and to otherwise act like a single battery set up. The second battery is charged via the electrical system, but cannot be discharged. So, when you flatten the primary battery, you just flip a switch and you have a second battery fully charged to get your running again.

A variation on this theme is to use an isolator to separate the batteries, but one is dedicated to keeping the truck running and the other has your high draw accessories wired to it. That way, when you draw a battery down with the winch, it's the secondary battery and you can still start the truck up. If you leave your dome light on, it will draw down the primary, but then you can still start the rig off the secondary, assuming you have not winched it to death as well. Both batteries are charged by the alternator when they are not being discharged. This is similar to what you described, but with the addition of being able to pull power from one battery to the other.

I have seen both set ups work well, but lean to the first option myself, there's less wiring involved.

Cebby

You can use an isolator or a large relay to keep the batteries separated.

Here's an isolator:


Here's the big ol' relay:

Tacoma Dude

I'll look into it, thanks guys!

RidgeRunner

Does anyone know the amp output of a stock alternator for comparison?

Mick

alanh

I'd like to add a note of caution here before anyone starts running wires without knowing just where the existing wires go on their particular rig.

I can't make any statements on how other 4Runners or Tacomas are wired, but on my 2000 4Runner the factory wiring diagrams show the alternator output going to a 120A fusible link and then to the battery. As far as I can tell, that is how it is actually wired too.

I'm not sure why they did it this way, but a number of the circuits come directly off the battery (through fuses) like headlights, ABS, etc. although some stuff like the dome light comes off there too. The starter motor is direct to the battery without a fuse. A bunch of other stuff is on the alternator side of the fusible link (through their own fuses) including ecu, turn signals wipers, etc.

I wish they would have said why they did it this way. I'm not sure if there is enough directly off the battery to keep the engine going or not. Some things like the headlights I can see. You don't want those going out at night if at all possible. But why the dome light I don't know. The starter relay is off the alternator, so if that 120A link blows, it doesn't look like I could start it without some work.

Anyway, I'm not sure what would happen with a 160A alternator and a really heavy load on the battery side (like a winch), but I wonder if it might blow that link. I'm guessing the stock alternator just shuts down or puts out its max current which wouldn't blow the link since its less.

A direct connection from the alternator to the battery would be bypassing that 120A fusible link which might have some unintended negative consequences if something goes wrong. (One scenario might be some failure in the alternator at which point the battery could supply several hundred amps into it and fry things good.)

I would agree that the stock wiring is not adequate for 160A. I've seen some writeups stating that it really isn't good enough for the stock alternator. In general, the wire gauges seem pretty darned skimpy given the current they might carry. I would also beef up the ground wire to the engine as well. Every amp going out of the alternator has to find a way back in, so the grounds should be as big as the + side.

Alan

midiwall

{fingers crossed!}


˟˟˟˟˟ yeah...


btw... the Viair 450 is in.

midiwall

For your truck (which is the same as mine) I think it's 40amp at idle, 60amp at 3000 RPM.

Cmar

Seeing as I don't know much about this, has anyone got any ideas what way the factory standard dual battery system is setup is in my diesel?

Bumpin' Yota

There is one problem with an Isolator - it drastically reduces the voltage to the rear batteries. Or at least that's what people who actually use one have stated.

My two batteries are directly paralleled with a run of 1/0. (About to be 2 runs of 1/0 as there is a 0.2v difference from up front to in back.) I've left the dome light on overnight and it did not kill my batteries and the truck still kicked over. Headlights would be a different story though....lol

If you must isolate you can use a hi current relay - something along the lines of a 120-250amp relay. I think a starter relay is rated for this, but I'm not 100% sure. Keeps them isolated till you flip a switch.


WATRD -

Why only 8ga? I would have done 4ga minimum when upgrading the big 3.

Corey

iTrader: (1)

Good job there Rob.
Something I may look into in the future, not for the winch, as I have ran that with the engine off just fine, but for the tunes.

Normally my lights never dim when I have the stereo cranked, but last night I noticed in a Van Halen tune when I had it cranked up, and the subwoofer also turned WAY up, my headlights were keeping time to the bass hits a bit.

I'm sure my tail lights were doing the same.

BajaTaco

YEA BABY!!!! VH ROCKS! Corey, ever heard the tune "down in flames"?

I will be using a simple isolator setup for the time being. If I ever get an electric winch, I will probably change the setup so I can combine the amps from both batteries for major winching. I don't think the volatage loss through the isolator is anything to worry about for my particular setup. The amount is negligible when you consider what I am using it for. For anyone who IS concerned about that, there are Schottkey diode isolators avaialble which have practically no loss at all - this is what ambulances and some government spec applications use, but they cost more. I am not going to parallel my batts. because I can't risk having them both go flat when I'm out in the sticks.

CMUpike

Great Post! can anyone chime in on an average price range for a yellow top?

WATRD

Two reasons, 1. That is what the manufacturer of the alternator recommended and 2. When I did the math, the stock wire from the B+ post is 8 gauge and with the additional wire, it should be able to handle 200+ amps, so it seemed sufficient.

WATRD

Time for a compressor show down!

Congrats!

WATRD

My HS9500 has a rated draw of close to 900 amps at stall load, so there is no way you would catch me running it with the engine off unless it was under no load at all.

I found that in a typical camping weekend, I used the winch, used the rocklights, ran the inverter and sucked 12 volts out for various accessories. The old battery had a pretty good capacity, but the alternator was not able to recharge it enough to really get caught back up. By the end of the weekend, it was obvious that battery was low and it wasn't until the drive back home that it got fully chaged back up. My hope with the new set up is that after drawing the battery down over the course of a day, I can let the truck idle for a while and with the added capacity, it will charge back up so I can start the next even instead of being already behind from the previous day.

I found that my lights dimmed when the stereo was cranked and they REALLY dimmed when I was on the trail with the rock lights and headlights on when the engine speed dropped to idle. That should be a thing of the past now.

WATRD

I found them online for as little at $120 and locally for as much as $220. Shop around.

WATRD

It's funny, I can't get a straight answer on this question. As near as I can figure, Toytota uses a couple of alternators. One is a 40 amp unit and is usually used on trucks that don't have poer windows/locks etc. The other is a 60 amp and is used on rigs with power windows all the way around.

Mad Chemist

Compressor show down? I'm waiting for the blender showdown!