Aux. Battery

[FirstDiesel]

Another newbie question here. On my 3500 there is an Aux Battery. Why?? How is it used?? Is it just a backup for the main battery or is it to supply power for accessories without draining the starting battery?? BTW, which one is the Aux??

Thanks

[Joe Pool]

FirstDiesel,

The second battery isn't an auxilliary battery like the gassers, it is there to boost the electrical system capacity for cranking the engine, heating the glow plugs and operating the fuel heater at startup. Just think of the two batteries as one larger battery.

Joe Pool

[wangotango]

Allow me to ref a page for simplification:

http://ourworld.compuserve.com/homepages/g_knott/elect27.htm

Our batteries are in parallel whereas there are 12 volts (DC) with more amps than one battery.

The same batteries in series would make our voltage 24v.

It's important to have the "amperage" in order to turn over these high compression engines and get the glow plugs going.

If a battery is rated at 750 CCA (cold cranking amps) it is normally rated at zero degrees F.

You may see the figure "MCA" on batteries as well. These are "marine cranking amps" which is normally a rating at 32 degrees F.

be careful / have fun

w/t

[NickLeinonen]

that starter draws lots of power at start up. with the compression ratio that diesels have, the starters have to be bigger, and they need more power. i did a starter draw test on my 6.5TD and i was using

[FirstDiesel]

I'm aware of the higher starter draw on a diesel and also about parallel batteries. (I'm an electronics tech) I was just wondering if there was some sort of isolator system involved here to allow 1 battery to power accesories without draining the other.

Thanks

[wangotango]

From the service manual it looks like this to me:

They are actually calling it an aux battery.

With a dual alternator/generator there are two charge indicator points in the ECM. I assume that existing wiring is in place from the factory. The same guage probably monitors overall output. Thus two gauges would be relatively simple to install.

The "right" battery is denoted as the aux and it seems (though I'm no electronics tech) from the print that this aux battery feeds the power distribution buss that feeds accesories and such.

Though they are definately using the two batteries to start the mutha'.

I am also using the aformentioned solenoid to send power back to the camper/trailer. So that isolates the camper/trailer accessories from the truck batts. Unless the key is on of course.

As far as the truck accessories go, it looks to me like one of the batteries will not be available for accessories, thus be at the ready for starting in the case you over-accessorize without re-charge.

I am also going to assume that the right-left jargon is from the front looking in.

These two pages may benefit you. If I can scan them I will send the m to you or try to post.

I would be glad to copy and mail to you if you like.

good luck

w/t

[ 06-08-2002: Message edited by: wangotango ]</p>

[Jackmchome]

There is no isolation between batteries. Those of us who have campers and/or trailers have added a solenoid type isolator in the 12v feed to the RV connector. Well, maybe not all of us, but it is the way to go to protect the starting batteries from being discharged by the RV.

[ 06-08-2002: Message edited by: Jackmchome ]</p>

[wangotango]

possible info at:

www.gmupfitter.com

w/t

[imported_]

The general should have done it right and made the truck 24v like the UN spec. My land cruisers are 24v and I love it. the winch pulls twice as hard, the starter rocks, the glow plugs take half the time to warm up. no down side except $$$$$. Has anyone done the 24 conversion on a 2500?

[2Horsehauler]

I see Wangotango and Jackmchome have installed solenoids to allow the RV battery to charge only when the engine is running. I want to do this but can't find a switched 12V ignition "run" terminal or wire to tap to control the solenoid (i.e. power only when the ignition is in the run setting). Can someone tell me where to find this run connection?

2002 3500 Duramax/Allison

[Jackmchome]

In the wiring under the fuse center under the hood, find a 16 guage (fat wire) yellow wire and tap into it. It will be hot in run and start.
You will also be able to disconnect the red wire from post #1, the 12v to the RV harness, and run it to the solenoid instead and add a wire from post #1 to the other side of the solenoid. I mounted mine on the fender between the fuse center and the firewall. Works neat!!

[Big O]

Big Blue
_________________________________________________
The general should have done it right and made the truck 24v like the UN spec.
_________________________________________________

Have you bought 24V parts? My old M38 Military Jeep was 24V and the parts veeeeeerry expensive, big and heavy. 24V headlights were hard to find and expensive.

[imported_]

Yup, lots of cash, my 24v alt for my land cruiser was $1800 can brand new. heavy and built to last. I just really like the low amps needed to turn the starter and half of the draw on the glow plugs.

cheers