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Dual Battery with DCDC causes issues with ESS (start/Stop)

TrickyO

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Hi,
I have been getting my rig setup for overlanding. I have installed a 120AH AGM battery and DCDC in the rear tub to power my fridge, lights and water pump. Since the JL Wrangler has a variable Alternator, the DCDC suggests connecting to an ignition source. I have connected to the Ciga Aux power in the back and I have the fuse in the IGN position so it is only getting power when the ignition is on. The DCDC works fine and goes into the right modes etc. The problem is my ESS (Start/Stop) no longer works and the dash show ESS not ready Battery Charging. If I disconnect the IGN source (pull the fuse) this problem goes away. I have fully charged the main battery, Aux battery and the new one. So the DCDC is showing that it is in float mode (fully charged). With the ignition override attached and powered the dcdc will start charging the battery at 12.2v and stop once if the voltage drops below 11.6v. Without the IGN source it is 13.2v start and 12.6v stop.

Any ideas on why this affects the ESS?
Given the variable voltage alternator have others achieved enough charge without the IGN override?

Jeep Wrangler JL Dual Battery with DCDC causes issues with ESS (start/Stop) 1606101006855


Jeep Wrangler JL Dual Battery with DCDC causes issues with ESS (start/Stop) 20200923_175831

Jeep Wrangler JL Dual Battery with DCDC causes issues with ESS (start/Stop) 20200923_102219
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WranglerMan

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Smart alternators are from my research not the best for a dual battery setup, see some useful info here https://www.redarc.com.au/alternator-vs-fixed-alternator

Any way the IBS is usually attached to the main crank battery in a stock setup and it monitors that voltage and charges accordingly but if the logic sees both battery volts the same it assumes there is a problem and it disables the ESS function but not sure that’s your issue.

I run a dual setup as well using two full size Full River 750’s and they are connected via a smart relay disconnect so 99% of the time the batteries are connected as one and the IBS is connected to my full size aux and the ESS battery was removed so it sees the voltage as the same and after (6) cycles ESS disables itself as it assumes there is a problem and only resets after one ignition cycle and then the count starts over but I have ESS disabled via a Smart Stop/Start module so I never see ESS disabled.

Not sure this info helps but maybe some other Overlanders can chime in but long gone are the simple days of an alternator putting out 14+ volts all the time and just have dual batteries with a simple setup
 

Gee-pah

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Hi Richard @Tricky0 :

I've read this post numerous times since you created it and haven't responded due to lack of anything constructive to say.

Will's @WranglerMan's post above though inspired me to say something I've been thinking that will actually--only for testing purposes though--introduce an issue he raises--the 6 ESS start stop limit per one cold crank of the engine.

First--I'm assuming that you are running a 3.6L JL and that little about it has changed about how it's configured for the Australian market I presume your Sydney home to be part of.

One thing you can do is temporarily place a fused jumper between two adjacent fuses in the Power Distribution Center (PDC) and disconnect the ESS battery to see if that solves your problem.

While this technique has been written up on the forum before, it involves opening the cover to the PDC: that black box on the top of the engine bay nearest the front passenger seat, and finding the fuses within the PDC closest to the driver's side front of the vehicle. Those two fuses are N1 and N2. A fused wire between them will permanently connect the two batteries in parallel. Out of the factory the PDC, as you may know, disconnects those batteries for an instant before cranking the engine and during ESS events. Let me know if you need links on the forum to this process.

Secondly, temporarily remove the negative cable from the ESS battery to the main one by disconnecting the factory cable on the main battery's negative post that is closer to the front passenger's quarter panel. (The cable closer to the driver's side is the body ground cable.)

What these two steps do is trick the vehicle into thinking that the main battery is also the ESS/Aux battery. See if this temporary change restores your ESS with the fridge charger running. If it does, it may point to problems with your ESS battery: a common occurrence.

I'd reverse both cable changes if you intend on running ESS, and like Will above said, this change will give you at most 6 ESS events per cold crank because the vehicle is designed from the factory to disable ESS after 6 checks of each battery's voltage (ESS/Aux and Main) being identical: suggesting a malfunction. Of course with you running 1 battery the vehicle will detect the voltages to be identical in this setup because you're only running 1 battery.

Other than that, the only other thing that I can think of is maybe your Intelligent Battery Sensor (IBS) that sits on the negative terminal of the main battery I believe, might be faulty.

Or maybe, set your DCDC charger, if possible, to not charge your refrigerator battery if the combined voltage of the two factory batteries, as detected in the cigarette plug, is under 12.5, AND restore that cigarette plug to its default behavior of always being energized, as per the factory, and see if that changes things.

Good luck.
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