3.6L ESS Aux Battery Bypass

MoparTH

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I've been running with no aux battery for about 1 1/2 years now, I would definitely recommend running something more than a 30 amp fuse and 10 gauge wire, I tried that and it let me down in about a week (melted the fuse holder also). I would suggest at minimum 8 gauge wire and at least 40A fuse, I went a different route and used the internal 150A fuse at N3 and used a short 6 gauge jumper. With just the radio at half volume and heater fan wide open is about 31 amps.

Aux Battery Current.jpg





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TroyBoy

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I've been running with no aux battery for about 1 1/2 years now, I would definitely recommend running something more than a 30 amp fuse and 10 gauge wire, I tried that and it let me down in about a week (melted the fuse holder also). I would suggest at minimum 8 gauge wire and at least 40A fuse, I went a different route and used the internal 150A fuse at N3 and used a short 6 gauge jumper. With just the radio at half volume and heater fan wide open is about 31 amps.
what if you turned your driving lights on too? I wonder if that would be over 40A? I like your idea of using the 150A fuse. Are you using the ESS still. If so I wonder if it causes that so called 7 cycle ESS error?
 

Rhinebeck01

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I've been running with no aux battery for about 1 1/2 years now, I would definitely recommend running something more than a 30 amp fuse and 10 gauge wire, I tried that and it let me down in about a week (melted the fuse holder also). I would suggest at minimum 8 gauge wire and at least 40A fuse, I went a different route and used the internal 150A fuse at N3 and used a short 6 gauge jumper. With just the radio at half volume and heater fan wide open is about 31 amps.
@MoparTH

I gather you have removed the Aux altogether.... ?

I started running with the Aux bypassed (Aux is still in it's housing, maintained with battery maintainer/tender) .... running with just the Main battery, just over 2 years ago., and have driven just over 29,000 with just the Main in play so to speak.. I have kept/keep, the Aux as a b/u start battery should I need it.

At first, I used, a fused N1-N2 fused bypass jumper.... at that time that one, was 10g and had a 30 amp fuse..

After say 6 months of running with the 30 amp fuse, and absolutely, no problems, I read on the forum, someone (maybe you) saying that 31+ a tad, could come into play so best to move to a 40 amp fuse.. which I did.. Never any problems doing that.... running with 10g and 40 amp.

Over the last 3+ months and about 4,000 mi., I have been running an N1-Main Pos., 10g wire jumper with a 40 amp fuse. Again, never any issues.. fuse holder shows no sign of heat damage...

By the way, I have a 3.6, Rubi.... the last few months, I have been running the heater fan at medium/high, window defrosters, usually both front seats heaters on, the radio going, etc. and never any issues with the 10g wire and 40 amp fuse..


@Jebiruph
 

MoparTH

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I still use ESS occasionally, it functions but the only difference I see is that it usually says "battery charging" for the first few minutes if driving if you look at the ESS screen.

what if you turned your driving lights on too? I wonder if that would be over 40A? I like your idea of using the 150A fuse. Are you using the ESS still. If so I wonder if it causes that so called 7 cycle ESS error?
 

Toycrusher

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I will say that I have new respect for the aux battery. I was having voltage issues and I thought my aux was on its way out. I did the bypass but still had issues. Interestingly, both my main and aux battery failed load test, but my main battery was definitely very shot. I was able to keep going over a month on just the aux battery. It finally got too weak and I had to bite the bullet and buy a new main, but I'm impressed how much I was able to squeeze from the 3 year old aux
 

JJT-NC

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I am running a 2020 JLRU 3.0; crapped out both batteries after flat towing 1,200 miles behind my RV. Was ACC on? Was the battery activated due to the supplemental braking system or other software gremlins? I don't want to find out - I would rather have a simple battery disconnect that kills both batteries.

I know this may be off topic here, but the level of knowledge on these systems is higher here than I have seen anywhere!

Since these batteries are connected in parallel (great diagrams Jerry!), would a top post disconnect switch like this cut all power (for towing and storage)? Thanks!
 
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Jebiruph

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  • Thread starter
  • Thread Starter
  • #457
I am running a 2020 JLRU 3.0; crapped out both batteries after flat towing 1,200 miles behind my RV. Was ACC on? Was the battery activated due to the supplemental braking system or other software gremlins? I don't want to find out - I would rather have a simple battery disconnect that kills both batteries.

I know this may be off topic here, but the level of knowledge on these systems is higher here than I have seen anywhere!

Since these batteries are connected in parallel (great diagrams Jerry!), would a top post disconnect switch like this cut all power (for towing and storage)? Thanks!
Since the battery sensor is what connects to the battery top post, I'm not sure how you could make that work. Here's a picture that shows which body ground cable will disconnect both batteries.

battery no ground.jpg
 

NCIC105

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I've seen quite a few posts related to failed Aux batteries causing flaky or dead electronics, stalling and failing to start/auto restart. I've come up with a simple way to temporarily bypass a bad Aux battery (also blown PCR fuse or bad PCR) and get back on the road. Warning - this post contains a lot of informed assumptions, so post your related experiences to help validate or invalidate any information I've provided.

Here's a picture of my bypass kit. The jumper is used to connect the N1 terminal to the N2 terminal. I wanted to be able to install the jumper securely, but still be able to quickly disconnect it. A fused jumper seemed to be the best and cheapest way to go. Removing the fuse is a simple way to disconnect the jumper and it protects against overloading the wire. I don't know how much current will pass through the wire, so I used the largest I could find.
bypass kit 2.jpg


Here's how I tested the bypass. I disconnected the Aux battery at N1 and the ground wire at the Main battery negative terminal to simulate a bad aux battery. The voltmeter confirms the disconnect with low voltage at N1.
aux bat disconnected.jpg


Here's a shot of the dead instrument panel due to the disconnected Aux battery.
dash off.jpg


Here's the jumper installed between N1 and N2, voltmeter shows the Main battery voltage at N1.
bypass installed.jpg


Here's the live instrument panel.
dash on.jpg


Here's the instrument panel after starting, only error indicated is open hood.
dash running.jpg



For those interested, following are some diagrams to illustrate how I understand it works. (See this thread for additional information on the dual battery system https://www.jlwranglerforums.com/forum/threads/3-6l-ess-battery-diagram.14401/)

Here's the battery voltages on a working system, the PCR is connecting the batteries in parallel, both batteries providing power to everything. Normal operation is verified with 0 volts between N1 and N2.
ess normal operation.PNG


Here's the effect of a failed Aux battery, no power to critical electronics. This should be verifiable by a voltage difference between N1 and N2.
ess bad aux.PNG


Bypassing is accomplished by jumping N1 to N2. This diagram illustrates the jumper getting power back to the critical electronics.
ess bypass.PNG



(updated 04/13/2019)
Additional 3.6L ESS system information is available here.
3.6L ESS Dual Battery Consolidated Information
https://www.jlwranglerforums.com/forum/threads/3-6l-ess-dual-battery-consolidated-information.25377/
Great job and very detailed graphics. Thank you
 

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