Jebiruph
Well-Known Member
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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.
10/18/2022 Update - Here's a newer post with updated information describing how to bypass the aux battery without using a jumper.
https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/
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.
6/26/2021 Update - Many have reported that the 30A fused jumper shown in this picture has not been adequate for their JL. Use the highest capacity fused jumper you can find and make sure the fuse is not rated too high for the wire, otherwise the wire will melt before the fuse blows.
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.
Here's a shot of the dead instrument panel due to the disconnected Aux battery.
Here's the jumper installed between N1 and N2, voltmeter shows the Main battery voltage at N1.
Here's the live instrument panel.
Here's the instrument panel after starting, only error indicated is open hood.
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.
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.
Bypassing is accomplished by jumping N1 to N2. This diagram illustrates the jumper getting power back to the critical electronics.
(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/
10/18/2022 Update - Here's a newer post with updated information describing how to bypass the aux battery without using a jumper.
https://www.jlwranglerforums.com/forum/threads/jumperless-aux-battery-bypass.95945/
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.
6/26/2021 Update - Many have reported that the 30A fused jumper shown in this picture has not been adequate for their JL. Use the highest capacity fused jumper you can find and make sure the fuse is not rated too high for the wire, otherwise the wire will melt before the fuse blows.
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.
Here's a shot of the dead instrument panel due to the disconnected Aux battery.
Here's the jumper installed between N1 and N2, voltmeter shows the Main battery voltage at N1.
Here's the live instrument panel.
Here's the instrument panel after starting, only error indicated is open hood.
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.
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.
Bypassing is accomplished by jumping N1 to N2. This diagram illustrates the jumper getting power back to the critical electronics.
(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/
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