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Old 05-23-2021, 10:07 PM   #1
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Brand: Thor Motor Coach
Model: Axis 25.2
State: Nebraska
Posts: 31
THOR #21813
Question BIM160 not charging chassis battery when on shore power

Howdy all,

So I've owned my 2018 Axis 25.2 for a couple months now. When I park it at my house and connect it to 120V 15A shore power (AC, fridge, and microwave off), it'll keep the house batteries well charged at around 13.1V.

Problem is, it does not charge up the chassis battery and it goes dead after a coupe days. There's around a 1 amp parasitic draw from the chassis battery from what I've tested. I put in an aftermarket radio but the other electricals are all stock.

If I hit the Emergency Start switch I hear the clunk from the BIM160 and if I hold it down the radio will turn on after about 20 seconds. If I let go I hear another clunk and the radio dies after a few seconds. It doesn't seem to keep the chassis and house tied together. This is all with the engine off.

I bought a Noco Gen5x1 charger to keep the chassis battery charged, but it didn't seem to keep up, I wonder if the "smart" electronics can't deal. I had a cheap 8A charger that would keep it charged if I left it connected.

Any ideas as to what I can do to troubleshoot?

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Old 05-23-2021, 10:45 PM   #2
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Model: 2016 Vegas 25.2
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THOR #1589
Check out the section on charging in Ed Felker's excellent crowd-sourced manual for Vegas/Axis under the Motorhome Tech Topics section. It was collated for earlier models, but I bet your electrical system is similar. Charging is all about BIRD and trombetta.

I just last week replaced the BIRD in my Vegas. I had the same problem, batteries not charging from engine or post. A little too soon to be sure, but I believe this solved my problem. Although the factory that makes them is only an hour away, since I only needed one I had to order it from M&M in California.
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Old 05-23-2021, 11:05 PM   #3
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Do a search for BIM problems on the forum and you'll see that many have had their BIM wired incorrectly from the factory. Basically the IGN and SIG wires are backwards. Swap them on the terminals and see if that doesn't fix it.
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Old 05-23-2021, 11:31 PM   #4
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THOR #21813
@Mr Sunshine -

Unfortunately I don't have a BIRD/Trombetta - in about 2018 they changed to the BIM160. Ed's guide is invaluable, though!

@16ACE27 -
I thought I checked it, but it may have been the battery leads that I checked, which were wired correctly. House side went to house, chassis side to chassis battery. Thanks for giving me something to try.

BTW - when not using your RVs long-term and not on shore power like on a RV storage lot, do y'all completely disconnect the batteries? I would think so. Sorry if it's a dumb question.
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Old 05-23-2021, 11:32 PM   #5
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The problem is that Thor installs the BIM incorrectly. They connect the chassis battery to terminal B, it should be connected to A. See the attached Precision Circuits document to confirm this.

Switch the leads so that the chassis is connected to A and the coach to B and it should work fine.

David
Attached Files
File Type: pdf Precision Circuits BIM 160-Rev7-1.pdf (711.5 KB, 11 views)
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Old 05-23-2021, 11:59 PM   #6
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Search is your friend....

I have posted numerous times on this issue that others have experienced. Here is one recent example.....

https://www.thorforums.com/forums/f1...0-a-26220.html

Read my posts in this thread.
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Old 05-24-2021, 12:09 AM   #7
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I did verify that the house/chassis batteries are going to the correct terminals as per Precision's documentation. That's not the problem (I hope). Have not yet checked the ignition and signal wires.


BTW, can anyone recommend an inexpensive in or on dash volatage monitor that can show both house and chassis batteries at the same time? My GPS/speed monitor shows the house voltage, but not chassis.
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Old 05-24-2021, 01:35 AM   #8
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BIM160 not charging chassis battery when on shore power

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Originally Posted by keefd View Post
I did verify that the house/chassis batteries are going to the correct terminals as per Precision's documentation. That's not the problem (I hope). Have not yet checked the ignition and signal wires.


BTW, can anyone recommend an inexpensive in or on dash volatage monitor that can show both house and chassis batteries at the same time? My GPS/speed monitor shows the house voltage, but not chassis.

Forget the documentation.....

The chassis battery needs to go to the BATT-A post and the house batteries need to go to the BATT-B post.

Then be sure the Emergency Start Switch goes to the SIG post. That leaves the IGN wite above the BATT-A post and the chassis battery.
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