Coach Bats Not charging from Alternator

Gunfighter · 11-20-2021, 05:48 PM

Good day everyone. I need some advice from all the usual suspects on an electrical problem. I recently switched out the 4 Interstate coach batteries on our 2018.5 37K. I decided to go with 4 6V batteries. Cribbing off this website I didn’t have any problem making the switch. I’m confident that they are set up correctly (12.6V off shore power/13.23 on). Batteries charged up nicely and clearly charging up well on shore power. Batteries fully charged on shore power will show 13.2 or so on light load. All connections are tight and secure. Well I thought this is great, then I started up the coach and guess what no charge to coach batteries from the alternator. Dash and voltmeter check of chassis batteries shows good charge at 13.8v. Check both banks of coach batteries with coach running shows no charge batteries voltage at 12.6v. Also everything charges fine on the Generator. Today I went to Precision Circuits Battery Isolation Manager Trouble Shooting guidelines. Copy was previously posted by RustyNuts and also is available on Precision’s website. I am going to repost it at end of this message as I have a couple interpretation questions to ask this group from the guide.
Operational test: I pressed the Dash relay and the voltage from Chassis term to Coach Terminal was 0.36 with ignition key on and 0.26 with key off. This is out of norm (<0.2V). Went to step 2 and had 12.00V from dash switch to ground terminal.
Question 1, next question whether pushing dash button relay clicks. Sounds like a click at the dash, yes can’t hear anything in battery bay. The asks if pushing dash button brings voltages of coach and chassis “close?” After pushing dash button coach batteries 12.61v and chassis 12.51v. Is that close?
Second test: Engine on and coach lights on Voltage from dash switch term to Ground terminal should be between 3.5v and 6.0v. tested several times and was 0.00. If not then on to checking chassis term and coach and ignition terminals were all within normal range chassis 13.98v and coach 12.62v and ignition 13.55v.
Third test: voltage dash switch term to ground term was low normal at 3.54.
So starting with test 2, I interpret that I have proper voltage at the B.I.M. for ignition, coach and Chassis. I am assuming second part of test 2 was just to confirm there was correct power/voltage at BIM and 0 volts reading means BIM fault?
Test one also shows that Chassis to Coach is a little out of norm with key off and over voltage key on. Last point is 12.61 to 12.51 close in the dash relay. So do I have a bad BIM? If not what am I missing as the Alternator is charging the chassis batteries but not the coach batteries. On shore power everything is charging correctly. Am I missing something that is from the alternator to the battery banks? I would appreciate anyone’s comments.

SloPoke · 11-21-2021, 01:01 PM

Quote:

Originally Posted by Gunfighter

Good day everyone. I need some advice from all the usual suspects on an electrical problem. I recently switched out the 4 Interstate coach batteries on our 2018.5 37K. I decided to go with 4 6V batteries. Cribbing off this website I didn’t have any problem making the switch. I’m confident that they are set up correctly (12.6V off shore power/13.23 on). Batteries charged up nicely and clearly charging up well on shore power. Batteries fully charged on shore power will show 13.2 or so on light load. All connections are tight and secure. Well I thought this is great, then I started up the coach and guess what no charge to coach batteries from the alternator. Dash and voltmeter check of chassis batteries shows good charge at 13.8v. Check both banks of coach batteries with coach running shows no charge batteries voltage at 12.6v. Also everything charges fine on the Generator. Today I went to Precision Circuits Battery Isolation Manager Trouble Shooting guidelines. Copy was previously posted by RustyNuts and also is available on Precision’s website. I am going to repost it at end of this message as I have a couple interpretation questions to ask this group from the guide.
Operational test: I pressed the Dash relay and the voltage from Chassis term to Coach Terminal was 0.36 with ignition key on and 0.26 with key off. This is out of norm (<0.2V). Went to step 2 and had 12.00V from dash switch to ground terminal.
Question 1, next question whether pushing dash button relay clicks. Sounds like a click at the dash, yes can’t hear anything in battery bay. The asks if pushing dash button brings voltages of coach and chassis “close?” After pushing dash button coach batteries 12.61v and chassis 12.51v. Is that close?
Second test: Engine on and coach lights on Voltage from dash switch term to Ground terminal should be between 3.5v and 6.0v. tested several times and was 0.00. If not then on to checking chassis term and coach and ignition terminals were all within normal range chassis 13.98v and coach 12.62v and ignition 13.55v.
Third test: voltage dash switch term to ground term was low normal at 3.54.
So starting with test 2, I interpret that I have proper voltage at the B.I.M. for ignition, coach and Chassis. I am assuming second part of test 2 was just to confirm there was correct power/voltage at BIM and 0 volts reading means BIM fault?
Test one also shows that Chassis to Coach is a little out of norm with key off and over voltage key on. Last point is 12.61 to 12.51 close in the dash relay. So do I have a bad BIM? If not what am I missing as the Alternator is charging the chassis batteries but not the coach batteries. On shore power everything is charging correctly. Am I missing something that is from the alternator to the battery banks? I would appreciate anyone’s comments.

Did you verify the fuse between the coach battery terminal going to the Dash push button?

Gunfighter · 11-21-2021, 03:05 PM

Quote:

Originally Posted by SloPoke

Did you verify the fuse between the coach battery terminal going to the Dash push button?

Steve thanks for the reply. No I didn't, now the obvious question, where is it located. I do not see any inline fuse coming from BIM to loom going forward. Looking at the wiring diagram I have I do not see a fuse?

SloPoke · 11-21-2021, 09:59 PM

On the left (big terminal) on the top... there is the smaller wire that goes to an inline fuse holder that is connected to the dash push button switch... I circled them in red in the attached pics...

Gunfighter · 11-21-2021, 10:20 PM

Thanks a million Steve. I have that Precision picture but not enough of an electrician to think of that fuse being for the "dash" switch. I have seen the yellow inline. I will check it first thing in the morning. As a footnote Jayco mounted the BIM upside down on my model. Big lugs to the top. No problem though locating the fuse. I have attached photos of the BIM and the inline fuse. Sorry about the side view of the BIM, it is at a 90.

FJB · 11-22-2021, 08:26 AM

If you have the inverter/charger like I have 2022 Seneca with 2000 watt inverter/charger. Check the little push button fuse on the inverter in the cargo bay, also if inverter/charger is not turned on while driving the batteries will not charge while driving.

Gunfighter · 11-22-2021, 11:33 AM

Quote:

Originally Posted by SloPoke

On the left (big terminal) on the top... there is the smaller wire that goes to an inline fuse holder that is connected to the dash push button switch... I circled them in red in the attached pics...

Pulled the 20A in line fuse and it is okay visually and checked with voltmeter. I exchanged emails with Tech at Precision Circuits and he suggested drawing down coach batteries to 12.5V or lower and then restart coach to see if with cause the BIM to "bridge and allow alternator to charge the coach batteries. Doing that now. Any other thoughts.

Rustynuts · 11-22-2021, 07:26 PM

The only thing I can think of at this point is either the BIM is bad or it is just sensing that the coach batteries don’t need any charge. Testing like Precision said would determine that….I think I would pull them down lower to about 12.3.

Gunfighter · 11-22-2021, 07:31 PM

Quote:

Originally Posted by Rustynuts

The only thing I can think of at this point is either the BIM is bad or it is just sensing that the coach batteries don’t need any charge. Testing like Precision said would determine that….I think I would pull them down lower to about 12.3.

Thanks Brian. That's what I'm doing right now. Will take all night. Doing it steady and easy with interior lights and refrig. on. Thanks to all who responded . I will let you know what happens.
Footnote: Precision had a really quick response to my overnight email. Good customer service.

Gunfighter · 11-23-2021, 02:40 PM

Well sometimes you get lucky. Discharged the coach batteries to 12.3v and started the RV. After about 1 minute or less the BIM bridged the alternator over from chassis to coach batteries. Steadily charged up to 13.00v while running. So – morale of the story is that the microcircuit will not close the “bridge” until your are below 12.5 -12.4v on Alternator. Shore power and Generator will immediately close the circuit via the converter with the coach/chassis. Thanks to all that responded. Hopefully I saved some others some angst if this happens to them. Thanks to all that responded. This website is a great resource and you guys are great.

SloPoke · 11-25-2021, 12:17 PM

That makes perfect sense.... as 12.6v resting is considered charged.

Jump in say hey · 12-17-2021, 07:40 PM

Have a 2006 GS 35. This summer the solenoid between chassis and coach was melted down when activating dash assist button. Mechanic left chassis to coach + battery terminal off and grounded against frame when installing new batteries in chassis. Installed a continuous duty solenoid. Question would a BIM work better in this replacement. Pros and cons. Thankyou.

Gunfighter · 12-18-2021, 05:28 PM

Quote:

Originally Posted by Jump in say hey

Have a 2006 GS 35. This summer the solenoid between chassis and coach was melted down when activating dash assist button. Mechanic left chassis to coach + battery terminal off and grounded against frame when installing new batteries in chassis. Installed a continuous duty solenoid. Question would a BIM work better in this replacement. Pros and cons. Thankyou.

I'm not sure what your 2006 had originally for battery isolation. Also hard to understand what exactly the mechanic put in for a “solenoid” to replace the burned out. If the solenoid connect chassis to coach continuously and either can charge and discharge the other then you may have a problem with overcharging either set of batteries. I do not know of any cons to have a B.I.M. on the pro side go online to Progessive or other manufacturer and look up what they do. Prevent overcharging and takes a longer term look at charging each side.

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