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Old 03-15-2016, 07:16 AM   #1
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Battery Control Center/Chassis and Coach Battery Charging

There have been several posts and questions about coach/chassis battery isolation. I have also been curious as to whether the chassis battery could be charged by the generator and/or shore power.

Some have posted that the chassis IS charged when on shore power, others have posted that it IS NOT. I have measured the chassis battery voltage a couple of times - once I measured 13.7 volts, another time 12.6 volts - both times on shore power. This left me somewhat confused. Now having read the documentation from the manufacturer, it all makes sense.

I reached out to Precision Circuits, the manufacturer of the Battery Control Center (BCC) on our motorhomes (P/N 00-10033-200). This appears to be a part they OEM for Forest River and may be in use on many FR coaches. I asked for a detailed technical document on operation and troubleshooting. Although the Tech Support person was on vacation, he did respond with the following -

"Please visit our website for the 00-10021-??? Series of Battery Isolation products. Your BCC comes equipped with one of theses (sic) and functions the same." There are tech documents available for the Battery Isolation Manager, a portion of which I've added below. If you look inside our BCC, you will see the BIM mounted within. It must be the "brains" of this panel, with the FR version a little more sophisticated - for step, awning and slide operation and power also controlled here.

From the BIM owners manual -

"Overview: The Battery Isolation Manager (BIM) monitors the Battery
Voltage of both the Chassis and Coach Batteries over long periods of time. If it senses a charging voltage, it connects the two batteries together. If the charging system is drastically overburdened, the batteries will be isolated, however, if the BIM sees a long term charging of both batteries it will allow the batteries to remain connected and allow the charging system to do its job. Once the batteries have reached a Float Charge state for one hour, the BIM will isolate the batteries to prevent overcharging, and will
only reconnect the batteries for charging if one of the Battery drops to approximately 80% charge, and the other is being charged. If the batteries are not being charged, BIM isolates the two batteries to prevent an electrical draw in one system from depleting the other battery. The long term monitoring of the batteries prevents the annoying Relay clicking that exists in simpler Isolation Modules today."

So the short answer is shore power or generator power will charge the coach and chassis battery through the converter if the BIM senses the need to do so (or at least that is how I interpret the text of the manual). It also explains why under some circumstances I read converter/charger voltage at the chassis jump start terminals and another time I read battery voltage. Of course, when operating on the road, the MB alternator charges all of the batteries (the coach batteries through the BCC).

I will talk to Tech Support directly next week when he returns from vacation to verify my understanding, but I hope this detail helps answer some of the questions that are out there.
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Old 03-15-2016, 07:47 AM   #2
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Originally Posted by KatanaPilot View Post
There have been several posts...
X2 on your analysis. Your voltage measurements will depend heavily on the "set point" of the BIM. When a converter goes into "Storage Mode" which is basically trickle charge at 13.2 volts or so, I would bet that the BIM wants to drop out the isolation solenoid (heavy duty solenoid switch that connects the battery banks) and separate the chassis from the house bank. All in all it may be a pretty tight test since the solenoid itself draws some current and so do your parasitic loads and there is a voltage drop from the converter to the battery bank where the BIM is sensing voltage. It is basically a "race condition" between the loads from the RV and the switch point in the converter that goes from normal mode to storage mode. I do know that the BIM has a long time constant and keeps the banks connected for at least a minute or two after the voltage has dropped from charging as well, since otherwise it would get into a fight with the converter as they both are switching modes independently but perhaps simultaneously.

When everything is operating as designed, all charging sources (alternator, converter, solar) charge all battery banks as long as the charging voltage is above the key set point. In my experience when the battery isolation solenoid fails (and they do) nothing seems to work right. On my 1997 Bounder, I would always watch the alternator voltage and wait to see it drop ever so slightly, seconds after starting up, as the house bank was brought on line by the BCC. My 335DS does not have one, but a quick glance at the Trimetric will show 14 volts on the house bank after starting the engine...priceless!

Remember, when the isolation solenoid fails, your boost start fails with it as all the boost switch does is manually energize the isolation solenoid regardless of system voltage.

Bottom line, when the BCC works...it all works! When it doesn't, all kinds of strange things will happen and you may not know where to start.
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Old 03-15-2016, 11:00 AM   #3
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Originally Posted by ScottBrownstein View Post

Remember, when the isolation solenoid fails, your boost start fails with it as all the boost switch does is manually energize the isolation solenoid regardless of system voltage.

Bottom line, when the BCC works...it all works! When it doesn't, all kinds of strange things will happen and you may not know where to start.
Thanks for the additional information. Our MBS motorhomes do not have the boost start feature. All of the functionality is there, but FR mistakenly thought MB did not allow a tie in from the coach to the chassis - which is strange, since the BCC by design already does that both ways!

Several of us have added the fuse, wire and switch to the BCC which completes the boost start feature built into the BCC on our MH.
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Old 03-15-2016, 10:21 PM   #4
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Originally Posted by KatanaPilot View Post
There have been several posts and questions about coach/chassis battery isolation. I have also been curious as to whether the chassis battery could be charged by the generator and/or shore power.

Some have posted that the chassis IS charged when on shore power, others have posted that it IS NOT. I have measured the chassis battery voltage a couple of times - once I measured 13.7 volts, another time 12.6 volts - both times on shore power. This left me somewhat confused. Now having read the documentation from the manufacturer, it all makes sense.

I reached out to Precision Circuits, the manufacturer of the Battery Control Center (BCC) on our motorhomes (P/N 00-10033-200). This appears to be a part they OEM for Forest River and may be in use on many FR coaches. I asked for a detailed technical document on operation and troubleshooting. Although the Tech Support person was on vacation, he did respond with the following -

"Please visit our website for the 00-10021-??? Series of Battery Isolation products. Your BCC comes equipped with one of theses (sic) and functions the same." There are tech documents available for the Battery Isolation Manager, a portion of which I've added below. If you look inside our BCC, you will see the BIM mounted within. It must be the "brains" of this panel, with the FR version a little more sophisticated - for step, awning and slide operation and power also controlled here.

From the BIM owners manual -

"Overview: The Battery Isolation Manager (BIM) monitors the Battery
Voltage of both the Chassis and Coach Batteries over long periods of time. If it senses a charging voltage, it connects the two batteries together. If the charging system is drastically overburdened, the batteries will be isolated, however, if the BIM sees a long term charging of both batteries it will allow the batteries to remain connected and allow the charging system to do its job. Once the batteries have reached a Float Charge state for one hour, the BIM will isolate the batteries to prevent overcharging, and will
only reconnect the batteries for charging if one of the Battery drops to approximately 80% charge, and the other is being charged. If the batteries are not being charged, BIM isolates the two batteries to prevent an electrical draw in one system from depleting the other battery. The long term monitoring of the batteries prevents the annoying Relay clicking that exists in simpler Isolation Modules today."

So the short answer is shore power or generator power will charge the coach and chassis battery through the converter if the BIM senses the need to do so (or at least that is how I interpret the text of the manual). It also explains why under some circumstances I read converter/charger voltage at the chassis jump start terminals and another time I read battery voltage. Of course, when operating on the road, the MB alternator charges all of the batteries (the coach batteries through the BCC).

I will talk to Tech Support directly next week when he returns from vacation to verify my understanding, but I hope this detail helps answer some of the questions that are out there.
Agreed. If you want to see it in real time, you can't take just one reading. Check the voltage on the chassis battery with everything off for a while. You should get 12.x. Then plug in shore power or turn on the generator and go check the chassis battery again. You will see a higher charging level voltage, the amount of which will depend on the level of charging the converter and battery manager sense is needed. But you will see an immediate increase. If you do the same on the house battery with shore power and generator off, measuring before and after turning on the engine, you will see the effect that direction.
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Old 03-16-2016, 04:36 AM   #5
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Interesting info. When I connected w Coachmen re my MBS they said the charger only charges the coach batteries when the unit is plugged in. The MBS chassis battery is not charged
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Old 03-16-2016, 04:59 PM   #6
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I will talk to Tech Support directly next week when he returns from vacation to verify my understanding, but I hope this detail helps answer some of the questions that are out there.[/QUOTE]

I have the same situation in a 2300. I am not unhappy with the BMI since it does what it is designed to do. It is only a problem if you are not hooked up to 110. The problem when driving to boondock you will probably end up with 80% capacity. My option is to connect a wire from the alternator found in the MBI to my solar controller through a blocking diode. I will then depend on the controller to keep the coach batteries at full charge. I have not done it yet because I am just working through the problem. Any opinions appreciated.
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Old 03-16-2016, 07:55 PM   #7
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Yes, it works

I just posted this on the Forester forum, as well.

Completed install today of new AGM coach batteries along with a Victron dual battery monitor.

While installing, did a full test of the Battery Control Center (BCC) and the integral Battery Isolation Monitor (BIM). I can unequivocally say that on my 2015 Forester MBS with the Precision Circuits, Inc. BCC, that the converter/charger (Progressive Dynamics PD9260) DOES charge both the chassis batteries and the coach battery when on shore power. Generator power should work just the same.

Here were the tests -

Plugged in shore power. Checked voltage at chassis battery and coach batteries - voltages the same. Disconnected cables from chassis battery - checked voltage across the cables - voltage the same. Waited for BCC relay/solenoid to open - voltage went to zero. Hooked battery cables back up to chassis battery and unplugged shore power. Plugged shore power back in, checked voltage with Victron - main (coach) battery 14.2 volts, auxiliary battery (chassis) 12.7 volts. Turned on headlights to create a load and drop the voltage of chassis battery, heard solenoid click in - chassis battery now 14.2 volts as well.

Pretty definitive to me.
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Old 03-16-2016, 08:29 PM   #8
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Originally Posted by KatanaPilot View Post
I just posted this on the Forester forum, as well.

Completed install today of new AGM coach batteries along with a Victron dual battery monitor.

While installing, did a full test of the Battery Control Center (BCC) and the integral Battery Isolation Monitor (BIM). I can unequivocally say that on my 2015 Forester MBS with the Precision Circuits, Inc. BCC, that the converter/charger (Progressive Dynamics PD9260) DOES charge both the chassis batteries and the coach battery when on shore power. Generator power should work just the same.

Here were the tests -

Plugged in shore power. Checked voltage at chassis battery and coach batteries - voltages the same. Disconnected cables from chassis battery - checked voltage across the cables - voltage the same. Waited for BCC relay/solenoid to open - voltage went to zero. Hooked battery cables back up to chassis battery and unplugged shore power. Plugged shore power back in, checked voltage with Victron - main (coach) battery 14.2 volts, auxiliary battery (chassis) 12.7 volts. Turned on headlights to create a load and drop the voltage of chassis battery, heard solenoid click in - chassis battery now 14.2 volts as well.

Pretty definitive to me.
There have been BCCs for more than 30 years, originally made by a company called RV Custom Products. Their original designs were built to charge the house battery when driving down the road. However, MORE THAN 20 years ago, they were updated to also charge the chassis battery when connected to shore power, eliminating the need to put a charger on the chassis when parked for a long time.

The biggest issue has always been the life of the isolation relays. Sure when you drive the relay is energized and connects the banks for what, 8 or 9 hours? The problem has been that when you turn on the converter, the solenoid might be energized for weeks if not months. The solenoids used are heavy duty, continuous rated parts. They still, however, fail and are stocked by almost every RV accessories store as a replacement part.

I have had long exchanges with the designers of the original BCCs and they put units into styrofoam coolers to verify performance and prove lifetime. Today, virtually all BCCs work in both directions, alternator to chassis and house and converter to house and chassis.
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Old 03-16-2016, 08:43 PM   #9
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Originally Posted by ScottBrownstein View Post
There have been BCCs for more than 30 years, originally made by a company called RV Custom Products. Their original designs were built to charge the house battery when driving down the road. However, MORE THAN 20 years ago, they were updated to also charge the chassis battery when connected to shore power, eliminating the need to put a charger on the chassis when parked for a long time.

The biggest issue has always been the life of the isolation relays. Sure when you drive the relay is energized and connects the banks for what, 8 or 9 hours? The problem has been that when you turn on the converter, the solenoid might be energized for weeks if not months. The solenoids used are heavy duty, continuous rated parts. They still, however, fail and are stocked by almost every RV accessories store as a replacement part.

I have had long exchanges with the designers of the original BCCs and they put units into styrofoam coolers to verify performance and prove lifetime. Today, virtually all BCCs work in both directions, alternator to chassis and house and converter to house and chassis.
Thanks for the additional information and history of BCC's. I'm new to RV'ing and originally took at face value the posts from FR and others indicating that there was no coach to chassis charging on the MBS platform.

Clearly, that was not the case and it appears that even FR did not understand how the BCC worked in the MBS.

Looks like a spare solenoid might be a good addition to the tool kit.
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Old 03-23-2016, 12:57 PM   #10
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The 'Automatic' odb2 adapter now graphs 'Battery Health'

https://community.automatic.com/auto...ry-health-beta

I use the 'Automatic' odb2 adapter, and really love the things it can do - including show details and a map of every trip, and store all my trips both on a smartphone and upload to the cloud via IFTTT - Onedrive for me.

They now have a 'beta' no-cost enhancement that tracks and reports Chassis battery health. Once I take the RV out of its hangar, I'll be able to post some results.
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