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Old 07-07-2019, 11:46 AM   #1
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Alternator not charging house batteries?

So we just got to our campsite after about a 1 hours drive. Noticed my battery monitor for the 2 house batteries was beeping. They were about 40% depleted. The monitor indicates the alternator is not charging. The vehicle battery was fine and is charging. Out campsite is not ready yet so I fired up the gen and the batteries are taking a charge. It will be a few hours before we can go to the campsite so I figured it wouldn't hurt to ask here where I should start looking for the problem? I figure its a fuse and was hoping someone may point me in the right direction.

Thanks.
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Old 07-07-2019, 12:02 PM   #2
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Did you have the battery isolation switch on during driving?
It must be on to parallel to the engine alternator for charging.


If the switch was on maybe the batteries need servicing/checked
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Old 07-07-2019, 01:17 PM   #3
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Obviously there is a break in the connection between Starting battery and Coach Battery.

Most often used method of connecting the two so the coach battery will charge while driving is a Relay/Solenoid. Depending on coach manufacturer's design it can be a stand alone controlled by ignition switch or by a more complex management system that activates this relay to charge starter battery when running off converter or generator.


Bottom line, find where the two systems are connected and get out the Multi-Meter. If there is more than 13 volts on one side of this relay and less on the other, the relay is either not being activated or is defective. Check for voltage at the control connections and if none, work upstream until you find where it stops.

Do this while engine is running.


BTW, do you have a switch somewhere that controls whether or not the coach batteries are charged while driving? There are newer devices that act as isolators and also switch off the charging to coach batteries when full to prevent overcharging. Being a solid state device it might have failed.

In closing, there's no better way to diagnose your problem than using a multi-meter and finding where the charging voltage stops on it's trip to the coach batteries. Checking fuses/circuit breakers is a good first step but be prepared for something less simple.
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Old 07-07-2019, 01:18 PM   #4
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Originally Posted by Iggy View Post
Did you have the battery isolation switch on during driving?
It must be on to parallel to the engine alternator for charging.


If the switch was on maybe the batteries need servicing/checked
I don't have one that I know of. It has always charged with no problems. I have not changed anything. I have an inverter powering the driver side of my ac outlets. Pulls about 450 watts with the fridge on ac. The alternator has always charged the house batteries.
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Old 07-07-2019, 01:26 PM   #5
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I don't have one that I know of. It has always charged with no problems. I have not changed anything. I have an inverter powering the driver side of my ac outlets. Pulls about 450 watts with the fridge on ac. The alternator has always charged the house batteries.
Actually I do have a battery isolation switch and it was not on. I am wondering if there is a fuse in the bcc located with my batteries. I am pretty sure there is a cable running from a post on it to the chassis battery or relay of some sort.
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Old 07-07-2019, 01:29 PM   #6
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I'm guessing this would be a good place to startClick image for larger version

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Old 07-07-2019, 02:04 PM   #7
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Press your boost start switch and see if you hear the isolation relay clunk. If not, you have either blown a fuse or the coil has failed. If it does clunk but the bank voltage does not come up and match the chassis battery, the solenoid may have burned contacts.

When the engine is running the relay should close on its own.
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Old 07-07-2019, 02:12 PM   #8
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Press your boost start switch and see if you hear the isolation relay clunk. If not, you have either blown a fuse or the coil has failed. If it does clunk but the bank voltage does not come up and match the chassis battery, the solenoid may have burned contacts.



When the engine is running the relay should close on its own.
I'll give that a try... thanks. One thing I did notice.... My converter is charging the chassis battery along with the house batteries.
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Old 07-07-2019, 02:15 PM   #9
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I'll give that a try... thanks. One thing I did notice.... My converter is charging the chassis battery along with the house batteries.
Well, that means the solenoid is working in that direction. Same solenoid for alternator to house bank. Either it isn't firing with the engine running or something wrong with the alternator circuit.

Easy check. Start the engine and push the boost start switch manually and see if the alternator starts to charge the house bank. If so, there is a fuse or circuit issue in your BCC.
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Old 07-07-2019, 02:37 PM   #10
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bclinton the following attached BCC schematics and a meter may help you
resolving your problem.

Thats If the schematics apply to your RV.

First if your 12V system is the same as shown on the schematics the battery
disconnect switch does not appear to be involved in the chassis - coach charging
circuit, also if the generator started without any problems, this seems to suggest
the coach batteries are not all that bad.


If the inverter was running when driving, it maybe that the alternator simply
did not supply the required 13.2 VDC required by BCC to permit the charging
connection between the chassis and coach systems.
Attached Files
File Type: pdf SDC 107 Battery ControlCenter copy.pdf (1.44 MB, 54 views)
File Type: pdf Forest River BCC 109177 copy.pdf (3.49 MB, 47 views)
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Old 07-07-2019, 04:36 PM   #11
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You guys are awesome. I will pro ably wait until I return home on the 15th to start troubleshooting. I would hate to make things worse at a Coe site with not many tools. Lots of good info to start the process. I will update with what I find out.... Thanks again...
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Old 07-08-2019, 12:07 PM   #12
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So......here's an update.....I heard from a tech......below is his message and my reply back. Bottom line today everything seems normal again. My only guess is the heat issue caused something to malfunction.


Reply to tech.....
Thanks. measured voltage as you described and everything appears to be back to normal now. Both the house and chassis batteries are charging that 14.2 with my converter on the RV off and the vehicle running. I haven't changed a thing and everything seems to be working correctly. Weird.....the only thing I can think of is the bay that the house batteries is in along with the inverter and the BCC was very hot yesterday. When I saw the victron battery monitor beeping at me for low voltage on the house batteries I opened the bay door and noticed it was very hot. The bay is right next to the engine and it was a hot day. Would heat cause the relay to malfunction? I am going to get a small fan and mount it in the space anyway. It is an open air bay and has plenty of ventilation but I suppose the engine heat alone was causing the air around the bay to get hot.

On Monday, July 8, 2019, 10:57:17 AM CDT, John Mock <jlmock@pacbell.net> wrote:


Hi Bill,

The SDC-107 contains an isolator relay whose purpose is to parallel
coach and chassis batteries for charging purposes.?? Measurement of the
voltages on the studs of the SCD-107 will tell you.?? Refer to the
troubleshooting guide for your equipment on our web site
rvcustomproducts.com.?? For example, with engine running, the voltage on
the chassis battery stud should be around 14.2vdc.?? If the circuitry and
relay inside is working, the coach battery stud will also be 14.2vdc.
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Old 07-18-2019, 06:35 PM   #13
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So....just returned after a 10 day stay. The issue with my alternator on the MH not charging the house batteries did not pop up on the return trip. Batteries stayed charged while my fridge and misc things pulled about 400 watts from the inverter. We moved from one site to another about 3 days ago and when we first started the MH the problem was there (house batteries at about 12.5 volts while chassis battery was at 14.1). I get to the site disconnect from shore power...start the MH and all seems fine again. I'm not sure what could possibly cause the problem intermittently. I guess I will just keep monitoring it until it fails completely
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Old 07-19-2019, 08:51 PM   #14
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Sorry, to hear that you are still having problems. Intermittent troubles are *&%$# awful. The following is a suggestion, with a schematic showing part of the BCC and connections to it.

The next time it fails (motor running, shore power disconnected) to prove wether the Ignition switch relay is operating correctly try to operate the slides. If they operate this suggests that the relay questionable, or the connection to ignition is not providing 12VDc to operate the relay. Maybe a loose connection on the ignition switch ?

This is all based on the assumption that your unit is wired the same as my 378

Hope this helps
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Old 07-20-2019, 08:36 AM   #15
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Originally Posted by mbtelguy View Post
Sorry, to hear that you are still having problems. Intermittent troubles are *&%$# awful. The following is a suggestion, with a schematic showing part of the BCC and connections to it.

The next time it fails (motor running, shore power disconnected) to prove wether the Ignition switch relay is operating correctly try to operate the slides. If they operate this suggests that the relay questionable, or the connection to ignition is not providing 12VDc to operate the relay. Maybe a loose connection on the ignition switch ?

This is all based on the assumption that your unit is wired the same as my 378

Hope this helps
Thank you for the help. We are heading out in a couple of weeks again. I will try this.
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Old 07-20-2019, 09:07 AM   #16
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This may not be 100% pertinent but I have read somewhere and going from a fuzzy memory that often Ford does not install a fuse that allows charging from the alternator to the house batteries? Something that has to be checked by the dealer before leaving the dealership.
Sorry if this isn't 100% pertinent to the original post
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Old 07-21-2019, 03:53 PM   #17
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Quote:
Originally Posted by mbtelguy View Post
Sorry, to hear that you are still having problems. Intermittent troubles are *&%$# awful. The following is a suggestion, with a schematic showing part of the BCC and connections to it.

The next time it fails (motor running, shore power disconnected) to prove wether the Ignition switch relay is operating correctly try to operate the slides. If they operate this suggests that the relay questionable, or the connection to ignition is not providing 12VDc to operate the relay. Maybe a loose connection on the ignition switch ?

This is all based on the assumption that your unit is wired the same as my 378

Hope this helps
This is all fine but the ignition interlock really has nothing to do with battery interconnect charging. Battery interconnect charging is accomplished via the priority circuit within the BCC (battery interconnect relay) and the ignition interlock relay you speak of is not part of that equation.
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Old 07-22-2019, 12:57 PM   #18
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BUBBLES I'm well aware that the relay itself has nothing to with the charging circuit.

But the 12v used to operate the relay is the same 12v used to determine if there is proper voltage to start charging the house battery from the chassis.

Determining if the relay operates may help determine if their is any power from the ignition.

Look at the schematic I provided
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Old 07-25-2019, 03:13 PM   #19
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BUBBLES I'm well aware that the relay itself has nothing to with the charging circuit.

But the 12v used to operate the relay is the same 12v used to determine if there is proper voltage to start charging the house battery from the chassis.

Determining if the relay operates may help determine if their is any power from the ignition.

Look at the schematic I provided
Negatory big ben. The 12 volts for the relay you speak of is energized via the ignition switch just being on. The engine has to be running for the charging interconnect solenoid to energize for charging from the engine alternator to the coach batteries. The interconnect relay for charging is controlled by a voter circuit that looks at the chassis battery voltage before energizing to also charge the coach batteries. The same thing happens only in reverse when the chassis battery charging is via the converter. The voter circuit looks at the coach batteries and if they are sufficiently charged then the interconnect relay energizes to also charge the chassis battery.
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Old 07-25-2019, 11:00 PM   #20
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Bubbles, see post #10 attachments for a complete explanation of how the BCC operates (see attachment below for a brief explanation how the charging circuit works) and refer to post #14 for schematic and testing conditions
I cannot find any reference to a voter circuit in the BCC documents

"Interconnect Relay
Control electronics on the circuit board parallels the coach and chassis batteries with the
interconnect relay. In addition, the batteries can be paralleled with a momentary pushbutton
switch on the driver's console that applies +12vdc to P3-1.
For the purpose of charging the coach and chassis batteries, power for the control
electronics is obtained from the ignition switch and coach battery through diodes D1 and
D2. Underway, when the charging source is the engine generator, +l3.2vdc on the
ignition line triggers the electronics. After a lSsec. delay, the interconnect relay closes,
paralleling the batteries. Should the battery voltage go below 12.7vdc, the interconnect
relay will open after around a 15sec. delay. When the vehicle is parked and on shore
power, when the converter brings the coach battery up to +13.2vdc, the interconnect relay
will close after the 15sec delay, charging the chassis battery as well. As before, the relay
will open when the battery voltage goes below 12.7vdc."
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