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Old 11-06-2016, 02:09 PM   #1
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Charging from the alternator

On this trip I've noticed our charging system while on the road doesn't seem to charge the coach batteries. I do have a solar system and Trimetric battery monitor. So the batteries are seldom below 90℅. Because we were running the furnace overnight we got down to 85℅ charge, and although we drove all the next day our charge didn't get up to 90℅. We we only adding about 1-2 amps while driving. The Genny charged the batteries that evening (it was raining and cloudy so no solar charge happening).

Is there a fuse I need to check, or some wiring to investigate? Everything else seems dandy, with the exception of our weird interlock episode yesterday.
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Old 11-06-2016, 07:09 PM   #2
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Just so you know your MB alternator is more than ample to charge up your batteries quicker in flight, when they are more depleted than you currently let them get. Batteries accept charging more readily from deeper discharge (50%), up to about 90%. The battery charge to full, 12.7v +/- takes longer, as the resistance increases as you approach full. Take that into account when you're in charge mode. Just sayin'
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Old 11-07-2016, 05:15 AM   #3
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My MBS was not charging the house batteries at all. Took it to my Coachmen dealer and after a while they figured out that something was installed wrong. I can not remember the name of the part. It allows 1 way flow of the electricity. No works like a charm. For sure when batts are low the best way to get them back up is to take the rig for a drive....
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Old 11-07-2016, 09:15 AM   #4
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MarsMan, on the solar system I have, the alternator will not be used to charge the house batteries unless the batteries are less than 12.5. If I want to use the alternator and the batteries are higher than that, I run a hair blower until they're lower. Then, you can start the engine of the MBS and hear the 'click' of the alternator starting to charge (and observe the power going into the batteries on the control monitor). Does that help?
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Old 11-07-2016, 12:45 PM   #5
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You have a 12v hair dryer?
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Old 11-07-2016, 12:53 PM   #6
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No 12 volt, namusmc. I turn on the inverter and run the hair dryer on 120 to deplete the house batteries to 12.5 or below. Then, start the MBS and hear the alternator click on and see it start to charge.
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Old 11-07-2016, 02:00 PM   #7
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Te clicking sound is from a relay/contactor in a 10x12 panel made by Precision Circuits Inc in my MH. It only connects to the alternator when the coach battery falls below (I think) 12.6V or 80%. In my case and yours the solar panel supply enough energy to run stuff connected to that battery (fridge etc) and trickle charge that battery keeping it above that threshold of 12.6V. I have installed a switch to disconnect the solar input to ensure the batteries charge while I drive. If you do little boondocking it probably doesn't matter but two weeks in Yellowstone on solar made it matter to me.
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Old 11-07-2016, 02:04 PM   #8
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Don't know a lot about MB motorhomes but i always thought a alternator was to maintain the batteries charge.
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Old 11-07-2016, 02:19 PM   #9
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Mike, the system the original poster talked about was a solar system on a MBS. Usually, the alternator would charge. But with solar, it lets the sun do the work first and only charges if the battery voltage is quite low (12.6-12.5 or below). Gerry, my solar is sufficient to maintain excellent battery charge. I mostly boondock, but in places with better sunlight than you had in Yellowstone, apparently. ;-)
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Old 11-07-2016, 02:27 PM   #10
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The basic charging systems are all the same in vehicles. Alternators, are just that, in that they alternate producing current as needed and called upon by the internal voltage regulator resident on every modern day alternator to charge the chassis battery. MH have an additional battery monitor interface that calls for current, when the coach batts slip below set minimums. The MB is equipped with an extremely high output alternator, which when operating correctly, will actually charge up the house batteries faster when in flight, than runing the genset.
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Old 11-07-2016, 02:32 PM   #11
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For sure, but in MHs they have a battery charge panel to ensure the coach batteries don't become overcharged. Also the panel isolates the two battery systems so that you never deplete the truck battery. The alternator takes its control from the truck battery and therefore the alternator almost always is regulating at about 14.7VDC to be able to supply motor , lights, etc. That's why it can charge the coach batteries so fast. I think the panel disconnects when coach batteries reach 13.7 V or so.
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Old 11-07-2016, 03:57 PM   #12
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char. The subject was "Alternator"
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Old 11-07-2016, 05:07 PM   #13
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Sorry.
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Old 11-07-2016, 05:09 PM   #14
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Sorry. I just know that my alternator will not charge my house batteries unless the batteries read 12.5 or less.
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Old 11-07-2016, 05:19 PM   #15
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My tow vehicle has a new stupid gas saving alternator control that keeps the system voltage around 12.6 volts at most times when the vehicle is running, therefore I can not use the normal charging line connection to top off the camper battery.

I plug a 100 watt inverter into the rear power socket in the Tow Vehicle, then plug a transformer type battery charger into the inverter. The charger output goes to the charge line circuit and supplies a solid 14.6 to 14.8 volts to fully charge the camper batteries while I drive.
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Old 01-30-2017, 09:55 AM   #16
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So I'm still in a conundrum about the charging of the coach batteries from the chassis alternator. I did find a loose and arcing connection from the chassis battery to coach batteries. It connects to the solenoid in the BCC. But even after tightening this connection, I get 14 v at the chassis battery when the engine is running, and 12.3 v at the solenoid (the chassis side connection). On the coach side I get 12.5 v, so it's no wonder I'm not flowing charge now, but this drop in voltage from the chassis battery connection to the solenoid connection should not be happening! What am I missing?
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Old 01-30-2017, 10:06 AM   #17
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Quote:
Originally Posted by backdoctor View Post
...I get 14 v at the chassis battery when the engine is running, and 12.3 v at the solenoid (the chassis side connection...
The question is why a cable coming from the chassis battery which is currently seeing 14.5 volts only reads 12.3 volts when it gets to its connection on the BCC solenoid? Something wrong there. Without the BCC seeing a higher voltage than that, it won't fire that solenoid and bring on the house batteries.

Are you measuring from the lug on the solenoid or from the crimped lug on the cable? While there should be no current flowing if the solenoid is not engaged, it is always a good procedure to measure the voltage from the crimped lug as well as the threaded stud. I have found numerous bad crimps that way.
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Old 01-30-2017, 02:46 PM   #18
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No kidding

Quote:
Originally Posted by ScottBrownstein View Post
The question is why a cable coming from the chassis battery which is currently seeing 14.5 volts only reads 12.3 volts when it gets to its connection on the BCC solenoid? Something wrong there. Without the BCC seeing a higher voltage than that, it won't fire that solenoid and bring on the house batteries.

Are you measuring from the lug on the solenoid or from the crimped lug on the cable? While there should be no current flowing if the solenoid is not engaged, it is always a good procedure to measure the voltage from the crimped lug as well as the threaded stud. I have found numerous bad crimps that way.
Attached is a picture of the crimp I found when replacing our fairly new coach batteries. One of the two batteries had been fried - I suspect because of this crimp. You would think a billion dollar plus corporation like FR would use hydraulic swage crimpers and not the $10 hammer type from Harbor Freight.
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Old 01-30-2017, 05:26 PM   #19
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Attached is a picture of the crimp I found...
Personally that is why I use a torch and rosin core solder, followed by heat shrink tubing. Better connections, easy and permanent.
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Old 02-01-2017, 08:50 AM   #20
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Wiring is always a hassle on boats as well as production RV's.

Boats chose multi strand copper wire that has been "tinned" .

Soldering terminal ends on can be hassle with a soldering gun or a torch.

Too much heat can fuse the nice flexible wire into a solid lump.

My solution is a roofers copper iron , well heated by a torch.

The terminal end should be mechanically crimped before the soldering.

The terminal is first cleaned and fluxed , and a hot copper iron will solder very quickly , even big lugs for a battery feed.

Boats and RV have similar service use , wet , vibrating and ignored when everything works.

A good heat shrink ,color coded, finishes the job.
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