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Old 12-12-2015, 05:53 PM   #1
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Charging House Batteries from alternator

How do I get the alternator to charge the house batteries while driving.

I had the generator going and showed 100% charged with voltage >13.0. After turning the generator off and continuing to drive with the inverter on the voltage slowly drops. I'm not running any lights and nothing is on.

Please help with any ideas or directions.

Thank you
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Old 12-12-2015, 06:33 PM   #2
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Well, the charge line through the umbilical is a long and relatively small gauge wire so it isn't delivering a whole lot of power to your batteries. With the inverter on, you are probably breaking even at best and slowly draining your batteries at worst.

Several members of the forum have run a larger cable aft from the tow vehicle to enhance current flow. If your tow vehicle has lots of extra alternator capacity, this may work solve your problem. However, lots of modern vehicles have pretty hefty power demands so there might not be a lot left over...

Mike
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Old 12-12-2015, 06:49 PM   #3
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I don't have a tow vehicle. I just thought the coach would supply power to charge the house batteries while driving. I thought I had read somewhere that the inverter had to be on in order to charge the house batteries converting the DC power from the coach's engine alternator to AC power to charge the house batteries while in motion.
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Old 12-12-2015, 06:57 PM   #4
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I think the OP is talking about the house batteries, not battery in a toad. Not entirely clear since he doesn't list what he has in his profile.

Edit: See I'm not quick enuf.

I believe on the Interstates w/ the Tripp-Lite inverter, the alternator will charge the house batteries w/ it off.
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Old 12-12-2015, 07:02 PM   #5
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I have a 2013 Interstate EXT Lounge

Can't find a way to add it to my profile.
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Old 12-12-2015, 08:26 PM   #6
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Originally Posted by ofdcb View Post
I have a 2013 Interstate EXT Lounge

Can't find a way to add it to my profile.
Go to "User CP" at upper left and then "Edit your details", then scroll down to "Additional Information", then scroll down to "Motorhome #1". There you can pick yours from the drop down menu.
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Old 12-12-2015, 09:44 PM   #7
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Quote:
Originally Posted by ofdcb View Post
How do I get the alternator to charge the house batteries while driving.

I had the generator going and showed 100% charged with voltage >13.0. After turning the generator off and continuing to drive with the inverter on the voltage slowly drops. I'm not running any lights and nothing is on.

Please help with any ideas or directions.

Thank you

The Battery Isolation Manager (BIM) will not connect the house batteries for charging from the alternator until the house batteries drop below 12.6V. If your house batteries are below 12.6V and not being charged with the engine running your BIM may be faulty. Airstream did have some incorrect wiring problems with the BIM on some 2013 models. Have it checked by your dealer if it is not charging as I've indicated above.


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Old 12-13-2015, 12:46 AM   #8
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Quote:
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I had the generator going and showed 100% charged with voltage >13.0.
WHILE CHARGING from the chassis (alternator), generator, or shore power, you cannot tell the state of charge (SOC) of the batteries. The SOC is indicated by the battery unloaded voltage. While you're charging, the voltage is set by the charging source. So ignore the 100% while you are charging.

Quote:
Originally Posted by ofdcb View Post
After turning the generator off and continuing to drive with the inverter on the voltage slowly drops.
After charging, wait about an hour for the voltage on the battery to be accurate. Before then, it's just surface charge, which will mostly dissipate in an hour or two. So you'll always see the voltage drop after disconnecting. Assuming you have Lifeline batteries, 12.8V is fully charged.

Assuming you have the Sunexplorer solar display, the % of charge on the display is not accurate. The Sunexplorer is calibrated for the wrong type of battery. Go by the voltage. For Lifelines, 12.8V is 100%, 12.5V is 75%, 12.2V is 50%, 11.9V is 25%, and 11.6V or lower is 0%.

After using the generator, the chassis alternator may not charge the batteries until some time has passed. Running the generator turns on the BIM relay, which connects the coach and house batteries. After the generator has been running for a while, the relay turns off. After the relay is off, the chassis alternator will not charge the coach batteries. You'll have to experiment to see how long your BIM relay stays off.

In contrast to Boxster1971's report, my BIM (2014 Interstate) will connect the chassis alternator to charge the coach batteries even when the batteries are higher than 12.6V.
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Old 12-13-2015, 08:27 AM   #9
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Instructions for the BIM contain helpful troubleshooting guide in both directions - coach power charging chassis battery and alternator charging coach batteries. might check the fuse on the side of the chassis battery (beneath drivers side). If it is blown the alternator will not charge coach. I don't recall the size of the fuse. I carry an extra in the MH, which is currently in storage.
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Old 12-13-2015, 09:15 AM   #10
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Thank you
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Old 12-13-2015, 09:59 AM   #11
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Have it checked by your dealer if it is not charging as I've indicated above.
I love your optimism. I've asked my dealer about the proper operation of the BIM. The technician at my dealer did not know what a BIM is, how to test it, where it is located, how it works, what it does, or how to spell "BIM".
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Old 12-13-2015, 10:19 AM   #12
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I love your optimism. I've asked my dealer about the proper operation of the BIM. The technician at my dealer did not know what a BIM is, how to test it, where it is located, how it works, what it does, or how to spell "BIM".

Probably because Airstream doesn't call it a BIM; they have labeled it the Battery Separator. The term Battery Isolation Manager (BIM) is form the component manufacturer, Precision Circuits Inc.

... and yes I'm an eternal optimist. 😊


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