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Old 05-02-2016, 09:39 PM   #1
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alternator not charging my deep cycle batteries

I used to have 2 deep cycle batteries in the front of my 5th wheel to power up when Im not on shore power. My alternator in my truck charged them fine. I then paid someone to add a 3rd battery and a power inverter and now my batteries are only charging on shore power and my truck is not charging them. I have a 2004 Forest River Wildcat. Any advice? Thanks!
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Old 05-02-2016, 09:47 PM   #2
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alternator not charging my deep cycle batteries

Your truck is not a very good source to charge your batteries through the umbilical cord.
I doubt it charged your two batteries very good as you claim.
It would take most if not all day to charge two batteries via the umbilical.
Your truck charging wire is good only to maintain while driving down the hiway, it's not meant to charge deeply discharged batteries.

You probably blew the charging wire fuse on your truck.


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Old 05-02-2016, 09:55 PM   #3
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Originally Posted by TURBS View Post
Your truck is not a very good source to charge your batteries through the umbilical cord.
I doubt it charged your two batteries very good as you claim.
It would take most if not all day to charge two batteries via the umbilical.
Your truck charging wire is good only to maintain while driving down the hiway, it's not meant to charge deeply discharged batteries.

You probably blew the charging wire fuse on your truck.



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Even while driving down the highway my truck shouldnt charge the batteries? The batteries dont charge at all and they are far from depleted. I would think if Im driving 5 hours, my batteries should charge. No?
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Old 05-02-2016, 10:15 PM   #4
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Even while driving down the highway my truck shouldnt charge the batteries? The batteries dont charge at all and they are far from depleted. I would think if Im driving 5 hours, my batteries should charge. No?


No.
At best especially if running fridge while traveling it will trickle charge your batteries and just maintain voltage , in 5 hours it will NEVER charge 3 deep cycle batteries.


The charge wire is 20 + foot long and small gauge, it cannot carry very much current.

As far as not charging at all "separate" issue, you need to check the charging wire fuse in you truck.
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Old 05-03-2016, 09:09 AM   #5
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Truck alt will never charge 3 deep cycle batteries. Ever. Too small for a very large load.
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Old 05-03-2016, 09:12 AM   #6
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Truck alt will never charge 3 deep cycle batteries. Ever. Too small for a very large load.


Agreed!
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Old 05-03-2016, 09:17 AM   #7
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OK...we need some definitions here. His alternator should put some charge back in his batteries, unless they are so depleted as to draw too much current and blow the fuse in his TV. Now that is often pretty hard to do since the cable length and gauge, as others have said, prohibits the alternator from putting any significant current into the batteries and even should probably prevent it from going into an overcurrent condition and blowing the fuse.

I would check the fuse and check the TV connector with a multimeter to see if the TV is supplying anything to the aux charge connection. The OP stated that it used to "charge" before he added another battery. Could be a wiring problem...who knows.

That being said, he shouldn't expect his TV to help all that much, even after a 5 hour drive, if the batteries are overly depleted.
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Old 05-03-2016, 10:11 AM   #8
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I'm not sure what the OP is driving but on most Fords the battery charging is controlled by the body control module thru a 12 gauge wire, 25 amp fuse, and relay. It takes a very long time to change a full size dead battery.
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Old 05-03-2016, 10:20 AM   #9
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I'm not sure what the OP is driving but on most Fords the battery charging is controlled by the body control module thru a 12 gauge wire, 25 amp fuse, and relay. It takes a very long time to change a full size dead battery.


Let alone 2 or 3
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Old 05-03-2016, 12:02 PM   #10
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Here's a test...with the unit just attached to the truck and the truck engine running....go to the coach battery posts with a voltmeter and take a reading on the negaive & positive posts.
IF you see anything over 13.2 Volts...your alternator charging system is working. If you see less..then you have a problem with:
1. The alternator...unlikely since it is working for the truck.
2. The wiring or fuse to your rear connector. Take a volt reading on the appropriate connector pins to confirm (13.2+V)
3. The wiring from your coach side pins to your battery bank. After checking #2 this is the only possibility. Check connections for continuity.

If all this checks out, then you are experiencing a system that is working properly to put a small trickle charge on your LARGE battery bank and will not under normal circumstances provide anything beyond a maintenance charge while driving. Plugging in or charging with a separate generator or large bank of solar cells are your choices for actually putting a bulk charge on your batts. Your converter should be sized to be 20-25% of your battery capacity in amp hours for maximum efficiency in cost of fuel and charging time.
With 3 coach batteries I assume you have somewhere between 225 and 300 amp hours of battery capacity so a charger with 50 to 75 amps charging current would be ideal.
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Old 05-03-2016, 12:08 PM   #11
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Another way to check things out is to isolate the TV from the trailer and check out your circuits.

Check if your TV is supplying voltage to its 7-pin connector between pins 1 (gnd) and 4 (charging voltage). Some vehicles only supply this voltage when they are running so you may have to start your vehicle to be sure.

If the tow vehicle is providing power, then check the trailerís plug between pins (1 and 4). You should be reading your trailerís battery voltage on this plug. You could put a 10 or 15 amp fuse between pins 3 and 4 on your trailerís plug and see of the running lights are lit. Someone on this site provided the attached photo showing how easy this is.

It could be that the wire from the trailerís pin 4 to your batteries is disconnected or an inline current limiting device (fuse or circuit break) is open.
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Old 05-03-2016, 12:27 PM   #12
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Alternators are designed to maintain the charge in a battery.
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Old 05-03-2016, 12:30 PM   #13
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alternator not charging my deep cycle batteries

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Originally Posted by mike.t View Post
Alternators are designed to maintain the charge in a battery.


Maintain is the key word not recharge.
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Old 05-03-2016, 01:03 PM   #14
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I'm not sure what the OP is driving but on most Fords the battery charging is controlled by the body control module thru a 12 gauge wire, 25 amp fuse, and relay. It takes a very long time to change a full size dead battery.
Not on the 2015 and later F-150's. It is an 18 maybe 16 gauge wire. It is hard to say which as it is the only wire in the harness Ford doesn't provide the gauge for nor would they tell me or the dealer. Based on the size and voltage measurements I took I lean to 18 gauge. The only way you will get charging level voltages on the newer models is if the battery if fully charged to begin with. Ford even stated through my dealer the charge line on the newer models is only to maintain the battery not charge it.
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Old 05-03-2016, 01:20 PM   #15
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A set of discharged deep cycle batteries will require a fairly high current to charge them. That high current through the small ( gauge) wire from the fuse block in the TV to the batteries ( and the resistance in the plug) will cause enough drop to reduce the voltage delivered to the batteries to be too low to charge them. A total resistance of 0.2ohms ( not much) will cause the voltage delivered to the battery to drop by 3V at 15 amps ( that's just 5A per battery). If you have anything running in the 5er while traveling, you will be good to just maintain the batteries.
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Old 05-03-2016, 01:28 PM   #16
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When you are hooked up to your TV, think trickle charger, trickle charger, trickle charger. That is what is being supplied through the plug, not a full charge. That is a different beast and requires a separate charger. And time. It is not instantaneous. Little wires and little plugs = little charge.
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Old 05-03-2016, 03:05 PM   #17
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Great info here. I am driving a 2003 dodge ram 2500 gas. I will try these tests next week as I am going on vacation tomorrow. Even if it just trickle charged it would be fine. When I leave my shorepower location, all 3 batteries are 100% charged. But as I am driving they end up being completely depleted. Maintaining the charge that I had before I left for a trip would be perfectly fine but this is not happening. when I had 2 batteries my truck would maintain and charge them quick and easy.
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Old 05-03-2016, 03:23 PM   #18
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Another thought. What is the age difference in the new and old battery. Whenever you hook more than one battery in parallel. They should be the same type and age. What is your inverter running while driving? Is the inverter powered while driving?
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Old 05-03-2016, 03:35 PM   #19
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Yeah mixing batteries is bad!


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Old 05-03-2016, 04:28 PM   #20
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Not on the 2015 and later F-150's. It is an 18 maybe 16 gauge wire. It is hard to say which as it is the only wire in the harness Ford doesn't provide the gauge for nor would they tell me or the dealer. Based on the size and voltage measurements I took I lean to 18 gauge. The only way you will get charging level voltages on the newer models is if the battery if fully charged to begin with. Ford even stated through my dealer the charge line on the newer models is only to maintain the battery not charge it.
I should have stated older Fords. Copper must have been cheaper then.
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