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Old 09-16-2021, 08:12 PM   #1
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I think my 5er is trying to charge my truck battery when parked

Well, today I finally looked at my Victron app and saw a 4 amp draw on the battery while parked. That was odd since nothing was on in the trailer except the gas detector thingy. So I unplugged the 7 pin connector and voila! the draw went away. I have LFP batteries in the trailer and they read 14.6V. I assume this means that my LFP batteries are trying to charge my truck battery.

And no, the brake disconnect was not activated.

I also saw that I get a whopping 4A going into the LFP battery.

So, maybe I need to look at a DC-DC charger. I wonder where the 7 pin charge line connects into the system? I just redid my entire DC system and I did not see a connection from the 7 pin connector.

If I do go with a DC-DC charger, I'll probably run a dedicated 6ga wire from the battery to an Anderson connector at the back of the truck.

Appreciate your thoughts if I have diagnosed this correctly.
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Old 09-16-2021, 08:29 PM   #2
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Truck Tow Charge line is hot all the time

So truck/trailer batteries are connected

Any time you park truck/trailer for long periods (overnighters etc) unplug trailer umbilical cord

My Ram is same way
Ford is off unless truck key is on
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Old 09-17-2021, 07:10 AM   #3
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You would think that running current backward into the truck would get the computer mad. A diode would fix that. All though motorhomes have generators charging coach batteries and no problem. What say the engineers?
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Old 09-19-2021, 06:45 PM   #4
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Almost all travel trailers and 5th wheel systems have a hot 12 volt pin in the 7 pin connector. Almost all tow vehicles have the 12 volt hot pin connected to the tow vehicle battery.

The two battery banks are always "on" when the 7 pin connector is plugged in.

The trailer side will also discharge the tow vehicle starting battery and the tow vehicle starting battery will discharge the house battery depending on which has lower voltage.

You don't need a B to B charger to separate them. Just unplug the 7 pin connector. It is not complicated.
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Old 09-19-2021, 08:34 PM   #5
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Quote:
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Almost all travel trailers and 5th wheel systems have a hot 12 volt pin in the 7 pin connector. Almost all tow vehicles have the 12 volt hot pin connected to the tow vehicle battery.

The two battery banks are always "on" when the 7 pin connector is plugged in.

The trailer side will also discharge the tow vehicle starting battery and the tow vehicle starting battery will discharge the house battery depending on which has lower voltage.

You don't need a B to B charger to separate them. Just unplug the 7 pin connector. It is not complicated.
So when I am parked at a rest area for an overnite sleep, I have to remember to disconnect my 7 pin connector and then remember to hook it back up before getting underway. Sure, that makes a lot more sense then adding a simple, $60 DC-DC charger with isolation.
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Old 09-19-2021, 08:40 PM   #6
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So when I am parked at a rest area for an overnite sleep, I have to remember to disconnect my 7 pin connector and then remember to hook it back up before getting underway. Sure, that makes a lot more sense then adding a simple, $60 DC-DC charger with isolation.
Should be Regular ROUTINE to do a walk around PRIOR to driving away....be it overnight spot, a rest area, a lunch break away from rig etc

ROUTINE...then unplugging/plugging back in----checking lights becomes Normal Routine and it's FREE
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Old 09-19-2021, 08:42 PM   #7
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Should be Regular ROUTINE to do a walk around PRIOR to driving away....be it overnight spot, a rest area, a lunch break away from rig etc

ROUTINE...then unplugging/plugging back in----checking lights becomes Normal Routine and it's FREE
OK, but I like to use technology to reduce the probability of making a mistake. You do you and unplug. I'll do me and add a DC-DC charger.
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Old 09-19-2021, 09:06 PM   #8
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OK, but I like to use technology to reduce the probability of making a mistake. You do you and unplug. I'll do me and add a DC-DC charger.
Even with the DC-DC Charger I do Hope you ROUTINELY do a walk around prior to travel

High tech can fail...and does.

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Old 09-19-2021, 09:07 PM   #9
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Even with the DC-DC Charger I do Hope you ROUTINELY do a walk around prior to travel

High tech can fail...and does.

Of course I do.
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Old 09-22-2021, 12:06 PM   #10
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Good news and bad news.

Good news: installed the Victron DC to DC converter. Easy install as the battery charge wire was right in the front storage area and easy to get to. Got it all hooked up. 18A @ 14.4 volts going to the battery. Wonder if I need a charge controller for that much current? The wire from the truck is 10ga and it is fused @ 30A.

Bad news: I shut off the truck and measured 18A still going into the trailer battery. I fixed the truck draining the trailer batteries and now my trailer is draining my truck batteries to the tune of about 21A. When the truck is off, the DC to DC converter still spits out 14.4V @ 18A and it does it by drawing 21A @ 12.6V from the truck battery.

So now I still have to unplug the truck when not running. Won't take long to drain the truck if the camper is pulling 21A.

I guess I could add an ignition controlled relay to the trailer charge line. Could have done that in the first place. Or just used the diode. Lesson learned. Crow eaten.
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Old 09-22-2021, 12:08 PM   #11
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Another EASY solution is to come off the truck battery with a RELAY.


Use ignition hot to close the relay. Ignition on, batteries connected. Ignition off, batteries separated.
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