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Old 02-28-2023, 11:15 AM   #1
mepright
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Help with question on batteries vs 7 pin harness

Hi all,

Just recently went to lithuim batteries in my fifth wheel, After a few days of charging and testing all seems to be working well. I am still waiting for my battery monitor to come in.

My question is: When plugged in ( 7 pin harness) to my 2021 3500 Duramax will there be any safety issues with the wiring being to small. Could I possibly hurt the the 220 alternator?

I am not looking to use the truck as a source for charging yet. Just want to make sure we are safe to plug in and travel.

Thank you

Mike Epright
 
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Old 02-28-2023, 01:38 PM   #2
rohrmann
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Your tow vehicle is not considered to be a primary charging source for your batteries, and it doesn't matter what type of battery you are using, no harm to your vehicle alternator or your rigs batteries should happen. The hot wire in the trailer connection will not change what amperage will reach the trailer.
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Old 02-28-2023, 01:57 PM   #3
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Thank you.

Mike
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Old 02-28-2023, 02:21 PM   #4
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The LL ion battery S can take a much higher amperage charge than a led acid battery and more than your truck alternator can supply. Charging the camper LL ion battery s can burn your truck alternator out especially at low RPMs. It’s not rotating fast enough for its fan to cool it and it will overheat and burn it self out.
There is lots of information on the internet about this Google will lithium batteries overheat my alternator.
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Old 02-28-2023, 03:59 PM   #5
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If you are only charging from your 7-way, then no worries about the TV alternator. Most new trucks won't supply but approximately 7 amps charge through the 7-way circuit
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Old 02-28-2023, 09:28 PM   #6
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The MOST I have measured going through the 7 way cable to my lithium batteries is about 7A.
The batteries were at 30% so if they were going to pull too hard they would have done so.
I added solar and a DC-DC charger for boondocking.

https://www.montanaowners.com/forums...hlight=charger
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Old 03-01-2023, 07:00 AM   #7
mepright
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Hi all,

After a few hours of reseaching the topic and being a novice, I do plan to add a DC to DC charger in the near future. As for the 7 pin harness with the 12v charging wire, would the truck have a fuse that could be remove and does the 12v wire on the 7 pin harness on the fifth wheel go to the converter or the battery bank? If the converter, would the converter protect the current back to the alternator?

Please know this is all new to me and I do appreciate everyones help in this matter.

Thank you,

Mike
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Old 03-01-2023, 07:26 AM   #8
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Mike, it goes to the battery. It is a controlled draw from the truck, so you cannot damage either side from the 7 pin. Many people think that you are charging your battery this way, but you probably aren’t coming close. As several above said, it is only providing 5-7 amps/hr. My Montana draws 10 amps/hr just sitting. If you have a residential fridge, you are drawing more. We have been towing Montana’s for almost twenty years. The 7 pin will not cause an issue. As for DC-DC charging, there are several methods. The most popular are the Renogy and BIM. We have the BIM system on ours. If doing it yourself, be sure to follow wiring size and disconnect guidelines. Failure to install properly can do a lot of damage. Ours has 80 amp disconnects at the RV and truck, 2/0 wire and the BIM. An Anderson connector in the bed of the truck provides the disconnect point when unhitching.
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Old 03-01-2023, 08:13 AM   #9
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Mepright
Check your trucks owners manual. I have a 2016 F350. It has a 30A fuse and a relay on the 7 way circuit.
BTW, I've had my lithium batteries and truck setup like this for 3 years. No problem.
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Old 03-02-2023, 07:20 AM   #10
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Thank you all for your comments and advice. I do feel more at ease with all the information shared.

Mike
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