Converter or truck charging battery

**NewRVer** · 03-20-2024, 09:23 AM

[QUOTE=roegs01;518826]My experience after about 8,000 miles towing since I replaced the lead acid battery with 100A Lithium.

Background
1. I have no dc-dc converter. I simply plug the 7 way into our '21 RAM 3500.
2. Lithium is fully charged when we begin trips via the onboard converter (lithium capable converter).
3. We travel with everything off in our 2930RL other than the refrigerator - which is running off propane.

While Towing
1. The Lithium battery shows that its being charged...but its a very low

One more question. How do you know how much charge the lithium is taking? What are you looking at? A shunt?

**roegs01** · 03-20-2024, 09:39 AM

[QUOTE=NewRVer;518832]

Originally Posted by roegs01

My experience after about 8,000 miles towing since I replaced the lead acid battery with 100A Lithium.

Background
1. I have no dc-dc converter. I simply plug the 7 way into our '21 RAM 3500.
2. Lithium is fully charged when we begin trips via the onboard converter (lithium capable converter).
3. We travel with everything off in our 2930RL other than the refrigerator - which is running off propane.

While Towing
1. The Lithium battery shows that its being charged...but its a very low

One more question. How do you know how much charge the lithium is taking? What are you looking at? A shunt?

I have a Renogy Battery and it has a Bluetooth App that I use. The two screen shots below show the charging rate (2.5 amps) while driving and the discharge rate that the refridge draws when I overnight at a hotel and disconnect the 7 way.

Click image for larger version.

Name: IMG_2386.PNG
Views: 6
Size: 325.5 KB
ID: 50143

**roegs01** · 03-20-2024, 09:40 AM

Double post....please delete.

**Conner58** · 03-20-2024, 09:45 AM

I have stayd overnight wth 7 way plugged in many times no problems

**roegs01** · 03-20-2024, 09:47 AM

Originally Posted by Conner58

I have stayd overnight wth 7 way plugged in many times no problems

You may not have a problem, but you may be unnecessarily drawing back towards your truck. Have you ever checked current flow?

**Hoopy Frood** · 03-20-2024, 10:00 AM

I've always unplugged from the truck, but my understanding is the newer trucks disconnect with the ignition turned off. But maybe not.

**retired_engineer** · 03-20-2024, 10:02 AM

Originally Posted by Hoopy Frood

I've always unplugged from the truck, but my understanding is the newer trucks disconnect with the ignition turned off. But maybe not.

I can't speak to other trucks but in both my 2015 and 2023 F-150s the Aux line was only active when the ignition was turned on.

**JKellerJr** · 03-20-2024, 10:28 AM

Originally Posted by Hoopy Frood

I've always unplugged from the truck, but my understanding is the newer trucks disconnect with the ignition turned off. But maybe not.

GM truck stay hot even if the truck is off. My '24 still does it

**JKellerJr** · 03-20-2024, 11:02 AM

Originally Posted by NewRVer

Ok. Great. So my next question is this. I want to drop a lithium battery into my camper. I have a 30 amp fuse in my Ford F250 super duty going to the seven way pin. Will the battery blow that fuse when its being charged or am I safe?

You won't have an issue. I've used lithium's since 2017. Our previous unit with 200AH and our current on with 400AH. Our current batteries are capable of charging at 200amps per hour and regularly take 100 amps an hour when being charged from shore power. That does not affect the charge rate of the truck, it puts out what it puts out.

I never have unplugged if I stop at a rest area or campground for a quick overnight. But at least theoretically it could be an issue. I had a discussion on another forum about that recently. I can't say for certain that its not doing anything but I have not had an issue over the last 7 years or so. But its also fairly rare that I'll stop like that. Normally we stop early enough and unhook. If it concerns you the easiest fix is adding a diode in the charge wire in the camper that only allows current one way.

I know on my truck the charge wire stays hot even when off. Someday, when I have time I'm gonna hook up to the trailer and unhook the truck batteries and see how much voltage makes it back to the truck batteries.

**powerscol** · 03-20-2024, 11:37 AM

Originally Posted by NewRVer

Wow. That’s very interesting and duly noted. Thank you all for the valuable info.

You will not have an issue. Your Ford drops charge power to the 7 pin when off. Easy to check to. Also the Ford trailer control module will limit the current draw to less than 30A.

Many folks are running a Renogy 20A DC-DC charger off of the Ford 7 pin wire without issue.

In addition you actually may get full charge out of the ford 7 pin as the running charge voltage can be up to or slightly above 14.4V. I have checked mine under full charge to my flooded 6V (series parallel to get 12v bank) when they were at 50% and the voltage hit 14.6V. I didn't have an amp meter so could not check that at the time. I can now. You will be fine - safe travels and happy camping.

Hope this helps