Charging 5er batteries while driving, question.

My truck doesn’t charge the 5th wheel batteries (2 group 27 batteries) while towing. I installed a Victron Battery Monitor system with dongle on the trailer. So I can get feedback to my cell phone or ipad on in/outbound current along with battery voltage and state of charge. I can see no charging going on while driving. I do see a small drain caused by what I assume is the fridge while driving.

A little history, DW and I purchase (last fall) from a private seller a very well cared for used truck and 5th wheel at a fair price. We were into camping for many years then got out because we just didn’t have time to use the class c we had. The truck is a 2008 Ram CTD 2500 , (80K mile) and a 2011 Montana 3150RL 5th wheel. If at all possible I would like to avoid getting into tow rating and waking up the weight police. I will admit I was a bit naive on all the weight issues related to 5th wheels when we purchased. I have weighed my trailer truck combo and just the truck on a CAT scale loaded and I am towing well under trailer GVWR and I strive to keep things as light as possible. DW and I both have some health issue (bad backs and arthritis) so we bought a used combo as a test to see if we can make this work (health wise) and it’s the right setup for us in retirement doing mostly summer travel. We felt we would take a lighter hit if we were forced into selling it with a used purchase. If it all works long term we may upgrade to new (3500 truck and new 5er or even a class A) in a year of 2. We went through this truck and trailer maintenance wise this spring to try to make sure things were as dependable as possible for use in the meantime. New shocks Timbrens, trailer tires, fluid, belts, brakes and so on and so on. The truck doesn’t feel overloaded and pulls the unit nice and everything runs and tows great so far. We put on maybe 5000 mile towing this summer and for the most part are very happy with the setup.

Back on focus, with all that said what is needed to get the trailer to charge the batteries while towing? I am assuming this is just a truck issue, is that wrong? Is it as simple as installing a fuse in the truck? Or do I need to have a wire run from the truck battery back to the factory trailer plug on one of the pins? Any knowledge shared would be appreciated. I can live with things the way they are, but it would be nice (if it’s an easy fix) to have the trailer batteries charge a bit while towing.

Thanks in advance for the feedback,
Bob

IT_Burnout
Explorer
Jul 24, 2017
Well I bought out O Reilly’s auto supply on those fuses 3 of them at $5.00 each. They don’t give those things away. Murphy’s law plays into my life so much I figured buying just one just meant another couple trips back to town and the store.

I plugged in the fuse and just like said the plug was hot at the back of the truck all the time. The fuse held just fine it didn’t pop. I went over to the trailer with the meter and got trailer battery supply voltage level from the plug on pins 1 & 4 so that looked good too.

The screenshot below is from my cell phone app that shows the draw my voltage monitor on the camper seen with no shore power hooked up and nothing on in the trailer including the fridge turned off. You can see it shows a -.20amp draw

I ran the landing gear up and down a little because the battery was fully charged. I was trying to draw the batters down just a little to get the truck to charge it some.

Then I plugged in the umbilical cord from the truck and had the truck running and you can see from the screenshot from my cell again 5.60 amp inbound charge into the battery. I did see over 6.30 amps when I first plugged it in. It didn’t take long for the charge amperage to drop off to 1.00 amp and under as the battery came back to 100% charge.

I think I am at least working now and have some inbound charge going to the batteries so that should help things some. I will see how it all works on the next trip in a couple weeks. Its nice being able to watch what is happening from the truck as I tow.

I had the battery disconnect switch turned on in all cases. But thanks for the heads up on that too. Makes sense that would isolate the battery from charging.

BTW I hear you on the 30 amp fuse blew for some reason. I will be looking over my shoulder on this deal for a while yet.

Thanks for the all the help.
Bob
laknox
Nomad
Jul 24, 2017
If you have a battery disconnect, it may have to be hot (on) to charge. I learned that the hard way when I showed up at my boondock site with batteries that weren't fully-charged, despite being plugged in at home for 3 days. I did also confirm that my rig will also not charge while plugged into my truck if the disconnect is cold (off).

Lyle
Old-Biscuit
Explorer III
Jul 24, 2017
IT_Burnout wrote:
Rather than my normal :h circling the truck 3 times and kicking the tires and shaking my head and cussing a bit and wondering just what to do next.

That may still be an option come tomorrow.....

Sorry ---just poking at ya :B

30A pink fuse blew for some reason.

Buy several....just in case.

Might want to ohm out the same pin on trailer plug.
IT_Burnout
Explorer
Jul 24, 2017
Got some alone time, and I went out to the barn and measure the voltage across pin 4 to 1 on the back of the truck at the connector and it was dead. Went under the hood and found 30 amp pink fuse in outlet 19 and pulled it out. I couldn’t tell if it was blown or not by looking at it. I put meter on it and ohm’ed it out and it was wide open (blown). I also check voltage on the fuse block outlet and one leg was hot with 12 volts as it should be. So I will pick up some new fuses tomorrow and see what happens. I hope it’s not a corrosion issue causing a short in the connector somewhere in the rear bumper. I did put the ohm meter across pins 1 and 4 and it was infinite ohms (no short shown) so it looks like when I install the fuse it should hold. Then I will have to plug into the trailer and see what happens. With a little luck this could be an easy fix. I do have to say it was nice to walk out there and have a plan on what to look for and how to attack the problem. Rather than my normal :h circling the truck 3 times and kicking the tires and shaking my head and cussing a bit and wondering just what to do next.
IT_Burnout
Explorer
Jul 23, 2017
korbe wrote:
Once you figure out the problem, as a note to the actual charging for example, when our 5er batteries reach about 50 percent or 110 ah available, a 9 hour drive will get our batteries back up to just about 100 percent, or 225 available.

That's good to know, I figured it might be a slow charging process but didn't have a clue how long charging might take. We are thinking about a trip to Alaska next year and if we do some hard days of heavy driving I was worried we would have to get shore power (we do haul a champion inverter generator) to keep our batteries charged every or every other day. I am hoping to get some charging going on to provide a little more flexibility on that front.
IT_Burnout
Explorer
Jul 23, 2017
Ok, yes your right, I meant to say converter not inverter I misspoke. I do understand and realize the difference, I do have a small standalone 400 watt inverter for small needs. What I guess I was trying to get at, is the converter is charging the batteries when plugged into shore power. Electrically thats the same spot (battery and cord) as what is being fed through the umbilical cord from the truck battery and charging system. Just wondering if any issue could be had with both in play. I guess if the truck isn’t running it probably doesn’t matter and current flow could be back to the truck from the trailer while plugged into shore power. Also I would have guessed pin 4 would have been switched through ignition switch so truck battery would be isolated and couldn’t be drained from trailer. But anyway I think I got a much better picture now, on how all that works. So I think I can pick up from here and figure it out. Thanks again.
korbe
Explorer
Jul 23, 2017
Once you figure out the problem, as a note to the actual charging for example, when our 5er batteries reach about 50 percent or 110 ah available, a 9 hour drive will get our batteries back up to just about 100 percent, or 225 available.
Old-Biscuit
Explorer III
Jul 23, 2017
RAM.....pin S/B hot

RAM ....#4 pin should be hot all the time......even with ignition key off

Having umbilical cord plugged into truck and plugging trailer AC cord into power pedestal NOT an issue

120V AC shore power supplies MAIN AC Panel which feeds Converter which supplies 12V DC system and charges battery.
Inverter (If you have one) takes 12V DC power and supplies 120V AC power to outlets/specific AC circuits for powering from battery

Separate systems
IT_Burnout
Explorer
Jul 23, 2017
Old-Biscuit thanks, with this diagram I should be able to dig deeper. I have a couple old DVM’s around the garage or pole barn so I can back track things and hopefully figure out what is going on. I follow you with everything across pin 1 & 4 with 12 volt and fuse #19 as supply fuse. But I am lost on ”RAM ---pin S/B hot” can you explain, not sure what that mean?

I am curious about something. Are there any issue related (say popping a fuse) to plugging into Alternating Current shore power with respect to the trailer, while it’s still plugged in with the umbilical cord into the truck? Like back feeding the truck so to say with the inverter, or does that leg have a diode in it somewhere, or isn’t it even an issue? You probably know what I am thinking might have happened with the previous owner. I guess I will know more once I get out there and work on it a bit.

Thanks, everyone for the feedback.
Bob
Old-Biscuit
Explorer III
Jul 23, 2017
Flip open the 7 pin connector cover on your truck

With voltmeter test for 12V DC between pin #4 and pin #1
(4/12V DC-----1/Grd)

RAM ---pin S/B hot
If not check fuse #19 in MAIN Fuse Panel UNDER the hood.
30A Trailer Tow Battery Feed

IF pin #4 is HOT then need to check where trailer umbilical cord connection are made-------access panel on 5vr overhang next to pin box

Truck alternator should 'maintain' trailer battery when truck/trailer umbilical cord connected.
Length of charge line and wire size limits ability to charge a low battery condition