Charging Trailer batteries...

[jelag]

So I have a 13, 3500 Laramie Longhorn.... and my RV has (6) 6 volt batteries... that's 3 sets of 2....

On my old truck I had to run a 6 gauge wire from the batteries to the trailer plug to get any kind of charging voltage back at the batteries... the 2013 is NEW TO ME.... and with the engine running I can see 13.2 - 13.5 VDC at the trailer plug with a volt meter.... and if I test the plug from the trailer I can read battery voltage on that plug....

So I know there is voltage back from the engine compartment, the fuse F30 is tested and good, but after 2 days on the road I'm just not charging the trailer batteries... at a rest stop, with the engine on fast idle my digital voltmeter in the trailer is just showing battery voltage... now, start the gen set and let the converter take over and I immediately have 14.2v and the batteries will charge...

Do I need to run a 6 gauge wire on this new truck... its seems like the alternator output on this truck is lower than my old truck....

Bob 4x4 or Sag2 got any idea here..... why can't the factory write a software routine where it sees a trailer plugged in... and adjust the charging voltage accordingly...

This is the pits having to run the gen set.... my old truck would by the end of the day fully charge the batteries...

Thanks ... Jim

 

[Tuesdak]

Recall you ran the 6 gauge wire on the other truck because factory wire to the trailer plug is too small to pass enough current to charge trailer batteries. Don't forget to upgrade the ground wire size from the plug(s) to the frame(s) as well.

I am not clear if your voltage readings are with the trailer plugged in - and if so it's indicating an open or high resistance connection between the trailer plug and the trailer batteries on the charge wire. Again you may just be seeing the small wire being the resistor to the amount of current the batteries want to charge.

 

[Sixpak]

Recall you ran the 6 gauge wire on the other truck because factory wire to the trailer plug is too small to pass enough current to charge trailer batteries. Don't forget to upgrade the ground wire size from the plug(s) to the frame(s) as well.

I am not clear if your voltage readings are with the trailer plugged in - and if so it's indicating an open or high resistance connection between the trailer plug and the trailer batteries on the charge wire. Again you may just be seeing the small wire being the resistor to the amount of current the batteries want to charge.

 

[grabinov]

Hey Jelag,

The reason to run bigger wire is, as mentioned, to pass more CURRENT. The VOLTAGE reading will be the same with a 6. 12 or other gauge of wire. So for now, don't worry about wire gauge. First you need to get voltage TO the RV from the truck. If you are reading alternator voltage (13.5v or so) at the trailer plug, the. Check to see if you have that same voltage at the trailer side of that connection. Follow the trailer electricl cable from the connector on the truck all the way to the electrical box where it connects on the trailer. Usually the cable will be split out there to provide the different signals - turn left, turn right, brake, charging... check for the same 13.5 volts there.

From there you Still may have a fuse, or a bad connection , in the wire that runs to the trailer battery bank. Just follow the 13.5 volts back from the truck till you lose it, then find out why. My guess is a blown fuse or a bad connection. I have never seen a well-wired trailer in my life, except where an owner took out the factory garbage and did it himself, correctly!

Greg

 

[jelag]

Guys.. my 5er has upgraded wires to the connector (12+ & -) We like to have some comfort and conveniences in the RV thus the large battery bank.. I guess I'll just have to add to the truck wiring to the trailer connector...

I know on my 05 I still fought getting the batteries up... it was always a lot easier when we were in cold weather as the ECM allows for a higher charging voltage... I just didn't want to run the gen set as often.. that's all... thanks for your thoughts..

 

[Bob4x4]

I prefer Boondocking so I have solar panels-charging is no issue for me with the Airstream since adding the panels

 

[B.G. Smith]

The biggest reason you are not getting a good charge in the RV battery bank is the alternator is regulated by the truck battery voltage. shortly after you start up the computer cuts the alternator back and the voltage differential between the truck and RV batteries is so small that it would take many hours to recharge your battery bank.In the old days a cab over camper fo instance with an extra battery would/might have a switch that you could switch to which battery you wanted to charge (truck or camper) and it would also switch the voltage sensing wire to the battery being charged. bg

 

[RustyJC]

We normally RV with full hookups, so our RV batteries stay pretty well charged from the RV's power converter. We do have a residential fridge, however, that's powered by the RV's batteries through a dedicated 1500 watt PSW inverter when we're on the road. The factory +12VDC charging circuit keeps the RV batteries charged up very well while we're traveling, and I never have any problems with low RV batteries powering the hydraulic levelers or slideouts at the end of a travel day. While the factory circuit may not be able to charge up heavily discharged batteries, it does a good job of maintaining a charge on fully charged batteries.

Rusty

 

[AEdelheit]

As others have mentioned I would check the trailer first, for me I would start at the trailer battery's, unhook the charge wire coming from the truck and check voltage. You should see same voltage as the truck, since there is no load wire gauge will not come into play, if the voltage is low then there is a wiring issue other then wire size.

6 batteries is a lot but all the truck has to do is maintain them, unless you really run them down low I feel the truck should be able to keep them maintained even with the factory gauge wire.

 

[Kirwin]

My experience is that the truck will only charge 4-6 amps to the trailer. So you will only get about 50 Amp-hrs charged to the trailer in a 10 hour drive. If you have anything on in the trailer, subtract that amount of Amp-hrs off the 50. The truck circuit will maintain the battery state of charge but will not recharge a discharged battery.

 

[Kirwin]

Keep in mind that trailer battery voltage will never equal truck alternator voltage if the batteries are not in a equilibrium state of charge. As long as you have current flow, battery voltage will be lower than alternator output voltage. If possible, with the tailer batteries topped off by an external charger, plug the trailer connector into the truck, disconnect shore power, start the truck and check voltage. With no 12 volts loads on in the trailer, and the batteries fully charged, you should see the same voltage on the truck batteries and the trailer batteries. Now turn on a large 12 volt load in the trailer and watch trailer battery voltage. They should start out equal, but the load will pull more current from the trailer batteries and trailer battery voltage will lower until the truck is exactly charging as much as the load is pulling from the trailer 12 volt system. This shows up in a voltage difference between the truck and the trailer that drives this current flow. Turn off the load and the truck will continue to recharge the trailer batteries, and trailer voltage will recover as the batteries return to a fully charged state. Depending on the amount of discharge, this can take a long time since the charge rate is only roughly 5 amps.

 

[Road Dog]

The truck computer is adjusting the voltage to charge the truck batteries so any charging of the trailer batteries is a side effect. Once the truck batteries are charged then it's simple trickle charging.

The best approach if you really want to charge on the road is a power converter and run 120V AC back to the trailer where a separate charger will maintain the trailer batteries. In that case, disconnect the +12V from the trailer connector.

 

[RustyJC]

The truck computer is adjusting the voltage to charge the truck batteries so any charging of the trailer batteries is a side effect. Once the truck batteries are charged then it's simple trickle charging.

The best approach if you really want to charge on the road is a power converter and run 120V AC back to the trailer where a separate charger will maintain the trailer batteries. In that case, disconnect the +12V from the trailer connector.

I believe you're recommending an inverter. A converter converts 120VAC to 12VDC; an inverter converts 12VDC to 120VAC.

Rusty

 

[AussieRam]

View attachment wire sizing.pdf
Hi Jim,
Greetings from Australia. I have just been working through a similar issue with my now 5 month old Ram Laramie 2500 4x4. My caravan is set up with 3 x 120amphr 12 voltage AGM batteries, these can be charged from fixed solar panels on the caravan roof through a solar regulator, or a 40 amp 240 volt battery charger, or a 12 voltage input from the tow vehicle. I also have an additional 12 voltage AGM battery in the RAM to provide power for a fridge and lighting for times when we want to camp in spots where the caravan won't get to.
The main issues are getting the wire size right, and getting around the ECM controlling the output voltage from the alternator. I have run 6 AWG cable for both positive and negative, with 40amp fuses in line, and use a 50 amp rated Anderson Plug to connect to the caravan. This fixes the issue with voltage drop, and resistance at the connection.
I have attached a file with better technical explanations.
The best way I have found to get around the alternator voltage is using a 12 volt DC/DC charger.
The link below gives details on this set up.

https://www.baintech.com.au/can-i-use-a-ctek-d250s-dual-in-a-vehicle-with-a-smart-alternator

Hope that this helps.

Trevor

 

[Road Dog]

I believe you're recommending an inverter. A converter converts 120VAC to 12VDC; an inverter converts 12VDC to 120VAC.

Rusty

I refer to all of them as power converters. There's DC - DC converters, AC - DC converters, DC - AC converters. Each industry comes up with it's own names. For RVs I've seen them called charger/inverters and charger/converters. Both charge the batteries and provide 120VAC to the plugs.

 

[RustyJC]

I refer to all of them as power converters. There's DC - DC converters, AC - DC converters, DC - AC converters. Each industry comes up with it's own names. For RVs I've seen them called charger/inverters and charger/converters. Both charge the batteries and provide 120VAC to the plugs.

In the RV industry, converters change 120VAC to 12VDC while inverters change 12VDC to 120VAC. Calling an inverter a converter to someone in the RV world only leads to confusion.

https://www.youtube.com/watch?v=B6bktF574IA

Rusty

 

[jelag]

I'm really amazed that most of you have offered my thoughts in my first post.. where on my 05 I had altered the wiring, and understand the issues with the ECM... I guess I was hoping for a work around that might be more functional... thanks for all your thoughts...

Aussie Ram... I had a chance years ago to travel to your country on business.. I worked with a wonderful gent in Wynnum QLD... and travel down the coast..

But I'd not considered the use of an inverter and sending 120vac back to a simple charger... or converter...

Thanks for all your thoughts..

 

[TCDiesel]

I quick using all the Small Gauge Wiring years ago, Here's picture of the cable we have been using for over 20 years, in the bed look to the right its the red plug-in. it 1/0 AWG the real spendy stuff bought at sound waves. the cable also has 250amp breaker installed. You do need to be careful on grounding the vehicle and vehicle to trailer ground. (Or you will have a fire) this pig tail has both ground cable 6AWG and hot Cable 1/0 AWG .. I use it for multi tasks, all our trucks have both Male and Female connections. This setup been in use for 20 years..early on we did not ground the vehicle correctly and it started a fire in the cab and burned the truck to the ground. Ford replace the truck BC they thought it was their issue with the ground cables under the dash.

 

[SnoKing]

I'm really amazed that most of you have offered my thoughts in my first post.. where on my 05 I had altered the wiring, and understand the issues with the ECM... I guess I was hoping for a work around that might be more functional... thanks for all your thoughts...

Aussie Ram... I had a chance years ago to travel to your country on business.. I worked with a wonderful gent in Wynnum QLD... and travel down the coast..

But I'd not considered the use of an inverter and sending 120vac back to a simple charger... or converter...

Thanks for all your thoughts..

Jim, with that much battery capacity the truck is not going to be much help. Time for solar system. Go to Quartzite and get solar install. People there are good at it.

Send me a PM with an email address, and I will send you a nifty spread sheet I created to help manage/understand amp hours. It can be set to different amp hour totals and computes the table. Do you have a decent amp hour meter installed. https://www.jamestowndistributors.c...bLMOD6oNV0Dkmni5rLzPmCH0RC_GlB0k6NRoClQTw_wcB

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[jelag]

I've got 4 new solar panels sitting at home that came off a surplus pile at a spot where I worked as a volunteer.. 120 W @ 18 vdc each, Panasonic's as I remember.. I just need to get it done... I was just needed more spare time in retirement....

Thanks for your thoughts...