Alternator Output to charge RV Batteries

[shayne.bates]

Summary: Seeking advice on how to custom wire a high capacity charge cable to my RV to use the large capacity of the RAM alternator, to charge ten deep cycle batteries while traveling.

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Questions:

1. How much is a safe current to load the alternator to, in addition to the truck requirements? Is a 50-80A (extra) feed to the RV reasonable and attainable?

2. How much current does the RAM 3500 dually need when running? (including 3 axles of RV electric brakes and a periodic switch on of a truck mounted air compressor (32A peak) which drives three train horns)

2. What is the present limit of the 7 pin trailer wire (assuming 30A?)

3. What is the best wiring method to install a higher capacity charge circuit?

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USE CASE:

Often stop overnight at Walmart and other locations while traveling the country and frequently use a 7,500W Cummins Onan quiet diesel generator. It occurred to me that the huge capacity in the tow behind electric golf cart could be utilized each night to power an extra mains inverter for the TV's and computers, while extending the capacity of the existing setup. All the batteries could then be charged up by the RAM alternator as we drive, so that the generator may be used somewhat less.

The present GC charger starts charging at 35 AMPS and reduces as the batteries become charged. Since I will have 3 sets of batteries 3 x 35A would be a total of about 100 Amps to charge the batteries at the same rate. A charge rate of somewhat less would also be OK.

The truck is a 2015 RAM3500 Laramie dually, with 180A alternator and would like to use as much of it's capacity to charge ten (yes ten), deep cycle batteries in my 5th wheel towed behind, and need to devise a high capacity, custom charging circuit that will not overload the alternator, but can use the plenty of capacity it has (180A).

The 7 pin connector is presently plugged into the rear LHS of the bed and charges the two existing Batteries in the 5th wheel which are in parallel.

I'm planning to add extra batteries to the 5th wheel increasing from 2 to 10.

One bank will have four batteries to run the existing 2,000 W inverter powering the refrigerator and 12V lights etc, and the other bank of six will be added to allow for a second 2,000W inverter to be installed and run the TV's and computers. Would like to have them all in parallel as one bank of ten.

Seeking info about max charging current from the alternator, and how I should install a dedicated wire run to charge the batteries. One other forum suggested a relay from the 7 pin with the heavier circuit run from the truck (where?).

Would appreciate more info. A detailed description of the intended setup is contained below:

Setup:

(1) The existing two batteries are interstate deep cycle about 600 CCA and 95 AH each.

(2) Planning to add two more in parallel to make four. The new two are new RAM batteries since I upgraded to AGM style batteries. The RAM batteries are about 650 CCA and 80AH each

(3) We also have a tow behind Golf cart with 6 x 6V, 208AH batteries. By installing battery switches and some circuit protection, I plan to use the GC batteries which will be three sets of twelve volt (6v+6v) batteries in parallel. This adds 1,248 extra AH (6 x 208AH) to the present total of 340AH to a new total approaching 1,600 AH

(4) Have already installed a zero gauge (0 AWG) set of copper cables from the trailer behind the RV, through to the front of the battery area. These are rated up to 250A. The expected extra load is an average of 300 Watts, or 25A - about 8 amps from each of the three battery sets. The peak load briefly to run a toaster etc will be 1800 Watts for about 5 minutes, which is about 150 Amps, or 50A per battery set. These batteries can easily run 180A when they drive the Golf Cart. Planning to install a 3 pole 60A breaker on each of the three parallel batteries to limit the total output to something between 2000-2500 watts.

Thoughts appreciated. This is a complex project with several stages. The 250A cable is in place, the Golf Cart voltage changing circuit is designed, and I am now thinking about the charge from the RAM, so any input is appreciated.

 

[CherryRed]

A few thoughts that come to mind.

What is the duty cycle of the 180A alternator. Can it be expected to run at or near full capacity and live a long life.

What engine RPM is required to get maximum output from the alternator.

Running the alternator at a high capacity will put a large parasitic load on the engine. Cummins has a lot of power, but you will take a hit in fuel mileage.

It would almost seem easier to add a second alternator under the hood (if there is space for one...) and run it as a separate charging system. Leece-Naville has a large selection of commercial grade alternators.

 

[BossHogg]

Summary: Seeking advice on how to custom wire a high capacity charge cable to my RV to use the large capacity of the RAM alternator, to charge ten deep cycle batteries while traveling.

I don't have specific answers to your questions since I've never attempted to do what you are doing. I can tell you that the amount of current flow will be determined by the difference in battery voltage between the RV and the truck with respect to voltage drop. The lower the RV battery voltage is compared to the truck's provided power feed determines the current flow.

I have wired in a power feed to the rear of my truck to support a winch on my flat bed utility trailer, wiring kits are available from etrailer (https://www.etrailer.com/p-sw2008.html) for example. The wiring kits provide nice quick disconnects.

For tapping power to a battery under the hood, you should review RAM's up-fitters guide (Ram Body Builder's Guide - Start Building an Upfit Ram Truck), this guide explains the proper place to tap the battery and which battery to tap. This is important because you need to tap before the battery sensor.

Please post back your solution, I'm interested.

 

[Jimmy68]

A truck set up for towing already has a charge wire in the 7 wire RV plug.
We have a few customers with mobile lighted signs and those trailers have like a dozen deep cycle batteries in them.
They charge just fine being pulled behind they're cars, SUV's and trucks.

 

[csuder99]

Questions:

1. How much is a safe current to load the alternator to, in addition to the truck requirements? Is a 50-80A (extra) feed to the RV reasonable and attainable?

2. How much current does the RAM 3500 dually need when running? (including 3 axles of RV electric brakes and a periodic switch on of a truck mounted air compressor (32A peak) which drives three train horns)

2. What is the present limit of the 7 pin trailer wire (assuming 30A?)

3. What is the best wiring method to install a higher capacity charge circuit?

This might not be what you want to hear but here's the conservative engineering answer:
1. Zero. The standard alternator can supply the needed current for the vehicle plus a trailer with electric brakes *in all conditions*. Sure, during the day in moderate climate you have might have 40+ amps reserve but going up a grade in hot weather with the lights on is going to cut into said reserve.
There is a 220A alternator option for application like yours with added current requirements.

2. See above. It won't max out the alternator most of the time but at times it will get close.

3. Actually 20A looking at the wire gauge.

4. Two options: Use the higher capacity alternator (not sure if that's a drop-in) and run a properly sized (2 AWG), fused wire from the battery to a separate connector in the back. (similar to this: NOCO SHOP - 50V / 600A, SMH SY175 Breakaway DC Power Connector) this would get you some 40-odd amps for charging.
Or add a second alternator (mounting parts should be available from RAM special equipment vehicles) which could yield 100+A. Again 2 AWG and high current connector.