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Old 01-05-2019, 08:06 PM   #15
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So Tuffr2 is right, it's a good thing....2 is better than 1.
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Old 01-06-2019, 05:19 PM   #16
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How many batteries do you have? You may have split systems with one alternator per battery
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Old 01-06-2019, 05:40 PM   #17
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My F-450 had two alternators, two batteries and the snowplow package.
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Old 01-06-2019, 08:12 PM   #18
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How many batteries do you have? You may have split systems with one alternator per battery
I believe there is but one battery under the hood, but I'll double check. Of course I'll have at least 2 in the RV, but I doubt the wiring to the RV connector is heavy enough to do very much.
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Old 01-06-2019, 08:27 PM   #19
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I believe there is but one battery under the hood, but I'll double check. Of course I'll have at least 2 in the RV, but I doubt the wiring to the RV connector is heavy enough to do very much.
Your Duramax will have 2 batteries. One is kinda hard to see on passenger side as it's kinda hidden by fuse block or something. That one probably not the easiest to change LOL!!

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Old 01-09-2019, 08:38 AM   #20
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To answer your initial question, yes, they supply a charge to a common system simultaneously. DC supplies a charge to the buss and and is either on or off, similar to how your batteries are connected to a common buss. The voltage regulators in each alternator are usually set to somewhere around 14V to charge you batteries and keep the systems in the vehicle running. Essentially, when the vehicle is running, the alternator is powering everything and the battery is just there to provide starting power and accessory power when the engine is shut off.
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Old 01-09-2019, 07:22 PM   #21
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Yeah my Ram has two alternators and two batteries and since Iím running a residential fridge in my fifth wheel Iím hoping it keeps the Creeks batteries charged up.
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Old 01-09-2019, 09:31 PM   #22
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Former heavy truck electrical engineer here... The alternators are in parallel attached to the same system. Basically, if you have two 150amp alternators it acts like one single 300 amp alternator. Generally, this is for vehicles that have extra electrical demand (emergency vehicles with lots of lights, computers, radios, or things that use electric motors).

Does it charge up your RV batteries faster? Sort of... Trailers are limited by the size of the wiring to the trailer. More amps available will not change the voltage drop cuased by long and small wires. On an RV if there is a large cable from the alternator to the batters (like under the hood of your truck) then you get faster bulk charging (the charge between 0 and 85% of capacity). After the batteries are 85% full, the batteries won't charge any faster from a larger (or dual) alternator.

So the purpose of dual alternators is to run all the extra stuff attached to the vehicle. Alternators need to be sized to run the vehicle. Batteries are only to start the vehicle. If the alternator is too small to run the vehicle, then eventually the vehicle will die because the battery will eventually get depleted.

If you look at diesel trucks today, most have 150 amp alternators just to operate themselves. There is a lot of electrical load in today's vehicles and especially with diesel emissions equipment. Thus, any truck that might have extra electrical vocation usually gets a larger or dual alternators.
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Old 01-10-2019, 07:11 AM   #23
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Dealer service dept said my truck does have 2 batteries along with 2 alternators. He said not to mess with the one on the passenger side. If I wanted to add or modify anything, to use the one on the driver side.
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Old 01-10-2019, 08:25 AM   #24
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Yes it will help charge your RV batteries better....if you have a larger cable running to the back to charge the batteries. The factory wire in the 7 pin plug is I think a 10 gauge with 30 amp fuse. That's a decent size but with the losses in the plug and such will take a long time to recharge 1 battery, let alone a bank of batteries.

As for how its wired, I think I read both alternators are supplying juice to one central source. It's an option available to supply extra power for things like a snow blade or dump bed and such. Also, with a thick gauge cable to the RV, would be handy to recharge a battery bank fast.

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Iíve thought about doing this. Does anyone know what electrical equipment would be needed besides heavier cable? Given that itís a long run back to the trailer, what gauge cable and would it even be worth it?
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Old 01-10-2019, 07:45 PM   #25
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Iíve thought about doing this. Does anyone know what electrical equipment would be needed besides heavier cable? Given that itís a long run back to the trailer, what gauge cable and would it even be worth it?
My truck is wired for my gooseneck dump trailer. I used 4 gauge wire from battery to bed with a 100 amp circuit breaker to protect it. I bough a set of blue plugs at NAPA like a tow truck uses with jumper cables to connect at the hitch and goes to the battery in the trailer. When I'm using the dump trailer and its loaded ( like 5.5 ton of gravel) it makes the alternator gauge drop down to below 12 volts on the truck so yes its pulling some juice. This would charge your camper batteries very quickly.

Between the plugs and wire and circuit breaker I probably have $125 to get to the trailer with 100 amp line. If you're gonna be dry camping any I'd think this would be a well worthwhile adventure especially since you have dual alternators.

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Old 01-10-2019, 08:21 PM   #26
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Thanks! Another question - What would be needed to keep the trailer from draining the truck batteries should I forget to disconnect the trailer?
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Old 01-10-2019, 09:02 PM   #27
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Several issues to remember in terms of charging house batteries in a trailer from your tow's alternator.
1. The alternator's output is limited by the charge state of the truck's electrical system. It does not known there's another battery in the trailer, its only another 12v load.
2. To charge most lead-acid batteries you need something like 14.2 to 14.4 volts. Anything lower is good for float and running 12 volt equipment in the trailer.
3. Voltage drop should be limited to 2% or less.
4. Voltage drop is largely depended on the round trip distance from the tow's battery and the trailer's battery (hot & ground wires) and the starting voltage. In my 5th that is about 40ft each way (80 ft total).
5. In many factory installs the hot and ground wires are 10 gauge. In my truck the running voltage is typically 14.4 volts. Thus at the house batteries I see about 12.8 volts on that hot lead from the truck. That's not going to recharge a low house battery.
6. In order to get into the 14.2 to 14.4 volt range required I would need 1/0 or 2/0 wire. Very big and heavy stuff to be running.
7. In a MH all of this changes because of the proximity of the various components.

Here's a link to a DC voltage drop calculator:
https://www.calculator.net/voltage-d...s=20&x=90&y=13

Bottom line do not expect to recharge house batteries in a trailer. You probably can operate limited amount of 12v equipment from the tow's electrical system.
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Old 01-11-2019, 03:20 PM   #28
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So that all sounds complicated and not likely that I would be charging a low battery during haul trip to next campground. After a night or two at a full service camp site with 50 amp or 30 amp connection, would the battery be fully charged for the trip. I just need to make sure the frig runs til the next plug in. As an option, I ordered the Onan 5.5KW generator. Should I run the genny for a bit before leaving for the next site? I'm assuming that running the generator will charge the house batteries.
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