Charge trailer batteries with alternators

austingta · September 11, 2016

I have dual alternators which are advertised to provide 380 Amps, and would like to use some of that to charge the batteries I plan to have in my travel trailer. I cant imagine I can get much current through the 12VDC+ pin in the trailer connector. What is the best way to access all this charging ability? Do I need to pull the power off my truck batteries and let the alternators recharge them, or is there a more direct way?

TIA

Dirtbiker · September 11, 2016

Your truck should be charging the batteries automatically. Mine always has as far as I know. The brain in the trailer should recognize when the truck is hooked up and let the charge go to the batteries in the trailer. Somehow it knows not to drain the truck battery when just sitting though. Unless all the batteries get drained maybe? I have never left it hooked up for very long.

EricV · September 11, 2016

The issue is not the amps you have but the length of wire and power loss from the truck to the trailer. It won't be enough to charge them much if at all. The best thing is a DC-input battery charger. It will give the trailer batteries the full charge. something like this http://www.powerstream.com/DCC.htm

sdeeter19555 · September 11, 2016

Or run a heavier wire from the truck batteries to the rear plug...it's something like 10ga now, something nearer to 6 or 4ga would carry enough to charge batteries on the move.

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rocnrol · September 11, 2016

Doesn't matter what you put to the trailer for power, the built-in charger in the trailer is a trickle charger and only charges so fast. Plugged into the truck or a 110VAC plug makes no difference.

So you understand, vehicles don't run off of the altinator, they run off of the battery, and the altinator tops up the battery. The addition of a second altinator allows you to add significantly more accessories and keep the battery topped up.

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sdeeter19555 · September 11, 2016

Unless his is different, mine is battery to battery, no charger?

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jhplak325 · September 12, 2016

Doesn't matter what you put to the trailer for power, the built-in charger in the trailer is a trickle charger and only charges so fast. Plugged into the truck or a 110VAC plug makes no difference.

So you understand, vehicles don't run off of the altinator, they run off of the battery, and the altinator tops up the battery. The addition of a second altinator allows you to add significantly more accessories and keep the battery topped up.

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Built in charger on trailers only comes into play when plugged into 110.

When plugged into a vehicle, then the trailer battery gets charged off of the vehicle battery.

And yes, vehicles do run off the alternator, batteries are used to start and to be a load balancer. You ever drive a vehicle with a bad alternator? They don't run vary long.

Colossus · September 12, 2016

The alternator isn't meant to be a charger, but rather a maintainer. As long as you are not running the batteries down requiring a lot of demand on the alternator, I don't see an issue.

austingta · September 12, 2016

In the old days, I know that alternators ran accessories and charged the batteries. You could start the car, disconnect the battery and the car would still run just fine. That was a way we would test the alternator or voltage regulator in the driveway.

I also know those days are over, and the battery is an integral part of the vehicle electrical system.

My idea was that I might be able to install a battery array in my RV to avoid the necessity and operating expense of buying a generator. I would like to be able to run the AC while boondocking.

Since I have 380 A @ 12VDC of charging capacity, it should be possible to run a set of batteries for a long while and start the truck and recharge them.

Maybe I should just invest in some big battery cables, run it to the trailer, and start the truck (maybe even activate the fast idle switch) and run it for a couple of hours to recharge the batteries?

BTW It seems the LML uses .5 GPH at idle which is significantly less that a generator even just for fuel. .

kstruckcountry · September 12, 2016

I've seen heavy cables run from the front of the truck, for powering a dump trailer. With what the cables would cost to effectively put out power, it may well be cheaper and easier to get a generator.

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waumo1 · September 12, 2016

My 2011 has a 30 amp circuit to the trailer connector (after I hooked it up). I think this would charge the trailer batteries in most cases on a long drive. Your trailer connection should have an isolator so as not to deplete the truck battery. I would definitely use a 120VAC charger when available. That said I don't use a trailer with batteries so maybe I missed something here.

vertigo · September 12, 2016

If you try to run the AC ( which is either 13k BTU or 15k BTU ) off of the batteries, you wont be able to do so for very long, if any. Which would make the added batteries and electrical connections rather worthless.

IMHO, if I were going to be boon docking, for any length of time or on a regular basis. I would go with solar to help keep your batteries charged.

austingta · September 13, 2016

I've seen heavy cables run from the front of the truck, for powering a dump trailer. With what the cables would cost to effectively put out power, it may well be cheaper and easier to get a generator.

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This reminded me that I do this with a big Warn winch I have welded to a ball mount. Pop it in and hook up the trailer and go get something. And I can use it on any truck.

But I digress...seems a good option is buy a big inverter and connect it to my batteries, and let it idle all night. I do have the fast idle switch option if I need to excite the alternators. Plug the RV into the inverter and I can have the same 120VAC power @ 5000 watts that the generator would provide, without the noise or purchase price or fuel use of the generator.

I'm looking into the nuances of this but I like it so far.

aeblank · September 14, 2016

You need to get on some rv forums. Irv2.com or similar. Talk about what you are trying to run, your goals, and the like. Idling your truck all weekend is not good.

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timdan94 · September 14, 2016

I can tell you that idling the LML for a long period of time will plug the DPF. The truck has to be run at above 30MPH to clean out the DPF. This is right out of the LML manual...

9-12 Driving and Operating Diesel Particulate Filter The vehicle has a Diesel Particulate Filter (DPF) as part of the exhaust system to reduce vehicle emissions. The DPF requires a unique exhaust tailpipe with an exhaust cooler. The exhaust cooler mixes air with the exhaust to lower the temperature before it leaves the tailpipe. The DPF, the tailpipe, or other exhaust system components must not be altered. Inspect regularly and clean any mud or dirt from the exhaust cooler, especially where the exhaust cooler connects to the tailpipe and the openings where fresh air enters the cooler. The DPF will clean itself as part of normal operation. Several factors including fuel consumed, hours of engine operation and miles driven are monitored by the Engine Control Module (ECM). The self-cleaning occurs approximately once per tank of fuel. { Caution Permanent damage can occur to the DPF or related components if the required Ultra Low Sulfur Diesel (15 ppm sulfur maximum) or low ash CJ-4 engine oil is not used. This damage would not be covered by the vehicle warranty. Under certain driving conditions, such as stop-and-go traffic, the filter cannot clean itself. A message comes on when the DPF is dirty and needs to perform a self cleaning. See Diesel Particulate Filter Messages on page 5-14. For the filter to clean itself, the vehicle must be driven above 50 km/h (30 mph) until the message goes off. This will take about 30 minutes. See Diesel Particulate Filter Messages on page 5-14. { Warning During DPF self cleaning or during extended idling in P (Park), the exhaust system and exhaust gases are very hot. Things that burn could touch hot exhaust parts under the vehicle and ignite. You or others could be burned. Do not park, or idle for an extended period of time, near or over papers, leaves, dry grass, or other things that can burn. Keep the exhaust area clear of material that could ignite or burn. See Parking over Things That Burn on page 9-11 for more information. { Caution Extended idle should be avoided because the DPF system is not capable of self cleaning at idle. (Continued) Chevrolet/GMC Duramax Diesel Supplement (GMNA Localizing-U.S./Canada- Black plate (13,1) 7132827) - 2015 - CRC - 10/21/14 Driving and Operating 9-13 Caution (Continued) During extended idle operation, monitor the instrument cluster telltale lights and Driver Information Center for messages and take appropriate indicated action. Continued idling with the warning light/message on could cause irreversible damage to the DPF requiring repair and possible replacement that might not be covered by the vehicle warranty. You will also notice a change in the exhaust sound and engine idle speed. This is normal. See Vehicle Messages on page 5-12. If you continue to drive with the DPF warning message on and the exhaust filter is not cleaned as required, the malfunction indicator lamp and the ENGINE POWER IS REDUCED message will come on and dealer service is necessary. See Malfunction Indicator Lamp on page 5-8 and Engine Power Messages on page 5-13. Vehicles with DPF have specific fuel and engine oil requirements. See What Fuel to Use in The U.S. on page 9-22 or What Fuel to Use in Canada and Mexico on page 9-26 and Engine Oil on page 10-6 for more information on those requirements. Extended idling in P (Park) can cause exhaust parts and gases to become very hot. Keep the exhaust area clear of material that could ignite or burn. See Parking over Things That Burn on page 9-11. If equipped with a Power Take-Off (PTO), monitor the instrument cluster for lights related to the DPF. See Accessories and Modifications on page 10-1 for important information if you are considering adding accessories or modifying the vehicle.

This reminded me that I do this with a big Warn winch I have welded to a ball mount. Pop it in and hook up the trailer and go get something. And I can use it on any truck.

But I digress...seems a good option is buy a big inverter and connect it to my batteries, and let it idle all night. I do have the fast idle switch option if I need to excite the alternators. Plug the RV into the inverter and I can have the same 120VAC power @ 5000 watts that the generator would provide, without the noise or purchase price or fuel use of the generator.

I'm looking into the nuances of this but I like it so far.