Dual Alternator Option on Tow Vehicle

DirtyMax88 · Feb 6, 2015

Good afternoon Everyone,
We are looking at a 2015 GMC Sierra 3500HD Denali, Duramax/Allison set up, with the option of dual alternators, 150 and 220 amp. Would it be worth it to get this option, and how much does your trailer actually draw from your truck when hooked up? I know you will just run some of the basic things, so I wasn't sure if the dual setup was necessary? We are new to this size of a trailer with this many bells and whistles, so I don't know how much it will draw when it's hooked to the truck. Also, can the trailer's batteries be charged by your trucks alternator(s) (with direct wiring, I would assume) Any info is appreciated! Thanks!

fredwrichardson · Feb 6, 2015

It all depends on what you are powering in the trailer. We have a Samsung residential refrigerator and we want to keep it on as we go down the road. The refrigerator is powered by an inverter that gets it's power from the house batteries. So we have the second alternator so that we can keep the batteries fully charged and also run our refrigerator. Also you do not need direct wiring in the newer RVs. They are wired so that the batteries can be charged by the truck using the 7 wire electrical connect.

If you have a propane / electric refrigerator then you could get by without the extra alternator.

DirtyMax88 said:
Good afternoon Everyone,
We are looking at a 2015 GMC Sierra 3500HD Denali, Duramax/Allison set up, with the option of dual alternators, 150 and 220 amp. Would it be worth it to get this option, and how much does your trailer actually draw from your truck when hooked up? I know you will just run some of the basic things, so I wasn't sure if the dual setup was necessary? We are new to this size of a trailer with this many bells and whistles, so I don't know how much it will draw when it's hooked to the truck. Also, can the trailer's batteries be charged by your trucks alternator(s) (with direct wiring, I would assume) Any info is appreciated! Thanks!

branson4020 · Feb 6, 2015

It may be just my rig, but there is so much voltage drop in my factory trailer-tow wiring harness that I can't get much more than 8A (by actual measurement) to the coach batteries, so for me the extra alternator wouldn't do a thing.

wdk450 · Feb 6, 2015

My towing charging circuit has a 25 amp fuse, and unless you have some welding cable from the alternators to the truck rear bumper, and a special high-amperage connector to the trailer's wiring, you aren't going to get very much current back to the trailer's battery system.

The original idea of the charging line from the tow vehicle to the trailer was to keep the trailer battery charged up enough in event of a truck-trailer disconnection, the emergency lanyard switch would have enough trailer battery current available to energize the trailer brakes and stop it in its tracks. Some people wanting to run refrigerators etc. have rewired their trucks with direct, high current 12 volt DC AND GROUND cables, using a higher current connector separate from the 7 pin standard one.

As to number of amps, remember that the built-in AC powered charger/converter in the trailer puts out about 60 amps maximum, and is usually just loafing along at less than 10 amps.

370 amps of 12 volt power? Maybe you could do some emergency arc welding with the truck.

Mburtsvt · Feb 6, 2015

DirtyMax88 said:
Good afternoon Everyone,
We are looking at a 2015 GMC Sierra 3500HD Denali, Duramax/Allison set up, with the option of dual alternators, 150 and 220 amp. Would it be worth it to get this option, and how much does your trailer actually draw from your truck when hooked up? I know you will just run some of the basic things, so I wasn't sure if the dual setup was necessary? We are new to this size of a trailer with this many bells and whistles, so I don't know how much it will draw when it's hooked to the truck. Also, can the trailer's batteries be charged by your trucks alternator(s) (with direct wiring, I would assume) Any info is appreciated! Thanks!

How much is the option? On my Ford it was only $380, (after the discount off of MSRP for the truck it came to $288.00). I do not think this was a bad deal. It will add resale value to the truck when I sell it.

Jim.Allison · Feb 6, 2015

You should have a higher amperage alternator in lieu of a dual alternator system. I Have a battery bank for a solar array, and my alternator is more than adequate for my system. The Dual alternator system is more for ambulances and utility vehicles where the alternators get a workout during long idle periods with multiple accessories.

I wanted the dual alternator system but now that I know more, I would not buy the option, primarily to avoid maintenance.

DirtyMax88 said:
Good afternoon Everyone,
We are looking at a 2015 GMC Sierra 3500HD Denali, Duramax/Allison set up, with the option of dual alternators, 150 and 220 amp. Would it be worth it to get this option, and how much does your trailer actually draw from your truck when hooked up? I know you will just run some of the basic things, so I wasn't sure if the dual setup was necessary? We are new to this size of a trailer with this many bells and whistles, so I don't know how much it will draw when it's hooked to the truck. Also, can the trailer's batteries be charged by your trucks alternator(s) (with direct wiring, I would assume) Any info is appreciated! Thanks!

SeattleLion · Feb 6, 2015

We looked at the dual alternator option for our Ford 350. Its really intended for auxiliary equipment that needs a lot of current. We have the Ford heavy duty alternator and dual batteries. That's more than enough for the diesel and the trailer. The wiring from the truck to the 7 pin harness isn't all that heavy. If all you want is to do is run power through your hitch, you won't need two alternators.

mountainlovers76 · Feb 6, 2015

You really do not need dual alternators, just go with the higher amp single. I have a 2008 GMC Sierra 2500HD and pull a 2014 Landmark with residential refer and have never had a problem with the single alternator keeping the coach batteries fully charged when traveling.

Seren · Feb 6, 2015

We have a 2014 3500 Denali and pull a Landmark and have had no problems with our residential refrigerator. Love the Denali.

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ILH · Feb 6, 2015

I have the dual setup on my truck. While the dual alternators aren't required, the dual batteries have been nice during deep draws on the system and also really cold winter starts.

jeffdee · Feb 7, 2015

I found the posting below at the Ford Truck Enthusiast forum site. It pretty well explains the function of two alternators in the Ford Super Duty trucks:

From Workshop Manual:
Principles of Operation
The PCM controlled single/dual charging system determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. This system is unique in that it has 2 communication lines between the PCM and the generator/regulator. Both of these communication lines are pulse-width modulated (PWM). The generator communication (GENCOM) line communicates the desired setpoint from the PCM to the voltage regulator. The generator monitor (GENMON) line communicates the generator load and error conditions to the PCM. The third pin on the voltage regulator, the A circuit pin, is a dedicated battery voltage sense line.
The generator charges the battery and at the same time supplies power for all of the electrical loads that are required. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm. The PCM is able to adjust the charging voltage according to the battery temperature by using a signal from the intake air temperature (IAT) sensor. This means the voltage setpoint is calculated by the PCM and communicated to the regulator by the GENCOM circuit.
The PCM simultaneously controls and monitors the output of the generator. When the current consumption is high or the battery is discharged the PCM raises engine speed to increase generator output.
In dual generator systems, the PCM keeps the secondary generator in a standby state where it does not generate current unless the primary generator is generating full power and more current is needed to support the vehicle loads. The PCM monitors the output of the primary generator and adjusts the control setpoint of the secondary generator to cause it to provide additional current when needed.
To minimize the engine drag when starting the engine, the PCM does not allow the generator to produce any output until the engine has started. The PCM turns off the generator during cranking to reduce the starter load and improve cranking speed. Once the engine starts, the PCM slowly increases generator output to help establish a stable engine speed.
The PCM controls the charging system warning indicator by sending a message over the high speed CAN to the instrument cluster (IC). The PCM turns the charging system warning indicator off when generator output begins. The charging system warning indicator is also illuminated by the PCM whenever the key is ON with the engine OFF.

Some of the comments with respect to one vs two alternators was that replacing the single, heavy duty alternator was much more expensive than replacing one or both of the dual alternators. The dual setup uses a commonly stocked 130 amp alternator.

TandT · Feb 7, 2015

My TV alternator was very anemic at charging my house batteries.

I purchased a small solar array to charge my trailer batteries at all times during daylight, whether I am hooked to the TV or not. Trace

Jim.Allison · Feb 7, 2015

Ditto X 2 Nothing beats solar for this keeping batts in great shape. Batts live longer and are always ready to go.

TandT said:
My TV alternator was very anemic at charging my house batteries.

I purchased a small solar array to charge my trailer batteries at all times during daylight, whether I am hooked to the TV or not. Trace

sengli · Feb 7, 2015

We ended up getting this option, on our former silverado, and now on our current RAM 3500. Although its useless for us. We bought our trucks off the lots, and didnt order them. The dealers order this because a lot thier potential customer buy these trucks for snow plowing duties (4X4). The electrically driven snow plow units use a lot of juice, at low RPM and the GM diesels have a special heavy duty under hood wiring harness attached already for this application.

blong · Feb 7, 2015

I was told by long time friend and truck mechanic no need for the dual alternators unless you have a lot of aftermarket accessories that run all the time and you idle a lot, so we opted out and went with single, have had no issues. You will love the new Denali, picked ours up in December, its an Awesome truck.

OEFVET · Feb 7, 2015

When I ordered my truck I ordered it with the snow plow package. The only reason I got this option was because the front axle is heavy duty. This way if I add larger fuel tanks to the truck the front axle can handle it. The snow plow package comes with dual 150amp alternators. The entire option was an additional $445. In my opinion it was well worth it.

porthole · Feb 7, 2015

If you checked the wiring for the trailer B+ circuit to the rear 7 pin you would find that it is most likely barely adequate for the 25-30 amp load that it is fused at.
So if your concern is just for the trailer use, dual alternators are better off left for those that will be looking to draw 200+ amps with accessories.

I haven't found anyone to give me a definitive answer as to whether either of dual alternators on the Ford will continue to work if either of them failed. But, I have yet to hear of any of the 6.7 alternators failing.

porthole · Feb 7, 2015

Interesting piece from the Ford workshop manual. It is consistently repeated using the word "generator", yet the Ford option is alternator. Alternators and generators have the the same basic result, delivering a usable DC voltage supply for the vehicle, but work a bit differently. Perhaps Ford is using the term generator as a generic term for the complete power package.

bdb2047 · Feb 7, 2015

Just for info I have single alternator checked amps at trailer breaker for feed from truck. At 1200rpm I had 7a not enough bring batteries to full charge but enough to maintain while traveling.

Jimsryker · Feb 7, 2015

TandT said:
My TV alternator was very anemic at charging my house batteries.

I purchased a small solar array to charge my trailer batteries at all times during daylight, whether I am hooked to the TV or not. Trace

Trace, is your solar array mounted on the trailer or is it free standing? I've seen both and for all the trees I've seen everywhere I camp, being able to move the panel to it's optimal location seems appealing. I also see the benefits of both for that matter. I have purchased parts for my TV to charge the house batteries while towing via a battery separator. Not an isolator but a separator. There's a difference. That may be my solution with a mobile panel I can move to the sun while parked at a location. If I ever get going on it, I'll update you all with photo's.

Regards

Dual Alternator Option on Tow Vehicle

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