Double Alternators

I opted for the 220A alternator on my truck when I ordered. 180A was standard. I figured with the heated front and rear seats, heated steering wheel, and blower fan on high in the winter, it could use the extra juice.

I didn't bother with the dual alternators. IMO, that's only needed for work applications, not personal use.

boogie_4wheel wrote:
Most cases the 2nd alternator will be a waste of money (for the purchase, and for the parasitic drag). With a 'stock' trailer connection on the tow vehicle you can only charge so fast, and the extra output of the 2nd alternator will wasted in most cases.

A benefit to the 2nd alternator would be to quickly bring the truck's batteries back to full after a long drag of the glow plugs/grid or extended cranking in cold weather. I recall a few years back Ford had an electric heater for quickly warming the truck that required the dual alt setup.

very good to know!

DiploStrat wrote:
Got to be a bit pedantic about this.

-- Do you mean two alternators in parallel, which is what most manufacturers do, or,

-- Do you mean two independent alternators?

Two alternators in parallel basically act like one bigger alternator and this may be all you need. (This is what I have on my truck to charge 150Ah of starter and 600Ah of camper. The advantage of this set up is that all all of the amps produced by the two alternators are available to all of the batteries. (Assuming, and this is important, proper wiring.)

With two, separate alternators you may have less total amperage available, but you have the possible advantage that the second alternator/regulator can have a different charging profile. (This may or may not be important.) This thread may be useful: http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/19027379/gotomsg/19029509.cfm#19029509 User Mike Tassinari has a very nice dual alternator set up. Do note that is is using cables that are MUCH larger than any standard tailer connector.

It is worth noting that with a large camper battery bank, say 200+ Ah, you may never drive long enough to achieve a full charge with any alternator(s) and you will probably need a secondary charge source - solar or shore power. As this secondary charge source is the one that will take the batteries from bulk through acceptance charge, to float, is is important that this charger have the proper profile to match the camper batteries.

Thank you for the info, I mean that the alternators would be in parallel. That seems to be the way the factory installs them when placing a factory option on an order.

Yes, I sure did order our 2004.5 Chevy D/A CC LB 4X4 truck with dual alternators and so happy I did. So cheap to order with and gives back as long as you own the truck in many ways.

There's 2 batteries under the hood for the truck. 2 group 31 big flooded batteries (225 minute draw of 23 amps each) in the truck's bed between the rear wheel well and the front of the bed on the driver's side and 5 more of the same in the 5th wheel. Just those 7 batteries not including the truck chassis batteries give us 1575 minutes of DC power at a 23 amp draw and the batteries last an average of 6+ years before I replace them.

Then I use the taken out batteries in our boats 2-3 at a time to power the electric trolling motors. 3 of the batteries are now just over 10 years old and still going strong. They last a very long time because they have never been drawn down low on charge thanks to the dual alternators. The batteries for the 5th wheel use power our 2500 watt inverter and run the coffeemaker, microwave, lights, computers, toaster, George Forman sandwich grill and several other items when not on shorepower and the recharge so quick when driving or even idling the truck's engine for half an hour or less. No need to ever start the Honda EU2000 generator as charging with it takes many hours even with both of my 25 amp and 40 amp Vectron battery chargers running off the Honda Gen.

What else the dual alternators do is prevent gray hair when boondocking and if we'd ever lose an alternator as I carry the spare serpentine belt required for a single alternator application under the rear seat, so no sweat ever as if the truck batteries went dead, simply jumper the added soleniod +, turn the ignition key and start the engine, and then drive away! All the 12V power you'll ever need with or without the RV even being with you! Even carry a 2000 watt inverter that's our backup that can be attached to the truck bed batteries and have 15 amps + of 117 AC from the truck anywhere/anytime for AC and NO generator is needed! Got to use the old noodle in that bump on your shoulders as it good for more than a place to put your hat.

A comment was made in a post as to too small of a charging wire going from the truck to the RV and that can be true it no addressed. I have a two #2 gauge fine strand welder cable wires going directly from the dual alternators under the cab in plastic sheaths and up thru the truck bed to the batteries there. A 100 amp slide switch under the hood to disable the current and the 100 amp solenoid that isolates the RV system and an 80 amp slow blow marine fuse at each end of the big cable/wire on the + wire. One + wire and one - wire and never use the truck body for the ground.

Then there's 2 of the same big wire cables that go to the 5 big batteries in the 5th wheel with a marine 400 amp barrel switch to cut the current from the 5th wheel batteries when wanted. I could put 10 batteries just in the bed of the truck if I wanted to just by adding them!

Dual alternators are simply the "rat's nutz!"

Hello,

New to the forum as I was looking for adivce for my next camper mod. I was going to add an inverter to run my 120vac fridge while towing and to have some(just a bit) AC power while dry camping.

Along with that I was wanting more battery so a couple of 6v 225ah batteries in series was in order. I was wanting to totally separate the truck battery and alternator from the RV side by adding a second alternator and a 2 pin Pollak connctor just for the RV batteries and inverter.

I really dont what to run anything else or have the whole camper on a massive inverter with a cross over. Just enought to give me the fridge or a few minutes of microwave use when stopped. My primary concern is separating the vehicle from the RV and enough power while idiling to run the inverter without getting into the batteries.

Yes I know the cost is excessive, but that aside, It seems pretty straight forward. What I am not sure of is should I externally regulate the power so I dont toast my batteries? we all know the alternator isnt the most efficient charger.

Also, will the alternator be able to power a 1000w inverter. I have looked and saw a few that were rated at 100+ amps at idle.

with that kind of idle amperage, I should be able to guarantee enough wattage to run a 5cuft fridge without getting into the batteries and have enough reserve to shut the truck off when I stop for an hour or so.

So it would seem that if I just took the alternator (with the proper ga wire) directly to the RV batteries via the 2 pin Pollack, common my grounds, and then tied the inverter directly to the batteries, it should be isolated from the vehicle batteries and electrical and provide enough power to charge and run the inverter. Should I get an external Regulator/charger?

Dry camping in a trailer is a little different than a overhead camper. With the overhead camper you have to have a way to separate the RV batteries from the chassis batteries while you are parked. It has been my experience that the isolators are much more unreliable than a separate alternator system. There is the option for a throw switch to isolate the RV batteries. The really only safe place to have that switch is under the hood as it is a direct open metal switch to the positive side of the chassis battery that you need to keep covered. It is connected from the Chassis battery positive terminal to the RV battery positive terminal so it is hot even when it is in the open position. Or you can unplug your camper at it's umbilical plug. All of these require that you think about what you are doing.

With a trailer you will most likely unplug your umbilical when camped. No problem there unless you are inclined to run off to the soda shop with your trailer unhooked but plugged in. :)

With a second alternator all the problems are solved. You just pull over. Park, hop out of your truck and pop on your dunce cap. ;)

boogie_4wheel wrote:
Most cases the 2nd alternator will be a waste of money (for the purchase, and for the parasitic drag). With a 'stock' trailer connection on the tow vehicle you can only charge so fast, and the extra output of the 2nd alternator will wasted in most cases.

A benefit to the 2nd alternator would be to quickly bring the truck's batteries back to full after a long drag of the glow plugs/grid or extended cranking in cold weather. I recall a few years back Ford had an electric heater for quickly warming the truck that required the dual alt setup.

My Duramax has a space reserved for a second alternator with mounting lugs. I agree with boogie_4wheel installing a second would just be a waste of money.

Two independent Alternators.

This is what I use to connect the Camper and the Trailer, It is separate from my other connector. I cut the cable in half. One end connected to a permanent cable clamp on the trailer RV battery, the other connected to RV battery in the camper. The jumper cable scissor clamps are not used.

I also used similar size wire to connect the two RV batteries under the hood to the other two..

The vehicle battery is in the stock position. I had to move the radiator overflow and build a bracket there to hold the 2 RV batteries there. I have a one hundred Amp fuse between the two under the hood and the two other RV batteries.

I did this mainly because the battery isolators I found greatly reduced the amp flow to the RV batteries in favor of the Chassis battery. The chassis requires a lot of amps with air conditioner etc, running.

Cables

Most cases the 2nd alternator will be a waste of money (for the purchase, and for the parasitic drag). With a 'stock' trailer connection on the tow vehicle you can only charge so fast, and the extra output of the 2nd alternator will wasted in most cases.

A benefit to the 2nd alternator would be to quickly bring the truck's batteries back to full after a long drag of the glow plugs/grid or extended cranking in cold weather. I recall a few years back Ford had an electric heater for quickly warming the truck that required the dual alt setup.