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Old 09-09-2014, 10:46 PM   #1
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Default Dual alternators, why or why not ....

I though we could discuss the positives and negatives of having dual alternators under the hood. This might turn out to be a trend in the RV world if more manufacturers start adding a second alternator under the hood.

In the Class B world I think that Advanced RV http://www.advanced-rv.com/ and Roadtrek http://www.roadtrek.com/ offer production vans with dual alternator setups. Let me know if any other manufacturers offer dual alternators and I'll update this post. I think you can order a van with dual alternators for a Sportsmobile conversion.

Advanced RV and Roadtrek may both be using Nations Starter & Alternator parts. Nations tagged both companies in a Facebook post

https://www.facebook.com/permalink.php? ... 7260728552


The "Why not" question came up in a recent discussion with Booster. It was along the lines of why not eliminate the isolator or battery separator and instead use one alternator for the "van" or chassis needs and one for the "house" or coach needs.

Some positives (depending on how you do the installation):
no isolator or battery separator to fail
no voltage drop caused by isolator
redundancy - you could fail-over to the coach alternator to supply the chassis power requirements
potential to use the second alternator as a coach generator

Negatives:
maybe load on the engine will affect MPG
more expensive (but still can be done on a moderate budget depending on the components you choose)
need to idle the van for the second alternator to be used as a coach generator (the thought being why idle an expensive motor when a cheaper generator will do the job)

That's all I can think of right now. Any thoughts on this? Feel free to pick apart my positive and negative points. Hopefully we'll all get a better understanding of this concept if this topic progresses.
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Old 09-10-2014, 12:14 AM   #2
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Default Re: Dual alternators, why or why not ....

Why not!
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Old 09-10-2014, 01:43 PM   #3
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Default Re: Dual alternators, why or why not ....

I guess a negative would be that you would lose the air conditioning capability, if you don't have a shore connection, but having the engine generator would not eliminate the possibility of having a gas/propane generator also if you wanted.

A question would be how the second alternator would react if you had a disconnect in the line to the coach batteries. I don't know how the alternator would work if it didn't have the battery reference voltage, or if the disconnect was switched while the engine was running.
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Old 09-10-2014, 02:34 PM   #4
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Default Re: Dual alternators, why or why not ....

I'm getting the second alternator in my next B. To be truthful I don't understand the pros and negatives. It is not an option but a standard with Advanced RV as I understand that aspects even when people bought Onan generators. One buyer I am aware of optioned not to have the second alternator.

Engine idling is obviously going to reduce mileage on a fill. Is it significant driving down the road? Advanced RV got a total average of 19.4 mpg with their 4 cylinder model on a trip from Ohio to Arizona and back. I kind of look at engine idling as a backup that I may not use at all or rarely considering my 14 hours of Onan over 65,000 miles and a year's worth of nights traveling. Would faster recharging be a plus with a second alternator?

Engine idling is only good for 2-3 hours before you have to get up and go and drive for 40 minutes in a Sprinter. That would give you 2-3 hours of air conditioning but would that be delivered through the batteries and inverter rather than direct AC like an Onan? This is also something I've considered. I can't recall ever running the Onan for the sake of air conditioning. We have always either followed the weather intelligently in our travels or simply stopped at an electrical hookup campsite. I don't plan to change that practice. We live mostly outdoors in campgrounds and the side sliding door and back door screens we had enabled us to stabilize the inside the B temperature. We are pretty good to go that way up to 90F dry climates. However, humidity is the killer. We had to run air conditioning in April in South Padre Island one time just to eliminate the sticky dampness inside. The temperature was comfortable.

The Sprinter diesel engine and a cab gasoline engine even more so would definitely be quieter and less annoying in sound while charging. That's a plus I think.
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Old 09-10-2014, 02:56 PM   #5
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Default Re: Dual alternators, why or why not ....

Do you think that a second alternator is only applicable to coaches with larger battery banks? No real benefit to coaches with 1 or 2 batteries (other than possible system fail-over use).

Re: disconnect in the line - there are lots of warnings on websites that disconnecting the battery from a running alternator is NOT a good idea. Some sites indicate possible damage to alternator diodes. How would having a second wire (on the second alternator) going to the chassis battery affect the primary alternator? You don't want to end up with only one alternator doing all the work.

Anyone know how Advanced RV or Roadtrek do their installations?
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Old 09-10-2014, 03:29 PM   #6
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Default Re: Dual alternators, why or why not ....

you are right. without at least 400 amps worth of batteries an extra alternator does not make sense. also without an inverter(at least 2500 watts) it's just another alternator-not a 'generator'. Roadtrek creates an engine generator 'with it's system -not the individual parts
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Old 09-10-2014, 03:46 PM   #7
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Default Re: Dual alternators, why or why not ....

gerrym51,

Are you implying that Roadtrek has a system like MEPS that uses an inverter to output 120v that is fed to a transfer switch? The house inverter then receives the output from the transfer switch and passes it on. If the incoming power is lost, then the inverter will produce 120v from the batteries.

A Roadtrek engineer told me that they call their secret system a generator but it is really only a Nations alternator feeding the batteries. They call it a generator for marketing reasons (more familiar to customers).
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Old 09-10-2014, 04:28 PM   #8
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Default Re: Dual alternators, why or why not ....

Quote:
Originally Posted by pattonsr
gerrym51,

Are you implying that Roadtrek has a system like MEPS that uses an inverter to output 120v that is fed to a transfer switch? The house inverter then receives the output from the transfer switch and passes it on. If the incoming power is lost, then the inverter will produce 120v from the batteries.

A Roadtrek engineer told me that they call their secret system a generator but it is really only a Nations alternator feeding the batteries. They call it a generator for marketing reasons (more familiar to customers).

No. what they call a generator is actually a system. High amp 1 wire 2nd alternator/at least 4 6 volt batteries( 400 amps)/tied into an inverter/charger of at least 2500 watts and the heavy duty wiring it requires. they also add solar panels but that is secondary.

If the goal is to get rid of the Onan then this system does it. as long as the engine is running it is supplying high amps to the batteries and the inverter is running appliances(up to the inverters watts.) however to take full advantage of a system like this you need enough battery power to run the inverter for a period of time.
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Old 09-10-2014, 04:42 PM   #9
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Default Re: Dual alternators, why or why not ....

Roadtrek is confusing people calling the second alternator a generator because it doesn't function power the same way shore power or an Onan generator does, no?
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Old 09-10-2014, 05:14 PM   #10
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Default Re: Dual alternators, why or why not ....

Has Roadtrek produced a diagram of their generator system? Until then it is all marketing spin. I expect Advanced RV to produce a detailed report on their upcoming power generation/advanced Lithium system. Roadtrek hides the details saying it is a company secret..
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