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Old 09-09-2014, 11:46 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, 01:14 AM   #2
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Default Re: Dual alternators, why or why not ....

Why not!
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Old 09-10-2014, 02:43 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, 03:34 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, 03:56 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, 04:29 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, 04:46 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, 05:28 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, 05:42 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, 06:14 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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Old 09-10-2014, 06:22 PM   #11
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Default Re: Dual alternators, why or why not ....

although i am going to buy most of the Roadtrek system- i am no apologist for them. they don't want to reveal details and that is their right. buy or not.
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Old 09-10-2014, 06:51 PM   #12
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Default Re: Dual alternators, why or why not ....

I don't know what Advanced RV passes on to their customers as far as detailed information (yet) but at their Advanced RV Fest & Open House they laid it all out on the table what they had done in the past and what was under development and had all their staff there to answer questions. There were no secrets or evasions. I would have a bit of trouble buying an RV where the builder put proprietary systems under a "locked box" and told me only they could service it.

There were a few people at the Open House who had no intentions to buy a new RV anytime let alone an Advanced RV soon but just showed up to learn. I thought it was worth while and it was also a festive social and rally. In hindsight I just wished I asked more questions but hadn't done enough research then to know what to ask.
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Old 09-10-2014, 07:00 PM   #13
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Default Re: Dual alternators, why or why not ....

Davydd-would you be happier with we use a high amp 2nd alternator heavily wired to at least 4 6 volt agm batteries heavily wired to a 24 volt inverter charger which feeds the inverter. as far as i know the full e-trek uses a 48 watt inverter for it's 8 batteries.


now i know and have found out all this. My wife could not care less how they do it. Just that they do it. She thinks the Onan is a buzzsaw and hates it.

My point is the people who want to know are the tech junkies like us. i wanted to know and was able to glean most of the info.

most people who buy these vans(li'll say women and most men) could care less about how as long as it does.
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Old 09-10-2014, 07:26 PM   #14
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Default Re: Dual alternators, why or why not ....

Most of the people I RV rally and social with very much want to know everything about their Bs. Most of them are quite a bit more knowledgeable than I. After all I did socialize with Booster at a BEE Social once.

I'm not sure what I am going to end up with yet because Advanced RV is doing quite a bit of research and development on lots of things. That's why I am patient about it. I do know I will not have an Onan generator or propane and that I want a pretty much transparent B that I can have full use of all systems all the time such as the appliances whether I am plugged in to shore power or not.

If you want that Chevy Ranger you don't have any other option than Roadtrek that I can see if you want E-trek like features. I am not sure I would rely on Sportsmobile with that as they seem to be a company that would just give you what you want good or bad. No one else is pushing the envelope. Maybe Great West Van but they've been pretty quiet as I guess the move to Alabama has eaten in to their time and effort.
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Old 09-10-2014, 08:58 PM   #15
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Default Re: Dual alternators, why or why not ....

There do appear to be several ways of doing the engine generator thing, but I think the second, dedicated, alternator is the best way once you want be output to the batteries for charging. I you are just looking at running the microwave, you can get a 200 amp separator, although doing it that way will give some of Marko's cons.

We have 375AH of wet cells, and they don't seem to want to charge at much over 100 amps, even when low, so the separator would handle it. If you had 400+AH of AGMs, you would probably easily pass the 200 amps when they were low, so then dedicated would be best I think.

If you ignore parasitic and efficiency losses, I think you could put together an interesting system with a dedicated second alternator. I am assuming no attempt to run the air conditioning off of the batteries for any real amount of time.

What if, and looking for comments and opinions

24v, or even 36 or 48 volt 2nd alternator at about 5000 watts feeding a matching voltage pure sine inverter of also 5000 watts. Output of the inverter to a transfer switch with shore power for the van 110 volt outlets and a shore charger of at least 200 amps, with ending current charging. Output of the charger to the 12 volt portions of the van and the batteries of 4-600AH.

This setup would give you some pretty slick things. You would have very high battery charging off of a real battery charger that could be much more sophisticated than the alternator is, saving the batteries from overcharge while driving. You would have lots of 110v available without battery drain while driving. You would have the capability to charge very fast off shore power if enough amperage was available. If not, a good charger will have a reduced charge rate available to use, I think. If you wanted to have a reasonable amount of 110v power when not running the engine or on shore power, you would need a second, probably much smaller 12v inverter for that. 1500 watts would run most of the stuff, including the microwave, for reasonable amount of time. Solar would be normal as you would hook up to 12v batteries like you do now.

Benefits would come from low current to the inverter do to high alternator voltage. You would always be using the large and high quality battery charger, except for solar (unless you did a high voltage solar and also went through the inverter), which would be very good for you batteries. You wouldn't have to worry about having a disconnect on the second alternator when driving with full batteries, as the charger will go to float.

Downside would include losses from inverting everything and ????

Might work.
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Old 09-10-2014, 09:31 PM   #16
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Default Re: Dual alternators, why or why not ....

booster- the key thing would be the wiring. i am no expert but i believe if you using higher watt outputs-whether it be 24,36,48, you need heavier wiring than the normal. thats why you just can/t slap on the components on an already van.
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Old 09-10-2014, 10:36 PM   #17
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Default Re: Dual alternators, why or why not ....

Just some general notes:

volts x amps = watts
higher voltage, smaller diameter wire needed to carry amperage
for 5000 watts for example, at 12v would need larger diameter wire than at 24v, at 24v you'd need larger diameter wire than at 48v

5000w = 416 amps at 12v
5000w = 208 amps at 24v
5000w = 104 amps at 48v
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Old 09-10-2014, 10:41 PM   #18
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Default Re: Dual alternators, why or why not ....

Quote:
Originally Posted by markopolo
Just some general notes:

volts x amps = watts
higher voltage, smaller diameter wire needed to carry amperage
for 5000 watts for example, at 12v would need larger diameter wire than at 24v, at 24v you'd need larger diameter wire than at 48v

5000w = 416 amps at 12v
5000w = 208 amps at 24v
5000w = 104 amps at 48v

see- i told you i knew nothing about wiring. is smaller diameter wire better/ all i know is it needs special wiring.
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Old 09-10-2014, 10:47 PM   #19
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Default Re: Dual alternators, why or why not ....

You could say smaller diameter wire is better because it costs less, weighs less and is much easier to physically handle and route. End connectors would cost less, crimping the connectors would be easier. The wire has to be sized correctly to safely carry the intended load.
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Old 09-11-2014, 12:26 AM   #20
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Default Re: Dual alternators, why or why not ....

A quick table below for comparison. It is MUCH more cost effective to transmit high voltage/low current and convert at the end. If you need 4/0 wire you would be paying over $7 per foot! And at nearly half an inch in thickness it would be horrible to work with.

Gauge - Conductor Diameter in inches - Conductor Diameter in mm - Maximum current - Cost

4 0.2043 5.18922 135 amps $1.47 per foot
1 0.2893 7.34822 211 amps $2.83 per foot
OO 0.3648 9.26592 283 amps $4.02 per foot
OOOO 0.46 11.684 302 amps $7.15 per foot

Note that this table is for solid wire. Stranded wire which you would find in automotive applications would require a larger gauge and slightly more cost.
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