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Old 11-21-2017, 12:30 AM   #1
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Default Underhood versus Onan

Don't yet own a Class "B" but hopefully will!

Many things I need to learn about!

After spending many hours reading forum posts and looking at websites, I am strongly attracted by the concept of an underhood generator as opposed to the more conventional Onan - obviously for the reasons of it being much quieter, taking less space, and resulting in one less engine to maintain.

In reality, we may not use any generator much. At present we mostly camp with our trailer in full hookup campgrounds. We do carry a Honda i2000EU just in case, but rarely use it - usually just for overnight stops at the Flying J !

If we move to a "B" though, I suspect we could well be camping more often at spots without hookups so I would want to have a gennie to be prepared!

I am keen on the underhood generators to the point of almost not considering a unit that is not so-equipped. I guess that would limit me to Roadtrek/Hymer unit.

I find it odd that other manufacturers are not going the same route. Just a matter of time, or are there big disadvantages?

The only disadvantages I can think of would be:

- extra wear on the vehicle engine (I doubt that would be an issue for us given the limited use we would make of it)

- the vulnerability of the extra alternator which often seems to be mounted low under the engine. I'm thinking of road salt/water on winter roads when we travel south each year.

- issues I have heard of with defects. I haven't read enough to understand if the problems are with the actual auxiliary alternators, or rather with ecotrek controllers, or the voltstart electronics instead.

For now, it seems a major plus in my books, and it will likely affect my choice of motorhome unless I learn reasons not to feel that way!

Any advice or comment? Are Onans as noisy and obnoxious as I have read? Our little Honda is pretty quiet, but if we downsize to a "B" I don't think we'll have room for it!

Am I putting too much emphasis on this one aspect when looking for a Class B?

Thanks for any comments


Brian
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Old 11-21-2017, 12:51 AM   #2
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.

You can always order an RV without the Onan option,
and install the underhood generator afterward.

It will come out cheaper than RT.

https://www.nationsstarteralternator...Kits-s/209.htm
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Old 11-21-2017, 01:07 AM   #3
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You might consider the third alternative. Use the alternator that comes with the van.

My Dodge Ram Promaster has a 220 amp alternator that will put out more than my AGM batteries can take.

Rather than trying to run the roof AC from the alternator-inverter I run the dash AC and rear evaporator/fan. That way it is running directly from the engine and not through the alternator-battery-inverter-roof AC.

Simple and reliable.
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Old 11-21-2017, 01:21 AM   #4
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Quote:
Originally Posted by BBQ View Post
.

You can always order an RV without the Onan option,
and install the underhood generator afterward.

It will come out cheaper than RT.

https://www.nationsstarteralternator...Kits-s/209.htm
Maybe true - I do have welding equipt and all kinds of tools left over from my past hobby or restoring British sports cars (Stil have a restored and much modified original BMC Mini!) but at this stage of my life, not so keen - plus I like a warrantee!

Thx .... Brian
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Old 11-21-2017, 01:34 AM   #5
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Quote:
Originally Posted by DCHitt View Post
You might consider the third alternative. Use the alternator that comes with the van.

My Dodge Ram Promaster has a 220 amp alternator that will put out more than my AGM batteries can take.

Rather than trying to run the roof AC from the alternator-inverter I run the dash AC and rear evaporator/fan. That way it is running directly from the engine and not through the alternator-battery-inverter-roof AC.

Simple and reliable.

Interesting, but I'm no electrician (retired mech eng!) but doesn't the existing wiring from your vehicle's alternator and fusing of same drastically reduce the charging that your regular alternator can provide to the coach batteries?

That was what I thought, and I am not sure I'd know how to work around this if it were to be an issue.

If it were feasible, why would Roadtrek not just do it that way?

I think that although it would cost me more $ rather go with an Onan, or a factory warranted underhood gennie arrangement.


The Onan mainly concerns me because of the noise issue that I have read about.

I need to hear one first hand to hear how bad it really is. I am sensitive to not being an annoyance to my neighbors, so that is probably the biggest consideration for me in making a choice!

Thx.... Brian
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Old 11-21-2017, 02:22 AM   #6
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Quote:
Originally Posted by Wingeezer View Post
Interesting, but I'm no electrician (retired mech eng!) but doesn't the existing wiring from your vehicle's alternator and fusing of same drastically reduce the charging that your regular alternator can provide to the coach batteries?
If you plan to use Li batteries then they can take the high amps and need special treatment. In this case an added alternator may be the thing to do.

Lead acid/ AGM's will take a lot of amps for a vary short time and at 14.5 volts the amps will taper off quickly. I figure you need no more than 20 amps per 100 Amp/Hr battery (40 amps for 200 AH of batteries)

You should not need to change any of the coach systems. Just connect the house batteries to the coach battery through some switching device automatic or manual.
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Old 11-21-2017, 02:38 AM   #7
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Quote:
Originally Posted by BBQ View Post
.

You can always order an RV without the Onan option,
and install the underhood generator afterward.

It will come out cheaper than RT.

https://www.nationsstarteralternator...Kits-s/209.htm
Quote:
Originally Posted by Wingeezer View Post
Maybe true - I do have welding equipt and all kinds of tools left over from my past hobby or restoring British sports cars (Stil have a restored and much modified original BMC Mini!) but at this stage of my life, not so keen - plus I like a warrantee!

Thx .... Brian

RT buys the underhood generator kit from Nations.

This is the same unit that goes into police cars and ambulances.

You do need to find out who does the police cars in your city.
It is not a difficult install. It is just a hassle and takes time.
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Old 11-21-2017, 03:41 AM   #8
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I agree with the posts above..
Unless you have some excessive power demands, and are going with lithium, an extra alternator is probably not needed. I have a Travato, with the standard promaster alternator, some solar, and two AGM batteries; and my power needs are always met. I removed the Onan genny because after 2 years, I found no need of it (and it IS a little loud and irritating). If I ever ran my batteries low (which I have NOT done in 30,000 miles), I could simply start and run the "underhood generator" that came on my promaster - the battery bank would be charged up in less than an hour.
We boondock almost exclusively, and stay away from really hot areas. We DON'T use a bunch of electric-centric appliances like toasters (toast is better in a pan), Kuerig coffee makers (I prefer my french press), Insty Pots (that aren't instant), electric cooktops, or blow dryers. You COULD use those things if you wished, but you would need to be plugged in.
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Old 11-21-2017, 02:42 PM   #9
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It is not just the obnoxious noise of the Onan, it is the fact that they require constant care, service, and all too often replacement of expensive parts. The one that I had for 4 years required the replacement of the carburetor and two fuel pumps. (at least it wasn't a Roadtrek, so it didn't have to be dropped 3 times at double the expense) And I religiously "exercised" it as advised by Onan and the techs that worked on it. I will NEVER own another.

I have the underhood gen on my 170. Those that have had issues were with the Balmar regulator being set incorrectly or failing. Mine wasn't set properly, but that was because I had to dump the lithium batteries and replace them with AGMs. (mine was one of the first out and wasn't ready for prime time) That said UG issues have been minimal compared to the voltstart and lithium issues. These issues have mostly been worked out to the point where the majority are now user errors.

Whether you need a generator or no depends on your RV usage. If you have managed for ages with your little Honda, that may be all you need even with a B.
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Old 11-21-2017, 03:04 PM   #10
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I agree that most don't need an engine generator for their power needs and battery bank size, but there a few thing to go along with that.

AGM batteries will accept a lot amps as mentioned, and they don't reduce the amount they will take because you want them to. 220ah of AGM will accept something like 150 amps when low, and up to about 70% state of charge. This much power for a long period is going to be very hard on a factory alternator. Most of them will have heat issues at 50% of capacity or less, and they usually don't have thermal sensors to reduce output to cool them. At that output, the batteries will also get hot.

About 40 amps per 100ah of battery is a good place to be to keep the batteries cool, and at 88 amps (for the 220ah) the alternator will likely last a lot longer.

I think the best way to do this would be with a battery to battery charger sized in the 80-100 amp range. It would limit the current to the batteries to it's rating, so the alternator and batteries will be happy. It will also do a "smart" charge on the batteries, so they will get better charging.

I will also point out, as usual, that running the engine for an hour will not get your batteries "charged up", at least not to full. Depending on how discharged they were, you might get to 70-80% full, but to get totally full will take something like 6+ hours longer. Nothing wrong with getting a short charge to get capacity for more time off grid, but you need to get to 100% full every 7-10 cycles if you want the batteries to not "walk down" on capacity over time.
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