Generator misinformation from salesperson...fact checking

Hi all, 

Aspiring full-time family here looking to purchase our first RV.  We are completely new to RVs as far as owning and operating one, though I lived in a Class C for a while with my family as a kid.  A salesperson recently "corrected" me on several points about the generator in a 2006 Monaco Cayman diesel rig with Onan diesel generator we were considering, and I know at least some of the information she gave me is wrong.  I've only got a basic handle on understanding the electrical systems myself, so I'd love some help sorting fact from error here. 

The situation that prompted this discussion was that the salespeople turned on the RV and the generator so my husband and I could inspect it thoroughly, but after about 15 minutes the generator and all power in the RV shut off unexpectedly.  The salesperson made several statements during our subsequent conversation that are suspect to me- please let me know if my understanding here is correct. 

1- She said the reason the generator shut off is almost certainly because the house batteries were indicated as being "low" when she turned it on. 
My take- There are actually many reasons the generator would turn off, including running out of fuel, being overloaded, being in poor shape.  I asked whether it maybe ran out of fuel, and she stated (#2):

2- Generators in diesel RVs run off of batteries only, they do not generate electricity using diesel/gas fuel.
My take- now this is just ridiculous.  My understanding was that in a diesel rig the generator typically uses diesel from the RV tank as long as it's above 1/4 tank.  The salesperson condescendingly corrected me again that, no, only a gas RV shares fuel with the generator; on a diesel rig the generator uses batteries exclusively, it does not generate electricity from diesel or gas fuel.    At this point I insisted on talking to a service person rather than a salesperson.  He *thankfully* confirmed that generators in a diesel rig do use fuel  : and they typically use the fuel sharing system from the fuel tank just like in a gas rig.  However, he still insisted that (#3):

3- A generator must have a constant supply of power from the house battery to run.
My take- I asked wouldn't the generator only need to battery (house or its own) to start, just like a car, once it's running it's self-sustaining and/or charging those batteries rather than drawing in them?  He said no, "because there's no alternator" like in a car, the generator needs constant power from the battery.  But I asked again, isn't there some system in place, similar to an alternator or not, to allow the generator to be self-sustaining, power-wise, after start-up since it is *generating* electricity, and in many cases isn't there a system by which it can charge the battery?  He said no.  But wouldn't that make running the generator completely impractical because it would run the house batteries down quickly? 

PS Don't worry, I will not be purchasing from this dealer.

Your last sentence says it all.  It's hard to believe (not really) that there is that much Stupid in one place.  Run, don't walk, away from there.

PS Don't worry, I will not be purchasing from this dealer.

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I don't blame you. The sales gal apparently knew nothing at all about generators -- she was just blowing smoke, and it's good that you were able to catch that. As far as #3, the generator doesn't put out DC current, just the household AC, so in that sense the service guy is right. Whether you are plugged in to shore power or running off the generator, the AC is fed to the converter, which converts the AC to DC and charges the batteries and otherwise supplies DC to the coach, usually via the batteries.

I would have taken this salesperson by the hand and walked into the sales managers office and once again go over everything this person told you just to see if she changed her tune. Then I would have walked out and not looked back.

The sales gal apparently knew nothing at all about generators --

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The chances are good that she knew nothing about anything!!!  There is a good chance that the sales managers knowledge may have been similar since it was part of his job to train her. Chalk it all up to an opportunity to view that particular model RV and nothing more.

I guess for #3, he is partly right, there is no alternator on the generator itself but... it is outputting 120V which will run the converter or inverter which charges the house batteries (and perhaps the chassis battery, depending on make and model of RV or if a Trik-l-Start or similar unit/circuit's are installed).

A diesel engine requires no 12V power itself to continue running. It does require 12V for the auxiliary control circuits and the starter motor though. It is stopped by simply cutting off the fuel supply using a fuel cutoff solenoid (hence one example of the need for 12V aux. power).  A gasoline engine, on the other hand, does require 12V to continue to run. Although a gasoline powered generator does not have an alternator either, some of the power necessary to run it may come from a magneto system in the flywheel to generate electricity needed for the ignition coil/spark plugs, much like a boats small outboard motor.

On that number 3 again, it depends, if there is an AC battery charger (and if it is functioning) hooked to the output of the generator then it should always charge the batteries.    As to the internal battery charging system on the generator, most gasoline RV generators do not have one, but I thought most Onan diesel RV units do have a  one.    To clarify that on the most bit for gasoline RV generators the very popular Onan Micro-lite / Micro-Quiet / QG 2800 and 4000 models do not charge batteries, but the 5600 has the option for battery charging alternator output.

p.s. modern diesel generators do require a battery once running to keep the control systems operating

Thank you, everyone, this was very helpful. 

And yes, our Onan diesel generator runs off the diesel tank.  We have an older Monaco DP.  If the diesel tank goes below one-quarter the generator will stop to make sure you don't run down the tank so much that you don't have fuel when you're ready to leave.  That salesperson doesn't know squat!

ArdraF

Well,, Most RV generators do indeed need a constant supply of 12 volts or better from the house system.. This can come from the batteries or it can come from the converter (The thing that charges the batteries) but they need it.... Runs the fuel pump (And possibly other thing) Not sure though if you have a diesel (or gasser) with a cam operated fuel pump that would not apply.. But I don't think they make 'em that way.

But with the generator RUNNING the converter should supply more than enough power to not only run the fuel pump but charge the batteries as well. 

So the salesman.. Was not entierly wong.. Just not entierly right either.. There is a different problem than low batteries.. What it is I can not tell at this time  Could be as simple as a tripped circuit breaker or on my RV a pulled plug

Wow!! If you can't dazzle 'em with brilliance baffle 'em with bull feathers. There are a number of reasons for the generator to quit. The most obvious is no fuel. There are also fail safe systems built in such as high temp/low oil shutdown, also if power output fails the engine will shut down to prevent further damage.
I am surprised everything shut down. Shouldn't house battery power be still available? In any case look for another dealer. That girl had better get some training before she starves to death. :

Did she actually start the generator or did she get 120 volts by turning on the inverter?  Inverters are fairly common in Class A's with large house batteries because they allow some 120 volt usage like watching TV or using the microwave for a few minutes to nuke some popcorn without having to start the generator.

If she turned on the inverter instead of the generator, it would indeed shut down in a few minutes if the batteries were low since it uses the power stored in them.

Maybe that dealer deserves a second chance?

Lou Schneider said:

Did she actually start the generator or did she get 120 volts by turning on the inverter? 

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I'm not sure what method she used to start it because we haven't started one ourselves yet.  She looked pretty confused at the control panel and the service guy came out to help on the outside of the RV as well.  It seemed like they had some trouble but I don't know if it was her lack of knowledge or a problem with the RV. 

Lou Schneider said:

Maybe that dealer deserves a second chance?

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Well, I should also note, we drove 3 hours to see this RV in 105 degree heat, and when we arrived, the dealer had their inventory packed so tightly in the lot that we couldn't even inspect the awnings.  They said it would take them 2 hours to move their inventory around to get the rig out to test drive, and since it was an hour until their closing time by that point, they said they wouldn't do it.  Nor would they hold it for us without earnest money. 

I was honestly shocked by the whole experience- in addition to the generator misinformation, that they would think that it was reasonable to propose that we put earnest money down on a rig that shut down on us for unexplained reasons in the middle of our interior inspection, that we can't thoroughly inspect externally, and one that they won't let us drive.   

Lou Schneider said:

Did she actually start the generator or did she get 120 volts by turning on the inverter?  Inverters are fairly common in Class A's with large house batteries because they allow some 120 volt usage like watching TV or using the microwave for a few minutes to nuke some popcorn without having to start the generator.

If she turned on the inverter instead of the generator, it would indeed shut down in a few minutes if the batteries were low since it uses the power stored in them.

Maybe that dealer deserves a second chance?

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Yes sounds like she was getting inverter and generator confused.

Why go to another dealer?
If they don't know that much about the RV maybe they don't know how much it's worth?
You could be taking advantage of them rather than the other way around.

glen54737 said:

Why go to another dealer?
If they don't know that much about the RV maybe they don't know how much it's worth?
You could be taking advantage of them rather than the other way around.

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Definitely good thinking.  However I wouldn't want to drive 3 hours (with 3 preschoolers!) and not be able to inspect or drive it.  I think I'd have to make a rather blind purchase, as far as testing out the thing ourselves before/after our mechanic does, and with our inexperience I think we'd better stick with RVs we can handle and test to a reasonable degree before buying.  Maybe after getting our feet wet in RVing and we know more ourselves, we'll try to wrangle a deal out of them.

If you run away from every potential purchase where the sales person or private seller is ignorant, chances are you won't be buying an RV.      Misinformation is rampant, so you have to educate yourself and fact-check everything you are told. Including what you will see in online sources (yes, this one too).  At least in a forum or blog format you usually get multiple opinions, so there is some built-in cross-checking.

As for RV sales people, just remember that their primary expertise is in selling, not in RV use, care and maintenance. They tend to glibly repeat what they've heard around the dealership.  A few facts coupled with a bunch of sales blather can sound really plausible but be totally off-the-wall (as this one is).

Thanks again, all.  This was all very helpful.
Hope to be RVing soon!