Full sized Cummins Onan generator or under hood alternator?

[Roadtrek Adventuous RS1]

Does a full size generator have more power and capacity over an under hood alternator?

I noticed that a lot of brand new RVs are being sold new without a generator, and instead uses a larger battery system, usually lithium and relies on things like a 12 volt air conditioning system.....

Really don't know if s 12 volt air conditioning system has as the same cooling power capacity over a generator and 120 volt HVAC system...

Normally, I would think that the generator and traditional HVAC system has more cooling power and capacity, but, I'm not sure?

Also, idling a diesel engine is not recommended, so does this also apply to a gasoline engine using an auto start for charging up the batteries which they get too low?

Any ideas?

[Davydd]

MB says you can idle their diesel up to two hours with an interval of driving for 40 minutes. So, no, you are not going to run your air conditioning all day unless you have something like a Volta high watt battery bank.

I plan my trips to where and the season so I don't use air conditioning from a Minnesota base. I never had run it more than 3 hours (South Padre Island in March) mainly to dehumidify. Subsequently, heating is more important for me.

I've had high amp hour lithium battery banks and under hood second generators since 2015. My newest Class B I opted for less amp hours (552ah) for other uses in an all electric van because I didn't need the previous 800ah battery bank. Nor solar panels either.

My under hood Delco-Remy 330 under hood second alternator puts out 270-280 amps per hour driving to replenishing my battery bank and 220 amps at high idol. More common Nations alternators which I first had a little less. Your MB alternator is governed to 40 amps maximum. An Onan generator is limited, as I understand it, to 120 amps per hours battery replenishment (someone correct me if I am wrong) but can run your air conditioning 12v or 120v. Probably makes no difference as you would have to run the Onan. But if you think a vibrating noisy top and bottom sandwich situation is acceptable when you are sleeping.

Edit: I forgot. There is always the shore power option when you need air conditioning. I'd seek and plan for it.

[mkguitar]

you could compare the output of AC or DC powered units by the BTU


and use the current draw to compare the input - the energy you must supply



for instance a 120 volt device which uses 1 amp could be comparable to a 12 volt device using 10 amps
that 1000 watt blow dryer at 120vac has an 8.33 amp current draw, a 12 volt equivalent would need 83.3 amps !





driving an alternator is not 'free power" akin to driving the auto air conditioner which sometimes we switch off when climbing mountains


idling is not an efficient way to make power, it'll cause wear and build heat. imagine trying to cool the inside of a van while the motor is throwing off and radiating heat into the van


i spent some time driving diesel trucks and buses with a "high idle" setting, about 1000 rpms. this was engaged to increase oiling to remove heat from the block prior to shutting down and/or to meet demand on the alternator when stopped.


Like many we "go where the weather suits our clothes" we try to go somewhere where we are not fighting the climate




mike

[KurtFranz]

My preference is for the Onan Generator and/or shore power for running an AC unit. Pretty simple and cost effective and you are not using the van engine as your generator so to speak. I would rather use the genny than my vehicle engine for that purpose. Also my wet cell house battery works well - at least when it was getting charged while driving That being said I have never seen or used a 12 volt ac unit. Sounds like it would be a great solution if practical.

Regardless, I am old school, have an old van, and am not up to snuff on all of the new technologies used today. Whatever works to "keep it simple stupid" applies to me.

I would like to know the bottom line on this as it is interesting.

[booster]

An Onan generates 2800 watts and can do it continuously. An underhood big alternator is rated at 3500 watts but in real world use heat cycling will reduce it to about 2000 watts on average unless you have the massive unit that ARV can put in Sprinters. Both can run air conditioners continuously.


In real world use, which is best is mostly dependent on your camping/travel style and how much battery capacity you have. If you drive5-8 hours a day and have enough battery capacity to run the AC all night an engine charging system works great except you might need run the engine during the day to to get daytime AC also.


The Onan would be able to give AC any time, anywhere, but at the cost of noise and exhaust smell.


If you are looking to have AC running all the time except for when driving, I think the Onan is best so you don't have to run the engine so much. You probably would only charge batteries from the van engine at a bit less than 100 amps with the AC running so you would put in an hour of battery powered cooling for every hour of running the engine. Basically for 10 hours of cooling you would need about 5 hours of idling if you started with discharged batteries.


If you are looking for over night sleeping cooling only, drive a lot, and have a lot of batteries, then the engine charging would be best choice, I think.


With no air conditioning in the picture, the engine charging wins hands down, IMO.



Some of the newer super efficient AC units will help reduce engine running time. The calcs above are more for the older units I am familiar with that use close to 100 amps of 12v DC when running.

[mumkin]

Like everything in RV options, there are pros and cons. And it depends on what you want and need. Here is my experience. My Libero had an Onan. Despite religiously exercising it monthly, it invariably wouldn't start when I actually needed it. It was constantly needing $4-500 annually in failing parts (carbs, fuel pumps). Add in the need for regular service just like all engines, as far as I can tell, it just sucks money, and too often fails when one needs it. And getting warranty service from Onan was impossible as they were always backed up for months, but expected you to leave it with them to hold your place in line. So, I continued to just get it plugged in if hours of AC was needed.

In 2015 I traded it in for a Roadtrek with the big second alternator (known as the underhood generator). I absolutely love them and would never go back to the Onan. No added service... no replacement parts every year... and as long as your engine starts, you have power. If I use something like the microwave, or higher power pull appliance, I just start the engine. I only have two AGM batteries and solar, and they take care of everything else. (12v fridge, lights, fan) BTW, I only drive gas rigs... Chevy or Promaster.

These days I use neither since I now travel minimally, so I also have no AC except the one under the hood. I plan my travels when it is cooler...

[Urlauber]

Still pretty new to this, but here is my take. I have an Onan propane generator and so far I love it. Quiet and efficient.
We just spent a couple of days in Arches NP and it got past 100F in the afternoons. The A/C made it survivable. I wouldn't want to idle the engine for the whole time, and you'd need an awfully large battery bank to generate that much cooling.

[RVclassB4me]

I can only run my rooftop AC on my Roadtrek SS Agile off my 400amps Lithium ion battery banks for about 3.5 hours fully charged (without shoreline power/without under hood generator running).

Most of the time I’m parked at some RV camp with shoreline power. So no issues.

But occasionally I’m middle of nowhere without any shoreline power. I did not want to run the Sprinter Diesel engine (under hood generator) for hours and hours while it is some 90+ degrees F with 90% humidity outside. So I set up a cargo tray at the rear bumper hitch to secure a gas/propane generator that I bought on sale from Costco. It’s an inverter generator (3200 watts running/4000 watts peak, as I recall). Runs on either gas or propane. I usually use gas. One tank will run for about 9 hours continuously.

The rooftop AC generates enough noise that I do not hear the generator all that much on the rear bumper. Also I put the generator on a rubber mat to reduce vibrations. Plus I installed an extension exhaust pipe to divert the generator exhaust away from the vehicle. I also installed THREE industrial grade low level CO detectors inside the Sprinter. The “consumer” grade CO detector the RV manufacturer put in will NOT alarm until WAY TO LATE.

So far no issues.