Mounted Genset vs Portable Generator

[RebelWithoutACausey]

Im getting towards the electrical rough in phase of my build and im torn between two generator options. I have to decide fairly soon, so looking for opinions of those who have experience with one or both.

First option, I have an Onan QG 4000 genset pulled off an RV with 100 hours on it. Option 2, I also have a Honda EU2200i portable generator. My electrical system currently consists of 2600w of solar, 10.2 kwh of lithium. All of my appliances will be electric.

Onan Pros:
-Mounted underneath, out of sight, out of mind
-4kw output
-Can be connected to my Cerbo GX to auto start when my battery bank gets low, wont have to think about it.

Onan Cons:
-I will have to buy and hang a gas tank, the control panel. Probably $600-800 worth of additional infrastructure just to use it. Im already blowing my budget on the build.
-PITA to work on or service, unlikely to be able to fix on the fly should it go down
-Expensive to replace
-Drinks 1/2 gallon of fuel per hour

Honda pros:
-Quiet as a church mouse
-Uses 1 gal of fuel in 8 hours
-I can tear it apart and fix it on the fly with like 4 tools
-Easy to replace if needed
-Doesn't require any additional infrastructure to be installed

Honda cons:
-Not weatherproof (big one)
-1/2 the watts
-Cannot be set up to auto start

If you were in my shoes, what would you choose and why?

Thanks!

 

[sportyrick]

One other thing about the Honda, someone can steal it, on board is more work but more secure in several ways.

 

[Ronnie-SKO]

I went with the 4000 watt Onan. Used an 18 gallon fuel tank I took of a junked tractor.


One issue I had was keeping the portable cool while driving, they can not be in a compartment, so tie it to the back bumper? At least for me I wanted built in, and remote start.



I really do not believe the honda would use only 1/2 gallon in 8 hours, maybe at very low load but not running a/c. As for the Onan yes 1/2 gallon per hour running a rooftop a/c is what mine uses.

 

[sportyrick]

Onan generators are designed to be enclosed while running that's why they draw their air from the end and discharge from the bottom, at least mine does.

 

[RebelWithoutACausey]

I don’t intend to run it while driving, so that isnt a factor for me. It will stay in my “garage” until I need it, and when I need it, i’ll be with it so theft also isn't much of a concern. It will only be used to charge batteries if the solar isn't able to keep up.

I can speak for the Honda fuel efficiency at low loads, but even if I had it running at full tilt, even 4 hours per gallon is significant compared to 1/2 gph.

That said, the convenience of the onan would probably sway me that direction if I knew it would be long term reliable. How many hours are on your onan, Ronnie?

 

[Ronnie-SKO]

My 4000 watt Onan does not have an hour meter. However I have used 5 years now, so my best guess is over a 1000 hours. It was used when I got it.

In another application I have the Onan QD 12,000 watt with over 6000 hours on it.

 

[ewo1]

For those of you who use ONAN gensets, I posted a link to a very comprehensive list of Onan Genset service manuals in this thread.

I would get what you need before the link goes away forever.
:marshmallow:

 

[Booyah45828]

This seems simple to me. If you have both units already, try the portable one first and see how it does. If it doesn't work out, then go through the hassle of mounting the onan. With 2.6kw of solar and a 10kwh battery bank I assume any generator will be for emergency power when the bank is dead? If so, then a portable unit can't be beat for rare use instances. Pull it out, turn it on, and let it charge you back up. If you find that you're running dead every night, then mount the onan and try that.

A couple bullet points for you to ponder over.

1) Honda's gallon of fuel per 8 hours is at idle with no load. The onan and honda will experience similar fuel consumption when ran at high outputs. Unfortunately, the honda has a small fuel tank, so only plan on running it an hour or so at max output, so plan on an external tank mod of some sort if you don't want to have to refill it every hour.

2) To piggyback off of 1, in my experience, inverter generators shine at fuel consumption and noise reduction when used at low/moderate loads. You'll be at a high load charging this bank as fast as you can, so you won't be fully realizing the benefits an inverter unit has to offer. The onan might do just as well or better in this scenario.

3) Portable units can be swapped out quickly wherever and whenever. Mounted units not so much. I know a lot of older rv's that the onan underneath is no more then ballast at this point. A lot of your older onans are prohibitively expensive to repair, if not impossible to do so.

 

[ol trunt]

I put my Yamaha inverter genny in a fan cooled slide out drawer and added a remote 8 gal tank. About the same amount of work as installing an Onan but cleaner electricity and no where near as much noise. Silent at 10 feet unless you cock your head just right

Jack

 

[RebelWithoutACausey]

To your 3rd point, that is pretty much my only hesitation with the onan. If SHTF mechanically to a point where I can’t fix it, I will have hated to go through the whole process of installing the thing just for it to be a boat anchor. In the RV shop I work at, I have seen plenty that are boat anchors but we are also talking about owners that let them sit for a year without starting. Trying to get a grasp of reliability from people who use them regularly.

I was told by the dealer I bought my solar components from that with the onan and my victron quattro, it should be able to fill the batteries from completely dead in two hours. Im not entirely sure how to do that math for the honda but thats another variable worth thinking about.

Trunt, I did see your install in another thread, I personally dont want to close in the honda under the bus if thats the one I go with. Im confident in my ability to secure it, not so confident in my ability to give it enough air while also keeping it safe from road debris.

 

[flattracker]

I went with an internally mounted Onan generator in both of my Crowns. You can get fuel tanks on eBay pretty reasonable. The new Crown has a 20 gallon tank. Since the generator and the bus both use diesel I plan to install a fuel transfer system that can move fuel either way to provide backup for bus fuel or generator fuel. The diesel Onan is very fuel efficient. Being installed in the spare tire bay, it is out of the weather. Providing remote start and monitoring capability was not expensive as I made my own wiring harness and bought aftermarket gauges. My experience is that Onan generators last a long time also.

 

[Booyah45828]

How long it takes to charge would depend on usable KWH from the bank, your charger, and the KW the genset is rated at. I feel 2 hours is pushing it, but I don't know what the specs are of the victron that you mention.

 

[RebelWithoutACausey]

The bank is 10.2 kWh, honda should be good for 2kw, onan 4kw, and the quattro is a 5kw inverter with 100 amps of charging.

Im really curious what the formula is to figure charging time.

 

[Booyah45828]

Basic formula is storage volume divided by charge rate. The problem is that your charge rate isn't linear, as there are multiple stages to it, depending on soc of the bank. It's also best to stick with kw when doing the math, as your 100 amps of charging is only half the story without voltage known as well. Also, is it 100 input amps or 100 output amps? For instance 100 amps at 12 vdc is 1.2 kw, which is less then both of your generators. 100 amps at 120vac is 12kw, which is much more then your generators. So it's a big difference between the two.

Also, there's likely conversion losses with the charger as well. So 2 kw of 120vac consumed might only yield 1800w of charging. Lithium can also provide 100% of rated capacity unlike lead, but some prefer not to discharge/charge outside a certain soc % for battery health.

Someone that knows more about lithium, chargers, and battery banks can comment better then me on this. But the little I know, you're not charging 0-100% with a 4kw genset unless you're only using half of your 10.2 kwh battery bank.

 

[RebelWithoutACausey]

Ok I’m tracking now. Its a 24v system so if it charges at 100 amps at 24 volts, thats 2.4kw. The onan would keep up, the honda would be at full bore and still be slightly under that.

So just for simplicity, not counting the charge rate based on the batteries SOC, from 0% to 100% would take roughly 4.5 hours.

Am I getting a grasp of it?

EDIT: I did some google fu and allegedly the honda burns .25 gph on full load. So if I need to run the genny for 4 hours in worst case scenario, the difference in fuel economy is 1 gallon to charge the bank with honda vs 2 for onan. I dont think that difference is significant enough to have it on the pros/cons list anymore.

EDIT 2: Also of note, if I use the honda to charge batteries, 100% of that power is used charging. If I run the onan to charge batteries, I still have 1600 watts left over to run appliances while I charge. I think I have my winner.

 

[HamSkoolie]

Ok I’m tracking now. Its a 24v system so if it charges at 100 amps at 24 volts, thats 2.4kw. The onan would keep up, the honda would be at full bore and still be slightly under that.

So just for simplicity, not counting the charge rate based on the batteries SOC, from 0% to 100% would take roughly 4.5 hours.

So some points that I didn't see mentioned.
Since yo mentioned a Cerbu I assume you have either a MultiPlus or a Quattro and with the size of your solar it's likely a MultiPlus.


You generator will have a maximum continuous output spec in Watts.


Your charger (whether it's stand alone or part of a MultiPlus) will have a maximum output spec which is the highest it will pump into the batteries but this is not how much is pushed during the entire charging process as it is staged with at least three levels of output. This is usually spec'd in Amps but you'll need to do some conversion to determine how much the MAX output is in Watts from the generator (be sure to add in a bit of inefficiency within the charger).


Your battery bank will also have a spec for the maximum input charging voltage. Since you said 10.2kWh battery bank I'm wondering if you have the EG4 rack mount batteries. If so the spec is MAX 100 amps input EACH but the recommended is a lot lower (for longevity). However, two EG4's would, to do max charge, require a charger of 200Amps capacity (I wouldn't recommend for that 60EA when rated at 100 but definitely go with the specific battery you have.


If you have the multiplus, the chargers aren't anywhere near that capability and so the smaller genset might be running at a lot less load than you're thinking.


We ended up buying the EG 6.5 "all in one" inverter because it was cheaper, 100% compatible with our same brand batteries, included TWO MPPT controllers built in, higher capacity charger, and the onboard screen could be relocated with just a single modular cable instead of having to buy a Cerbu and display.


Bottom line, be sure to line out a planned system and understand the specs and compatibility/capability in all the interfaces.