Can you run a onboard generator with an external generator!

[Doug M]

I have a 50 amp Lithium 2414 TH with2 AC units. I have a onboard Onan 4000 generator installed. I can only run one AC at a time with the 4000 watt onboard generator. Can I or how do I hook up an external generator so I can run everything with a internal and external generator. I was told I can run a 4000 watt inverter generator externally along with the onboard Onan. Please advise and thank you in advance.

 

[TJ&LadyDi]

I think this can be tricky. I am assuming that you want to feed additional 120VAC to the on-board inverter rather than 12VDC to the low-voltage electrical system. Phasing of 120VAC comes into play and, if you get it wrong, substantial damage can be done.

If you are talking about feeding 12VDC directly to the low-voltage electrical system, I'm not sure how you can do it. It may be possible but is outside my area of expertise.

In either situation, I would strongly suggest consulting a qualified electrician.

TJ

 

[Kevin D Pem]

I would say no you can't. Inverter generators that will tie together tie the DC bus together and use one inverter. Most inverters will fail if left in the circuit when other source is applied. This includes UPS systems as they have sensing circuit and relays to be certain only one system is engaged at one time. Two generators could be tied together if they are both standard generators by using a meter to time the connection and then they would work as a servo type system.

Two methods do work. Wire one AC to it's own external cord, or
Use a large enough inverter to power everything and supply large cables connected to the battery bank from the generator. Because I use a large inverter and seldom connect to the grid, I use this method. My external generator that supplements my battery bank is what is called a poor boy generator that is an automotive generator connected to a gas motor. Between the poor boy and solar I can run most anything I have.

 

[Jim]

My input, for whatever it's worth.

I have a 50 amp Lithium 2414 TH with2 AC units. I have a onboard Onan 4000 generator installed. I can only run one AC at a time with the 4000 watt onboard generator.

I would have thought your generator would handle both of these at the same time. But I guess you wouldn't be here asking questions if that were the case, right? Let me ask, did you add the second air conditioner yourself?

Also, there is a good possibility that putting a "soft start" device on the air conditioners will avoid the "surge" necessary to fire them both up. I've seen this work for lots of people who want to run two air conditioners but the "surge" is more than the generator can provide. Here is a link to some that you can research.

Can I or how do I hook up an external generator so I can run everything with a internal and external generator.

I can't image that being possible. It's not like adding a second water source to an existing water source, and getting twice the volume, which is what It sounds like your thinking. But as @Kevin D Pem mentioned, you could separate one of the air conditioners from the main wiring and then wire it independently to the external generator, and run it that way.

 

[Doug M]

Thanks all for the good information. Not the answer I was looking for, but what I thought would be correct. I didn't think running both was an option, but had to ask. Anyway, ill look into the soft start and just run one at a time for now. Thanks again and happy Camping!!

 

[Chuggs]

Hybrid inverters may allow you to do this...depending on how it's wired. Generally, RV manufacturers do NOT wire rvs to do parallel generator operations. Airplanes, and large motor yachts have adopted the capability. It requires additional tie breakers and some form of phase synchronization to parallel them. It's becoming less used...modern circuits generally keep the ac power sources independent. The busses they power are capable of switching to the other source in the event of a failure...but generally...they do not tie the generators together to simultaneously power the same bus.

We did it on Jet Airplanes back in the day. We would connect multiple generators to a common main ac bus...but could manually adjust the frequency to phase align them before closing the bus tie breaker. Some of the small inverter generators have circuitry built-in to synchronize their phase...to allow parallel operation. Hybrid inverters can generally tie two ac sources...check manufacturers recommendation.

 

[VTPete]

You might put a call into Magnum Technical Pre-sales. They have alot of experience in AC Coupling or Inverter assist scenarios where their inverters are pulling from batteries, solar, external sources/Generator etc...
Might be some food for thought here..

https://www.magnum-dimensions.com/sites/default/files/MagArchive/AN-0002-AC-Coupling-Rev-5-10.pdf

https://www.solar-electric.com/lib/wind-sun/Magnum_MSH4024RE_Solar_Wind_Hydro.pdf

@redbaron wrote a useful battery guide that's also a good reference and mentions this principle:

RedBaron's Simple Guide to Battery Life in your RV

This guide explains the 12-volt battery system found in all RV’s and how to properly maintain them. There is specific information relating to Magnum Inverter/Chargers and Newmar motorhomes that use these chargers. Even if your system does not...

rvforums.com

 

[Chuggs]

Doug, I reread your post...

You can actually install an automatic transfer switch.

An automatic transfer switch can accept two sources of power...and default to the priority source when available...or secondary source when the primary is not present.

They make these for solar Installations so that the solar powers during the day, but utility would power at night.

Making the power from an add-on inlet box which will be connected to your external generator, could be wired as the primary. Then run the power from your second a/c's breaker to the other auto transfer switch input. Wire the output of the ats back to the wire going to the a/c unit.

Once wired...that air conditioner would function from thee source it normally uses. If you see a need to run the generator...start your normal generator...but only turn on the #1 a/c unit for the time being. Then hook up your external generator to it's inlet box and start it up. When the ats sees power...it will switch the #2 A/C to the external generator, as it has priority if present. Finally, turn on the second A/C. Just know that if the external generator quits...both a/cs will be back to trying to run on the onboard generator.

Does that make sense?

It's a specific work around for the #2 air conditioner only...

You can do it even cheaper with a manual transfer switch. It would be wired the same...but you manually select 1 or 2 for your power sources.. they usually have a 0 position as well, which removes power from the A/C. These are only like $12 on Amazon...and since you have to manually hook up the external generator...a manual transfer switch wouldn't be that much effort to set for the desired source.

I have done something similar...but I am manually selecting main AC power or Inverter power to run my front A/C unit. It's a Leviton 20A rated dpdt switch. This allows switching the neutral along with the line from the selected source of power.