Smaller Generator with Boosting Inverter Charger - Any Experience?

[Bohemian]

Does anyone have any experience in downsizing the generator (say from 5.5 KW in a Bighorn) to a smaller generator (say a 3.6 KW, or 2.8 KW in a bighorn) and backing it up with a boosting inverter charger (like the Magnum SMH3012). and a large battery bank?

Bighorn 5th wheel (as an example, One I am interested in)

Cummins Onan QG 5500 Propane RV Generator
Total 5.5 KW (46A)- LP 0.8 gal/hr - 3.2 lb/hr @ 50% power

or

Cummins Onan RV QG3600 LP - 3.6kW RV Generator (30A)
Magnum SMH3012 Hybrid Inverter Charger - 3.0 KW Boosting Inverter Charger
Total 6.6 KW boosted (55A)- LP 0.6 gal/hr 2.4 lb/hr @ 50% power

or

Cummins Onan QG 2500 Propane LP RV Generator (21A)
Magnum SMH3012 Hybrid Inverter Charger - 3,0 KW Boosting Inverter Charger
Total 5.5 KW boosted (46A)- LP 0.4 gal/hr - 1.6 lb/hr @ 50% power


Considerations are, of course, all the heavy electrical uses: 2 ACs, residential frig, microwave

Advantages are the generators can be smaller and don't need to support peak current like motor startup which will be assisted by the inverter kicking in and adding it's current to the generator's current. This will support less weight for generator, lower cost of generator, lower LP usage by generator (especially during idle) Works well with solar added. More space for batteries.

Disadvantages. More battery capacity needed (cost, weight) (Maybe Li Ion LiFePO4, more cost, less weight, greater efficiency, life, available A-HR)

 

[Jim.Allison]

I did not down size the generator but, yes and it works quite well, I have a 5500 LP, and the Xantrex will kick in, just to provide a little boost while the generator spools up, or if shore power needs a little help. The inverter is lightning fast, any lollygagging on the generator or shore power behalf, and the inverter is there to lend a hand. I kind of feel like the inverter is showing off a little, because it will react in 1/24 of a second and will provide the extra power even when it is not necessary. Couple this with auto gen start, and you will have quite the system. When I installed my generator, inverter and solar, I did not realize that I could do what you are suggesting, later I realized that such a system could be built. But it is too late for me. These systems also have the capability of balancing L1 and L2 as well.

Does anyone have any experience in downsizing the generator (say from 5.5 KW in a Bighorn) to a smaller generator (say a 3.6 KW, or 2.8 KW in a bighorn) and backing it up with a boosting inverter charger (like the Magnum SMH3012). and a large battery bank?

Bighorn 5th wheel (as an example, One I am interested in)

Cummins Onan QG 5500 Propane RV Generator
Total 5.5 KW (46A)- LP 0.8 gal/hr - 3.2 lb/hr @ 50% power

or

Cummins Onan RV QG3600 LP - 3.6kW RV Generator (30A)
Magnum SMH3012 Hybrid Inverter Charger - 3.0 KW Boosting Inverter Charger
Total 6.6 KW boosted (55A)- LP 0.6 gal/hr 2.4 lb/hr @ 50% power

or

Cummins Onan QG 2500 Propane LP RV Generator (21A)
Magnum SMH3012 Hybrid Inverter Charger - 3,0 KW Boosting Inverter Charger
Total 5.5 KW boosted (46A)- LP 0.4 gal/hr - 1.6 lb/hr @ 50% power


Considerations are, of course, all the heavy electrical uses: 2 ACs, residential frig, microwave

Advantages are the generators can be smaller and don't need to support peak current like motor startup which will be assisted by the inverter kicking in and adding it's current to the generator's current. This will support less weight for generator, lower cost of generator, lower LP usage by generator (especially during idle) Works well with solar added. More space for batteries.

Disadvantages. More battery capacity needed (cost, weight) (Maybe Li Ion LiFePO4, more cost, less weight, greater efficiency, life, available A-HR)

 

[Bohemian]

Thanks Jim and Amy.

Which Xantrex are you using? I could not find a Xantrex with this capability. Please tell us more about the balancing L1 and L2. Is that like the power management systems where one leg is dropped on overload? Like on the Precision Circuits Power Management System?

I am still learning about these capabilities and planning the system.

 

[Bohemian]

I see what the Xantrex says. It seems to say that boosting function on the Xantrex units is only for "brief" periods like motor starting and implies that it is not for extended periods of constant use. I also think I understand the L1. L2 balancing. No, it's not a load dropping function. It optimizes the inverters current between the two legs, L1, L2.

I see that 50A RV electrical service is standard 120V/240V split phase service (though the 240V is not usually used in the rig). Are there any causations or exceptions to this in the RV industry?

 

[Bohemian]

OK, I am missing some pieces to RV 120V wiring.

It looks to me that when one is on 50A service one has 120V/240V split phase service (L1 and L2 120V circuits are in opposite 180 degree phases, 240V is available). When one is on 30A or generator one is on 120V single phase (dual phase) service (L1 and L2 are in the same 120V phase, no 240V is available). Simple wiring diagrams show one set of devices on one phase (L1) and another on the second phase (L2). The 30A adapter cable has a single phase input and bonds it to the second phase, so both L1 and L2 are fed from the single phase.

I imagine the transfer switch in the generator does the same thing, bonds L1 and L2 to the single phase of the generator output when on generator, and passes L1 and L2 independently when on shore power? is that correct? Does something else bond the 2 phases?

So far everything seems fine. All devices on both L1 and L2 work as long as one does not overload the services, and as long as no one has installed 240V devices.

Now to my confusion starts.

Magnun Inverter/Changers doesn't talk about the 2 phases in the documents I have found, though Magnum shows the back of the inverter/Charger and has duplicate sets of AC in and AC out connections that could/should be L1 and L2 phases, Precision circuits Power Management device talks about auto detect of the 50A split phase, 30A dual phase, and generator states and handling it according to their fixed protocol.

Xantrex, however, explicitly documents both L1 and L2 circuits and says that they can be configured for split phase 120V/240V operation or dual phase 120V single phase operation. Same for the Xantrex power management device. This seems to me to be a problem since some times the inputs will be split phase (50A 120/240V) and some times dual phase (30A single phase). There is now possible phase conflict. How is this solved.

This is now further complicated with boosting inverter/converters. These are inverters that can add additional power/amperage to the AC electrical circuits while simultaneously being powered from shore power, 50A dual phase, or by generator/30A, single phase, sources. This boost must be in phase with both L1 and L2 under either case. Also, possibly further subdivided into more circuits by power management systems.

So, help, how do all the pieces fall together?

 

[danemayer]

I imagine the transfer switch in the generator does the same thing, bonds L1 and L2 to the single phase of the generator output when on generator, and passes L1 and L2 independently when on shore power? is that correct? Does something else bond the 2 phases?

The automatic transfer switch that comes as part of the generator prep has separate L1 and L2 lines and the shore power 50 amp L1 and L2 are routed through those lines. The Onan 5500 generator also has separate L1 and L2, usually 30 amps each (some models 30/20).

Magnun Inverter/Changers doesn't talk about the 2 phases in the documents I have found, though Magnum shows the back of the inverter/Charger and has duplicate sets of AC in and AC out connections that could/should be L1 and L2 phases,

Heartland ships the Magnum (or other) inverter as part of the Residential Refrigerator Option. The output is 120V going into a dedicated transfer switch that feeds the frig. The other input to the dedicated transfer switch comes from the circuit breaker panel for when on shore power. There's no need to talk about 2 phases.

Precision circuits Power Management device talks about auto detect of the 50A split phase, 30A dual phase, and generator states and handling it according to their fixed protocol.

The Precision Circuits Power Control System manages selected devices that are assigned to L1 or L2. Except for detecting whether you have 50 or 30 amp shore power, I don't think it cares about phases.

If you're trying to design an advanced solar or multi-battery system with sub-panels, perhaps someone can help if you can be more specific about what your future plans look like.

 

[Jim.Allison]

BTW This is 75% of a complete solar system also.



Since the inverter/charger is fed with 120v from L1 and L2, it chooses the most qualified line or draws from both of them to output 1 30 amp line to a subpanel.

There is no association between the generator / shore power and the inverter/charger through your existing transfer switch. The inverter has its own internal transfer switch and neutral bonding if required.

I find it much easier to view the inverter/charger and sub panel as an independent appliance fed by L1 and L2 from the main panel.

The feature that activates the system to fill in with power has an adjustable set point, and can be enabled or disabled.

I understand that there is little difference between the Magnum and the Xantrex as the Magnum engineers all came from Xantrex, since I really did not understand this system when I started and cannot endorse either one, but I can say that my Xantrex Freedom 3012 works flawlessly. Any problems that I have had is my own learning curve and involved the digital display and an understanding or lack of understanding of all the features. I could have just as easily bought a Magnum.

I provided the following links for your study, since the basic operation of the Magnum and Xantrex are very similar, this owner's guide and install guide might assist you in understanding your topics.

http://www.xantrex.com/power-products/inverter-chargers/freedom-sw-12v_newgen.aspx

http://www.xantrex.com/documents/In...om-SW-NewGen/97-0019-01-01_Rev-E(artwork).pdf

http://www.xantrex.com/documents/In...om-SW-NewGen/97-0020-01-01_Rev-E(artwork).pdf

Good luck will be looking for updates.

 

[Bohemian]

Thank you all. I am on a fast learning curve. As with many technical matters a technical person who is out side of his own field tends to consider all the possibilities and all the complexities. Often in a single application many of the possible features of flexible devices are not used. That, even though one can often see more efficient or better ways to use the device (if only there were one more programmable function). I have been reading the guides, specs, install manuals. I almost always find documentation leaves out some critical considerations.

It appears to me that if one is using a power management option in either of these systems: 1) the PMS module takes care of the concerns, and 2) uses only a single phase inverter setup (dual phase mode, not split phase mode).

I will also be in Hershey soon and having some discussions with the suppliers. I expect there are some undocumented modes for the Xantrex considering the extra connections (or future possible plans or software)

The biggest questions are practical ones. Is a 2.5 KW generator enough or is the 3.6 KW preferable. How much is the fuel savings over the 5.5 KW generator in real use terms and how much does that extend boon docking.

As to not thinking about phase. If one configures these improperly for split phase and then wires them for dual phase one will find out quickly that phase matters a great deal. Do it yourself people need to be aware. I really hate doing a smoke test.

Since we have no 240V devices in most systems, that is a moot point for most. Single phase systems will work fine. If shore power was dual phase ( one phase, no 240V) rather than split phase (two phases, 240V L1 to L2), the questions would not exist.

I am getting there. Some simple explicit application and internal wiring diagrams would have helped a great deal.

BTW, what model Magnum is Heartland installing for the residential frig?

 

[Bohemian]

Investigating further, I see that most of these devices that are appropriate to our use have only one single phase set of inputs and can not handle split phase inputs. However, the Xantrex SW3012 3000 watt inverter ?charger has inputs that can handle either split phase or single phase as it's documentation talks about configuring for one or the other. The shoreline inputs are split phase and the generators are single phase. Somehow this is taken care of in most installations (perhaps only one side is hooked up)