Inverter generators power to fuel ratio

If you are interested, you can also try 1/4 loading too...

In general with gasoline/propane/natural gas power gensets (at least AC gensets with fixed RPM requirements), below ~50% loading, the fuel flow remains at about 50% number. So, the sweet spot seems to be be 50% or higher loading.

With the Honda eu2000i and similar, because they can throttle back to lower RPMs at lower AC loading--They can be more fuel efficient at lower loading. However, near 100% loading, they may be less efficient (the inverter power conversion adds losses over a simple AC Alternator).

-Bill

Just watch the "maximum loading" too. Many residential gensets really do not like running more than ~80% of rated power continuously or they can overheat the alternator wiring/components.

With constant loads like battery charging--It is much easier to "sneak up" and fry a genset with heavy/continuous loads.

Also--For stuff with poor power factor (motors, many battery chargers, some electronics)--It is VA rating that is usually the electrical limit and not Watts...

Say you have a well pump motor that runs a 1,000 Watts and 0.67 PF--The VA loading would be:

• 1,000 Watts / 0.67 PF = 1,493 VA

So--You could be over current on the genset even though way under watts (and fuel flow is generally following the Watts loading, not the VA loading--because of a bunch of math).

-Bill

Assuming this is the correct battery:

http://pdf.wholesalesolar.com/battery-folder/surrette/S-550.pdf

As always, get all the information you can find from the Mfg:

http://rollsbattery.com/uploads/pdfs/documents/user_manuals/Rolls_Battery_Manual.pdf

These are 6 volt batteries at 428 AH capacity (20 hour rate). You have 2series x 2parallel for a 12 volt @ 856 AH battery bank

In general, we recommend 5% to 13% rate of charge and 10%-13% rate of charge is "ideal" (5% is needed for equalization and smaller weekend/seasonal folks will sometimes charge at 5% with few panels, smaller genset).

If you have a current meter on your inverter-charger or a DC current clamp meter, you can adjust directly for your desired target current (say 10% or 85.6 amps for your bank).

On the AC side with the genset you have have various issues to deal with. Depending on the genset (local temperatures, altitude, etc.) you have a maximum genset capability. Say you have an 1,800 Watt rated consumer genset... At the very much (cool weather, sea level) you would want 80% of the genset capacity or:

• 1,800 Watt * 0.8 = 1,440 Watt max
• 1,800 Watt * 0.5 = 900 Watt min (fuel efficiency)

And note that for consumer gensets, generally maximum Watts = VA (volt*amps) rating. This means that "poor power" factor is also a limiting parameter too.

You can measure the AC current directly (meter, clamp meter) and figure out VA:

• VA=V*I
• I = VA/V
• 1,440 Watts(Or VA) max / 115 VAC genset = 12.5 amps (AC) max recommend
• 900 Watts min / 115 VAC = 7.8 Amps AC minimum (fuel efficiency).

You can also figure out (roughly) the math for AC to DC conversion--A typical "decent" quality inverter-charger may look like:

• VA = 85.6 amps DC * 14.75 volts charging * 1/0.90 charger eff * 1/0.80 typical power factor = 1,772 VA (estimate)

Charger Efficiency may run 80 to 95% efficiency. Power factor may run from 0.67 to 0.95 (power factor corrected supplies).

-Bill

The 13% rate of charge is based on taking a Flooded Cell Lead Acid battery from 20% to 100% state of charge (i.e., a fork lift battery) without active cooling/temperature monitoring/thermal management of the battery bank.

For the solar side, we suggest ~50% to 80% or to 90% as a typical genset charging range. And 20% rate of charge for a genset based charging is not going to "fry" the battery--But it is something that I would monitor (especially the first few times) to ensure that the battery does not get above ~110F (hot batteries are unhappy batteries). Lead Acid batteries are "very efficient" charging below 80% state of charge--As the battery approaches full charge, the efficiency drops (current, instead of "charging battery" goes into making Hydrogen and Oxygen gasses, and heat). At 100% State of Charge, pretty much all charging current goes into gassing and heat (at 100%, it is very possible/likely to overheat a lead acid battery with 2-2.5% state of charge if done for too many hours at a time).

For solar charging, having a remote battery temperature sensor (common option for higher end solar charge controllers, not too common for AC battery chargers--for some reason--cost, more wires to connect/fail/break?) helps prevent thermal run-away (as battery gets hot, charging voltage and, therefore, current is reduced).

Since other than for active equalization which you should be monitoring closely (which should be monitored unless is it is a short time period "auto-equalize" cycle), people are not going to run the genset at 20-30% current very often or much over 80% state of charge (waste of fuel and generator wear and tear).

I will stop here--I think this answers your question without and excessive amount of hand-waving (I hope).

Very happy to help--All I ask is that you help others when you can.

-Bill