Generator charging

mountainman · June 2020

During the summer I vacation in a TT surrounded by the Virginia mountains.
Being on the northwest side and covered by trees solar's not a really good option.
Afternoons for~5 hours from 1to 6
I run my 1700 2000 surge generator to power a 10000 btu ac. (1250 watts)
Would 5 hours of daily charging
With a 25 amp battery charger be
Sufficient on a 208 ah 12 volt battery at 75% soc?
If necessary I could bulk charge an hour or so before I run the ac as to not over load the generator.

InCogKneeToe · June 2020

Ok, I will give some of what My System does.

420ah of Batteries, when I wake up in the morning, my system is at 12.2-12.4v (while running a small fridge). So a fairly deep discharge. 50-55%. My Panels are roof mounted facing West, shaded from the AM. Sun.

So those Mornings, I need to run my Generator, and a 30a Charger. The Charger hits Float in under 1 hour of run time.

The 30A Charger consumes around 350 watts, so assuming, your AC is 1250 Surge wattage, you are safe running both at the same time. If it is 1250 running, Surge wattage would be 500-600 watts higher. Maxing your 2000 watt Generator for a short period or tripping it's breaker. But most likely, if the AC starts while the Charger is on, the Charger will just do a restart also.

mountainman · June 2020

The ac takes 1250 running.
Your 420 ah battery and 30 amp charger ~7% charge rate.
My 208 ah battery with a 15 amp charger ~7% charge rate.
If yours takes less than an hour to float
At 7% I could use a 15 amp charger Then if it wouldn't run both at the same time.
Couldnt I just charge for an hour then crank up the ac and leave the charger
On to float finish the battery.

BB. · June 2020

I am not quite sure what your question is MountainMan...

More or less, with gasoline gensets, when loaded to 50% or more of capacity, they are running at best fuel efficiency.

On the downside, pretty much every Watt that you take >50% of capacity, is a direct draw on fuel used (i.e., 50% capacity, 50% fuel flow, 60% of capacity is ~60% fuel flow).

Inverter gensets tend to be somewhat more fuel efficient down to 25% of rated capacity, but at higher loads (above 50%?), they tend to be less efficient than the plain old genset (the inverter costs power too).

Of course, if you already have the genset running, hour/maintenance wise, that is "free" for additional loads (genset already turning).

Personally, for home gensets (as opposed to commercial/industrial units), I would suggest running them at 80% rated power maximum (for continuous loads, such as battery charging and possibly an A/C system running on high for hours at a time).

You can do some estimates of fuel usage... Say 15 Amp @ 12 volt charger and ~4kWH per gallon (>50% loaded genset):

15 amps * 14.75 volts charging * 1/0.80 charger eff = 277 Watts
277 Watt load * 1/4,000 WH per gallon = 0.07 gallons per hour (>50% loading)
$3.00 per gallon * 0.07 gallons per hour = $0.27 per hour to run 15 amp battery charger (>50% loading)

Numbers above are really rough. For example, the 4kWH per gallon of gasoline, could easily be (from rough factory numbers, as I recall):

1,600 Watt Honda inverter genset * 0.25 rated load * 9 hours per 1.1 gallon tank = 3,272 WH per gallon
1,600 Watt Honda inverter genset * 1.00 rated load * 4 hours per 1.1 gallon tank = 5,818 WH per gallon

-Bill

mountainman · June 2020

@BB my generator is non inverter 1700 2000 surge. Question is would running at 90% burn up the generator?
Window ac pulls 1250 watts running
And 277 watts for a 15 amp charger
1527 watts so 90% loaded.
Not including ac start up surge.

InCogKneeToe · June 2020

The Surge is what I would be concerned with. Neither the Charger or A/C unit will suffer much from Voltage Drops.

My son recently rand my 1250/1500 watt Generator at around 1600-1700 watts. He said the Small Generator was surging so I started using the Big One.

Well Duh!, the only thing that happened was increased fuel usage and increased oil usage. Nothing he was running suffered a failure, even the BluRay, and did not even trip the Gen's Breaker (but it must have been close). I changed the Oil, and the Gen, ran like a Champ.

BB. · June 2020

The 80% rating of name plate--It is my suggested design goal. If your genset runs well, and the wiring/alternator does not appear to be getting hot/overheating (good cooling air to genset, etc.), then why not run it at 90%.

Surge wise--The inverter-generators tend to have limited surge capability (the inverter shuts down imeadiately with over current on the output).

The standard genset type, will (many times) simply lug through the surge (as current over loads, the output voltage slumps)--But will start the A/C (surge load) and keep on chugging.

Given that many of the non-inverter gensets are 1/2 the price of inverter generators (and arguably more capable for "ugly loads"), if it lasts >1/2 as long as the more expensive version--Why not run it.

The Honda euXXXX seem to run >2,000 hours (good oil, changes per manual, etc.)... And we had one member here that was over 6,000 hours (a bit hard to start, burned some oil).

There are just so many vendors/designs/different users/etc... The "general" suggestions and rules of thumbs are not going to "predict" how your specific genset is going to perform.

Many gensets seem to have problems around 500 hours... Things like the generator/alternator coupling failing, slip alternator rings, regulators go south, etc. And even on the "better brand" inverter gensets, there have been known issues with the pole pieces rusting/failing to be retained in the rotor over time, etc...

You are welcome to mention the brand/model of your genset and see what others have experienced.

Running 10 hours a day--500 hour life = 50 days (25 weekends), and 2,000 hours = 200 days/100 weekends.

Some folks have installed Hour Meter kits on their gensets (examples, I have never tried one):

https://www.amazon.com/generator-hour-meter/s?k=generator+hour+meter

And there is always the argument of breaking in with dino oil, and running long term with synthetics.

I purchased a oil filter plug with Magnet (does get the fine steel/iron particles)--Not a bad idea for light engines with no oil pump/filter.

I have always wondered about retrofitting some sort of oil filter system to an euXXXX -- And wondered how long the engine would last. Never found a filter kit on the Internet.

The typical industrial engine runtime equivalent to "car mileage" is 1 Hour of operation is 35 MPH * 1 hour... (my car's GPS unit does give "average" MPH --- And low and behold, it displayed ~35 MPH average (freeway commute in mixed traffic, family use around town/trips)

500 Hours * 35 MPH = 17,500 "car miles" equivalent
2,000 Hours * 35 MPH = 70,000 "car miles" equivalent
6,000 Hours * 35 MPH = 210,000 "car miles" equivalent

I like to run the "models" of various "things", and see how they compare (to cars, fuel usage, etc.). They certainly are not exact, but gives some good ideas of what is happening.

-Bill

mountainman · June 2020

My small generator is a power boss 2000-1700 with a Briggs engine from lowes.
Its 3 years old and discontinued now. it runs a 10000 btu ac ~5 hours a day for 8 weeks a year July-August . Then sits in the shed for the rest of the year.
Roughly 850 hours run time. 7 hours per 2 gal tank

at 70-75% load.

BB. · June 2020

Roughly:

1,700 Watt genset * 0.75 A/C Wattage usage * 7 hours * 1/2 gallon tank = 4,462.5 WH/gallon = 4.5 kWH per gallon

At 850 Hours, probably approaching 1/2 of a (hoped for) 2,000 Hour "good life"(?). Probably already a "not bad life" for a Briggs and Stratton small engine.

Everything seems good (math/fuel wise)...

-Bill

Generator charging

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