running a kubota 7kw gen

castilloj · June 2010

Hello everyone , im planning on buying a kubota 7 kw diesel generator. My question is what can i actually use with it? can it charge my inverter batteries?(i have a 2500 watt outback inverter) could i run a 18,000 btu with a fridge ,freezer?
Any ideas?
Thanks

BB. · June 2010

Re: ruiing a kubota 7kw gen

castilloj,

You can run my entire suburban 3 bedroom home on that thing with lots of power left over!

Well--There are two ways of looking at using the genset--1. what can you run off of it... And 2. what are your needs and will this guy fill them or not.

1. is pretty easy--a Diesel engine should be operated at 60-75%+ of its rated load to keep the cylinders from glazing, from coke/carbon forming in the combustion chamber, and for efficient fuel usage.

0.60 * 7,000 watts = 4,200 watts minimum power loading (more or less).
18,000 BTU / 3.413 BTU per watt = 5,274 watts (assuming an electric heater)

Now, at 4.2 kW--that guy may be consuming around 0.5 gallons per hour...

Generators (engine driven alternators) to vary in frequency output--so if you are going to connect to an Inverter/Charger--make sure that they are rated to be compatible with a generator. Some Inverter/Chargers are really designed for utility power and may not phase lock onto a wandering generator.

2. is to look at how much power you need (peak, average, etc.) and what it is needed for (off-grid, emergency backup, battery/inverter or not, optional loads, etc.)...

Typically, for off grid and emergency power--people tend to reduce their loads as much as possible. This reduces the costs of building an off grid power system, plus reduces maintenance costs (fewer batteries to replace every 4-8 years or so), and less fuel for the generator set.

If you live in an area requiring A/C--the newer AC systems use 1/2 the energy of the older systems--and you can get smaller mini-split A/C systems that will run on 300 watts when set to low. Also, they have heat pump units too--so you can heat your home ~2x as efficiently than just using a resistance heater.

For example, my home--in an emergency--can run very nicely on a 1,600 watt generator--and frequently down to 400 watts or so (fridge, freezer, a few lights, radio, etc.)... 1.1 gallons of fuel will run it for 4-15 hours (depending on loads).

So--what is it you are looking for?

-Bill

icarus · June 2010

Re: running a kubota 7kw gen

As Bill suggests, generators that are not run ~50%+ of rated are very fuel inefficient. Calculate your load and work backwards.

7 kw is a pretty big generator for most houses as a standby. 7 kw would probably be big enough for example to run a deep well pump, and a electric oven at the same time.

The short answer is you can use it for nearly any use you chose up to ~7kw depending on the duty cycle of generator.

Tony

castilloj · June 2010

Re: running a kubota 7kw gen

So these are the main things I'll be using with the generator.
Fridge- 6.5 amps full
Freezer 5 amps
Air conditioner 24,000 btu 12.7/11.7 amps
And I'll also be using a tv and a satellite receiver.
Also a wAning machine.
Now with all this could it also charge my 24 v battery system?
I have a 2,500 watt outback power inverter.
Thanks

BB. · June 2010

Re: running a kubota 7kw gen

Yes, you can probably run your stated loads on the 7kW genset--Assuming tha this is a 120/240 VAC 60 Hz split phase output genset (and not 3 phase or other variation) and that you can properly connect a transfer switch and balance the 120 VAC loads across the 120/240 VAC output. (my guesses below--you did not supply line voltage for each device):

Fridge- 6.5 amps full

6.5 amps * 120 VAC = 780 Volt*Amp

Freezer 5 amps

5 amps * 120 VAC = 600 Volt*Amp

Air conditioner 24,000 btu 12.7/11.7 amps

12.7 amps * 240 VAC = 3,048 Volt*Amp

And I'll also be using a tv and a satellite receiver.

~200 watts or so (really depends on TV--Big/small/etc.)

Also a wAning machine.

Not sure what this is (probably a typo?)

Now, battery charging depends on the size of your battery bank (bigger bank needs more charging current); (right charger for the job); and how much power you use (lots of energy at night, or just enough for a TV, fridge, and a few lights); etc.

Voltage (24 volts) is part of the equation--but Amperage (average and peak) plus time, for example:

20 amps * 24 volts * 10 hour a night = 4,800 Watt*Hours per night

Can it charge you 24 volt battery bank--I don't know--What is the Amp*Hour rating of your battery bank (200 or 2,000 AH) and how much power (amp*hours or Watt*hours) per night do you consume (or plan to consume).

What is your plans for the 2,500 watt outback power inverter? Is it a pure 120 VAC 60 Hz inverter? Is it an Inverter/Charger? etc...

There is no "simple answer" to your question. It depends on the genset specifications, your loads, how you use your loads, and your expectations.

I hate to pry--but what is it that you want from your diesel genset? Emergency Power after an ice storm? Full off-grid home? Etc.

People will run a nice genset 24 hours a days for months/years on end (with downtime for maintenance).

However, this is not going to be cheap? Running 24 hours a day could easily (my uneducated guess) take 12 gallons of diesel per day. At $3 per gallon, that is $36 per day or $1,000+ per month fuel bill (and ~350+ gallons of fuel per month).

Can it be done, easily--Is this what you are looking for? Probably not.

In general, for off-grid / "conservative/conservation" life style--It is almost always better to address your loads first (insulation, skylights, double pane windows, energy star appliances, using a small laptop computer instead of a big desktop system, turning things off when not in use, turning off standby loads like DVR's and Satellite systems when not used, etc.).

Once you have done that--then looking for the smallest battery bank / inverter / charger / solar panel array / genset that will supply your needs becomes a lot easier and more cost effective.

-Bill

castilloj · June 2010

Re: running a kubota 7kw gen

Sorry for typo , that was washing machine.
What I would like to do is run the genset maybe 10 hours a day while the rest of the hours using my battery system. The batteries I'm using is 8 rolls S600 batteries which give 600 amp Hrs. @100 Hr. rate or 450 amp Hrs. @20 Hr. rate. I'm also installing 16 100 watt solar panels to help with charging the batteries. The genset I was looking is a phase 1.

I plan on using 8 amps using box fans at night for 10 hours.
My inverter is a inverter/ charger and where I'm at I'm completely off grid .
The homes here are all concrete ,so it gets really hot during the day .

stephendv · June 2010

Re: running a kubota 7kw gen

Is your genset rated for continuous use? If not, it won't handle running every day for 10 hours.
Secondly, note the max charge current on your outback inverter, I'm assuming you have the VFX2812 which has a 125A charger at 12V, so about 1.5kW max for charging.

Dave Angelini · June 2010

Re: running a kubota 7kw gen

You are asking if you can run 8 amps AC of 120v fans off your 900 AH 24V battery system all night. Yes you can but you will be deeply discharging the Surrettes.

You are asking if 10 hours of gen time is ok with all the solar you have. This is far to much time These batteries will be charged in 3 or 4 hours and alot less time with the solar.

If it is hot where you are then there are far better ways to use that 8 amps or less at night to keep cool.

Drop me a line! Where are you located?

BB. · June 2010

Re: running a kubota 7kw gen

You really need to tell us what voltage you are talking about when speaking of current 8 amps at 120 vac vs 24 vdc:

8A * 120V = 960 watts
8A * 24V = 192 watts

Have you looked at adding insulation/double pane windows/shading to your home? Would be much better to keep the heat transfer to a minimum before paying to fire up the A/C or heat.

Yes, you are on the right road with using the Genset + Solar to charge the battery bank and use the inverter for evening/night loads.

However, you really need to get a better handle on your loads and equipment.

Check the model number for the Outback inverter/charger--Some were not designed to operate on a genset (generators tend to wonder a bit in frequency and some of the inverter/chargers were designed for connection to the grid). You may need a separate AC battery charger in this case (or another brand/model of inverter charger).

Are you off-grid already? Or is this a new home/installation for you?

In the end, if you can run your heavy loads during the day and/or using the genset (for example A/C when needed)--and design the rest of your system to run off of solar panels + batteries for the rest of year--may be a good compromise (with your wallet). If your area has cloudy/stormy winters--you may choose to run the genset X hours per week instead of installing even more solar panels.

If you can let us know approximately where you live--we can look up the solar irradiation numbers for your area.

In the end, measuring/predicting your loads both power levels (watts) and in time (hours per day) is really needed to size your system properly.

-Bill

castilloj · June 2010

Re: running a kubota 7kw gen

I'm located on the northwest point of Haiti called mole st Nicholas. Iam off grid there is no city power. When I mentioned I'm using 8 amps ,that's what I see on my outback power mate when I'm using my 24 v system .

icarus · June 2010

Re: running a kubota 7kw gen

Not to put too fine a point on it, but take some of your generator fuel $$ and go by some insulation for the structure. Every dollar spent on conservation will save many dollars in energy costs, whether or not it is PV or generator power. Consider awings and other shading strategies to keep the building from picking up so much heat. For example, a covering of tin or plywood a foot away from the south walls and roof facets would keep the direct heat gain off the building, significantly reducing the net heat build up, and therefore reduce the cooling load. Just one idea.

Tony

PS I realize that Haiti is probably not a easy location to procure a lot of exotic stuff, but creativity might be able to reduce your loads substantially.

solorone · June 2010

Re: running a kubota 7kw gen

I realize you are remote and no power, but as has been mentioned conservation will save you a load of money. Your fuel bill will $280 to $330 a month at my cost $3 a gal. and that does not count your hauling cost. Careful of the grade of diesel that is available, and look into an injector cleaning agent.

Then there is the noise, can you remote it from the house, or build a sound wall between the gen set and house. I also set my exhaust 25' into the air and of course located it down wind.

If you go this route I guess it goes with out saying spare parts are a must, as is regular maintenance, especially adjusting the tension on the alternator belt, you will kn ow when this is needed, as your hertz will fall off. Parts supply from Kubota have been a bit of a problem of late for myself, but they make a fine unit.

I have a friend in central Alaska with a large solar array, and he solved this part of the problem with 2 gen sets.

running a kubota 7kw gen

Comments

Categories