Generator Questions / Comments

[Vikas]

Many years after purchasing my generator, today finally I had to hook it up to the house. It is a yellow Champion (Costco special) 7000/9000 one with the remote start. So far, I have turned on couple of refrigerators, gas water heater (exhaust bloer for it), fios box, router, wireless router and a computer and it is holding steady. I am trying to figure out the fuel consumption. It has a gauge but it does not register anything until the tank more than half full. I certainly do not want the gas to run out while it is providing the emergency power as it unfortunately does not have the intelligence to turn off the power before shutting itself off (contrary to the owners manual claims). Knowing it is pretty bad idea to add the gas while it is running, I am planning on adding some gas after running it for an hour or so and then turning it off.

The generator has a small LED display panel which can show either the voltage or the frequency or the run hours. Between the voltage and the frequency which is the better measure to estimate the load on the generator? I am seeing about 250 V and 62 Hz on the display.

If I don't open the refrigerator, it should probably be able to hold the internal temperature for at least four hours or more, correct? I would like to run the generator for couple of hours during the day to "recharge" the refrigerators and then give four hours of rest to the generator before firing again. I will be losing the internet though :-(

 

[eljefino]

Neither. Voltage and frequency should hang steady. You could use a kill-a-watt meter if you have it hooked up via 120 only. You could use a (digital) bathroom scale to see how many gallons per hour you go through: gas is approx 6.5 lbs a gallon.

I bet you're using 1000 watts, maybe, with what you have. This generator is a little lot oversized and will use its share of fuel. But yeah it'll carry the house if you want it to.

 

[meep]

Vikas, neither Hz or voltage will really give you a real indication of load. V sometimes could, unless the genset has some basic voltage regulation circuitry in it, which makes any reading non-linear. You'd really need an inductive, clamp-on ammeter on each hot leg to know.

Your plan for a couple of hours of runtime throughout the day is your best bet. You will be surprised to see how quickly your fuel stores get chewed up when running. Even with such a small load as you describe, consumption will be fairly high, and also predictable. the manuf may state run time such as 7 hours on a full tank at half load. You may want to start with that as a baseline, and just assume that any load beneath half, even zero, be calculated as a quarter load. I would guess that your running (not peak/startup loads) is around 1600 watts or so with the items listed above.


That's a huge generator BTW--- depending on the size of your house, you can probably run A/C....

 

[Donald]

When I have needed a generator for a few days and the temp was over freezing I would run from about 6 AM to midnight. Typically its no big deal for the generator to run out of gas while its powering things. Not much different than when your street power flickers and then goes out.

I would suggest you run the gas with Stabil as you never know when street power will come back on. Have a CO detector or two (preferably with digital display) in rooms or areas of the house near the generator.

 

[Donald]

Do you have a well pump?

 

[georgemiller]

If you have natural gas why not convert generator to run on NG.

 

[JTK]

Like said above, I wouldn't sweat the gen running out of fuel while on the fly at all. The power they put out is relatively dirty and oscillates all over the place anyway, and most of your power gobbling goodies have their own power supplies that filter all that out.

Let it run out and cool a bit, check the oil level, refuel and go for it again.

 

[strat81]

Originally Posted By: meep

That's a huge generator BTW--- depending on the size of your house, you can probably run A/C....


I have a B&S that puts out 6000r/7500s (model 30469) and it will run my central air if no other loads are placed on the unit. The house is small, only 1k sq ft on the main floor, so the A/C unit is relatively small.

However, the surge draw at start up is pretty massive, so the generator must be warmed up or it will stall.

My home is all-electric, so I wanted something that could handle cooking and the water heater (not simultaneously).

The manufacturer rates fuel consumption at 7 gallons for 13 hours at 50% load. I've never measured it. It has a gauge, but it's not accurate.

And since this is BITOG: I run M1 TDT 5W-40 in it.

Interlock and inlet install thread I did over at Arfcom:
http://www.ar15.com/archive/topic.html?b=10&f=17&t=651376

 

[earlyre]

We have a 17kw generac whole house gen.(Nat. Gas. Would be 20kw on lp gas) The central a/c is the only thing not hooked to it.

 

[Noey]

We have a 9500, if you're going to go thru the hassle of buying and installing, you might as well have everything working when the power goes out.

The factor being left out here is load...typically what you're running in the house when the generator is on. Even thought the gen is "on", it's idling when there's no draw, so it uses less gas. Likewise, the more stuff you have going on in the house, the more load, and consequently the more gas being used.

Electrical appliances like a nice, constant flow of juice, so the idea of running the fridge for a few hrs and then shutting it off, and then turning it on sounds economical, but you run the risk of blowing the compressor when you switch the juice back on. Likewise with just about anything, they experience the sudden jolt of juice as a surge.

The best plan is to run what you typically do for less time, turn the gen off for a while, refuel and start again. You should also switch off all the individual circuit breakers before turning off the gen, and then slowly turn them on alternating sides of the panel.

After all the storms, I couldnt imagine living without a gen again, regardless of fuel consumption.

 

[JHZR2]

Originally Posted By: JTK
Like said above, I wouldn't sweat the gen running out of fuel while on the fly at all. The power they put out is relatively dirty and oscillates all over the place anyway, and most of your power gobbling goodies have their own power supplies that filter all that out.

Let it run out and cool a bit, check the oil level, refuel and go for it again.


Id hate to let electronics just black or worse, brown out when the generator runs out.

But youre right, the power these things put out are horrible. Voltages go way out of spec, and frequencies usually are bimodal at 60 and 62Hz.

 

[Vikas]

This is the order in which I did it.

Go in the basement, turn off the main breaker. Then turn off all the individual breakers. Now go upstairs, open the garage door by hand, drag the generator little bit, start it to verify it starts, turn it off, drag it all the way out of the garage, face the exhaust side to the street, hook up the big cable, put about 2.5 gallon of gas in it, restart, verify the led, go downstairs, slide the interlock panel up, turn on the generator breaker, turn on the breaker marked "basement lights", turn on the basement light switch and then curse at the darkness! Turn off the generator breaker ...

Go up again, turn off the generator, verify all the connections, turn it back on, come downstairs, turn on the generator breaker.

Still no lights, notice another breaker also named "basement lights" and turn that one on. Still nothing; another breaker named "basement outlets" and I see the Fios light turning on! Turn on the fridge and hear the familiar hum!

Eventually managed to turn on the correct breakers to get both the fridges and the rest of the internet and computers working!

Later my neighbor dropped by with his laptops and phones to charge. He comes back in ten minutes and tells me they got their power back!

This brings interesting question. How would I know if the line power is back? I wish I had thought about this and had asked the electrician to install something when he installed the interlock panel.

 

[Vikas]

Another comment: generator breaker is ganged 30+30. The A/C is ganged 50+50. I would think running A/C on generator would be out of question.

 

[Skid]

Originally Posted By: Vikas
Between the voltage and the frequency which is the better measure to estimate the load on the generator? I am seeing about 250 V and 62 Hz on the display.


Both are somewhat irrelevant as voltage and frequency have to be fixed for a particular power standard (unless overloaded, etc.). You need to see current for an indication of load. For non-resistive loads (like motors) without power factor correction, the phase angle between voltage and current is also important. Ignoring that, though, AC power is basically RMS voltage times RMS current.

Fuel consumption varies based on the load and the efficiency of your generator, which varies by the load. At low loads, maybe 15% efficient... high loads, maybe 30% efficient.

Gasoline varies in terms of energy content as well... ethanol blends have less energy than straight gas.

Back of the envelope:
1 gallon of gas, 120 Megajoules of energy (assumes some oxygenation here).
A watt is 1 joule per second.
Say that you have 1000 W of load, and 20% efficiency at that load.

120 MJ at 20% efficiency = 24 MJ.
24 MJ / 1000W = 24 kiloseconds.
24 ks = 40 minutes.

 

[Skid]

Perhaps next time the tank is empty, you can add gasoline in small increments, perhaps a quart or half gallon at a time and notch a dipstick with the fluid level as you go for future reference.

 

[eljefino]

Originally Posted By: Vikas
Another comment: generator breaker is ganged 30+30. The A/C is ganged 50+50. I would think running A/C on generator would be out of question.


Look at the motor plates on the blower and compressor. You never know. The house could have been wired bigger for an older previous AC or to future-proof if a bigger one was wanted.

When I did the numbers on what it'd cost per Kilowatt hour, a gasoline generator at $3.50/gal is 10-15x more expensive than 14 cents/ KWh. This helps me with my goal of running half the house, not the whole thing, skipping laundry/ dishes etc.

My 3250 surge/ 2500 continuous, 120 only generator will run my shallow well pump, which has me giggling for joy.

 

[rjundi]

Originally Posted By: earlyre
We have a 17kw generac whole house gen.(Nat. Gas. Would be 20kw on lp gas) The central a/c is the only thing not hooked to it.


Seems a bit oversized or do you have electric heat?

My 6800Watt nominal/8500 Peak does fine with well pump, fridge, boiler, one heavy draw(oven or dryer), and lights etc.

 

[strat81]

Originally Posted By: Vikas
This brings interesting question. How would I know if the line power is back? I wish I had thought about this and had asked the electrician to install something when he installed the interlock panel.


http://www.homedepot.com/p/Reliance-Controls-PowerBack-Utility-Power-Return-Alert-THP108/202216506

 

[Bebop367]

I have a 5500 watt generator with Briggs 10 HP. Running approx. 3500 watt load for 4 days and nights I use 9 gal. of gas per 24 hours. That may give you a rough starting point to estimate fuel requirements.

 

[rjundi]

My similar size generator (Rigid with Yamaha) seems to burn 2 gallon per hour under normal load. I think it is rated for 1/2 gallon per hour at 50% load.

I am seasoned power loser! Mostly 2-3 hr spurts.

I work 100% from doing remote IT. I found buying a $120 UPS gives me about 6hrs of Xfinity Phone/Internet, along with wireless router/switch so I can work off battery with laptop. Not sure if you have that need but it sure is nice not to listen to the obnoxious generator and drag it out.