If load is known, is it best to size generator just above load or in such a way that under load about 50% of generator capacity is being used, or other?

I understand startup load vs continous load. I also understand a staggered startup could assist if generator is smallish. I can make the decsion on what startup is required later.

I ask because I am seeing run times expressed at 50% load. For example 7 hours on 5 gallons gas at 50% load.

I also ask because I assume it is better not to "redline" continuous load.

Let's also assume we are comparing generators in the 2k~3.5k vs. the 5.5k ~9k. From what I am seeing there's about a $500 difference in the dual fuel models.

More information about the actual situation would be helpful but in general if the generator can handle the initial start up loads (sometimes called Lock rotor amps or LRA) then the rated running capacity of the generator can usually handle the running load of the appliance virtually indefinitely. Depending on the appliance(s) you want to run most do not run continuously at 100% after start up.

I am trying to understand if it is advantageous to upsize the generator to reduce wear on it by lowering the amount of capacity that is being used.

For example,a generator with a continuous load rating of 2500 watts with a 2200 watt load vs a generator with a continuous load rating of 5000 watts with a 2200 watt load or even a continuous load rating of 6500 watts with a 2200 watt load.

Beat it like a rented mule and it dies fast or run it like grandma and 2 gallons of sweat rea are in the car and it goes for a substantially longer service life?

There are times when it is favorable to be higher in a power band than not. RPMs higher on a foreign bike than a Harley. Don't use overdrive when towing a heavy load to reduce transmission wear etc. I am just trying to understamd which is better for a portable generator.

If absolutely necessary to know what it is running for load, then sometimes a travel trailer with a 15500 BTU ac unit and accessories, other times potentially used as a partial feed for house.

edited typos

This message has been edited. Last edited by: ffips,

I think, generally speaking, one should not run a combustion piston engine (including a generator) at a steady hard running rate at or near top RPM. I think I would not run it steadily at more than 75% of the stated top RPM while under a full demand loading. There will be exceptions due to design and manufacture, of course, but this is for the vast majority.

It's sort of like knowing your car has a top speed of 140 MPH and trying to cruise for hours and hours at 135 MPH. It just won't survive.

Generators typically need a load applied after warm up, they don't like to idle long term, bad for them. There's a happy medium point.

Good luck to you.

The motor powering the generator will run at a pretty constant RPM regardless of electrical load. Your issue will be electrical load capacity. Running a generator at full capacity will wear it out sooner, and will subject the motor to the same strain in terms of torque load. A generator should be sized for roughly twice the run load because that is what gives you the capacity to let things start and stop on their own. If you go smaller you will have to manually phase equipment on to avoid tripping the breakers on the generator. Go much larger and you're just wasting money.

Generators run on "cruise control" and the load will determine gas consumption.

Think of a car on cruise... the faster you go will affect your mileage, as would going up a hill.

With a generator, increased load is like going up the hill, it places additional resistance on the generator forcing the motor to use more gas to maintain RPMs.
On the other hand, too little load on the generator will allow the motor to run free causing it to have trouble maintaining constant RPMs due to feathering the gas leading to surging.

The best way to determine your generator size is to factor a constant 40-70% load of the running watts. That will give you ample starting load capability, and will be in the generator's optimal running band.

I have a Generac 5500 and my household load is usually between 2250 and 3700 watts. I have my panel set to evenly split the load between busses (another issue people overlook with generator loads) and have never had an issue.

Answers to questions I have, too. I also have some input and piggyback some questions.

Home Depot is running a decent deal on a few generators today:

https://www.homedepot.com/Spec...BOTD&et_rid=87953223

Here's a 4,000/3,500 gas unit for $269:

https://www.homedepot.com/p/Sp...let-801187/206403560

Or a 7,500/6,000 gas/LPG unit for $599:

https://www.homedepot.com/p/Sp...-GEN7500DF/204789149

I'm thinking about the 7,500/6,000 unit. Hurricane season is coming soon and I'd like to be more prepared this year than last. We'd be running a light, portable AC unit for a bedroom (size escapes me now), fridge, microwave and charging mobile devices.

The 7,500/6,000 should suffice, correct?

 
My working philosophy on any electrical device, be it a genset or simply a 15 amp duplex, is to plan on only using 80% of the rated load. I think there is something to that effect in the NEC, but I've never read the whole thing. Perhaps skins can clarify.
 

quote:

Originally posted by Edmond:
I'm thinking about the 7,500/6,000 unit. Hurricane season is coming soon and I'd like to be more prepared this year than last. We'd be running a light, portable AC unit for a bedroom (size escapes me now), fridge, microwave and charging mobile devices.

The 7,500/6,000 should suffice, correct?

I run that much of a 3750 watt generator with no issues and have never blown a breaker.

quote:

The 7,500/6,000 should suffice, correct?

Yes it should. If you get a smaller one, don't get the one linked. It doesn't appear to have 240v plug, only trailer plug (120v) visible. Meaning you can't wire it into an interlock switch or generator subpanel.

The number of amps you are pulling will be a limiting factor on small generator applications. Be sure to size for both amps and watts.

I'll answer this one with authority. You run the smallest generator that will handle the load. Period.

First off, electrical supply in the US is pretty reliable. Your power outage will be a few days at most (usually.) Worst case scenario, a Cat 5 hurricane demolishes everything and you are without power for 2 months.

Second, generators can use an enormous amount of fuel. A 2500 watt inverter generator will use half the fuel of a 5000 watt, and 1/3 the fuel of a 7000 watt. Try to find 12-18 gallons of fuel a day when all the gas stations are closed due to lack of power....

Its much easier to use 5 gallons of gas a day, than 15 gallons of gas.

The amount of wear on a generator isn't really related to how much load is placed on it, or how long you run it. The amount of wear on a generator is on how you maintain it. Rule of thumb is if it has a oil filter, you change the oil every 100 hours. No oil filter, you change the oil every 50 hours. Running a portable AC unit 24 hours a day to stay comfortable, is 48 hours use in 2 days (for the math illiterate). NO ONE changes the oil every two days, as required. No one. And that's why every house in my neighborhood had a blown up generator in the front yard for the trash man during the 2004 Hurricane season (no power for two months). The majority of people do not know how to maintain a small engine, do not check the engine oil at every fuel fillup, and do not change the oil every 50 or 100 hours as required.

So if you want a reliable generator that last a long time, thats on you. Are you going to maintain it properly? Are you going to keep fresh oil in it (at all times)? And dont store them with fuel in them. Today's fuel is only good for 90 days. You probably wont use a tank full of fuel every year, so best to store them empty and refill them with fresh (non-ethanol) fuel if they sell it in your area.

I have a 2200 watt inverter generator at my house AND a 4000 watt generator. I run them both out of fuel. I also run them for an hour every 3 months, to keep the engine and electronics in good shape. The 2200 watt will absolutely keep a small window AC unit running all night long(plus the internet modem and small electronics), sipping gas while doing it. The fridge doesn't need plugged in constantly. You should be able to cycle it off and on about 50% of the time to keep everything cold. (4 hours plugged in, 4 hours unplugged)

quote:

Originally posted by bubbatime:
NO ONE changes the oil every two days, as required. No one.

I agree with a lot of your post, but I actually did change my oil every 50 hours during our power outage after Irma...

quote:

Originally posted by DrDan:

quote:

Originally posted by bubbatime:
NO ONE changes the oil every two days, as required. No one.

I agree with a lot of your post, but I actually did change my oil every 50 hours during our power outage after Irma...

You and I are the minority. Most folks don't read the manual. Most folks get an oil change in their car every 6 months and use the car every day. So in their mind, they should be able to run a generator for 6 months without changing the oil, just like their car can.

quote:

Originally posted by bubbatime:
.

The amount of wear on a generator isn't really related to how much load is placed on it, or how long you run it. The amount of wear on a generator is on how you maintain it. Rule of thumb is if it has a oil filter, you change the oil every 100 hours. No oil filter, you change the oil every 50 hours. Running a portable AC unit 24 hours a day to stay comfortable, is 48 hours use in 2 days (for the math illiterate). NO ONE changes the oil every two days, as required. No one. And that's why every house in my neighborhood had a blown up generator in the front yard for the trash man during the 2004 Hurricane season (no power for two months). The majority of people do not know how to maintain a small engine, do not check the engine oil at every fuel fillup, and do not change the oil every 50 or 100 hours as required.

Good point bubbatime about among other is the oil change. I just read my manual on a 5500 watt port gen which has a yamaha motor. The manual says change oil every 100 hrs. It has no oil filter. Regardless whether you have filter or not you'd have to worry about how much oil you have on hand during an extended outage if you wanted to run it for two weeks.

Another point is how few port gens have oil filters. Just a cursury view of the home depot listing and I couldn't find one.

Update found a kubota powered genset that rated 7000 watts weighs in at 518lbs costing $ 5398.00 It has an oil filter and large oil pan providing a 200 hr oil change interval. Man thats heavy comes with lifting ring and forklift pockets. Its rated at 66db at 23' which I know is quieter than mine cause its LOUD

Think I'll stick with 100 hr on my loud yamaha

I appreciate the responses. It will help in the end decision. I am investigating for a few reasons. I would like the ability to go off grid with the RV if desired. I know there are solar options etc, but feel a dual fuel generator offers a good alternative. I also understand that noise will be a factor and likely limited within campgrounds. Also, since moving in December, we have lost power more often than the last several years combined. We are now serviced by a EMC/REA power company, and toward the edge of their service territory.

Ultimately, I doubt I NEED a big generator as we borrowed a 63cc tailgator from a neighbor that kept the freezer going. We also figured out the plug in the bed of the truck runs the freezer too.

In extreme times, we could get by keeping the fridge and freezer going. It would simply be 1st world issues to be without other niceties.

If we have to shelter in place, the RV can be used and then few creature comforts would have to be sacrificed. Between keeping the RV going, and a fridge and freezer, we would be glamping on site.

Currently looking at the Champion Power line products.

Do most come with a meter on them telling how many hours it's been run or do you manually keep track?

quote:

Originally posted by ffips:
.....
Currently looking at the Champion Power line products.

Got any other links? Asking me for permission to track GPS. Which size are you considering? Based on your desired loads 7kw is a little big, but generators are like gun safes, you don't want to buy the size for the number of guns you currently own.

Some off grid folks put thousands of hours on Champion inverter generators and they last just fine. If you are going to put a lot of hours on something though, I would spend the $1000 to get the Yamaha or Honda 2000ish watt units.

Champion is a Yamaha clone.

An unrelated question.. when running an inverter, do I need to use a grounding pole with it? Or just place it on a piece of plywood in the open?