Sizing a generator for the house......

[actaeon277]

Go Big.

The calculations that have been put forth are a good starting point, but I must disagree with the amount needed to bump the size up for motor starting. The typical motor can draw between 6 and 8 times normal operating current for a brief moment when it starts. Logically you have to assume that all of the motors could start at once and provide for that. I've gone down this road a few different times and am of the opinion that 14kw is the smallest size I would recommend for just about any home with a sump pump and a well pump.

What is often missed is an understanding of what happens to devices that are fed with an AC voltage that has a frequency that is less than the standard 60 Hz. When your sump pump starts and you hear the generator change tone, sound different, you are hearing the governor sense that the speed of the generator has dropped to a point where it has to feed more fuel to the engine and increase the speed back to the target speed. The generator speeds up, assuming you have enough HP to meet the load, then the load drops and the generator is running too fast, fuel is then reduced. This ends looking like a dampened wave over time that shows how frequency reacts to the spike in load.

All of this means that your electronics in your home are being beat up with power at a frequency that is fluctuating well beyond the designed point. The end result is shortened or ended life of some of your electronics.

The bigger the generator, the more horsepower, and therefore the greater the ability to overcome those spikes in load with limited fluctuation in output voltage and frequency.

Sorry for the length, hope this provides some useful input to your decision process.

First, I think I'd stay off the electronics, unless you have a big safe genny. I don't consider most electronics necessary, except heater control.

Second, have enough for everything to start at once?
NIPSCO struggles when a steel mill starts up a single building, much less the enire mill, and surrounding community.
The sub I was stationed on didn't have enough to account for starting current for every load at the same time, and power was more life and death there than I've seen anywhere else, except maybe a hospital.

Yes, bigger is better.
But is it always necessary?

 

[awames76]

i have a 2000 peak got cheep good for a saw or camping, going to look for a 8k this year

 

[bulletsmith]

First, I think I'd stay off the electronics, unless you have a big safe genny. I don't consider most electronics necessary, except heater control.

Second, have enough for everything to start at once?
NIPSCO struggles when a steel mill starts up a single building, much less the enire mill, and surrounding community.
The sub I was stationed on didn't have enough to account for starting current for every load at the same time, and power was more life and death there than I've seen anywhere else, except maybe a hospital.

Yes, bigger is better.
But is it always necessary?

All true, though when the mill starts they don't press the button on everything at once. Like you said, the sub would never be able to handle it. We don't really have control of when the sump or well pump kick on though. You and I both know that the urge to watch tv can be quite strong. The truth is that electronics exist in places we often forget about. Your furnace, Microwave, Refrigerator, Stove... all have electronic controllers that are powered on even when not in use.

 

[indyjohn]

Yes, bigger is better.
But is it always necessary?

Well, that depends on how much attention you want to give to the system and how much work you want to put forth managing it.

If you want everything to be automatic, go big. If you have the resources to turn stuff on and off at the right time, not big is ok.

Personally, I don't want to manage the well pump, freezer, HVAC, hot water heater. However, my budget doesn't allow for that... so we improvise..

 

[longbarrel]

You just need a transfer switch and an 8/12 circuit panel. Wire your desired load to the other panel, and the transfer switch will do the rest. When utility power comes back on, transfer switch will move to normal power, when utility power is dropped, generator will fire and and transfer switch will engage the 8 to 12 circuits you need.

 

[teddy12b]

Thanks for all the great advice and Dave, yeah I remember shooting with you up at Young's and I hope everything's going well for you.

Part of my motivation for a portable unit is that my wife and I live within 5 or 10 minutes of both her parents and mine. It'd be nice to be able to pick up this generator and toss it in the back of my truck and go get the old folks taken care of. If having a portable generator keeps my in-laws at their house instead of mine, then it's worth every penny even if it only happens once. I'm kidding my in-laws aren't too bad, but it's easier to get everyone wired up and share a generator until I need it back that is. If it wasn't for having parents nearby, and the $5,000 to $6,000 cost difference I'd do the permanent install gas lined whole house generator in a heartbeat. Those generators are amazing and there's no reason to not like them. For me, I've just got plenty of reasons on why I'd like or prefer a portable unit.

Where we're at I think the longest we've lost power for was three days or so. That's not a big deal and we don't watch a whole lot of TV anyway. I'd just be looking to power some of the basics. Most of my house is filled with LED lightbulbs as well so there isn't a whole lot of draw there either.

 

[Tactically Fat]

On power oscilations/ clean / dirty Hz...

Could there be some kind of surge protector installed in-line that would mitigate and even out stuff like that?

 

[actaeon277]

On power oscilations/ clean / dirty Hz...

Could there be some kind of surge protector installed in-line that would mitigate and even out stuff like that?

You can filter only so much. Voltage spikes are in the tenths of seconds and generally easier to protect against.
Frequency variations due to changing loads tend to be measured in seconds, and are harder to protect against.
Though if you want to spend the $$$$$$$ you'd have a bunch of batteries supplying your loads through a high end inverter, and the generator would be charging the batteries.

 

[lizerdking]

The OP said he wanted to have it so that his wife could also use it. I don't want my wife to have to deal with the issues of being prosecuted if she accidentally killed someone.

He said an electric start for the wife, assuming pull starts are hard on a woman's smaller frame. He didn't imply she couldn't follow basic instructions...

You can filter only so much. Voltage spikes are in the tenths of seconds and generally easier to protect against.
Frequency variations due to changing loads tend to be measured in seconds, and are harder to protect against.
Though if you want to spend the $$$$$$$ you'd have a bunch of batteries supplying your loads through a high end inverter, and the generator would be charging the batteries.

Or a standard UPS for your PC's/TV would be fine. Most of your "sensitive" electronics should be on one of those anyway, utility power isn't always "clean"

 

[actaeon277]

He said an electric start for the wife, assuming pull starts are hard on a woman's smaller frame. He didn't imply she couldn't follow basic instructions...



Or a standard UPS for your PC's/TV would be fine. Most of your "sensitive" electronics should be on one of those anyway, utility power isn't always "clean"

Depends on the quality of the UPS. There are some cheap UPS out there that don't filter very well.
But, a UPS would be a good idea.

 

[Tactically Fat]

When i win the lottery, I'll have a huge Tesla battery installation.

And a 100kw genset. Just because.

 

[indyjohn]

Though if you want to spend the $$$$$$$ you'd have a bunch of batteries supplying your loads through a high end inverter, and the generator would be charging the batteries.

Here's the inverter I want: DonRowe.com: Samlex America EVO-4024, 4000 Watt, 24 Volt Pure Sine Wave Inverter/Charger with 110 Amp Charger

Choosing batteries is a bit tougher and can be very expensive. I understand to get the longest life out of them, they should be exercised regularly.

 

[Cameramonkey]

He said an electric start for the wife, assuming pull starts are hard on a woman's smaller frame. He didn't imply she couldn't follow basic instructions...



Or a standard UPS for your PC's/TV would be fine. Most of your "sensitive" electronics should be on one of those anyway, utility power isn't always "clean"

Depends on the quality of the UPS. There are some cheap UPS out there that don't filter very well.
But, a UPS would be a good idea.

Not all UPS units are the same. There are two basic types; standby and online. Standby deliver utility power directly to the devices as they charge the batteries. When they are needed, power continues to be delivered to the outlets via energy stored in capacitors for a split second as a relay kicks in and starts delivering power from the batteries through an inverter. This is the most common unit you will find on the shelf.

What you really need to protect the sine wave is an online aka double conversion UPS. They arent really that much more expensive. I think in the 1500va range its a $200 increase over standby. Those isolate the load from the utility line by putting the batteries and inverters between the load and the utility. (not parallel) Electricity flows into the unit, where it is immediately fed into the battery pack via an AC/DC inverter. That energy is then converted back to AC via a second inverter and and delivered to the outlets. They always deliver clean power no matter what the utility is doing.

Putting a standby UPS on a dirty power feed will not help your devices much, but will instead cause the UPS to switch to battery frequently, causing a premature failure. They will switch when they see power anomalies, so if its really dirty, you could expect the relays to fire several times a minute as it tries desperately to correct the power issues. And the constant switching to battery can still cause sensitive devices to freak out as some of them can still detect that switch to battery when that relay throws.


As to the sizing, Personally I would want a smaller unit that only runs the necessities. Do you REALLY need to be able to do EVERYTHING you can on utility power? Heat, cooling, refrigeration and SOME lighting is all you need to be comfy during an extended outage. And wont a smaller generator last longer on a given amount of fuel? So unless its a natural gas model, you will do better with more runtime vs status quo.

 

[actaeon277]

Here's the inverter I want: DonRowe.com: Samlex America EVO-4024, 4000 Watt, 24 Volt Pure Sine Wave Inverter/Charger with 110 Amp Charger

Choosing batteries is a bit tougher and can be very expensive. I understand to get the longest life out of them, they should be exercised regularly.

Or, just forgo the electronics during an outage.


Yup, power and power conditioning can be expensive. Kinda like guns. You can go cheap. You can go expensive.
At work we have hundreds of sola transformer/conditioners and UPS systems.
In fact, just had a transformer short on the charging end of a UPS system. I think the power supply was 46 pounds. Real fun to bolt back into the cabinet.

 

[actaeon277]

Not all UPS units are the same. There are two basic types; standby and online. Standby deliver utility power directly to the devices as they charge the batteries. When they are needed, power continues to be delivered to the outlets via energy stored in capacitors for a split second as a relay kicks in and starts delivering power from the batteries through an inverter. This is the most common unit you will find on the shelf.

What you really need to protect the sine wave is an online aka double conversion UPS. They arent really that much more expensive. I think in the 1500va range its a $200 increase over standby. Those isolate the load from the utility line by putting the batteries and inverters between the load and the utility. (not parallel) Electricity flows into the unit, where it is immediately fed into the battery pack via an AC/DC inverter. That energy is then converted back to AC via a second inverter and and delivered to the outlets. They always deliver clean power no matter what the utility is doing.

Putting a standby UPS on a dirty power feed will not help your devices much, but will instead cause the UPS to switch to battery frequently, causing a premature failure. They will switch when they see power anomalies, so if its really dirty, you could expect the relays to fire several times a minute as it tries desperately to correct the power issues. And the constant switching to battery can still cause sensitive devices to freak out as some of them can still detect that switch to battery when that relay throws.


As to the sizing, Personally I would want a smaller unit that only runs the necessities. Do you REALLY need to be able to do EVERYTHING you can on utility power? Heat, cooling, refrigeration and SOME lighting is all you need to be comfy during an extended outage. And wont a smaller generator last longer on a given amount of fuel? So unless its a natural gas model, you will do better with more runtime vs status quo.

At work, they handed us some of those cheap "standby" UPS for cranes to run the radios. The idea was, if the crane lost power, they'd still be able to use the radio to make a call for maintenance. (overhead crane, power comes on rails through "shoes").
The power was so dirty, the UPS switched so many times, that we had two problems. Relays in the UPS started to hang up, or electronic switching devices would fail. Second problem, the batteries kept running down because they kept switching to battery.

 

[Cameramonkey]

At work, they handed us some of those cheap "standby" UPS for cranes to run the radios. The idea was, if the crane lost power, they'd still be able to use the radio to make a call for maintenance. (overhead crane, power comes on rails through "shoes").
The power was so dirty, the UPS switched so many times, that we had two problems. Relays in the UPS started to hang up, or electronic switching devices would fail. Second problem, the batteries kept running down because they kept switching to battery.

And funny thing about APC brand UPS units. The standby units are known to do a full reset when you flicker the power quickly and enough times. A colleague complained that he had a burst of flickers in the span of a couple seconds. Then the UPS outputs shut off and the management card went to factory default. I thought he was crazy until I did it manually here by wiggling the power cord barely inside an outlet. So weird.

 

[jon5212]

I agree with all the others, I'd say for your house you need a bare minimum of a 10kw set. Forgot about the hot water heater, maybe it's gas and you don't have to worry about it, but if its electric there is about 3-4kw right there in heat. Adding A/C if you use it could be another 1-2 KW startup power so you are almost maxed with a 8KW generator.

 

[Hohn]

Auto transfer switching is the way to go, and gas or LP powered.

Do not massively oversize a methane/propane powered engine. They wear quickly when run too cold. Try to keep it over 70% of rated load.

 

[jd42k]

Here's a link to my cloud showing photos and a user guide of my generator power up instructions.
https://app.box.com/s/0prtj2s2zok1ft8il8bf

I did this for my wife who doesn't know squat about anything electrical.

I plumbed the gas line myself (everything else too) even though I had a quote from Nipsco for + $400 to install a larger gas meter.
I have a gas furnace, stove, dryer and water heater. I installed a tri-fuel motor snorkel from US Carburetor. I only use natural gas to run it.

It powers my well, HVAC and other necessary circuits.

I ran the generator to my main using a dedicated breaker that is controlled with an interlock switch that will only work when the main is off.

Comments/feedback/questions are welcome.

JD

 

[Brandon]

We have a 7500watt portable gen set with a manual transfer switch.
Bedrooms, living room, and kitchen are what are powered via the circuits.

We have a couple of small space heaters and a larger window ac unit if things get bad enough.
The weather alert radio and all the tv's are on a battery back up as is the cable modem/router.

Will it be the normal standard of living? No/ Will it take the misery out of a power outage? Yes - (did a couple of years ago with a smaller gen set for around 4-5 hours)

I bought my gen set at a pawn shop also. It is a large Honeywell looked brand new, oil was clean, they let me run it for about 20 minutes and test all the circuits with some power tools they had on the shelf.