Calculating load for portable generator

[KVA]

Sewage ejector pump - 30 amp breaker
sump pump - 15 amp breaker
fridge -
general lights
furnace and water heater are gas

I'm thinking a 10,000 watt would work?

 

[KVA]

I also forgot to add it's a gas heat pump. Also i never seen a 30 amp double pole on a sewage ejector pump in a house. Usually a double 20. I was going to put in a 10 circuit 50 amp man transfer switch but they don't come with 30 amp dpdt switches.

 

[stevebea]

Sewage ejector pump - 30 amp breaker
sump pump - 15 amp breaker
fridge -
general lights
furnace and water heater are gas

I'm thinking a 10,000 watt would work?

What size pump motor is on your grinder pump and sump? Do you have a well pump?

 

[hurk27]

You are going to need to calculate the amount of current/wattage not how much the breaker rating is, lets say you have a 2hp ejector pump, 60% effecenty@240 volts, 2*746/.6=2486.67 watts you can further get to amps by 2486.67/240 volts = 10.36 amps

1/2hp sump pump @120 volts = 5.1 amps

But go by the acual ratings on the motor.

The furnace statement doesn't make sense? a heat pump is a reverse cycle AC system not gas? if you are talking a forced air gas furnace then yes the only power there is the blower and controls or about 3 amps load, if it is a true heat pump then you will need the actual ratings from the outside unit+ the furnace, fridge can be anywhere from 150 watts to 1200 watts but you need to look for the rating and use its actual rating.

Lights can be a big load if they are incandescent, CFLs/LEDs are much more generator friendly.

so figure actual loads, not the breaker handles, or you will be way over sizing the generator.

PS a 10kw generator is about 41.67 amps @ 240 volts if loads are balanced on each leg.

you need your peek demand load + 125% for sizing a generator,

 

[KVA]

You are going to need to calculate the amount of current/wattage not how much the breaker rating is, lets say you have a 2hp ejector pump, 60% effecenty@240 volts, 2*746/.6=2486.67 watts you can further get to amps by 2486.67/240 volts = 10.36 amps

1/2hp sump pump @120 volts = 5.1 amps

But go by the acual ratings on the motor.

The furnace statement doesn't make sense? a heat pump is a reverse cycle AC system not gas? if you are talking a forced air gas furnace then yes the only power there is the blower and controls or about 3 amps load, if it is a true heat pump then you will need the actual ratings from the outside unit+ the furnace, fridge can be anywhere from 150 watts to 1200 watts but you need to look for the rating and use its actual rating.

Lights can be a big load if they are incandescent, CFLs/LEDs are much more generator friendly.

so figure actual loads, not the breaker handles, or you will be way over sizing the generator.

PS a 10kw generator is about 41.67 amps @ 240 volts if loads are balanced on each leg.

you need your peek demand load + 125% for sizing a generator,

Thanks for all the helpful info. I know not to go by breaker size just used those numbers for a rough idea. What i was really concerned with is the peek numbers. Since most of the loads involved motors I was concerned that a couple of these loads would come on at the same time and overload a smaller generator like a 7500 watt. Mostly because of the sewage ejector is a grinder type which i never had experience with. It is on a 30 amp breaker so it draws more power over a standard ejector.

I decided to use my clamp meter and get amp readings on the circuits under a load for a more accurate number.

 

[KVA]

You are going to need to calculate the amount of current/wattage not how much the breaker rating is, lets say you have a 2hp ejector pump, 60% effecenty@240 volts, 2*746/.6=2486.67 watts you can further get to amps by 2486.67/240 volts = 10.36 amps

1/2hp sump pump @120 volts = 5.1 amps

But go by the acual ratings on the motor.

The furnace statement doesn't make sense? a heat pump is a reverse cycle AC system not gas? if you are talking a forced air gas furnace then yes the only power there is the blower and controls or about 3 amps load, if it is a true heat pump then you will need the actual ratings from the outside unit+ the furnace, fridge can be anywhere from 150 watts to 1200 watts but you need to look for the rating and use its actual rating.

Lights can be a big load if they are incandescent, CFLs/LEDs are much more generator friendly.

so figure actual loads, not the breaker handles, or you will be way over sizing the generator.

PS a 10kw generator is about 41.67 amps @ 240 volts if loads are balanced on each leg.

you need your peek demand load + 125% for sizing a generator,

Also yes i know a 10k is 41.67amps that is running numbers, peek is 50 amps 12,000 watts. The peek numbers are more important in this situation because most of the loads involve motors.

 

[G._S._Ohm]

The peak amp draw on my central HVAC is about 5x that of steady state but the start up surge duration is also important.

The gen people must have some rules of thumb for this because I've never seen a gen that had a surge rating 5x higher than the continuous rating.

$2400 to $3200 seems reasonable for 10 kW uninstalled.

 

[hurk27]

Something else to keep in mind when choosing a portable over a fixed home generator is many portable gen sets do not come with a receptacle large enough to provide the max load the generator can deliver, I have seen many job site 10kw gen sets with only a 20 or 30 amp twistloc, and with two or more 20 amp duplex's, so look for one with at least a 50 amp twistloc. if you have natural gas or propane available you might want to check with home depot as you can get a 10kw with the transfer panel for less then what a portable can cost, and the fact that natural gas burns so much cleaner the engine last much longer and can be set up to automatically start and transfer so you sit back and enjoy having power without lifting a finger when power goes out.

 

[hurk27]

Well forget the above statement on the fixed generator set as the prices went up drastically since I last looked at them, this 10kw Generac with the 100 amp ATS panel used to be around $1200.00 to $1500.00 just a few years ago now is over $2700.00:rant: I still like the fact of the cleaner burning NG over petroleum as even the oil doesn't get dirty and you can go 2 years on synthetics for oil changes, but you do have to derate the gen set by 1kw on NG over propane or petroleum gas, even though they use the same engine/alternator on both NG or LP.

I plan on maybe getting away from the inverters/batteries I'm using now as they will only give me about 8 to 12 hours of back up (except the computer and home theater) and plan on getting a 15kw whole house with a ATS I just wish they made a inverter output gen set at that rating as when there is very little to no load the engine can slow down and very its output based upon the load being drawn without changing the 60hz frequency, it would be a big savings on fuel, an optimum system would be inverter out with the option of batteries to give an instant power availability like a UPS system and have the engine only start start and run as needed when the batteries get to a certain point something in the line of the newer hybrid cars, the alternator would be set to just charge and maintain the batteries, something in the line of a 36 or 48 vdc system, but it would be a expensive system to buy, but would save a lot more on fuel.
Might be worth it in an area that suffers from frequent outages, but I live in town and I have four sub stations that we can be supplied from, so outages are very rare and if they do happen its only for a couple hours at max, all though back several years ago we had a bad winter storm in march that we didn't have power for 4 days so it can happen.

My problem is my drainage system for the foundation, the drainage was an after thought and they installed a perimeter drain pipe around the outside of the footer and brought it into a sump pit under my stairs in the lower level (bi-level) when it rains that sump runs constantly, if it quits it can flood my basement which is completely finished with a large family room with fire place and bar and bedroom and bath, I have two pumps in the sump (one higher then the other) for a back up it used to have a 12 volt pump as the back up but it was to small and would never keep up, so I installed two new pumps one 1/2 and one 3/4hp, both now are backed up via inverters but like I said the batteries wont last over 8-12 hours so it is a worry for me if I go on vacation.

 

[G._S._Ohm]

it used to have a 12 volt pump as the back up but it was to small and would never keep up

Sizing a sump pump methodically seems pretty involved, what with catchment area, soil permeability, rainfall rate & duration, etc.

Do you remember the hp and head for this pump? Would a larger A-h capacity 12v deep cycle battery have helped?

Knowing what doesn't work is almost as good as knowing what does. Nextag and Grainger can give you a range of sump pump popular sizes but I'm more curious about the minimum sizes that may work.