Sizing a propane standby generator

[James Riley]

I have a well pump and motor on it's own meter. I do not have the specs on the motor. It pulls up from about 60' down, at about 45 gpm. And my bill is for about 800 kWh per month. The coop utility power goes out periodically and we want to have a propane generator that I can use to keep my water available and a small milk house heater on when the power goes out. I'm not sure what size to buy. How many watt generator do you think I should buy? Thank you.

 

[plugsandsparks]

You will need to measure the current taken by the motor and heater to even get a rough idea of the size needed. A motor starting can demand quite a high load for a short time which will challenge an undersized genny.

 

[James Riley]

You will need to measure the current taken by the motor and heater to even get a rough idea of the size needed. A motor starting can demand quite a high load for a short time which will challenge an undersized genny.

Thank you. I don't know how to do that.

I'm not above paying an electrician but I can't seem to find one.

 

[Megawatt]

Thank you. I don't know how to do that.

I'm not above paying an electrician but I can't seem to find one.

A 15kva transformer should be fine. I have a well thats 360 feet deep and it has a 5 HP motor in the bottom of the well and it pulls around 7 amps

 

[James Riley]

A 15kva transformer should be fine. I have a well thats 360 feet deep and it has a 5 HP motor in the bottom of the well and it pulls around 7 amps

Thank you.

I have a breaker below the meter. I was going to turn that breaker off, tie in the generator below that breaker, with it's own separate breaker. I would turn off the generator breaker, turn on the main line breaker and go about my business. Then, if the utility power went out, I would go out and turn off the main line breaker, then turn on the generator, and then open the generator breaker to run the well. I would reverse that process when the utility power came back on. If there is something inherently wrong with that proposal, I'm all ears.

Thanks again on the sizing question.

 

[Lucien Nunes]

The generator and utility feed breaker must be interlocked to meet code. Otherwise by mistake you could feed generator power back into the utility line and electrocute the guy working in the hole in the road. For the generator sizing, you really should try to get some specs on the pump or measure the current.

 

[James Riley]

The generator and utility feed breaker must be interlocked to meet code. Otherwise by mistake you could feed generator power back into the utility line and electrocute the guy working in the hole in the road. For the generator sizing, you really should try to get some specs on the pump or measure the current.

Thanks!

 

[ChipFanDave]

What type of pump is it ? Any chance of a picture of the starter ?

 

[James Riley]

What type of pump is it ? Any chance of a picture of the starter ?

I'm not sure. I've had it replaced several times in the last 21 years. On the second-to-last one, September of 2016, I specifically asked for it to be bumped up since my water right is 45 gpm and I was only pulling 25 gpm. They put in a "Submersible GRUNDFOS Model # 35530-11, 35 gpm, 3450 RPM, 3 HP, 230 Volt, 17 full load amps, intake depth 52', 2" pipe. There has been another one put in since then (about 2 years ago) but I lost the specs on it. It could be the same. I have an email into the guy who did it and he said he'd look, but I haven't heard back. But if we assume the last pump (above) is the same, what do you think?

 

[plugsandsparks]

Any idea how big the heater is?

 

[James Riley]

Any idea how big the heater is?

It's just one of those little milk house jobs you get at the farm store. They have an off, fan, 1300 and 1500 watt setting with a high -low control knob. I set it on 1300 and to come on around 40 degrees.

 

[plugsandsparks]

As already mentioned would be surprised if 15KVA could not handle a 3HP pump. Best to start it with no other loads on. A transfer switch is the way to go but remember it needs to be sized for the house max supply, not the generator.....
Any chance you could hire one to try it out as you may well get away with a smaller one. Also, i dont know about the US but propane does limit your choice in the UK, a good second diesel is where i would be looking with an inbuilt tank.

 

[James Riley]

As already mentioned would be surprised if 15KVA could not handle a 3HP pump. Best to start it with no other loads on. A transfer switch is the way to go but remember it needs to be sized for the house max supply, not the generator.....
Any chance you could hire one to try it out as you may well get away with a smaller one. Also, i dont know about the US but propane does limit your choice in the UK, a good second diesel is where i would be looking with an inbuilt tank.

Would the house max supply be the twin 30 amp breakers, or what the utility is actually sending to the property? Because I have no idea how big their system is.

The only reason I chose propane is because I have a 1k gallon tank on the property that allows me to fill bottles. And someone told me that propane never goes bad.

 

[plugsandsparks]

Would the house max supply be the twin 30 amp breakers, or what the utility is actually sending to the property? Because I have no idea how big their system is.

The only reason I chose propane is because I have a 1k gallon tank on the property that allows me to fill bottles. And someone told me that propane never goes bad.

Sorry, i dont know, you generally size it to the rating of the supply. With what you are wanting it really is an electrician type job. There are a few US sparks here but we are mainly UK.

 

[James Riley]

Sorry, i dont know, you generally size it to the rating of the supply. With what you are wanting it really is an electrician type job. There are a few US sparks here but we are mainly UK.

Thanks. I wish I could just get one out here. I'd pay, but apparently they are all too busy building new houses. I guess I'll just continue taking 5 gallon buckets down to the river, breaking the ice and lugging them back up the ice/snow covered slope. Old school.