Help! Selecting generator....

stonebase · Sep 9, 2004

I am trying to design an emergency power backup system for our home that we recently built. We are total electric (natural gas is not available) and I am working on obtaining a couple of 100lb propane tanks to fuel our gas log fireplace.

I'm working with my electrical contractor in coming up with a bid on isolating certain circuits and dedicating them to a manual transfer switch with receptacle into which I would plug in a portable generator.

On the emergency circuit I wish to wire my sump pump, well pump, septic pump, freezer and refrigerator and a circuit with a few plugs and lights. Possibly the microwave also.

My question is how big of a generator do I need for this type of set up. So far my research has me choosing between a 5500 and 7500 watt generator. Does anybody have a similar setup they would care to comment on?

Also, where to purchase the generator has become an issue also. Do I buy a high end (Honda) generator from the power equipment dealer that I purchased my tractor from? Or do I opt for the less expensive brand (ie Troy Built) from the big box retailer? Does using this piece of equipment maybe twice in a years time justify spending more for the brand name? Or do I opt for the less expensive? What really is the difference in quality of the two?

Any feed back to help make my decision easier would be greatly appreciated.

Thanks,

John /forums/images/graemlins/smile.gif

Fireman_dcb · Sep 9, 2004

Stonebase,

We have a 2400 sq. ft house with forced hot air heating - we bought a Honda 5500 watt generator and run it through a 6 circuit manual transfer switch. This lets me run everything we'll need - TV/ satelight/ radio, fridge, freezer, microwave, cordless phone and a couple of other outlets - almost everythign we'd need except for the hot water heater or the central A/C. The thinking was that we could live without A/C and we could always heat up water on the propane stove for a couple of days.

stonebase · Sep 9, 2004

Thanks Fireman,

Forgot to mention earlier, our house is similar in size 2350 sq ft. I understand to run an electric furnace/heat pump such as ours is a big draw of power not practical for generator size we are considering. My thoughts like yours is that we could survive in the summer without A/C and in the winter we could rely on the gas log to throw the heat in the great room/kitchen/dining area. My only concern is that for a prolonged outtage would we have enough heat to prevent pipes from freeaing?

John
/forums/images/graemlins/cool.gif

mahlers · Sep 9, 2004

With all of those loads, I would go with at least a 7500 W generator. You didn't mention your hot water heater - that's the item that will really drain quite a bit of juice, and believe me, the last thing you want on a cold rainy morning is to take a cold shower. Figure at least 4500 watts for the heater alone, and then figure you'll be running your well pump at the same time as your heater.

Also, you should consider the possibility that several high-drain devices (well pump, sump pump, septic pump) might be running at the same time - and you don't want to keep blowing the breaker on your generator. It's really easy to start looking at 10,000+ watt generators.

I've been using a 6100 watt Robin/Subaru industrial generator for a few years, and it works great. I do have to manually switch working circuits, though. For example, I have to shut off the water heater if I want to run the well pump. I'm presently looking at an Onan RS20,000 that Costco has on sale for $500 off with free shipping. The whole thing comes out to about $8500 with the automatic transfer panel, and it will run the entire house and do it completely automatically. Seems like a lot of $$ right now when I don't need it, but every winter we lose power at least ten times and I kick myself repeatedly for not getting an automatic system.

Regarding the Propane tanks - look into a real 300 gallon system. The 100# tanks are a giant PITA to deal with... It's much easier to have the propane guy come out and fill up a 300 gallon tank a few times a winter than it is to drag those 100# tanks down to the filling station every week. Many filling stations won't even let you fill them and put them back into your car, either - it's often illegal to transport more than 40# of bottled propane at a time. I found out the hard way.

Inspector507 · Sep 9, 2004

<font color="blue"> My question is how big of a generator do I need for this type of set up </font>

6.5KW minimum

Click here

Bob999 · Sep 9, 2004

The driver for your generator size will be the starting load for the pumps in your system. Well pumps range from half horsepower to much larger units depending upon the depth of the well and the number of gallons per minute the pump will put out. Most motors have coding that gives an indication of starting load- the typical starting load is a multiple of the running load.

You need to start with your largest pump starting load and then add other loads that will be steady state to get a minimum generator size.

JJT · Sep 9, 2004

I can run my whole house on a 5500w continuous, (6500w surge), generator. The biggest draw I have is a 1 horse deep well pump, (240v), everything else is small. The house is 3000 sq feet with oil fired heat and hot water. We've had 12 hour power outages in the middle of the winter and have had no issues. It's a 6 year old Coleman and it runs fantastic.

My parents have the same generator and it will not start their deep well pump. They just switched over to a 10K w generator from Harbor Freight, (on sale $1300). I'm thinking you need a similar size, with 3 different pumps you may need to run 2 at the same time.

v8dave · Sep 10, 2004

I'm going through the same decision process.

As has been noted by some other posts, your problems will be with the motor starting. If possible check the nameplate rating of the units. I have one air conditioner (I've decided to not run on backup) that has RLA of 19.9 and LRA of 115 both at 230 volts. RLA = Run Load Amps, LRA = Locked Rotor Amps. That 4.6 KW motor takes 27 KW to start.

Select a heavy generator for this purpose. The Hondas are reliable as a stone, but they advertise their light weight (as in portable). But, the light weight ones don't have much excess motor start capability. The contractor models are beefier, they are made to start air compressors.

Onan generators understand motor starting but are costly. It is a real decision point without any clear answers. But, you should really look for a heavier motor start generator. You may find a quality generator with a modest running capacity but has a very large motor start capability.

I've just posted this same company elsewhere on TBN tonight. Iv'e had good luck dealing with nooutage.com even though thay are in Maryland and I'm in California. They have good rating charts to compare multiple products.

stonebase · Sep 10, 2004

Thanks everybody for the comments and links. Maybe to further define my needs I would say I am looking to bridge the gaps of the "typical" outtages we experience (usually 2 to 6 hours) that come at the most inoppertune times like when you need to get ready for work, etc.

I guess my next question is that say I buy the 7500 instead of 10000 Watt generator is it possible to manage the transfer switch panel in such a fashion to alternate the circuits to allow them to run on a staggered basis (I have no previous experience with a transfer switch system)

Thanks,

John /forums/images/graemlins/cool.gif

snowman · Sep 10, 2004

I think that to run the circuits on a staggered basis, you would simply flip them on and off as you see fit.

As to what size unit you should get, I have a 12,000 watt gas Yamaha (9,000 continuous, I think) that works great - paid about $3,500 for it in 2001. I'm on a private well and use propane for heat and hot water; my primary concern was being able to have running water and heat in the winter. I have two furnaces in the house and the generator can run both along with everything else easily.