Generator Sizing

[DennisArrow]

Here in NW Georgia, we have to worry about ice storms and an infrequent basis but wind/tornado outages a couple of times a year. I use a 5000 Watt/240V with 6500 surge to power my home, barn, 2 wells and electric fence. Yes, we coordinate which well to run at a time, usually the one at home. We leave the breakers for the heat and A/C off and selectively use the hot water heater.

Everything else is left on and yes, running the wells and hot water is a bit of forward thinking; but easily done. The system works great in the winter as we use a Harmon TLC 3000 wood stove with electric fan to heat the house and haven't run either of the 2 heat pumps in like 10 years anyway.

If we go without power in the summer for DAYS instead of hours, we just go down to the guest house/airstream 27 ft. trailer parked in the barn and fire up the 3K Honda that travels with it. PLENTY of power for the AC, TV, and whatever for as long as we need it...................

OOOOOPS I just gave away my EOTWAWKI plan................but that is a whole nother scenario..........God bless.........Dennis

 

[RalphVa]

I put all our loads into a spreadsheet and totalled everything up. Then I had the experience factor of having run a 4 kw generator on our garage, kitchen, family room, master bedroom and den (wouldn't run heat pumps and well pump; would run the well pump if I turned everything else off to start it). A big factor, as others have pointed out, is coming up with the startup wattage of big drawers. On most heat pumps, you'll find the maximum amperage posted on it. One thing that we had to do was to put in some relays to keep the emergency heat coil on the heat pump from coming on with the generator. Ductless heat pump systems (like maybe your Mitsubishi) don't have these. On our smaller heat pump, we had a starting condenser installed that greatly reduced its starting load.

We've a 12.5 kw generator connected to a 200 amp box, but the box has load management relays for 5 of the biggest loads: the hot water heater, clothes drier and some others. The management system just won't let them come on if the generator doesn't have space for them.

In most cases, your generator will be loafing along. Our average kw usage, for instance, over the year is only 1 kw. Because of this, I didn't want a huge diesel generator setting out there and getting carboned up in wet stacking mode because it just wasn't being loaded.

Ralph

 

[RSKY]

Thanks to all of you for your input.

How much did your whole house unit cost? Total cost, installed and everything?

We may go the whole house route or we may go ahead and get the 6800-watt unit for $1000 and install a switch at the breaker box. Then if there is an ice storm we would have our neighbor keep the generator fueled up, have one of the sons-in-law come over weekly and change the oil, and use the money we didn't spend for a whole house unit to buy tickets to Key West and spend a week or two there. Last time we did that we stayed in a bed and breakfast right behind Sloppy Joe's.

RSKY

 

[fish6942]

I have the same rigid 6800 and it works fine for running fridges, freezer, lights and well pump. However, I would never consider using it to power our heat pump.

 

[RalphVa]

Our 12.5 kw Isuzu was near $10k from Central Maine Diesel. I had 2 boxes @ 200 amps each plus a manual transfer switch and some essential breakers in it used with the 4 kw generator. Had to move everything into a new 200 amp box except for really big loads that got moved or left in the one 200 amp breaker. Cost us around $5k for the one electrician to do the work over a 2 month or so time period. I came down with congestive heart failure right at that time and wasn't able to do a thing. My wife was a gofer for him.

Used one low voltage line from our security system that we weren't using to run relay current up to the upstairs heating coil, to disable it when the generator is on.

Ralph

 

[grsthegreat]

costs depend on your situation. I can install a 14KW Gaurdian or Siemens propane generator with 200 amp transfer switch for abour $3,300 for parts plus whatever labor is involved. In most situations it takes about 4-6 hours in labor to do the wiring, plus building a concrete pad and setting unit.

Getting a water cooled unit adds about 8 grand to the costs overall...but the generator jumps to a minimum of 25KW.

Then again, im doing a job now that has 2 transfer switches and a 60KW water cooled unit thats running about 22 grand.'
'

So its all realitive and varies per job.

 

[s219]

I bought a 21kW Isuzu from Central Main Diesel for $7500. Probably spent another $800-1000 in materials and supplies, and $1400 to build a shed for it. Have not had a power outage yet, but it should be able to handle our 4-ton geo-thermal system along with other necessities.

Here it is before we finished building the shed around the generator:



I'll do a full thread once I have time. Lots of pictures and notes to share.

 

[daybreak1998]

I have just about made up my mind to buy a Rigid 6800-watt (8500-watt surge) generator. It has a Yamaha engine and electric start.

My question is, can anyone convince me that this is too small for my uses. I have gas central heat with an electric blower, also have one of the Mitsubishi heat pumps in the sunroom. I heated for nearly three weeks during 2009 with two sets of gas logs. I have a gas hot water heater.

During the 2009 ice storm I bought the only thing I could find which was a Chinese made 3500/4000-watt pull start. With extension cords covering the floor we were able to run the freezer, both fridges, and the TV or what ever else we needed. Just could not run everything at one time. The little generator ran under nearly full load for 17 days being stopped only to refill gas and change the oil.

Can I run a 3.5 ton central unit with the Rigid 6800-watt genset?

By my calculations I can run everything else but the central air. Am I wrong?

Thanking the people in advance who are more knowledgeable than I on this subject.

RSKY

Howdy,
It all really depends on what you want. Do you want to live like there is no power outage? Do you want some things working, but not all at once?

You said you have central gas heat. OK, then with that being said the 6800 watt generator will work for you. Will that keep you heated enough to survive? Can you get by without the heatpump in the sunroom? Are you on well water? those items can be worked around each at one time. In a power outage situation, I never think about using the electric oven or electric stovetop. Microwave, sure, coffee maker, sure.
If you are looking for something with enough oomph to run the A/C unit... then you need to look at the spec for the unit. All the electrical load data can be had the manufacturer. You could even cheat by looking the your breakers which serve your A/C unit. The Ridgid 6800watt generator will be connected via a dual pole 30amp breaker. With its specs saying 8500 surge, will probably not handle it. I would assume your A/C unit probably is on dual 40amp breakers.

How often do you loose power? When you loose it, it is off a long time? Is it hot out? is it cold out?
Because you lived for 17 days with a little unit, the 6800 unit will run a lot easier with some headroom. The unit also states it is a clean AVR regulator. A lot better on electronics than the little Chinese made 3500/4000 unit.

Also, think about how you will connect it all to your electrical panel.

 

[kenmac]

Getting a water cooled unit adds about 8 grand to the costs overall...but the generator jumps to a minimum of 25KW.

.

It also appears you can get a Generac that is 22 KW with a 2.4 liter engine that runs 1800 RPM or a 1.5 liter engine in a 25 KW that runs 3600 RPM for a few $$ less but, would probably burn more fuel running at the higher RPM

 

[nickc]

check out this website centralmainediesel.com you my find a more appropriate set-up there good luck. some pretty cool gensets there. also interlockkit.com