Technical > Home Improvement > Generac GP17500E Generator

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Re: Generac GP17500E Generator

reply to garys_2k

reply to garys_2k

reply to SwedishRider
JimCT in your response regarding owning vs renting propane tanks you indicated that you were able to purchase propane at $1.61 pr gallon. Here in Central Florida I was not able to find a local dealer offering propane at less than $3.50 per gallon. I found these websites providing information on propane technology and pricing.

»www.propane101.com/index.htm

»www.usepropane.com/

»www.propanefl.com/index.htm

The website below was most perplexing because of the large differences in the actual price consumers paid per gallon and the additional delivery charges indicated:

»checkpropaneprices.com/

One of my objectives is to purchase a generator that is capable of starting and running a 42,000 Btu central air conditioner. Briggs and Stratton claims that their 12 Kw generator would support a 48,000 Btu central AC and Generac claims that their 14 Kw generator would support a 48,000 Btu central AC.

I compared the fuel consumption of a 10 Kw Generac operating at full load and a 20 Kw Generac operating at 1/2 load and discovered that the 10 Kw generator consumed more fuel per hour than the 20 Kw generator. I was trying to calculate the approximate run time 400 gallons of propane would provide and found this brochure from Cummings Onan to be particularly enlightening. They indicate that a normal residential load is 3 Kw and that their 20 Kw air cooled generator uses 1 Gallon of propane per hour at 1/4 load or 5 Kw. I have not found a chart for any generator that lists propane consumption at very low loading like 1 Kw. Has anyone reading this thread had experience with a whole house generator and what the actual propane consumption was per day? I wonder if a 20 Kw generator producing 1 Kw would require more fuel per hour that a 12 Kw generator producing at 1 Kw.

reply to Mr Matt

reply to stomperz71
I live way out in the country, closest house being maybe 1/2 mile away. So noise is not a issue. I too have a geothermal furnace (3.5 ton Waterfurnace) so far no problems running that but I use a closed loop instead of well pump for water. Like you said not very often do you pull more then 50 amps per leg but I like to be able to use the full potential of my generator if need be.

reply to stomperz71
Generators should be sized to normally use 60-80% capacity of the generator.

Huh?

To make that easy...a 10kW genset should be loaded to 6-8kW on a continuous basis. Scale accordingly...

This is to insure voltage stability. Operating a larger capacity genset with a negligible to light load is not recommended.
--
Right is right, even if everyone is against it; and wrong is wrong, even if everyone is for it - William Penn

Interesting. I'd thought you'd want to be able to power "essential" loads first (refrigerator, sump pump, well pump, some lights) -- including starting loads for those motors, plus maybe optional loads, the largest of which may be central AC.

It would seem that many generators sized to do this would end up running mostly very lightly loaded due to being sized to meet the starting current requirement for all the motors and the AC system (which is usually three more inductive loads: compressor, air circulation fan and condenser fan).

Looking up information on sizing a standby generator is pretty confusing, too. Lots of websites with rules of thumb on loads (X for "a refrigerator," Y for "lighting") that seem mostly useless if you can look at real nameplate ratings and add up numbers from lamps. Here's an example: »www.consumerreports.org/cro/reso···tor.html

Then, the warning about starting loads, advising you to figure 3X running loads for starting motors (even though the LRA rating is often well above 3X the rated load on motors).

All of this seems to point to winding up with a generator that may be running at less than 1/2 of full load with about ALL of the motors you used to size the thing running.

Maybe the Generac "Nexus Smart Switch" ATS is the way to go, where it will let you prioritize high loads and will shed a running lower priority load if a higher priority one wants to run. I'd give up my AC for 10 minutes if my sump pump needed to run.

It is certainly necessary to manage loads connected to the generator manually if there is no controller, especially if motor loads are involved.

Also, sizing the conductors properly is imperative as the genset does not have the 'infinite capacity' of the utility system. Voltage drop and its effect on motors is far more noticeable. No 'spaghetti lines', thank you!

The objective is to use the -smallest- generator possible for the connected loads subject to the 60-80% loading criteria. People always want to get a bigger generator "just in case" they get the Motherhumper Frigidbitch HVAC unit in the future. Lurch knows the one I'm talking about...

I hate when the office orders up a 300 kVA genset for a 100 amp load. I usually have to get them to send out a switchable load bank to add a few hundred amps of load to get the genset to run properly.

Sometimes 'more' is not 'better'...
--
Right is right, even if everyone is against it; and wrong is wrong, even if everyone is for it - William Penn

reply to garys_2k
My home has two central air conditioners one for the first floor and one for the second. According to formula provided by garys_2k, based on the the name plate, the combined running amps on the 42,000 Btu condenser and air handler is 25, therefore the starting current should be 75 amps (LRA 109) and the 30,000 Btu condenser and air handler is 20 amps therefore the starting current should be 60 amps (LRA 73). Generac selection guide recommends a least a 14 Kw generator and load management system.

The manufactures representatives would only quote full and one half load fuel consumption from the specification sheet for each generator and indicated that they did not have figures for low load operation. When I reviewed the specifications for the 14, 17 and 20 Kw generators I discovered that the engines on the 14 and 17 Kw units were identical 992cc and the 20 Kw unit was 999cc only 7cc larger displacement than the others. The question is if the displacement of all three engines are so close, would that mean that the low load 1, 2, or 3 Kw fuel consumption would be about the same. If that were the case it would be prudent to purchase the 20Kw unit to reduce the triggering of the load management system. Would there any other reason to purchase a smaller capacity generator as John Galt recommended that have not been mentioned?

I thought wet stacking was only a problem with diesels, not propane.

How many millions of trucks sit in rest areas and truck stops with their engines idling for hours running air conditioners or providing heat while the driver sleeps?

Until recently diesel railroad engines were never shut down. Sometimes they would sit and idle for hours. Now they do shut them down because of fuel costs.

Running these engines at light loads is not the kiss of death some are trying to allude to. Truck drivers especially independent owner/drivers would not do it because they would have to bear the cost of repairs.

reply to Coma