Generator Installation - Alternating Similar Loads 3

[ELMPE1]

I am installing a generator serving lights and 2 refrigerators and 1 freezer for a Volunteer Fire Station. Each is the typical household appliance. Plans are for a 20A circuit for each.
To reduce the generator load (...and size/cost), I would like to alternate turning the appliances off and on so that only one is actually loading the generator at a time (Ex: Refrig No. 1 on from 8:00 to 9:00; others off. Everything off from 9:00 to 9:15. At 9:15 Refrigerator 2 comes on and runs until 10:15 then turns off. Everything off from 10:15 until 10:30 when the freezer comes on for an hour.) I believe, with colder thermostat settings, the items in the appliances will be O.K.
What is the best way to do this? Right now, I am envisioning a panel with 3 each 20A breakers and a 60A feeder from the genset plug to the panel and then three branch circuit receptacles w/programmable timers of some sort. What is the cheapest, adequate design (VFD...very cost conscious...only applicable for hurricane season...)? What type of timer would be recommended?

Thanks in advance for the help.

 

[TheBlacksmith]

You already have had a disaster (hurricane), overly complicated scenarios are not the wat to go. How big is your genset? I have run 2 refrigerators, a freezer and lights for 5 days after a hurricane and again for two days after a bad storm on a 5 kw 11 hp generator and it still works. Setting covered in the garage with fresh oil, stabilized gas waiting the next time the power goes out.

 

[waross]

I hope that you are not addicted to ice cream. Refrigerators used to be designed to run for 18 hours per day. Eight hours a day will probably melt your ice cream.
If you are using simple addition of breaker and feeder capacity to size your gen-set, you may be a little oversized.
60 Amp x 120 Volts = 7200 VA.
I estimate your refrigerators at about 900 Watts/VA and the freezer at 1400 Watts/VA.
You need about 3200 Watts to run all three, plus about another 3000 watts reserve to start the freezer. This assumes staggered starting.
I suggest a sub panel for the refrigeration and selected lighting. Mount a manual transfer switch beside the sub panel. When starting the gen-set, turn off the refrigeration breakers and then operate the transfer switch. Then through the breakers for the refrigeration, one after the other. Best results if the freezer (largest) is energised first. Allow about a 2 to 5 second interval between switching breakers.
Set size- About 8 Kw unless you have a ship load of other loads that you haven't told us about.
If you want a better answer ask a better question. eg: actual ratings of the equipment and actual lighting load.
I was once located by an extended family who had installed a total of 11 new diesel sets; ALL TOO SMALL.
Don't trust me but take a chance that I may know what I am talking about when I say;
"DON"T GO SMALL ON A GEN SET!"
When you are on the grid, the distribution transformer and the grid will accept a very large overload with very little noticable effect on the consumer.
An overloaded generator slows down and stops (if your lucky). Sometimes it just slows down, some of your refrigeration trips off and some burns up due to low voltage.
"DON"T GO SMALL ON A GEN SET!"

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

I agree with the others that your plan seems overly complicated for such small loads. For what you would spend on the timing and switching hardware, the engine-generator could be increased to the correct size.

I think Bill's suggestions make a lot of sense.

 

[itsmoked]

Not a good plan. You could easily be dropping a load of food poisoning into a disaster. That would certainly reduce the effectiveness of a group of workers.

You need an adequate generator. Please tell us what the load currents are of your appliances and we can help with the size check.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ELMPE1]

I want to thank all the responders for the good, practical advise. After looking at some of the starting watt versus running watt information, I think I just need to get all the nameplate/manufacturer information and buy a genset that is plenty big enough.

Thanks again

 

[waross]

Total all the nameplate Watts including lighting. Add 200% of the largest motor if you can live with staggering the first start manually. Once you are online and running the chance of two refrigeration compressors starting simultaneously is very remote.
If you want to be conservative, add all the motors which may start simultaneously at 300%.
Why add motors at 300% when starting currents are typically about 600%.
It has to do with current phase angles, Watts, VAs, and VARs.
Don't ask for the whole explanation unless you really, really want it.
Normally, using 300% for motor starting on a gen-set works well.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LIBERTYELEC]

Considering the labor costs involved to do a "timer" scenario added to the cost of the relevant timers and additional materials, it would more than likely be less expensive to buy the right size generator. Not to mention the reliability issues.