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post #1 of 6 (permalink) Old 04-30-2019, 04:51 PM Thread Starter
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I run a small farmers market, and we are looking to purchase a new generator. On a heavy day, we'll be running 4 or 5 mini refrigerators, maybe 2 small chest freezers, our sound system (only has one speaker) and maybe 5 small fans. Any advice on how many watts to purchase? Any advice is welcomed and very much appreciated! Thanks!
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post #2 of 6 (permalink) Old 04-30-2019, 07:05 PM
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YOU need to determine required wattage yourself. Look at all those units you will be using and add up wattage. On refrigerators and freezers you need to consider starting wattage. I'm no expert on that so would probably add about 50% for each for startup wattage.

Hopefully someone else who knows more than I will chime in on that.
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post #3 of 6 (permalink) Old 05-02-2019, 12:22 PM
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Here's a generator load calculator that may be helpful...
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File Type: jpg portable-generator-wattage-chart.jpg (208.9 KB, 14 views)
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post #4 of 6 (permalink) Old 05-08-2019, 11:40 AM
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I see some things in that chart that I wonder about, ex a central ac 24000btu is 3800/11400 run/additional starting watts. then a heat pump is 4700/4500. Why would a heat pump require fewer starting than run plus they do show capacity in btu for a comparison. Most heat pumps are central ac units so why such a big difference in starting watts? Lastly, most heat pumps have "emergency" heat strips that are also used in a defrost cycle, where basically when heating, it reverses the compressor, or the coolant routing to what is a cooling cycle and kicks the resistance heating coils in to provide heat to the outside unit to melt any frost that has formed.. I had a GE executive heat pump back about 40 years ago that would frost solid and even with the heat strips going would take quite a bit of time to defrost. I not have a Trane unit that is about 4 years old that rarely frosts up.


I know non of this really applies to his application. The best thing to do would be to look at the wattage/amperage ratings on the specification plate on each unit and add them up. For the most part it would probably be unusual if all were to start at the same time. If everything had been shut down it would probably be best to start the heavier draw appliances one at a time to prevent any sudden overload condition.
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post #5 of 6 (permalink) Old 05-08-2019, 11:55 AM
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Quote:
Originally Posted by jkingrph View Post
I see some things in that chart that I wonder about, ex a central ac 24000btu is 3800/11400 run/additional starting watts. then a heat pump is 4700/4500. Why would a heat pump require fewer starting than run plus they do show capacity in btu for a comparison.
General rule of thumb for traditional A/C units is that added starting load is 3x the running load. This is borne out by Generac's load chart. Modern heat pumps use technology like Soft Start / capacitors to reduce the startup load. Heat pumps also tend to equalize the pressure gradient across the compressor when idle.

Last edited by tabora; 05-08-2019 at 11:59 AM.
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post #6 of 6 (permalink) Old 05-08-2019, 12:01 PM
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Originally Posted by tabora View Post
General rule of thumb for traditional A/C units is that added starting load is 3x the running load. This is borne out by Generac's load chart. Modern heat pumps use technology like Soft Start / capacitors to reduce the startup load.

Makes some sense. Since largest part of startup is compressor, although a big fan is also involved, plus squirrel cage. By traditional A/C do they refer to central air or just window units? I suspect the smaller are window units, possibly 110/120 volt.


I remember back when we had that old heat pump, I could go out in the winter when it was defrosting and the old analog electric meter would be spinning very fast. Now with the new digital meter I have not noticed so much, plus the newer unit is more efficient, so our electric bills have remained fairly stable over last 8-10 years.
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