Refrigerator run-time?

[Traveler 45C]

I’m trying to figure my AC daily load use to determine the correct size inverter for my boat.

How many hours per day does a typical refrigerator actually run?

 

[Pascal]

xantrex uses 1/3 duty cycle in their charts... it depends on the temperature in the boat, tstat setting and how often / long the door is open.

if know i'm going to run on inverter, I try to get groceries a day before so that temp stabilizes before running on inverter and i can then lower the Tstat.

although, this really affects your decision on battery bank size, inverter capacity is determined by the fridge size (+ other loads).

 

[Nonchalant1]

Referigerator run time doesn't matter for inverter size at all. What's important for inverter size is the amps it draws (like 7 amps for a refer) and the surge it requires on startup every time it kicks on. Most inverters are made to handle surge much greater than their rating, like a 1500 watt can handle 3kw surge, but you might check the differences between brands.

I run a 6.5 amp 120v refer on a 1200 watt inverter. Works fine and it handles the surge. However, the same inverter can't handle a 6.5 amp 120v water pump because the surge on startup is much larger.

The reason to worry about refer run time is to size your battery bank that'll power the inverter. There are a number of previous threads on that subject.

Doug Shuman
1978 53MY

 

[Traveler 45C]

Yes, Doug, that’s what I’m trying to do, size the battery bank. I know in my original post I said, “size the inverter”. Whoops…

Anyway, I need to estimate how much time that a typical fridge will run. Best guess here, I know there are many variables.

1/3 duty cycle? Do I read that as running 1/3 of the day, 8 out of 24 hrs?

 

[Nonchalant1]

Yeah - I'd count it as running 1/3 of the time.

I can tell you this: My house bank is 4 Rolls 8HHG25PM 8 volt batteries with 275 amp-hr. rating each, hooked in series, to provide 275AH @ 32 volts (that's the equivalent of a 733 AH bank of 12 volt batteries). For simplicity, I use the house bank for all battery needs. If I want more amps, I'll increase my house bank. That way whatever power I use comes from the one large bank. I also have a starting bank of 4 Interstate 8V195's that only starts the starboard engine, nothing else.

I use a 1,200 watt (32 volt DC to 110 volt A/C) inverter to run only my 6.5 amp (19.0 cu ft) refrigerator and my cell phone charger, and the same bank to run 32v lights, heads, water pump, etc. We can stay on the hook 2 nights before the inverter shuts off due to "low charge" which is about 50% of the bank's capacity, I think. I've done that, and there's still enough in the house bank to start the port engine. This includes running the genny 60-90 min to use the stove for breakfast and dinner, etc. Of course, I could parallel the starting bank overnight to get more inverter time, but I don't want to chance running both banks down.

I usually run either the engines or the genny up to 4 hours per day when we're on the hook to keep the house bank charged. I don't usually go two nights without charging.

Hope this helps,

Doug

 

[Traveler 45C]

Doug,

Yup, that helped a lot. Thanks.