Inverter

windward54 · Oct 27, 2009

I guess it really depends on the size of the inverter and the current draw of the fridge and the microwave. Better make sure you are not exceeding the capacity of the inverter, especially when the fridge comes on. Electric motors have a higher starting electrical need than once it starts running.

Mulf · Oct 27, 2009

You know what they say about the word "assume" !

You also need to determine that the solar panel is wired to the house batteries and how long the solar panel can keep the house batteries charged when the inverter is drawing current to run the fridge. A solar panel came from the factory on my boat but it is only there to top off the start battery, it isn't even connected to the house battery.

Benny · Oct 27, 2009

Congratulations, they are a sturdy and roomy pocket cruiser. To answer your question, we will need the following information;

1) What is the size of the inverter in Watts?
2) What is the draw of the refrigerator in amps at 120V?
3) What is the size of the solar panel in watts?
4) What size is your battery bank in amp/hour?

As a general rule for a small dorm fridge you will need at least a 1000W inverter. The surge required to start the compressor is at least 2-4 times its running draw.

On the bright side those refrigerators if used sensibly will maintain temperature for 3-4 hours when off. There are a couple of suggestions, a) precool the fridge to maximum at the dock b) A full refrigerator is more efficient than an empty one c) Every time the door is opened cool air spills out so the less it is opened the longer it will stay cooled. D) provide adequate ventilation for the refrigerator. E) a small battery powered interior fan will help distribute the cold air. These suggestion are also valuable when running the cooler on the inverter as they will reduce electrical consumption.

Here in Florida's Gulf Coast if you are going to use the boat in the summer to overnight you will need an A/C unit wether it is a small window unit, a portable unit or a carry on. So you might as well consider purchasing a gas powered generator. A 2000 watt will power the a/c unit, the refrigerator and an inboard battery charger; keeping you cool and charging your batteries overnight. Use with a carbon monoxide alarm detector.

Chuck Creel · Oct 27, 2009

Well first of all , as mentioned you must determine the wattage of the appliances you want to use and how long. My boat has a 130 WATT solar panel which produces abt 7 Amps of charge rate. My ice box kit draws abt 3 amps an hour so 10 hrs a day at 3 AH eguals 30 AHrs per day plus any lights required at night llike anchor lights, cabin lights etc. here is a link to a site that might help determine size of house bank and usage of inverter.
http://www.theinverterstore.com/tips.php
Scroll to bottom of page

Scott B · Oct 27, 2009

Are you sure the frig is 110v and not 12v?

Maine Sail · Oct 28, 2009

oldgranpop said:
Thanks for the prompt reply. It is the larger size inverter (#2000). Oldgranpop, St. Pete., Fla

As others have mentioned you need to do an energy budget BEFORE you kill your batteries. It is not as simple as "can I flip this switch and make it work?"

A little more info about:

Microwave - What size in watts (eg: 1500 watt)

Battery bank - How many batteries, how many banks, what is the group size and amp hour rating of them?

Fridge - How much does it draw?

Solar Panel - How many watts, is there a charge controller?

Alternator - How many amps? Internal or external regulation?

Other Items - What other electronics do you have on-board that you use while away from the dock?

The above information can help us determine just how long you can run these items for before hitting the critical 50% state of charge on your house bank.

I am guessing your inverter is a 2000 watt. Is that the continuous rating or the intermittent rating?

wufibugs · Oct 28, 2009

Again, I come bringing a passel of questions and a wealth of ignorance to the discussion.

1. What would be more efficient, a 12V fridge running off the batts, or a 120 running off the inverter, assuming both units were otherwise similar in construction? My guess is that because there is some loss of energy converting direct to alternating current, the former would probably be a more efficient unit.

2. Aside from what might be unnecessary cost, in inverters, is bigger better? I assume a 5k rated inverter is not less efficient than a 1k when both are running a 200 watt device.

3. I assume we are talking pure sine wave inverters?

4. The article Chuck provided the link to, from the inverterstore, was very interesting and informative. It seems to recommend batts be connected in parallel, but there are at least 2 possible ways of doing that. I am still working on that. What I was wondering is, if the batts are connected in parallel, I assume there is really no longer dedicated "cranking" and "house" batts. They form one large energy source, albeit with the potential of single component faillure.

Benny · Oct 28, 2009

Wofibugs

1) It depends on the draw of the appliance. It is not fair to compare a 12V marine refrigerator at perhaps $800 with a dorm refrigerator at $79.99. The former may use 2.5 amps/hour and the latter 4 amps/hour through an inverter. The tale don't end there as the 12V will probably have 8-10 cf instead of 1.7 cf of interior capacity.

2) Bigger is better depending on your needs. The 1K inverter will be more efficient than the 5K when running a 200W load. A inverter is most efficient when the load it is handling is close to its maximum capacity.

3) Pure or modified.

4) There are boats that have a starting battery independent from the house battery bank. The house battery bank may be composed of one or multiple batteries connected in parallel or series depending on the desired voltage.