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Old 12-19-2013, 09:18 PM   #1
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Running Refrigerator on Inverter

Have just installed an inverter to run our 21 cu. ft. household type side by side ref/freezer. Previously when underway would run generator during day for refrigerator and other needs: chargers, bilge blowers, AC, etc. At night we would shut the generator down and holdover was fine for about 18 hours, When staying at anchor for extended periods running the generator for the refrigerator is not a very efficient way to go as the duty cycle of the refrigerator is about 30-40% so we are running the generator 60% of the time to no advantage.
I have installed a 1500 watt run / 3000 watt surge cheapo inverter dedicated to the refrigerator which has a run load of about 185 watts (measured). For a starter I have installed four golf cart batteries with a dedicated 30 amp charger and the system works fine. I may add more batteries later as I have not been out long enough to see what the holdover time is with the 4 batteries. I installed a relay and there is an audible alarm should we lose 110 power going to the refrigerator. This would be mostly in case the inverter tripped for some reason. So right now I am running refrigerator 24/7 off the inverter charging with it own charger, off shore power or generator,
Here is my question: Is there any advantage to adding a manual transfer switch or a relay that would transfer the refrigerator load to shore power when she is berthed for extended periods of time?
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Old 12-19-2013, 10:06 PM   #2
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I'm sure a simple rotary switch, or slide selector would work just dandy.
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Old 12-19-2013, 10:14 PM   #3
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Quote:
Originally Posted by Whistledoc View Post
Have just installed an inverter to run our 21 cu. ft. household type side by side ref/freezer. Previously when underway would run generator during day for refrigerator and other needs: chargers, bilge blowers, AC, etc. At night we would shut the generator down and holdover was fine for about 18 hours, When staying at anchor for extended periods running the generator for the refrigerator is not a very efficient way to go as the duty cycle of the refrigerator is about 30-40% so we are running the generator 60% of the time to no advantage.
I have installed a 1500 watt run / 3000 watt surge cheapo inverter dedicated to the refrigerator which has a run load of about 185 watts (measured). For a starter I have installed four golf cart batteries with a dedicated 30 amp charger and the system works fine. I may add more batteries later as I have not been out long enough to see what the holdover time is with the 4 batteries. I installed a relay and there is an audible alarm should we lose 110 power going to the refrigerator. This would be mostly in case the inverter tripped for some reason. So right now I am running refrigerator 24/7 off the inverter charging with it own charger, off shore power or generator,
Here is my question: Is there any advantage to adding a manual transfer switch or a relay that would transfer the refrigerator load to shore power when she is berthed for extended periods of time?
Depending on the inverter, there may be a 120 volt AC circuit that will power through an automatic transfer switch within the inverter. If not it could be added so that flow would be virtually seamless.
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Old 12-19-2013, 10:40 PM   #4
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Originally Posted by Whistledoc View Post
Have just installed an inverter to run our 21 cu. ft. household type side by side ref/freezer. Previously when underway would run generator during day for refrigerator and other needs: chargers, bilge blowers, AC, etc. At night we would shut the generator down and holdover was fine for about 18 hours, When staying at anchor for extended periods running the generator for the refrigerator is not a very efficient way to go as the duty cycle of the refrigerator is about 30-40% so we are running the generator 60% of the time to no advantage.
I have installed a 1500 watt run / 3000 watt surge cheapo inverter dedicated to the refrigerator which has a run load of about 185 watts (measured). For a starter I have installed four golf cart batteries with a dedicated 30 amp charger and the system works fine. I may add more batteries later as I have not been out long enough to see what the holdover time is with the 4 batteries. I installed a relay and there is an audible alarm should we lose 110 power going to the refrigerator. This would be mostly in case the inverter tripped for some reason. So right now I am running refrigerator 24/7 off the inverter charging with it own charger, off shore power or generator,
Here is my question: Is there any advantage to adding a manual transfer switch or a relay that would transfer the refrigerator load to shore power when she is berthed for extended periods of time?
Not knowing the details of how you operate/cruise your boat I can only suggest from my experience. It looks like you may benifit from a larger battery bank. With a boat your size I would think 1000 amp-hrs or more. I would install a bigger charger to reduce genset time. You didnt indicate what size your alternators are but they also should have the rating that will support your cruising style and keep the batteries topped off. Of course this is all mute if you dont mind running the genset most of the time.
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Old 12-19-2013, 11:31 PM   #5
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You will lose efficiency at some undefined level when you take shore-power 120 VAC, turn it into 12VDC with a charger, then turn that back into 120 VAC with the inverter so it would be more efficient to power the refrig from shore power. That efficiency loss may or may not be a practical consideration depending on your total shore-power use and your rates.

Don't know if you want to get into it, but the transfer relay question brings up the issue of switching the grounded neutral between the inverter and shore-power. If you manually pull the refrig plug from the inverter and plug it into an outlet supplied by the generator or shorepower and don't mix the systems at all you avoid that concern. If you use a transfer switch you probably want to address that. Some inexpensive truck or auto inverters do not play well with marine distribution systems -- for example I have a Samlex that won't turn on if the neutral is grounded externally. "Marine" inverters may or may not switch the neutral and they may or may not have transfer relays that pick up generator or shore power, and that info may not be easy to find, so it can be a frustrating search. Magnum makes a line that does both, and I am fairly sure that Victron's inverters do also, but I can't confirm that.

We could also do the public math to figure out how the 30A charger will have to run each day to power the refrigerator, but you didn't ask that. I think you may want a higher-capacity charger like Dave says.
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Old 12-20-2013, 03:07 AM   #6
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Re-quoted so as not to burn my eyes
Quote:
Have just installed an inverter to run our 21 cu. ft. household type side by side ref/freezer. Previously when underway would run generator during day for refrigerator and other needs: chargers, bilge blowers, AC, etc. At night we would shut the generator down and holdover was fine for about 18 hours, When staying at anchor for extended periods running the generator for the refrigerator is not a very efficient way to go as the duty cycle of the refrigerator is about 30-40% so we are running the generator 60% of the time to no advantage.
I have installed a 1500 watt run / 3000 watt surge cheapo inverter dedicated to the refrigerator which has a run load of about 185 watts (measured). For a starter I have installed four golf cart batteries with a dedicated 30 amp charger and the system works fine. I may add more batteries later as I have not been out long enough to see what the holdover time is with the 4 batteries. I installed a relay and there is an audible alarm should we lose 110 power going to the refrigerator. This would be mostly in case the inverter tripped for some reason. So right now I am running refrigerator 24/7 off the inverter charging with it own charger, off shore power or generator,
Here is my question: Is there any advantage to adding a manual transfer switch or a relay that would transfer the refrigerator load to shore power when she is berthed for extended periods of time?
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Old 12-20-2013, 03:28 AM   #7
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Have a 24-volt refrigerator running off a 24-volt system. No complaints so far. Should I be worried?
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Old 12-20-2013, 06:07 AM   #8
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[QUOTE=av8r;200042]You will lose efficiency at some undefined level when you take shore-power 120 VAC, turn it into 12VDC with a charger, then turn that back into 120 VAC with the inverter so it would be more efficient to power the refrig from shore power. That efficiency loss may or may not be a practical consideration depending on your total shore-power use and your rates.

I am sure you can calculate the efficiency loss and what the added cost will be, but given the low cost of the transfer switch the recommendation is a good one. The transfer switch will also provide flexibility in the event the inverter fails as you can then go on shore or generator power at the flip of a switch.

As to the size of the charger, it is unfortunate you have a cheapo inverter. The marine inverter / charger for 1500 watts would usually provide a 100 amp charger which would cut your generator time by 66% and would also allow for a pass through of shore power or generator power when connected. The pass through of the generator power would reduce your generator run time because it would eliminate the draw on the batteries when the generator is running.

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Old 12-20-2013, 06:27 AM   #9
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four golf cart batteries with a dedicated 30 amp charger

I too think the charger is far too small.

I suggest a truck 135A dual belted alternator with a marine 3 stage V regulator , powered by the noisemaker.

I also would suggest a SOC meter so you can have a gas gauge for the house batt set.
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Old 12-20-2013, 08:06 AM   #10
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Thanks for the input. This how I arrived at 30 amp charger. Refrigerator is pulling 185 watts which equates to an amp and a half of 120. That equates to 15 amps of DC. Allowing for inefficiencies ...say 20 amps of DC. With a duty cycle of about 30% I am puliing 6 amps of power per hour out of the bank or 6 x 24 = 150 amp hours in a 24 hour day. Assuming I can cram all 30 amps of the charger into the battery each hours, that leaves me charging with the noisemaker a minimum of 5 hours a day. So I would say all of you are correct.

In actuality, I looked in the electrical storage area and found a spare 30 amp charger still in the box so I in stalled that just to get the system going. Had nothing to do with mathematics or numbers. It was what I had. But it seems that you all (here in Alabama we say "y'all" not....to be confused with the nautical tern "yawl") are correct and I can ask Santa for a bigger charger for Christmas.
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Old 12-20-2013, 08:50 AM   #11
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WOW! I found your avatar interesting so I lurked back in history to see what the boat looked like. You sir have one of the coolest boats I have ever seen. The custom work in the interior in incredible. I hope I see her on the docks some day.
New member and what kind of animal is it?
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Old 12-20-2013, 08:55 AM   #12
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WOW! I found your avatar interesting so I lurked back in history to see what the boat looked like. You sir have one of the coolest boats I have ever seen. The custom work in the interior in incredible. I hope I see her on the docks some day. New member and what kind of animal is it?
+1!!!! What a work of art!
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Old 12-20-2013, 10:24 AM   #13
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I'm a bit surprised that the "cheapo" inverter is OK for the fridge. I have a Zantrex Freedom 3000 charger/inverter with a link 2000 monitor. My Dometic fridge was once OK with the inverter but became unhappy with it about two years ago and won't run on the inverter at all now. Dometic says it is a common issue with inverters that have questionable sine. Everything else, including my other various computer and appliance chargers seem OK with it.

I guess I would have made this a priority fix by now, but I've had so many other projects, and meanwhile, I'm plugged in at the dock. The refer is also propane, so when cruising, I just switch. Still, I miss that seamless switch to the inverter when I unplug.
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Old 12-20-2013, 11:32 AM   #14
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I would be surprised the inverter would support the frig myself, the start up load for a unit that size is rather large, I have a 2500 watt unit and works fine while the engine running is feeding the inverter with a nice 13.8vdc, but when at rest you hear the frig chattering trying to start. Not a big deal for us as we only need the inverter while underway.
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Old 12-21-2013, 03:47 AM   #15
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"Here is my question: Is there any advantage to adding a manual transfer switch or a relay that would transfer the refrigerator load to shore power when she is berthed for extended periods of time?"

One advantage would be if the inverter were to fail you would be able to switch your refrigerator back to the regular 120 volt buss.
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Old 12-21-2013, 06:53 AM   #16
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and I can ask Santa for a bigger charger for Christmas.

Run from a smaller (under 10KW ) noisemaker many chargers do not deliver the power as advertised .

That is why a BIG smart alternator is a better choice if short recharge times are desired .

Best is when only the house requirements like a range force noisemaker use and it can take care of the house DC system seamlessly with that amount of run time.

Depending on how you run the math every hour of noisemaker is $5 to $10 , so run time reduction will help the cruise budget a good deal.
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Old 12-21-2013, 07:05 AM   #17
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in short....if it's a decent inverter and it works so far...I would say just use the inverter 24x7...don't worry about switching.

4 golf cart batts are fine unless you plan on staying out longer or running the genny less.

FF I think is correct that a 30 amp charger is a bit small if you are going to use it to charge the batts with a big genny. I just happen to have a little Honda 1000 that I run when all I am doing is charging the house batts....if you use a big genny...then I would suggest way more charging capacity.

Other than that and if your inverter is good enough quality or your fridge doesn't care about what the inverter is sending...why not 24/7????...the little inefficiency when going to shore power ...who cares at that point?
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Old 12-21-2013, 08:35 AM   #18
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In all the cruising yachts I've been involved in since my first large boat venture, Florida Bay Coasters, to the present day, we have ONLY installed AC refrigerators, from 5 cubic feet through 21 CF, run on inverters (Heart , Trace , Xantrex , Outback).

I find the design, engineering, efficiency and up-scale interiors of modern, mass-produced refrigerators superior to the RV/marine DC units ( which seem to be locked in a time-warp in the '70s). Ditto stand alone ice makers.

Only recently has my thinking advanced to running fridges and ALL AC installations 24/7 on inverted power.

With a small dedicated inverter for fridge only with other AC needs coming from shore or generator, I see no I advantage in not having a transfer switch for the fridge. May add to the life of the batteries , too?
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Old 12-21-2013, 08:36 AM   #19
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Other than that and if your inverter is good enough quality or your fridge doesn't care about what the inverter is sending...why not 24/7????...the little inefficiency when going to shore power ...who cares at that point?
My inverter automatically switches, but sometimes I let the inverter run to keep my fridge going. I have an easy way to run shore power to the boat around the standard 30 amp inlet and if the shorepower voltage is too low I'll do this so my breakers don't keep tripping out.
When I do this I add a 15 amp car type battery charger to my regular 30 amp boat charger to augment charging.
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Old 12-21-2013, 08:46 AM   #20
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