Dedicated inverter for refrigerator

Does anyone see the merit of hardwiring a small dedicated inverter to the fridge, so that it is not affected by houseloads that may be max'ing out the regular house inverter?

Also, wouldn't a large inverter running at low loads (like 15%) be running at low efficiency levels?

You can do that if you want to.


My choice is a 12/120 volt AC/DC refrigerator that senses the incoming voltage and switches back and forth automatically. No inverter needed.


Remember that an inverter powering a refrigerator will have to run 24/7 and there's a standby current drawn by the inverter even when the refrigerator compressor is not running.

What Wes said .......
and I believe there would be some loses in conversion from 12VDC to 120VAC .... FB

Ex Sailor said:

What Wes said .......
and I believe there would be some loses in conversion from 12VDC to 120VAC .... FB

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I suspect the OP has an existing 120 vac refrigerator other wise he wouldn't be asking the question.

Ex Sailor said:

What Wes said .......
and I believe there would be some loses in conversion from 12VDC to 120VAC .... FB

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Not necessarily. With our 12/120 V unit we frequently turn off the inverter at night when anchored to save total power and run the fridge on 12 V only.

sunchaser said:

Not necessarily. With our 12/120 V unit we frequently turn off the inverter at night when anchored to save total power and run the fridge on 12 V only.

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If you have a 12/120 volt refrigerator, why would it not be running on 12 volts DC whenever you're away from shore power? Why would you have to switch it manually?

mbevins said:

I suspect the OP has an existing 120 vac refrigerator other wise he wouldn't be asking the question.

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Possibly, but it would have been simpler if he stated that in his original post.

I thought most / all? 12V/120V fridges actually run on 12V and 120V is reduced via transformer/rectifier to provide 12V DC to run the compressor.
If that's true??? Inverter to provide 120V just adds another conversion and loss... Doesn't make sense...Unless it ONLY a household 120V only?

Depends on the fridge. Running a 60 cycle unit on 50 cycle or vice versa an inverter has merit. Also bigger inverters are more efficient so you might consider running all ac appliances through a larger inverter and charging with dual frequency chargers. Your choice of appliances are going to dictate your electrical needs. Doha is 50hz no?

I would go dedicated sine wave inverter. Generally a lower standby power loss than the big inverter, a backup if one fails, and certainly important enough to have its own dedicated power supply.

Ted

Bacchus said:

I thought most / all? 12V/120V fridges actually run on 12V and 120V is reduced via transformer/rectifier to provide 12V DC to run the compressor.
If that's true??? Inverter to provide 120V just adds another conversion and loss... Doesn't make sense...Unless it ONLY a household 120V only?

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My new Isotherm has two separate wiring harnesses for the ac and dc current. But both go into the power supply unit.

A very good friend of mine leaves his Xantrex in the inverter mode all the time. He says that it is not inverting when the boat is on shore power or his generator is running. When he leaves the slip the inverter starts its inverting program automatically. (generator not running.) Is he correct?

Codger2 said:

A very good friend of mine leaves his Xantrex in the inverter mode all the time. He says that it is not inverting when the boat is on shore power or his generator is running. When he leaves the slip the inverter starts its inverting program automatically. (generator not running.) Is he correct?

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He could be if his inverter has a built in transfer switch. Still his inverter is drawing a small amount of power. No big deal when underway but it's a drain if he is anchored with the engine off.

In my case, the inverter only powers the 120 volt receptacles including the microwave and coffee pot so I leave it off unless I want to use those appliances. I will also leave it on to charge my laptop.

Hi Guys

I have a 3000 W inverter to run a domestic 110V fridge and a domestic 110V freezer. Two separate units. The boat reports so far 475 hours and I had zero problems with all the equipment involved. After 3 years there is no rust in the cooling units and the Xantrex runs like a baby. Battery consumption? until now I never had to start the genset to charge batteries. Apart from that, I have two 135 W solar panels and lots of sunlight.

I will never think about switching to 12V equipment

makobuilders said:

Does anyone see the merit of hardwiring a small dedicated inverter to the fridge, so that it is not affected by houseloads that may be max'ing out the regular house inverter?

Also, wouldn't a large inverter running at low loads (like 15%) be running at low efficiency levels?

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Yes we made this choice.
we living onboard full time never at dock all AC was on one big inverter and when we switch to generator to inverter all time we get a short power cut.
electronic fridge don't like that and made some bug and TV and CD player stop all time.
so we decided to instal 1000Watt inverter only for fridge TV and CD player also when we on generator.

Bacchus said:

I thought most / all? 12V/120V fridges actually run on 12V and 120V is reduced via transformer/rectifier to provide 12V DC to run the compressor.
If that's true??? Inverter to provide 120V just adds another conversion and loss... Doesn't make sense...Unless it ONLY a household 120V only?

Click to expand...

That is a true statement. a 12v/120v fridge is slightly more efficient when running on 12 volt only for this reason.

O C Diver said:

I would go dedicated sine wave inverter. Generally a lower standby power loss than the big inverter, a backup if one fails, and certainly important enough to have its own dedicated power supply.

Ted

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Yes this is my thinking... as a redundant system for this important item and to minimize standby power loss. Refrig will be household as I have no interest in 12v or marine units. Unfortunately that's another big 1k chunk of change out the door.... so is the joy of owning a boat!

"That is a true statement. a 12v/120v fridge is slightly more efficient when running on 12 volt only for this reason."

Many of the newer 12V reefers are way more efficient as they slow the compressor to keep the cool, rather than cycle off and on a single speed compressor.

A 120V reefer is a lightly loaded AC current user , and will operate just fine on a cheapo inverter, sine wave is Required for Air Cond and heavy loads.

All inverters have a limited operating range in which they are most efficient.

To add to what FF said, today we have digital inverter refrigerators which are super efficient as they ramp up motor speeds and vary them to required loads. That's why you can operate a 500watt refrig with a 500watt inverter... there is no "locked rotor" startup draw. Similar result when adding a VFD to a motor

BTW, what is that limited range where inverters are most efficient? What % of rating?

Check the manufacturers specs for your unit. I'm shopping victron right now and the sweet spot is around 10 to 15 percent of output.

Bacchus said:

I thought most / all? 12V/120V fridges actually run on 12V and 120V is reduced via transformer/rectifier to provide 12V DC to run the compressor.
If that's true??? Inverter to provide 120V just adds another conversion and loss... Doesn't make sense...Unless it ONLY a household 120V only?

Click to expand...

There's a fairly recent thread on Cruisers Forum with some info about the Danfoss compressors. Seems they actually always run on a 3-phase AC created from either DC or household AC. The 3-phase AC is said to be better and more efficient than either DC or household AC, even with any conversion losses factored in.

It was clear in that thread that a DC source is inverted to 3-phase AC. It wasn't clear (to me, at least) whether household AC is directly converted to 3-phase AC... or whether it's first converted to DC and from there to 3-phase AC.

(I don't actually have much of a clue about what 3-phase AC is.)

For OP, I'm beginning to think some fridge features may outweigh efficiency concerns, assuming a boat big enough to have stable (and plentiful) AC and DC power onboard. Want frost-free? Household fridge, driven by an inverter. Don't need frost-free? AC/DC fridge or AC-fridge-with-inverter, perhaps chosen to fit the avialable installation space. And so forth...

-Chris

ranger42c said:

There's a fairly recent thread on Cruisers Forum with some info about the Danfoss compressors. Seems they actually always run on a 3-phase AC created from either DC or household AC. The 3-phase AC is said to be better and more efficient than either DC or household AC, even with any conversion losses factored in.
..................

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It was on the Internet so it must be true.

WesK said:

It was on the Internet so it must be true.

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As it happened, several of the posters on that thread are electrical engineers, they also pointed to parallel threads on other fora, and it sounded plausible. Stemmed from a post by sailorchic about her new (AC-only) fridge.

But I take your point.

-Chris

ranger42c said:

As it happened, several of the posters on that thread are electrical engineers, they also pointed to parallel threads on other fora, and it sounded plausible. Stemmed from a post by sailorchic about her new (AC-only) fridge.

But I take your point.

-Chris

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Seems like just about everyone on boating forums is an "electrical engineer".

WesK said:

Seems like just about everyone on boating forums is an "electrical engineer".

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Except for me, of course.



-Chris

My former boss used to say "Engineers dream things up, technicians make them work."

cafesport said:

Check the manufacturers specs for your unit. I'm shopping victron right now and the sweet spot is around 10 to 15 percent of output.

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I looked at the 800w and 3000w models. The specs sheets show maximum efficiency (low 90%'s) and no-load power draw (about 8 and 20 watts). I don't see anywhere in their specs about sweet spots. Maybe a quick call to tech support can answer that.

However using simple logic, during time away from the boat the refrig may operate for only a few hours per day. During the rest of that time the inverter is in idle yet the big unit is burning 1/3+ kilowatt per day in idle alone! The small, dedicated one about 1/10 kw.

I think I just answered my own question

ranger42c said:

For OP, I'm beginning to think some fridge features may outweigh efficiency concerns, assuming a boat big enough to have stable (and plentiful) AC and DC power onboard. Want frost-free? Household fridge, driven by an inverter.

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I'd hate to open up an expensive brand new refrig, but it might be worth opening the case just to reach the wire that feeds the heater coil in the insulation (frost-free). A simple switch would allow turning on and off that feature and thus cutting the power needs by 1/3.

makobuilders said:

I'd hate to open up an expensive brand new refrig, but it might be worth opening the case just to reach the wire that feeds the heater coil in the insulation (frost-free). A simple switch would allow turning on and off that feature and thus cutting the power needs by 1/3.

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That'd be a nifty feature. It'd be even niftier if builders of typical AC/DC marine fridges (NovaKool, Vitrifirgo, Norcold, etc.) included both frost-free and a control switch like that. I'm not aware of any frost-free AC/DC fridges...

-Chris