Wiring dedicated inverter for new AC only fridge

[HeadedToTexas]

I am ready for cold beer and hard ice cream, so I finally gave up on my N'ercold DE0061 refrigerator and am going to an AC only model. My plan is to power the new fridge from two sources, AC via shore power or generator, and my house battery bank via a dedicated inverter.

The right Victron Phoenix will get power from the old Refrigerator breaker on the DC panel. I hope to keep switching power supplies as simple as possible, but also protect myself from stupid actions. I could simply wire the AC sides to the same outlet and plug the fridge in, then power up only one breaker at a time.

Protecting myself from stupid actions would seem to dictate a switch such as the one below sitting between the supplies and the outlet. Is there a more conventional or ABYC way of wiring it?

 

[Comodave]

To keep it really simple maybe just use the inverter full time. If you are plugged into the dock or genset do you care about the small inverter losses? If you are plugged in the battery charger will replace the power used out of the batteries to run the inverter. If you just use the inverter then you don’t need any switches to select the power source.

 

[Lepke]

Going thru the inverter for all your power is the easy way, but you have to have enough inverter power for every ac need that will be used at the same time.
Mine works that way and if the batteries are low, starts a generator.

 

[Jeff F]

A fancier inverter will incorporate the functionality you want and switch automatically between AC and DC. Like a Victron MultiPlus 12/500/20. That's overkill as you probably don't need the charger, but it'll work. There are many non-Victron offerings out there.

I think I'd do as Commodave suggests and leave the 12v on all the time. No harm, and no real benefit in switching to AC.

ETA: just looked more closely and that Victron is for Europe only it looks like. But it illustrates the switching.

 

[Comodave]

I thought he was going with a small inverter for just the refer. Maybe I misunderstood???

 

[kthoennes]

Jeff is right, just get an inverter with what they call an auto transfer switch and never think about it again. That's what I did. Not hard to find.

 

[ranger58sb]

I am ready for cold beer and hard ice cream, so I finally gave up on my N'ercold DE0061 refrigerator and am going to an AC only model. My plan is to power the new fridge from two sources, AC via shore power or generator, and my house battery bank via a dedicated inverter.

Faced with AC-only fridge and freezer...

And preferring quiet early morning coffee or late afternoon hors d'oeuvres...

And definitely preferring generator OFF overnight...

We installed a larger inverter/charger with auto-transfer, wired it to several breakers on the panel...

So we can not only service the fridge/freezer loads overnight or while underway, but also most other normal 120V outlet loads (coffee maker, microwave for short bursts; TV/stereo, small device battery charging, etc. ).

Seamless.

Wiring between battery bank and panel was much easier than it would have been to pull wires to individual appliances, too.

-Chris

 

[johnrupp]

I’d go with post # 2. Get the appropriate size Victron inverter and run the fridge through it. DC panel to inverter to fridge. No reason to complicate it beyond that.

John

 

[O C Diver]

If all you want to run off the inverter is the refrigerator, you can buy a transfer switch that plugs into the inverter and wired or plugged into a shore power circuit or outlet. When I researched this, if you're handy, a relay will accomplish the same thing for a fraction of the cost.

If the inverter only powers the refrigerator, and your AC and DC panels are located in the same cabinet, it would be pretty easy to wire the transfer switch and inverter in the cabinet. Further, if the refrigerator has a dedicated circuit on the AC panel, that wire could be connected to the output of the transfer switch, and the AC breaker could be the input for shore power.

By limiting the inverter to maybe 150% of the refrigerator requirement, it should be easy to power it off the DC panel.

If you feel this is within your skill set but need input, PM me.

Ted

 

[mvweebles]

A fancier inverter will incorporate the functionality you want and switch automatically between AC and DC. Like a Victron MultiPlus 12/500/20. That's overkill as you probably don't need the charger, but it'll work. There are many non-Victron offerings out there.

I think I'd do as Commodave suggests and leave the 12v on all the time. No harm, and no real benefit in switching to AC.

ETA: just looked more closely and that Victron is for Europe only it looks like. But it illustrates the switching.

That's an inverter + charger. Probably more than OP wants

OP - I'm not crazy about running via the inverter 24/7. Inverters have a decent parasitic draw. Here's a 1200W PSW Inverter with ATS and power cord. $170, though out-of-stock right now. Something like this would do the trick.

https://invertersrus.com/product/aims-pwrix120012sc/

Peter

 

[HeadedToTexas]

Sorry guys, we do have a 3000 watt inverter/charger to handle all of our AC needs when on batteries. We do not leave the inverter on 24/7 because of that parasitic load. That is what is driving me toward a small dedicated inverter to power this new refrigerator. A smaller 250 watt inverter like the Victron Phoenix 12/250 has a far smaller parasitic load to keep those quiet morning coffee and late afternoon hors d'oeuvres quiet.

 

[Comodave]

That is what I thought you meant. I would just power the refer 24x7 from the small inverter. When you are anchored you would power it off the batteries. When you are on genset or shore power the small parasitic loss from the inverter isn’t really relevant as you have unlimited power. It makes it a simpler install.

 

[O C Diver]

Sorry guys, we do have a 3000 watt inverter/charger to handle all of our AC needs when on batteries. We do not leave the inverter on 24/7 because of that parasitic load. That is what is driving me toward a small dedicated inverter to power this new refrigerator. A smaller 250 watt inverter like the Victron Phoenix 12/250 has a far smaller parasitic load to keep those quiet morning coffee and late afternoon hors d'oeuvres quiet.

A 250 watt inverter produces 2.1 amps continuous at 120 VAC. Thought your refrigerator amperage was going to be higher than that. I was thinking the 500 watt unit was probably the minimum.

Ted

 

[Comodave]

I did a 400 watt dedicated inverter for a chest freezer in our last boat. 250 may be marginal.

 

[kthoennes]

We did a 1000 watt inverter with a transfer switch, inside the fridge cabinet (with a fan). The price difference was minimal so I figured I'd overkill it, way more than the fridge needs. The only thing I put on it was the fridge, and a multi-port usb charging outlet on the outside of the fridge cabinet. Minor draw, but on our boat there's a handy little shelf next to the settee where everybody can pile their phones and other devices for charging. Gets the electronic mess off the galley counter.

 

[Jeff F]

Sorry guys, we do have a 3000 watt inverter/charger to handle all of our AC needs when on batteries. We do not leave the inverter on 24/7 because of that parasitic load. That is what is driving me toward a small dedicated inverter to power this new refrigerator. A smaller 250 watt inverter like the Victron Phoenix 12/250 has a far smaller parasitic load to keep those quiet morning coffee and late afternoon hors d'oeuvres quiet.

Modern fridges cycle very frequently and run at low power. So zero load parasitic draw may not be as big a concern as you think.

I'd run the fridge on the house inverter, and spend extra money if need be on getting a very energy efficient fridge.

I live unplugged, and run my 2kw inverter/charger 24/7. My base consumption for inverter and fridge in moderate temperatures is about 1.5 kwh per day.

An inverter with a 50% zero draw duty cycle and 20w zero draw is 0.24 kwh/day excess draw. That's really not much in the scheme of things... Once running I don't think there is any meaningful efficiency difference between a big and small inverter with a 200w load.

 

[mvweebles]

The zero-load draw of a Victron 3000W multi-plus is listed as 15W, or just over 1-amp, or around 15AH in a 12-hour period. For argument's sake, let's say the parasitic loss of a 400W inverter is half - around 7-8AH in a 12-hour period. Let's go further and consider a 24-hour period. Going with a 400W inverter saves 15AH compared to just using the 3kw house inverter. Most boats have at least 400AH capacity (mine has 700AH LFP).

Really? If you're running that close to capacity, maybe spend the money on an additional battery.......

Peter

 

[HeadedToTexas]

The Magic Chef model I have on order shows actual loads between 1.2 and 1.5 amps depending on where you read that spec. I will have a more confident number once I receive the unit. At that point, I plan to order either a Victron Phoenix 12/250 or 12/375. They have very low parasitic loads.

It would certainly be simple to just run the new fridge only on the dedicated inverter, but one place I'm less clear is the impact on the batteries of constantly being charged and discharged. If I was living aboard, the house bank would constantly being charged and discharged, but I'm not and most of the time these days is spent with virtually zero DC load. The Xantrex Freedom 3000SW is set to charge, but not invert. The Balmar Smartgauge hovers at a consistent number (which is a separate issue).

Would adding the load of that constant dedicated inverter powering the fridge have any negative impact on our aging AGM batteries?

 

[AdmiralS]

The Magic Chef model I have on order shows actual loads between 1.2 and 1.5 amps depending on where you read that spec. I will have a more confident number once I receive the unit. At that point, I plan to order either a Victron Phoenix 12/250 or 12/375. They have very low parasitic loads.

It would certainly be simple to just run the new fridge only on the dedicated inverter, but one place I'm less clear is the impact on the batteries of constantly being charged and discharged. If I was living aboard, the house bank would constantly being charged and discharged, but I'm not and most of the time these days is spent with virtually zero DC load. The Xantrex Freedom 3000SW is set to charge, but not invert. The Balmar Smartgauge hovers at a consistent number (which is a separate issue).

Would adding the load of that constant dedicated inverter powering the fridge have any negative impact on our aging AGM batteries?

It would NOT. The charger float would basically offset the inverter for the fridge. The fridge would NOT run the batteries down to say 95% then charge. You would just see them sit at 100% SOC. Its really no different than a DC fridge. Just swapping the DC fridge load for the inverter load.

Also, the dual voltage fridges are running DC all the time, when you power them with AC it is just converting back to DC anyway.

We have a dual voltage fridge on our Helmsman and we haven't run it on AC in the 5 years we have had the boat

 

[HeadedToTexas]

Roger that. Thanks Admiral. Despite spending my share of time working in Montrose, I had to look up Stony Point. Beautiful part of the country. That whole part of the Hudson River Valley is just spectacular.

 

[SteveK]

Are you looking to AC power the fridge due to AC fridges being less costly to purchase than AC/DC ones? What Admiral said is why I run mine 24/7 on DC even though it runs with AC

 

[HeadedToTexas]

One of the wise users here at TF observed that when it comes to boat refrigerators, you either get one that runs on either AC or DC or one that keeps your beer cold and ice cream hard, but not both. That has certainly been my experience with the N'ercold DE0061 in my boat. And the dirt home refrigerators have never struggled with keeping beer cold and ice cream hard. My read is that the easiest, and clearly the cheapest ($260 vs. $2000), path to reliably cold beer and hard ice cream is to get rid of the Norcold and install a suitably sized residential refrigerator. Yes, the jury is out on that. More as I know it.

The issue in focus over the past couple pages is how to power that residential fridge when off shore power. The consensus is to use a small dedicated inverter to convert DC from the house bank to AC to power the fridge and just skip the notion of AC/DC altogether. The longer that strategy sits with me, the better it sounds.

 

[Comodave]

We put an Isotherm CR271 in our current boat. It is both 12/120 volts. It freezes ice cream and refrigerates extremely well. Initially it froze everything in the refer because we had set it to the maximum setting of 8 since we always had to do that with boat refers. We gradually turned it down to 3 and it freezes well and cools the refer without freezing the contents. It was expensive but it just works great so we are happy.

 

[luna]

If you have determined that an onboard residential refer. is in your future, I would consider these issues.

- It's likely that this refer. has a defrost element in it. These things will draw about 5 Amps of 120V AC. for around 5 minutes every 6 hours or so. Should you chose to power this refer with a small inverter, size it for more than this 600 W load.

- It's now common to find that the skin of the refer is used as the heat rejection surface. You will need about 1 1/2" of clearance on all surfaces to allow convection or better yet, a constant breeze to move the heat away. Different refers. utilize different methods of heat rejection, chose wisely to ensure things stay cold and hard.

- The method used to provide power in my mind depends on the boat's use profile. If your boat lives most of the time at a dock (home port, or at a transient slip) that has AC power, like most boats do, why would you power the thing using an inverter? Converting AC to DC then back to AC makes little sense, plus if simply powered from the grid, the batteries don't see the load.

- You say you already have a 3 Kw. inverter/charger, but don't use it much due to the parasitic loads. If it is a modern pure sine wave inverter and you opted for the inverter control panel, there is likely a method to put the inverter in Search Mode that will only turn it on when a reasonably large load (like your refer.) is detected, thereby reducing the parasitic load significantly. If it is a Modified Sine Wave inverter, expect to replace the refer's control board about once a year. Gone are the days of mechanical timers and switches to control things, today it's all electronics that are not designed for MSW which is understandable as the refer. is intended for your house.

If it was me and I had an existing 3 Kw PSW inverter/charger with an auto transfer switch, I would power the refer. with what I have and live with the current draw until battery replacement time, when I would increase the bank capacity to compensate and be useful in powering the next think that gets added.

 

[HeadedToTexas]

Good point, luna. The Magic Chef model I have on order does not have a defrost element. Pros and cons with that, of course, but in addition to cold beer and hard ice cream, my objectives were to minimize energy use as my battery bank feels limited at just under 600 AH of AGM batteries. They have had a tough 4 year life and I am less than impressed with their power delivery.

The new refrigerator will fit snugly top to bottom, but there is plenty of room on each side for ventilation. I have yet to design a trim for the sides, but I am leaning toward black plastic mesh to facilitate air flow.

We do spend way too much time at our marina today, but we have big ambitions and this project is addressing the future. Time on anchor and underway is where we want to be. To that end, running off an inverter makes sense to me.

The Xantrex Freedom SW 3012 is a pure sine waver inverter. We use it a lot when away from the dock, but are not away from the dock as much as we'd like. I wouldn't say we don't use it much, and especially not because of its parasitic load. That said, if its only function at certain times, like during the week when the only loads are the bilge pumps and the refrigerator, it makes sense to me to create the needed AC with an inverter that has far less parasitic load than the big 3000 watt inverter. I appreciate that we are trading cost for simplicity.

The SW 3012 also has search mode. The new refrigerator will draw plenty of power to work with Search Mode. That may well be the answer, but the SW 3012 still has quite a bit more parasitic load in Search Mode (8 watts) than a small inverter like the Victron Phoenix 12/250 and at 90% efficient, the big SW 3012 will draw quite a bit more power when the refrigerator compressor is running than would a smaller dedicated inverter. Lots to consider.

 

[O C Diver]

- It's likely that this refer. has a defrost element in it. These things will draw about 5 Amps of 120V AC. for around 5 minutes every 6 hours or so. Should you chose to power this refer with a small inverter, size it for more than this 600 W load.

No.

If a refrigerator / freezer has a defrost cycle and has an Energy Guide label, the power draw (amperage) has to be disclosed on the refrigerator electric label and the defrost consumption has to be included in the energy consumption. So if the defrost cycle draws 5 amps, the manufacturer's label would disclose a 5 amp consumption rate.

Ted

 

[Jeff F]

...and at 90% efficient, the big SW 3012 will draw quite a bit more power when the refrigerator compressor is running than would a smaller dedicated inverter. Lots to consider.

I think you're asking the right questions.

I'm not sure that a smaller inverter is more efficient. I haven't done a detailed comparison, but don't think you'll find any big differences in efficiency. Victron quotes maximum efficiency on the Phoenix at 89%.

 

[HeadedToTexas]

So 90% or 89% on a 140 watt load is virtually no difference if that's how efficiency is calculated. I suspect it has at least something to do with a 3000 watt inverter versus a 250 watt inverter, but that is a question to which I am still pursuing an answer.

If efficiency is on the load and independent of the rated capacity, then it's definitely worth figuring out the Search Mode on the SW 3012.

 

[luna]

O C Diver.

Just so I understand your point, is the "Energy Guide Label" the same label as "refrigerator electric label" that you referenced?
What does the info. on the Energy Guide label (typically Annual Energy Consumption in kWh and Annual Cost, based on $0.12 per kWh) have to do with sizing an inverter to power the refer?

Regardless of your responses, if the refer. has a defrost element (H to T says his Magic one does not) and that element draws 5 Amps at 120 V AC (mine does) would you power it with an inverter that is not capable of producing the 600W of power required to run the defrost element? If so why?

What I don't get is the "No" part.

 

[Jeff F]

That said, if its only function at certain times, like during the week when the only loads are the bilge pumps and the refrigerator, it makes sense to me to create the needed AC with an inverter that has far less parasitic load than the big 3000 watt inverter.

I don't understand. If you're plugged in the big inverter is on but in pass-through mode, right? You don't care about parasitic loss then, and the fridge is running on the shore power.