12v Fridge vs 120v using small 12v Inverter

[fo4imtippin]

So im finally getting my list of interior things finalized for Black Friday/ Prime day discounts and things.. Im not doing any propane in my build (other than small tanks for the grill). When im out camping for some of my multi month trips, the fridge will run 24/7 non stop. Not having run a generator or my main house inverter when im away for the day leads me to a 12v fridge as my large inverter may have a 25w-75w idle draw.


For a background, im doing a 48v solar system with an all-in-one. I will probably use the bus for a year or 2 before i implement that system. Im building almost everything i can to run 12v to reduce the need to have the inverter conversion loss when im not running the A/C.


For the price of a 12v fridge vs same size 120v fridge, its about a $1000 difference.
Reasons to buy a 12v:
More efficient because there is no inversion loss.


Reason to buy a 120v:
Price

If the fridge craps out i can replace it for much cheaper and get from any best buy
I can spend that extra 1k on a large 460ah lifepo4 battery with the savings.


Just putting it out there for feedback. Is this a stupid idea? Is that small 500w inverter running 24/7 going to have enough idle draw to offset the losses im trying to save by not running the main house inverter? Do we think that a small inverter is less reliable than the DC compressor (inverter?) in the 12v fridge.


Below are two fridges in the running.. Appreciate your thoughts and opinions on this..
12v

https://www.homedepot.com/p/Equator-...DC-S/322231231


120v
https://www.homedepot.com/p/Magic-Ch...00WE/302245066

[Ross]

I have a 12 VDC fridge from Truckfridge.com, undercounter unit, about $700. I'm quite pleased with it. I only use it while traveling, a couple of months at a time. All my lights and appliances are 12VDC and yes, I use propane for heat, cooking, and hot water. I love that the only thing that needs an inverter is a microwave. To me, having a power system that works well, off grid, is worth the effort and cost.
Why no propane? Black iron pipe is simple, cheap, and bulletproof.

[Danjo]

I have a 5 cu ft 12v chest refrigerator/freezer by Unique. That company discontinued portable units but there’s many others out there. I got it for $1000.

It’s performed well. Having the flexibility to make either compartment a freezer or fridge has allowed me to load up an entire compartment full of drinks for an outing or make it a freezer to store fish. Chest freezers are also a lot more space efficient so you won’t need as big of a fridge

I don’t have any experience with running a fridge off an inverter. I’ve tried to stay natively 12v as much as possible

[Jono14]

A 120V fridge can work fine and it may come down to how much solar you have and the rest of the system design. If you have a small system, then the inverter idle amounts become a reasonable percentage of the available energy. But if you have a large solar array and live in a sunny place (Fla I see?) you may routinely have more energy than you need.

12V fridges are efficient and have better insulation (part of the higher cost), so their overall energy needs are lower even before inverter losses. The Home Depot examples: The 120V version looks like 140W when running and the 12V version states 45-75W so less than 1/2. Lets guess that the compressor runs 18 hrs / day (being conservative, could be less) the 12V will use ~1,050 Wh and the 120V will use 2,520 Wh per day. This difference (~1,500 Wh) is on the order of your inverter draw (50W x 24h = 1200Wh) - so now we are up to ~2,700 Wh additional energy needed per day for the cheaper fridge.

But again, this only matters to your lifestyle if the difference compared to 120V means you drain the batteries and have to plug in or turn on a generator when you otherwise would not have needed to.

There are also some very efficient small inverters out there - for example Victron's 48V/500W Phoenix inverter can do 900W peak and uses just 3 watts in standby mode! Cost is about $180. (In the Home Depot Q&A someone states that 120V fridge startup surge is 4.5A =~540 Watts) - So this inverter would cover that and could be wired from battery to fridge directly and you can shut off the main inverter.

So I would look back at any power need calculations, think about how much solar or other sources you have and you may find that your energy budget can easily "afford" the inverter and somewhat less-efficient fridge. (note that there will also be a little loss and some additional cost for a 48->12V converter that will be needed in the system as well.) - Or, if the higher energy budget means less boondocking and more campsite costs, maybe the $1,000 for the efficient version will feel more worth it.

[rossvtaylor]

You're asking the right questions and I'm sure you did (or will do) this math...but you'll need to know the idle current draw of both inverter options to be able to compare and answer your original question.

Personally, I really like and almost always recommend a good 12V DC refrigerator. This is because, usually, the people who come to me asking about this are looking at the cheapest possible 120VAC fridge and they're really inefficient...and they aren't factoring in the inverter idle consumption. Having said that, I have a really efficient (and fairly pricey) 120VAC fridge for my Crown and the inverter draw is just part of my planning.

For other new folks who might be wondering about this exact issue, this might help them factor in the inverter part:

https://www.youtube.com/watch?v=lAV3xlup7RU&t=5s

[magnakansas]

I have two. one goes bad I only lose half the capacity. each will two gallons milk, 18 eggs, two pounds of butter. maybe dozen large apples. I have most of my busses equipment divided. two awnings, two fridges. two engine driven air conditioning systems, two roof mounted 120v systems, etc. I wont likely ever be totally out of a thing working.

william.

[desrtdog]

I went with a 120V fridge precisely for the cost factor. Got a 2.6 cu-ft Galanz retro looking fridge with a chiller compartment (no separate freezer) on sale at Lowes for < $200. Was not too concerned with the inefficiencies as I have a 600Ah battery bank and a 2000W inverter charger, and this is essentially the only AC load I am running. It works well - keeps a constant 38-40 F at mid setting, and the draw is about 1.1 amps...

[Drew Bru]

Originally Posted by desrtdog

I went with a 120V fridge precisely for the cost factor. Got a 2.6 cu-ft Galanz retro looking fridge with a chiller compartment (no separate freezer) on sale at Lowes for < $200. Was not too concerned with the inefficiencies as I have a 600Ah battery bank and a 2000W inverter charger, and this is essentially the only AC load I am running. It works well - keeps a constant 38-40 F at mid setting, and the draw is about 1.1 amps...

We've had the same experience. Rather than a chest or cooler style 12v fridge, we opted for a small apartment-sized (7.4 cu ft?) 12-v fridge. Its the only real energy consuming appliance we use and the battery bank and solar array are more than enough to keep up with things. We've rarely been below 90% on the batteries. We wanted to feel more like we were living in a home vs. camping so we tried to keep the appliances and whatnot as "normal" as we were used to (aside from the Nature's Head toilet)

[Rwnielsen]

I have a 24 volt system. My propane water heater needs 120v to run the controls and ignition so I bought a cheap 24-120v inverter for intermittent use (switch). I bought a Bodega combo backup freezer that will run on 24v.
I've been seriously considering a Norcold 12v fridge but....I wound up buying a RCA mini 2-door for around $150. The key to this is a Victron 24/375 inverter. These things essentially shut off under no load conditions, 1.5 watts I believe. The refer and inverter cost around $360. I could conceivably buy 4 or 5 spare refers and still be under the Norcold.
I'm sure Victron has a solution for you.

[Iceni John]

I plan on having two small (4 or 5 cu.ft.) 120VAC chest freezers, one used as a freezer and one as a fridge (a fridger). The fridger will use an external electronic thermostat like what the beer-making folk use, and it will override the freezer's own internal t'stat without any modification. Australians have been using fridgers for off-grid living for decades, and they use only a tiny fraction of the power used by a conventional upright fridge. Each freezer/fridger will have its own dedicated inverter, maybe a small PSW Samlex/Cotek (would more than one Cotek be Cotex?), so if both of them want to turn on at the same time it won't overload a single inverter. Plus, having two freezers and two inverters guarantees that I'll never be without cold storage: redundancy is always good! Each freezer/fridger can be easily reconconfigured to be the other in case one of them carks, and small chest freezers are dirt cheap at Home Despot and replaceable everywhere. What's not to like? I just hate the idea of an upright fridge that loses all its cold air every time the door is opened.

John

[LargeMargeInBaja]

In our ExpeditionVehicle, we use a SnoMaster 61qt dual-zone.
It sips 12vdc.
Four years, zero issues.
And we acquired it used.
.
We operate a small organic teaching farm near the outskirts of Eugene, Oregon.
Based on our experience, we acquired an identical SnoMaster 61qt for each of our delivery trucks.
They are just right for farmers markets.

[mmoore6856]

Originally Posted by rossvtaylor

You're asking the right questions and I'm sure you did (or will do) this math...but you'll need to know the idle current draw of both inverter options to be able to compare and answer your original question.

Personally, I really like and almost always recommend a good 12V DC refrigerator. This is because, usually, the people who come to me asking about this are looking at the cheapest possible 120VAC fridge and they're really inefficient...and they aren't factoring in the inverter idle consumption. Having said that, I have a really efficient (and fairly pricey) 120VAC fridge for my Crown and the inverter draw is just part of my planning.

For other new folks who might be wondering about this exact issue, this might help them factor in the inverter part:

yea always do the math and have your kid do it too to double check. im going 12 with that same 12 volt from home depot as they are getting things in stock for off grid. im going to use a new charge card when the special deal come then pay it off in a few months

[Danjo]

Originally Posted by rossvtaylor

You're asking the right questions and I'm sure you did (or will do) this math...but you'll need to know the idle current draw of both inverter options to be able to compare and answer your original question.

Personally, I really like and almost always recommend a good 12V DC refrigerator. This is because, usually, the people who come to me asking about this are looking at the cheapest possible 120VAC fridge and they're really inefficient...and they aren't factoring in the inverter idle consumption. Having said that, I have a really efficient (and fairly pricey) 120VAC fridge for my Crown and the inverter draw is just part of my planning.

For other new folks who might be wondering about this exact issue, this might help them factor in the inverter part:

That’s some good stuff Mr. Rogers!

This is an especially important point if you’re in places where it’s overcast for many days and you’re relying 100% on solar as I am, and even more so if you have a small PV/Battery Bank

[mmoore6856]

we also want it as its 10 cubic feet inside

[Rucker]

Originally Posted by Danjo

That’s some good stuff Mr. Rogers!

This is an especially important point if you’re in places where it’s overcast for many days and you’re relying 100% on solar as I am, and even more so if you have a small PV/Battery Bank

Agreed, great video.

Back during the planning phase for my bus I designed a power saving circuit that turned the inverter on only when the fridge called for power. I bought all the components in case I needed to add that functionality in later-if my power calculations were wrong.

Because my 450 watt solar system provides enough power to run the dorm-sized fridge even with the idle current of the 2K watt Renogy inverter here in California, the power-saving components still sit in the box.

I encased the fridge in a cabinet with 2" polyiso, which helps reduce the compressor cycling.

Another factor in fridge design is managing the exhaust heat from the coils, which will add to your overall cooling load if not handled in some way.
I arranged the fridge cabinet such that I could put ducting and an exhaust fan on the compressor motor and coils if needed, but so far the additional heat from the fridge is manageable with the split system.

[DeMac]

Originally Posted by Rucker

Agreed, great video.

Back during the planning phase for my bus I designed a power saving circuit that turned the inverter on only when the fridge called for power. I bought all the components in case I needed to add that functionality in later-if my power calculations were wrong.

Because my 450 watt solar system provides enough power to run the dorm-sized fridge even with the idle current of the 2K watt Renogy inverter here in California, the power-saving components still sit in the box.

I encased the fridge in a cabinet with 2" polyiso, which helps reduce the compressor cycling.

Another factor in fridge design is managing the exhaust heat from the coils, which will add to your overall cooling load if not handled in some way.
I arranged the fridge cabinet such that I could put ducting and an exhaust fan on the compressor motor and coils if needed, but so far the additional heat from the fridge is manageable with the split system.

----------------

No fridge on Freddy D, though I did something similar with the life-safety & lighting circuit. I installed a GTD & DualLite system.


(Hubble Auxiliary Transfer/ Relay Control Device)

(ATSD Terminations)







(Sealed enclosures, doors removed for photos)

Interruptable Power Supply
(Batteries, BMS & Inverter)
•True SineWave output 98% eff
•Automatically transfers <1sec
•Adjustable Output Distibution to four bypassable LV dimmers
•AC Lockout
•Low Voltage Battery Disconnect
•Brownout Protection
•Overload & Short Ciruit Protection
•Compact, All Steel Enclosure

We are set up for full time split phase, we only use the auto transfer, batteries & inverter for backup power, on demand.

I've installed back up power to fire protection circuits & egress circuits, in countless commercial spaces, as required by our local Fire Inspector. Fail-safe 🔥 Fire-safe.

[Rwnielsen]

https://www.amazon.com/gp/product/B0...YTXHYQ2K&psc=1

I bought one of these a while back to put behind my refer for a small computer fan. I also have two charge controllers that if I put a swinging door on, these might be handy for the same reason. I believe the refer boys call these "clicks-on's".

[fo4imtippin]

Thank you everyone for your feedback. After factoring all of it i went with a 120v fridge and the smallest Victron inverter that could power it.


Most of the reviews i could read online for the 10 cu ft sized 12v fridges were not very assuring. I usually take reviews with a grain of salt. After shopping around for fridges, i realized that i already owned a 10cu ft fridge out in our tiny house. Its an Insignia from Best Buy that has wonderful reviews. Its right next to my bed, so i wanted it very quiet. I have a personal review to know that its a good energy efficient fridge. The worst part about it is that this particular fridge, doesn't have anywhere i can screw brackets into as it has little tubes all around the fridge that i would puncture with a self tapper. I have to reach all the way out to the hinge brackets to secure it down.


The math was easy for me. For the price of a 10cu ft 12v fridge ($1600 is the low-end), I bought a fridge ($400), 460ah lifepo4 battery ($1110, and victron 12v inverter. ($90).


The fridge uses about 1/2kwh per day. I have everything except A/C and water heater running 12v on my bus and i without solar yet, i can last 4 days without plugging in the 12v charger.


I did make one small mistake sizing my victron inverter. I bought the phoenix 12/375 inverter. This fridge only uses 60w when the compressor is on. I falsly assumed that this was an inverter unit since its so quiet. I have had the inverter installed with 6 gauge wire for a few months, but just bought the fridge. When i plugged it in, i was getting overload warnings on the victron. After 2 overloads, it would start and run fine. I don't suspect this is good for the fridge long term and i cant afford to loose my food if it doesn't resolve.


After plugging the fridge into shore power and a kill-a-watt, i was pulling 739 watts at startup. The peak rating on the victron is 700w. So i had already sized up the victron i bought, but i guess im going to have to buy the 12/500 which has a 900w peak rating. I already told my wife all the things we can do with the smaller one as she rolled her eyes.. haha.


At some point ill add a transfer switch to change the load to my 120v panel if it is energized so i have some redundancy.

[flattracker]

I am using a 1000 watt sinewave inverter for my fridge in the "new Crown". This is for when I only need power for the fridge. At all other times power comes from generator, 3000 watt inverter , or outside power. To mount my fridge, I made support clamps that hold up the fridge from underneath and clamps that hold the fridge from the top. It does not move around. No fasteners are attached to it. I will post pictures soon.

[Rucker]

We all probably have a few electrical devices that sit in the closet because the 'learning curve'.

Fridge motors draw heavy current upon start. If that draw (in, say, watts per second) exceeds the inverter's continuous rating it relies on capacitors to provide the (hopefully temporary) demand, though at a cost: the capacitor discharge and charge cycles generate heat, which degrades the electrolyte in the capacitors.

To the degree you draw watts above the continuous duty rating of the inverter you consume a little more of the life of the device.

As I understand it induction motors similarly suffer because the windings heat up with low voltage, and over time they too will succumb.

So a skimpy little inverter coupled with a mass-produced fridge may work for a while, or even for a long while; but eventually one or the other will crap out, and usually at the least convenient time.