Running refrigerator on inverter

[Tang]

Hi

My marine refrigerator should be able to run on 110v and 12v.

It runs perfectly fine on shore power but doesn’t run on 12v. It could be a fault, or I guess that the previous owner could have disconnected the 12v supply to save on the amps.

I have a built in inverter connected to the house batteries and the refrigerator runs fine on that.

I’ll look into the problem but in the meantime are there any downsides of just running it through the inverter rather than it’s own 12v supply? I presume that the refrigerator has to convert the 12v itself anyway so there are inefficiencies either way?

The boat only gets used for short coastal trips and gets connected to the battery charger via shore power every night.

 

[rslifkin]

It'll be fine. Assuming the fridge uses a Danfoss compressor, then yes, it's converting power either way. Adding the inverter losses may cost you a little, but nothing major if you'd have the inverter on anyway.

 

[mvweebles]

Agree with Rslifkin - no heroic measures needed. But chances are there's a blown 12v fuse somewhere.

Peter

 

[Tang]

Thank you both.

 

[kchace]

Just as an FYI, running a fridge off the inverter vs direct dc can use a lot more power. For example, in the case of my new (to me) setup. New Novacool fridge which works very well, is specd at 12v - 5.9A = 70 watts. Running off AC 0.8A = 96 watts. Ok, but it’s actually much worse since a typical inverter is only about 80% efficient. To get 96watts while running at 80% efficiency requires 120 watts to be input.

The bottom line is 10 amps coming out of the battery bank to run the fridge off the inverter or 5.9 when running directly off of the batteries.

(I know the specs given for inverters are often higher than 80% but if you actually look at the graphs of the efficiency - if they’re even published by the mfg - that 85% or 88% efficiency is at a very specific power level only which is hardly ever the usage level.)

Ken

 

[Ken E.]

Ken, my real-life experience mirrors yours. Having used both a household 110 volt fridge and chest freezer through an inverter and replacing them with 12 volt- only Danfoss units, my ah usage was roughly cut in half.

 

[kchace]

Ken, my real-life experience mirrors yours. Having used both a household 110 volt fridge and chest freezer through an inverter and replacing them with 12 volt- only Danfoss units, my ah usage was roughly cut in half.

Yes. I ran this issue down when I was trying to understand why my new to me boat was using 11 amps DC when as far as I could tell only the fridge was running. I figured something else was on that I didn’t know about. Turns out, no, it was just the fridge running through the inverter. The PO replaced both fridges and didn’t connect the DC sides. He kept the boat mostly at the dock, so no big deal to him. In my case, I’m mostly on a mooring or anchored so it does matter to me.

Ken

 

[O C Diver]

Ken, my real-life experience mirrors yours. Having used both a household 110 volt fridge and chest freezer through an inverter and replacing them with 12 volt- only Danfoss units, my ah usage was roughly cut in half.

Ken,

That unfortunately is a meaningless comparison. Simply, the amount of refrigeration required to maintain the internal temperature of a refrigerator is based on the insulation. If the walls, ceiling, floor, and door were one foot thick of the best polyurethane foam insulation, it would take almost no refrigeration. Leave the door open and the refrigerator will never reach temperature. You could also compare a high dollar Yeti ice chest to the same size cheap Walmart cooler. If you're not comparing two identical refrigerators with different compressors, the comparison is pretty much meaningless.

My 10 cuft. Summit refrigerator with polyurethane insulation consumes about half the DC electricity going through an inverter, as compared to my <7 cuft. Norcold running on DC.

Ted

 

[Marco Flamingo]

Simply, the amount of refrigeration required to maintain the internal temperature of a refrigerator is based on the insulation.

Yes, but there is more going on than just insulation efficiency when running through a stand alone inverter. Most inverters have a "standby" usage. No matter how much insulation, and how much that insulation saves amps, when the fridge motor shuts down there is still a draw as long as the inverter is standing by. Those little extras (like the length of the wire runs) add up regardless of insulation. Figuring out the "full cost" is necessary to decide whether one wants to pay the price.

 

[O C Diver]

Yes, but there is more going on than just insulation efficiency when running through a stand alone inverter. Most inverters have a "standby" usage. No matter how much insulation, and how much that insulation saves amps, when the fridge motor shuts down there is still a draw as long as the inverter is standing by. Those little extras (like the length of the wire runs) add up regardless of insulation. Figuring out the "full cost" is necessary to decide whether one wants to pay the price.

As mentioned in my post, my Summit was measured in DC power consumption. My Victron Battery Management gauge measures all DC killowatt consumption including the inverter over my chosen 24 hour test period.

Ted

 

[GoneDiving]

Agree with Rslifkin - no heroic measures needed. But chances are there's a blown 12v fuse somewhere.

Peter

Or undersized cable. DC fridges do not like undersized wiring and frequently trip on undervolt. Most have adjustable low volt cutout settings. What's the dc voltage at the fridge with the compressor running? It sounds like the fuse/wiring may have been disconnected for this reason.

I'd agree that running via the inverter will work but a direct battery connection would be more efficient/better in the long run.

 

[Ken E.]

Ted, my example is apples-to-apples. I converted a Kenmore 11 cu ft household 110 fridge to Danfoss 12 volt. Actually, a shop converted it for me, Sea Freeze in Bellingham, who specializes in this type of work. No change was made in the insulation. I don't have numbers since I did this about 10 years ago, but the ah saved was significant.

 

[Alaskan Sea-Duction]

In the end, Most if not all marina refrigerators all run on 12vDC. You have one connection which is straight DC, then you have 120vAC converted at the refrigerator with a transformer to 12vDC.

 

[O C Diver]

Ted, my example is apples-to-apples. I converted a Kenmore 11 cu ft household 110 fridge to Danfoss 12 volt. Actually, a shop converted it for me, Sea Freeze in Bellingham, who specializes in this type of work. No change was made in the insulation. I don't have numbers since I did this about 10 years ago, but the ah saved was significant.

Ok, so how old was the refrigerator. Was it made in this century? So what you're saying is that you think it's fair to compare a last century, piston technology compressor to a Danfoss compressor instead of comparing the current rotary compressor technology of the last 10 years to a Danfoss?

In case you missed it, refrigerators have become more efficient over the last 50 years, partly due to insulation and partly due to compressor design.

From: https://www.cleanenergyresourceteams.org/your-old-refrigerator-energy-hog

For instance, refrigerators built in the 1970s may use five times more electricity than new, high-efficiency ones and may cost $200 per year more to run than new ENERGY STAR® models. A 20-year-old refrigerator could use 1,700 kWh of electricity every year, compared with about 450 kWh for a similarly sized new ENERGY STAR model. At an electrical cost of 12 cents per kWh, that represents a savings of $150 per year and a potential payback of about 7-9 years. Also, if your old refrigerator requires costly repairs (exceeding a few hundred dollars), then it probably makes sense to replace it with an energy-efficient model.

Ted

 

[GoneDiving]

This thread has gone way off topic so I might as well continue the slide ?

Has anyone compared the efficiency of a modern inverter based residential fridge to a 12v DC one? I'd guess a lot more money has been spent improving residential units to keep pace with legislation, star ratings etc. However, improved compressor and control efficiencies would be offset by the nice to have hidden evaporator coils, frost free functions etc, all of which draw some parasitic power.

I'm firmly in the residential camp: I have plenty of power and battery storage, a 500ltr residential unit costs the same here as a 90ltr Engel, a truck load of warm provisions is frozen solid in under 12 hours and inverter models act as great soft starts. ~1kwh per day would power both but the residential unit is 5x the capacity.

Apologies to the OP.

 

[HeadedToTexas]

It runs perfectly fine on shore power but doesn’t run on 12v.

Have you figured out why it won't run on 12 volts? I have exactly the same situation, but mine ran on 12 VDC up to a couple weeks ago. Now, AC only. My fingers are crossed that it's a fuse that I failed to check after getting plugged back in to shore power.

 

[Jeff F]

Mine stopped working on 12v, and everything to the fridge tested fine. Ran it on 110v until that too failed about a year later, then replaced the control unit. Both sides work now.

I haven't done any rigorous testing, but didn't notice any big jump in my daily power consumption when switching between inverter-supplied AC and 12vdc. Typically both are on 24/7.

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[Tang]

Have you figured out why it won't run on 12 volts? I have exactly the same situation, but mine ran on 12 VDC up to a couple weeks ago. Now, AC only. My fingers are crossed that it's a fuse that I failed to check after getting plugged back in to shore power.

Not yet. I’ve only recently purchased the boat. I was told that it didn’t work, so to get it working on 110v was a bonus. I’ll pull it out and put the multi-meter to work later this week and if I solve it, then I’ll let you know.

To everyone else, no need to apologise, I’ve enjoyed the discussion!

I think in the medium term I’ll find a modern and efficient household appliance assuming I can find one that fits. I think mine is probably the original from 1986!

 

[SDTugs]

What does your residential unit draw on inverter? I am new to my current boat and the maybe 25 year old Amana 19 draws 55 amps. That seems insane. It seems like a modern unit would use about 13 amps a day. What have you noticed?

 

[jgwinks]

The household fridge in my boat is labeled 1 amp but that's at 120 volts. On inverter that would be 10 amps at 12 volts plus any inefficiency in the inverter itself. So call it 11 or 12 amps. Looking at my battery monitor that's about right considering other things are running at the same time. I haven't isolated it to be sure.

 

[SDTugs]

The household fridge in my boat is labeled 1 amp but that's at 120 volts. On inverter that would be 10 amps at 12 volts plus any inefficiency in the inverter itself. So call it 11 or 12 amps.

Gotcha. So I am about to be in the market for a new unit. What do you have in your boat? I have an old Amana 19.