Residential fridge power data

[corn18]

I finally got around to setting up my Victron system so I can do remote monitoring. Got some data on the 18 cu ft residential fridge. It took four hours of compressor time for initial cool down. Averaged 115W for that four hours. Then it went to maintenance and seems to have a 50% duty cycle. 15-30 minutes on followed by 15-30 minutes off. Average 90W while compressor was on and 0W when it wasn't. So that is 45Wh. For my 12.8V system, that is 3.5Ah. This kindof irritates me because the fridge/freezer were never opened the whole time. Seems like a lot of Wh for a fridge that was never opened. Glad I have a lot of batteries and solar.

[dalford]

That sounds right… mine draws about 50 watts an hour once it is cooled down.

If you think that is a problem put a digit thermometer in the fridge and turn it off for an hour. Don’t open the door and see what the temperature reads.

I’ve seen many posts on here where folks say they run for 4-6 hours without power to their fridge and all is ok? I wonder how they determine OK. I did it because my inverter died and drove 5-6 hours and the internal fridge temp was well above 50 degrees.

[corn18]

Originally Posted by dalford

That sounds right… mine draws about 50 watts an hour once it is cooled down.

If you think that is a problem put a digit thermometer in the fridge and turn it off for an hour. Don’t open the door and see what the temperature reads.

I’ve seen many posts on here where folks say they run for 4-6 hours without power to their fridge and all is ok? I wonder how they determine OK. I did it because my inverter died and drove 5-6 hours and the internal fridge temp was well above 50 degrees.

Great idea on a thermometer. I will put a Ruuvi wireless sensor in there and connect that to my Cerbo so I can monitor the fridge and freezer temps remotely.

[Chuck_S]

Good to see some real test data. 3.5Ah over 4 hours? That's 21Ah over 24 hours or a little less than half the capacity of the typical Group 24 battery. Yep you need lots of batteries! The ability to run one of these on one battery doesn't seem likely.

-- Chuck

[Bob K4TAX]

Good information all the way around. Thanks for taking the time and posting our results.

Bob

[corn18]

Originally Posted by Chuck_S

Good to see some real test data. 3.5Ah over 4 hours? That's 21Ah over 24 hours or a little less than half the capacity of the typical Group 24 battery. Yep you need lots of batteries! The ability to run one of these on one battery doesn't seem likely.

-- Chuck

Yup, a factory Group 27 RV/Marine battery won't last long for a residential fridge for sure.

Originally Posted by Bob K4TAX

Good information all the way around. Thanks for taking the time and posting our results.

Bob

I will collect more data when it is full of stuff.

[dalford]

Originally Posted by Chuck_S

Good to see some real test data. 3.5Ah over 4 hours? That's 21Ah over 24 hours or a little less than half the capacity of the typical Group 24 battery. Yep you need lots of batteries! The ability to run one of these on one battery doesn't seem likely.

-- Chuck

Need to reread his post.. it was 3.5Ah per hour once fridge was cooled down…so if he ran for 12 hours then he would use 42Ah from his battery.

Obviously the residential fridge is not ideal for any long period of time without bigger batteries and either solar or generator for charging.

I have used mine overnight and all I have is 210 amp, 6 volt batteries (no solar). I was good in the morning and my fridge used a little over 30% of my SOC (I also have a Victron).

OP, since you have a Victron I found it interesting and useful to measure the DC draw of every DC appliance on your rig. I made a spread sheet of all the DC load draws.

[corn18]

Originally Posted by dalford

Need to reread his post.. it was 3.5Ah per hour once fridge was cooled down…so if he ran for 12 hours then he would use 42Ah from his battery.

Obviously the residential fridge is not ideal for any long period of time without bigger batteries and either solar or generator for charging.

I have used mine overnight and all I have is 210 amp, 6 volt batteries (no solar). I was good in the morning and my fridge used a little over 30% of my SOC (I also have a Victron).

OP, since you have a Victron I found it interesting and useful to measure the DC draw of every DC appliance on your rig. I made a spread sheet of all the DC load draws.

The data show that for cooling, it was 115W for 4 hours. At 12.8V that is 36Ah. That's a lot if all you have is 40Ah usable from a single RV/Marine battery.


I do have all the data on all my DC and AC draws. Lordy, there are a lot of little things that just draw small amounts but add up quick over a 24 hour period. And the AC side gets killed by the inverter efficiency. At low loads, the MPII is right around 92% efficient. Get above 25% load and that goes down to 90%. 1/2 load is 85% and full load is 80%. Ouch. Good in the winter if I need to heat my basement.

[dalford]

Originally Posted by corn18

The data show that for cooling, it was 115W for 4 hours. At 12.8V that is 36Ah. That's a lot if all you have is 40Ah usable from a single RV/Marine battery.


I do have all the data on all my DC and AC draws. Lordy, there are a lot of little things that just draw small amounts but add up quick over a 24 hour period. And the AC side gets killed by the inverter efficiency. At low loads, the MPII is right around 92% efficient. Get above 25% load and that goes down to 90%. 1/2 load is 85% and full load is 80%. Ouch. Good in the winter if I need to heat my basement.

I’m confused, I thought the 115w was initial cooldown and then once it was cool it drew about 3.5Ah average or about 45 watts. At 3.5Ah over 4 hours would be 14 amps draw from your battery. I would assume you would cool your fridge before you relied on battery power to do it. I’m usually on shore power or connected to my truck that keeps the batteries charged and the fridge cold.

I see now how you worded it was confusing. It was 115W per hour for 4 hours…not 115W for the 4 hour period.

Anyway…. Cool it down, if you can, before you go camping…

[corn18]

Originally Posted by dalford

I’m confused, I thought the 115w was initial cooldown and then once it was cool it drew about 3.5Ah average or about 45 watts. At 3.5Ah over 4 hours would be 14 amps draw from your battery. I would assume you would cool your fridge before you relied on battery power to do it. I’m usually on shore power or connected to my truck that keeps the batteries charged and the fridge cold.

I see now how you worded it was confusing. It was 115W per hour for 4 hours…not 115W for the 4 hour period.

Anyway…. Cool it down, if you can, before you go camping…

Yup, it was cornfusing. With 10kWh of battery, I am fine with letting the batteries cool down the fridge. With my VRM working, I can turn the inverter on from home before I go pick up the 5er from storage so the fridge is cool when I get there to load it up (or bring it home). I can also turn on the AC remotely now with my MicroAir thermostats so it is all comfy by the time we are loading up.

[tomkatb]

Curious as to how you measured watts.

Because there is a 10-20% loss in the conversion to ac. In addition the inverter on standby consumes 1-2 ah per hour on standby.

The residential fridges have the nicest features. But, you need lots of batteries and probably a generator.

Best in motorhomes I suspect.

[corn18]

Originally Posted by tomkatb

Curious as to how you measured watts.

Because there is a 10-20% loss in the conversion to ac. In addition the inverter on standby consumes 1-2 ah per hour on standby.

The residential fridges have the nicest features. But, you need lots of batteries and probably a generator.

Best in motorhomes I suspect.

DC VxA on my Cerbo display. Measured at the input to the inverter.

[dalford]

Originally Posted by tomkatb

Curious as to how you measured watts.

Because there is a 10-20% loss in the conversion to ac. In addition the inverter on standby consumes 1-2 ah per hour on standby.

The residential fridges have the nicest features. But, you need lots of batteries and probably a generator.

Best in motorhomes I suspect.

I measure the current draw from the battery with the Victron battery monitor. I turned all DC devices off and then turned one at a time. VXA


You are right about the 2A draw from most Inverters in bypass mode but I guess you wouldn’t care if it was in bypass since you would be using shore power?

My residential fridge is in my 5th wheel.. almost 10yrs old.. I love it but I don’t boondock enough for it to be an issue for me. There has been a couple of times that I boondocked and once for over 3 days at Gros Ventre in the Grand Teton’s. I planned accordingly (generator).

[GolfingDave]

For a truer picture you need to let it run through a defrost cycle when the fridge is likely to pull 7-8 amps or so for 15-30 minutes if you have the patience to wait.

If a newer fridge(with a control board) a lot are automatically set to defrost a set time after initial start up for the first defrost. Otherwise it depends on more factors, compressor run time, door openings, last defrost time length, etc.

[corn18]

Originally Posted by GolfingDave

For a truer picture you need to let it run through a defrost cycle when the fridge is likely to pull 7-8 amps or so for 15-30 minutes if you have the patience to wait.

If a newer fridge(with a control board) a lot are automatically set to defrost a set time after initial start up for the first defrost. Otherwise it depends on more factors, compressor run time, door openings, last defrost time length, etc.

Dang, didn't even think about that. Looks like it hit a defrost cycle yesterday and it lasted 4 hours. Holy crap!

[Twinboat]

Originally Posted by corn18

That's a lot if all you have is 40Ah usable from a single RV/Marine battery.


:

What does that even mean ?
Where are you getting this " Usable " data from, 0about your batteries.

The 50% limit, often touted on this and many RV sites, is nothing more the a myth.

[corn18]

Originally Posted by Twinboat

What does that even mean ?
Where are you getting this " Usable " data from, 0about your batteries.

The 50% limit, often touted on this and many RV sites, is nothing more the a myth.

Yes and no. 50% DOD is a reality for non true deep cycle batteries. You will do damage to a starter battery if you drain it below 50%. RV/Marine batteries are a gray area but I consider them starter batteries, not true deep cycle batteries. A true deep cycle battery is fine to 80% DOD but going further MAY result in reduced overall battery life. 100% DOD is NEVER good for an FLA, SLA or AGM type battery. The best of these three deep cycle batteries is actually FLA but it requires strict adherence to charge/discharge cycles and maintenance. And they are terrible at self discharge. That's why a lot of folks go SLA or AGM, especially for RV applications.

[Aussieguy]

X2 ^^^ what corn18 fella said
80% for decent deep cycle batteries is doable.

Trogan even had it in there user manual for their true deep cycles 80% discharge is allowable and will shorten battery life..
They have a chart on............ cycle life V discharge.

I worked it out once that it would be around 6 months loss of life
that is the price you pay for the convenience of lower discharging IF you choose to go to go that route..


It is NOT that if you go to 80% the battery will self destruct and you have to immediately replace it!

[corn18]

The normal charts showing cycles vs. DOD are a little misleading IMHO. Sure, higher DOD = fewer cycles but it also means more power available. I like the charts I make that show total lifetime Ah vs. DOD. For FLA true deep cycle batteries, the total lifetime Ah is actually the same for 50% DOD vs. 80% DOD (according to the Trojan data I have). For AGM deep cycle, they do take a 6% hit on total lifetime Ah for 80% DOD vs 50% DOD but they are much less finicky about charge cycles and have a MUCH lower resting power loss. And no maintenance.



These charts are for the Trojan T105 FLA 6V deep cycle battery. I have some for AGM, but can't find them right now.

[ScottBrownstein]

There is a lot of variation, depending on the design of the reefer. Most big, energy star units are actually powered by a built in inverter running the compressor at variable speed. As such they actually run all the time and don't cycle like grandpa's reefer used to. My unit is a 22 cuft Frigidaire and it runs an average of 96 watts...all the time. Cycle is a little complicated with peak load of 600 watts during the 15 minute defrost cycle. After that it draws around 150 watts on compressor high, catching up from the defrost cycle and then drops to 50 watts for the rest of the time. This then repeats about every 8 hours. This turns out to be around 110 AH per 24 hour period. I can go a while on my 4 FLA battery bank.

Graph is attached.