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Battery usage with residential fridge

I recently installed a LG residential fridge in my coach to replace the rm7832 original. I have the fridge plugged into the inverter plug. I have 2 Northstar SMS-AGM8DK -DT SMS Series batteries (the previous owner only installed two instead of three because he put them in wrong and could not fit three...sigh). The batteries are in great shape and fully charged.
My question is,from Foretravel owner's experience how long will the batteries operate the fridge and the inverter. I do not do any boondocking but have to park the coach overnight in front of the house before departure on my trip. How many hours can I expect to have battery power?  Any educated answers from expert would be appreciated!
Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Battery usage with residential fridge

Reply #1 –
You need to post the amp hour rating to get any help. Not the cold cranking or other numbers.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Battery usage with residential fridge

Reply #2 –
Quote from: craneman –
You need to post the amp hour rating to get any help. Not the cold cranking or other numbers.

Looking at the internet batteries are 228Ah, 2 batteries, 50% rule so total of 228Ah. 

Other factors to consider, amp draw of refrig. 
How many hours is overnight?
What are the outside temps overnight?
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Battery usage with residential fridge

Reply #3 –
Run generator to charge batteries until it is time to turn gen off, or use a very long 120v extension to house. One or two 100' lengths of 20-amp extension cables with 6 guage wire will come in handy in those situations when an overnight camping outlet is far away. Also carry 50-amp to 20-amp connectors and use your coach shore cable. I have seen some who buy a long length of indoor 6 gauge solid-wire Romex and just use it at their home so coach at curb can be powered by an home outside outlet. To extend battery life, charge to 100%, not deplete lower than 50%. Turn all other appliances off with disconnects. Many devices still draw current when turned off with a push-on/push-off button power switch. Plug things into a power strip and turn power strip off. Assume batteries will be about 60% after 8-10 hours on inverter. Run generator in the morning to partly charge house batteries, to relieve the alternator from having to do the heavy lifting. You will know more after your first use. Do not use boost to preserve start battery capacity.

Re: Battery usage with residential fridge

Reply #4 –
I think you could be OK but I would sleep in the coach over night and check the voltage if y you wake
up at night and check it in the morning. If you are above 12.2 you are OK. Also you could leave the
generator on auto start and that would keep you OK.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: Battery usage with residential fridge

Reply #5 –

This might help you determine your usage for the frig?  May be better ones out there? 

Poniie PN2000 Plug-in Kilowatt Electricity Usage Monitor Electrical Power...

As an Amazon Associate Foretravel Owners' Forum earns from qualifying purchases.

2000 GV320 4010 build #5712  2019-?
1999 Bounder 2000-2008
Bardstown, KY
🥃The Bourbon Capital of the World🥃

Re: Battery usage with residential fridge

Reply #6 –
Plug the fridge into a " kilowatt "
The meter will show watts used over time.
Use that number for the math

Real world  , watch the volts and see how long it will run .  Mine is a little 10ft model and will run 25 hrs easy .

Re: Battery usage with residential fridge

Reply #7 –
Here is another way to estimate, I just grabbed the 1st LG fridge that I found:

643 Kwh/year = 1760 Wh/day
1760 x 1.2 = 2112 Wh/day (inv efficiency)
2112 Wh/12 volts = 176 Ah/day
228 Ah/176 Ah = 1.3 days (turbojack 228 Ah est)

Also verify your inverter idle current. For most modern inverters this is quite low. This can drastically affect how long the batteries will last.
 
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Battery usage with residential fridge

Reply #8 –
Yes the amp hr is 238 and I would be running it about 10 hrs. The outside overnight temp would be about 45f
My fridge is Energy Consumption (kWh/Year)=
459

So I do think I would be ok overnight
Peter    Alberta Canada
'98 U320 40'  Build 5359 M11 450 HP, Aqua hot, Blu Ox

Re: Battery usage with residential fridge

Reply #9 –
Updated to your numbers

459 Kwh/year = 1257 Wh/day
1257 x 1.2 = 1508 Wh/day (inv efficiency)
1508 Wh/12 volts = 125 Ah/day
238 Ah/125 Ah = 1.9 days
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Battery usage with residential fridge

Reply #10 –
I have a Samsung RF18A5101SR

Running it draws less than 13 watts. When the defrost mode kicks on wattage can increase to 360.

23 hrs @    13 watt/hrs = 299 watt/hrs/day
  1 hr  @ 360 watt/hrs = 360 watt/hrs/day
                                        ———————-
                                        = 659 watt/hrs/day X 1.2 = 791 watt/hrs/day max
                                            791 watt/hrs/day / 12v = 66 amp/hrs/day

900 amp/hr Lion battery X 0.80 = 720 useable amp/hrs / 66 amp/hrs/day = 10.9 days provided the refer is the only current draw.

Tim
Tim Dianics
Pam Sapienza
Vader PupZilla Labrador Canine Beast (AKA Pup)
Columbia, MO
1996 U320 4000
2021 Jeep Gladiator, Diesel

Re: Battery usage with residential fridge

Reply #11 –
Quote from: TGordon –
provided the refer is the only current draw.

Tim

You will also have the other 12v items pulling some of that power from your batteries also.  Based on the above numbers you should be good for your overnight sitting.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Battery usage with residential fridge

Reply #12 –
Quote from: TGordon –
I have a Samsung RF18A5101SR

Running it draws less than 13 watts.
Tim just fyi

I did a quick search, the running current is 3 amps, this would be 345 watts. However, typically a high efficiency refer runs just a few minutes per hour.

The energy star rating of 540 Kwh/year would be an average of 1480 Wh/day or 62 Wh/hr.

62 Wh/hr /345 running watts = .18 hrs or 10.8 minutes running per hr.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Battery usage with residential fridge

Reply #13 –
In our U320, the LG ,combined with all the other draws (laptops and phones charging, ghost draws, etc), would draw our 600ah lithium battery bank down to a little over 50% over night.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Battery usage with residential fridge

Reply #14 –
I found that the phone and various chargers draw a lot . More than my fridge. I turn the charging post off at night . My morning volts are around 12.7

Re: Battery usage with residential fridge

Reply #15 –
Yes. These armchair calculations are fun, but you really need actual experience running everything. In our van we can get through one night dry camping on the batteries in cool weather (running 12v refer and propane heater). We understand that and recharge as needed if solar can't quite recover each day.
Peter and Tammy Fleming
1991 U300 GV 40 - Sold, owned for 4 years
Downsized to Roadtrek Popular 210 class B

Re: Battery usage with residential fridge

Reply #16 –
My coach has the Samsung RF18 residential fridge.  With just the fridge and nominal system (HWH computer, microwave plugged in, etc) running, the coach will pull about 14amps from the batteries according to the Victron BMV-712.  With the fridge unplugged, the coach pulls about 3-4 amps DC.
Keith
2003 U320 38' #6197

Re: Battery usage with residential fridge

Reply #17 –
Quote from: prfleming –
Tim just fyi

I did a quick search, the running current is 3 amps, this would be 345 watts. However, typically a high efficiency refer runs just a few minutes per hour.

The energy star rating of 540 Kwh/year would be an average of 1480 Wh/day or 62 Wh/hr.

62 Wh/hr /345 running watts = .18 hrs or 10.8 minutes running per hr.

Thank you.
11 minutes per hour is interesting

My calcs are worst case for batteries, refer only, no coach load. I will determine coach load, no refer, later.

Tim
Tim Dianics
Pam Sapienza
Vader PupZilla Labrador Canine Beast (AKA Pup)
Columbia, MO
1996 U320 4000
2021 Jeep Gladiator, Diesel

Re: Battery usage with residential fridge

Reply #18 –
Quote from: WS6_Keith –
My coach has the Samsung RF18 residential fridge.  With just the fridge and nominal system (HWH computer, microwave plugged in, etc) running, the coach will pull about 14amps from the batteries according to the Victron BMV-712.  With the fridge unplugged, the coach pulls about 3-4 amps DC.

Our 22 CU. FT. Frigidaire and all the other normal items shows 12 amp draw on the BMV-712 when we go to bed. Normal items plugged in are microwave, coffee maker, 120 volt bathroom night light , laptop and Mobley.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean