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!
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?
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.
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.
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... (https://www.amazon.com/Poniie-PN2000-Electricity-Electrical-Consumption/dp/B0777H8MS8/ref=sr_1_10?crid=DV5MUMKLGX96&dib=eyJ2IjoiMSJ9.4QNXLgTfiTz9u_zhXEALjvl2QSRt7iVQBx2-nLYAsYUyu20bx1mCa_668D-TG2LXffGlghv9HMCBzkKF-tNFJPVT03gG6iYKssJVpfMy2je-u5BArNVCKMCzsp8l96TvG9ODof7nCYZXZCl_gXOlznTE68UwS171Z9xRNVC9q1Cy2_SsHJowuHpr3Ew8RgEyrvJFVdfEeOPUIae5aNLuldTPLujpLnklCJFBaCaSp9M3Kc0E-3xMss1Gcx_I_c7K8P9vN7xRsrx6zo7oB9cbgpvNqYhu54FrvNFJ60N8JJQ.2oYGG6ntIUO0oaHHIxr4W919_TmyXfDcHi48boKurl4&dib_tag=se&keywords=electric+consumption+monitor&qid=1719250034&sprefix=Electric+consumption+%2Caps%2C128&sr=8-10)
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 .
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.
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
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
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
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.
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.
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.
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
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.
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.
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
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.