12V (2-way) fridge run time on battery

LCYoungJr

(New, to me, 2018 T@B 400)
Anyone got real-world numbers for how long the 12V (aka 2-way) fridge will run with just solar panel charging (in good direct sunlight) and no shore power?
(I'm trying to determine if my battery is getting weak and needs to be replaced.)

pthomas745

You have the "dual 6V" setup or the "single large AGM?"  If these are the original batteries, "replace them" is the easy answer.  Both of these battery setups are "225 amp hours".  From an AGM battery, you have 50 to 60 percent of those amp hours "available" before you begin to draw the battery "too low".  So, at the most, you have 135 amp hours to use.  "About 135 amp hours".

Not sure what exact fridge you have.  The "Cruise 65" fridge "might" use 30 amp hours over 24 hours.

The Norcold fridge (NR751BB) are usually reported to use about "3.7" amps when running, which is common for a compressor fridge.  It may only run 1/2 of the time, so figure less than 2 amps per hour, which puts the power use to about 30-40 amps per 24 hours.

I believe your solar on the roof is almost 200 watts.  On a perfect day, in beautiful lab conditions, that theoretically can produce 16 amps per hour.  (This is a fantasy!).  But, lets give you 10 amps over 8 hours of decent sun.

If you turn the fridge on with the sun on the panel, there "should" be plenty of charge to run the fridge and have amps left over for whatever battery charging might be needed.  The only time the fridge would use those two amps an hour (average) would be when the solar is not able to charge.  You can just do the math on that.  12 hours would be 24 amp hours, etc.

So, the next morning, the battery may be down to about 100 amp hours available.  Same as above: 10 amps of solar would run the fridge and...provide charging for the battery.  Maybe...you could be back to a full charge before the sun goes down.  Rinse and repeat.  (Remember: 10 amps is the assumption here...half that much solar input would make a real difference.)

So: what is happening with your battery?  Does your 400 have the Victron solar controller or the non-bluetooth controllers that were originally installed?

LCYoungJr

pthomas745.  Great info!  Thanks.
I have the Norcold NR751BB fridge.  I also have the Zamp Solar ZS-30A solar charge controller.  (Don't know of any app for this one.). I'm not sure what battery setup I have yet.  I tried to remove the cover this morning to check it out, but it's not an easy task.  I assume the battery/batteries is/are AGM because that's what the Zamp controller is set to.
As far as what's happening with the battery/batteries, I haven't done any systematic testing, I'm just curious what to expect if the battery/batteries are are performing normally.

Mickerly

Solar panels don't power the trailer. The battery(es) power the trailer. The solar panel recharges the battery.

As mentioned above, the refrigerator draws 3.7amp/hr when running. The guess of 2amp/hr during normal use is reasonable. 2amps/hr times 24hr is about 28amps/day, not 30 to 40. There are other loads on the trailer. Your total draw is probably 3 to 5amp/hr or approximately 48amp/day. This will give you a guess at the size battery you need. The refrigerator holds temperature really well. You can put a few frozen water bottles in the freezer and disconnect the battery at night for longer camping time. 

Quality, ridged solar panels make about 6.5amps/hr for each 100watts of panel on average. To get this value, the panel needs to be perpendicular to direct sun; not any shade or at any angle. The panel will make some power when not in an optimum position, but nothing near 6.5amps/hr rating. Don't forget, the world is not flat. Near the Canadian border, the ground is 44 degrees off perpendicular to the sun on average. The angle varies with the season.

Portable panels let you adjust that varable out. A panel attached to the trailer is not adjustable and the output will vary with the season. A portable panel will give more power for the same time period if you are willing to adjust it every hour or two. 

I would recommend a couple test runs with your rig to figure out it's normal output. How you camp, where you camp, and when you camp will make the numbers different. 48amp/day is a good guess for your power needs. It may be less in moderate weather, more if running heat or the fan.

Ghannan

For our 2-way in our 2024 tab 400, we use another 20 amp hours overnight, and the solar panel (190 watt) refills the battery by noon or 1pm in the sun in southern California.

WayneW

We have a 2021 320 Boondock, so a different trailer, but our results are similar to @Ghannan. We’ll be down about 15-20 amp hours overnight, depending on Alde use, ambient temp, etc. We have a 105 watt solar panel on the roof and a Renogy 100 watt solar suitcase. In full sun we’ll be back to 100% by noon or so. 

XenanMe

I had a 2018 400 for 6 years. Three years on the original batteries and 3 years on lithium. On the original batteries I could get about 2 days without solar. Using just the fridge, water pump and charging my phone. With solar (200 watts) and direct all-day sun it was indefinite. With the fridge running, each night the batteries would go down to approx 70-65% then charge back up during the day.   If your batteries are in the vented box (something Nucamp added in late 2018/2019 models) then they are most likely 2 6 volt Harris AGM batteries. Probably nearing their end of life.

LCYoungJr

Thanks to all for the great info.  I determined I have two 6V AGM batteries and I've pretty much decided that they need to be replaced.  In another post, I found a recommendation for the Litime 12V 230Ah that will fit in the space where the two old batteries came out (https://a.co/d/dsxIiCn).  The price is also pretty good for a lithium battery.

AndreO

@LCYoungJr,

I also have a 2018 400 (no solar).. Lithium is the only way to go.  Not only are you restricted to 50-60 % of an AGM but the fridge has a feature to protect its compressor from running under voltage. Your AGM will hit that voltage limit at closer to 75% of your amp hour rating. (However the fan will still run fooling you to thinking the fridge is cooling.) It will also cycle much more frequently as it's temp doesn't drop. Not to mention the compressor draws 5 amps startup before settling down to its lower 3.5 run time draw so the increased frequent starting reduces run time even more.

To add insukt to injury the AGM charger that came with the 2018 would take 4-5 hrs to charge ( using shore or generator) up to 90% and a further day to 100% reducing run time even more the next day. Lithium charges to 100% much much faster.

My old 225 Ah AGM would only actually cool for 4 hrs on a hot day before the voltage dropped below the compressor cutout. Lithium maintains voltage to almost zero amp hrs. (However min 20% is recomended to maintain battery longevity.)

Nucamp had lots of complaints about the fridge before they finally figured that out, which is why they only offer Lithium now.

Don't forget you have to upgrade your charger for lithium as well! Good luck.