Help me understand: How does a fridge not drain away your battery?

[BlakeA]

I have a Dometic CFX3-35 in my 4runner. It is powered by a Jackery 500 all the time. While driving, the Jackery is being charged by either the 12 volt outlet or the 110 volt inverter in the back of the 4runner.
While camping, I charge the Jackery with a 100-watt Goal Zero suitcase solar panel. I went this route because I did not want to install a second battery and I did not want to run a 12volt always on outlet to the back.

 

[jdlobb]

I have a Dometic CFX3-35 in my 4runner. It is powered by a Jackery 500 all the time. While driving, the Jackery is being charged by either the 12 volt outlet or the 110 volt inverter in the back of the 4runner.
While camping, I charge the Jackery with a 100-watt Goal Zero suitcase solar panel. I went this route because I did not want to install a second battery and I did not want to run a 12volt always on outlet to the back.

This is probably the set up I’ll go with as well

 

[billiebob]

Great question. I rarely spend more than 2 days in a spot. My 1 battery solution is I unplug the fridge overnight. If you don't open the door the fridge should drop less than 2 degrees overnite. And everything recharges, cools as soon as you start driving. I've done this for up to 5 weeks in the heat of the summer without issues.

Otherwise you need 2 isolated power sources. I kinda want that but see no real need....

ps, I travel alone so I can control how often the fridge is opened.

 

[burleyman]

I'm ignorant. Do any of the refrigerators have a time delay in the low voltage shutdown feature to prevent shutting down due to starting current inrush and wiring resistance voltage drops?

 

[john61ct]

I'm ignorant. Do any of the refrigerators have a time delay in the low voltage shutdown feature to prevent shutting down due to starting current inrush and wiring resistance voltage drops?

I doubt it. The setpoint is so low it does nothing to protect the battery, should really just be a final failsafe for when your adjustable primary protection fails.

Starter current draw should not be an issue on House circuits.

A fridge intended for off grid use should not be running off the Starter batt directly.

 

[Vanhalo]

But i'm a little terrified of waking up in the morning and not being able to start my truck.
Now, this doesn't SEEM to be an issue, or why would anybody have them? But I don't understand exactly why. How much power do they draw? Do you HAVE to have a backup power source like a Goal Zero generator or a dual battery set-up to use one safely?

My lithium PLB40 will generally last 24 hours for a 66L Snomaster fridge running in fridge mode on both sides.
After killing my OEM battery i decided to only use the Lithium alternative.

One day I might use a Battle Born but until then I will use the PLB40 with a solar panel or the Jeep's alternator.

 

[Photobug]

That begs a follow up question though. I think everything I've seen here is about the power draw in amps and amp hours. Most of the extra battery packs are rated in watt hours. What size battery would I need to safely maintain the fridge, under normal conditions (say 80 degree ambient temp) for a day or 2? Would a 150Wh or 200Wh batter get the job done? or do i need something closer to 500Wh?

I am not sure if this has been covered yet but the WH stated is total for a given battery. You don't have all those WH available. Depending on Chemistry you are only supposed to drain your battery to 50% for lead acid, so a 100AH gives you 50AH usable. Other batteries like AGM or lithium allow a deeper discharge, just something to consider. This would give you 2 1/2 days of use based on Dreadlocks 20AH for an average fridge.

Consider adding solar down the road to extend this to longer times for boondocking.

 

[john61ct]

AGM loses life cycles even faster than FLA if discharged much below 50%.

The unique chemistry of Oasis Fireflies mean they are not as quickly "damaged" by such abuse, but they also last much longer uf it is only occasionally.

The key metric there is **average** DoD, and a 10-15% difference can mean double the cycle lifespan.

With LFP in fact the same relationship curve holds, but since you are starting out with thousands of cycles rather than hundreds, and they are so expensive,

most owners are happy to use 75-85% of capacity.

 

[VoodooCLD]

Medium on the ARB Fridge is 11.4v which it shuts off at

View attachment 612862
This is a batteries state of charge for a given voltage:

So 11.4v cutoff on your starter battery is draining it down BELOW 10% SOC, again I'm stoked your managing to crawl back out of the woods doing stupid **** like that.. but I know for a fact my vehicle will not even try to crank over at 11.4v.. not to mention the severe abuse this is doing to the cells and those batteries wont last.

I wanna point out that this chart is misleading. I'm glad they offer the specifics of the cut off points, but I found it to be not very practical for doing calculations up front. I've had the 63 quart blue classic model for a few years and just got a new 37 quart classic 2 model a few weeks ago. After wiring my jeep wrangler with an ARB fridge wiring kit I set the low voltage disconnect to high and noticed it shut off pretty quickly. When I checked the battery it was at 12.48. Not even remotely close to 11.8v cutoff listed in the manual. I verified the voltage drop of the wiring is between 0.00 and 0.01v measured with a fluke 87v. It turns out when the compressor is running the fridge sees a much lower voltage than what the battery is at. And even when it shut off because the LVD tripped you'll see that the resting voltage wasn't high enough to restart (12.6 for high). So I ended up turning it down to medium, which for all practical purposes is still conservative. And I wouldn't hesitate to set it on low if I had even just a single deep cycle battery for my main since I carry a lithium jump pack. So for anyone looking at the specs and doing calculations, realize that ARB did a good job designing the unit and it won't destroy your batteries. It just looks bad if you're calculating using resting voltages and not under load voltages that the fridge actually sees.

 

[john61ct]

Such charts need to be different for every model battery

only useful with a resting bank, isolated many hours

and the V-SoC relationship changes as batteries wear with age.

A ballpark guideline, at best

 

[67cj5]

Can any of the external lithium batteries (jackery et al) be wired to both the car and solar for charging with it auto switching? I wanted to do a dual battery in my Jeep, but there are too many times I'll move to my truck for trips so something portable makes more sense for me. Would love to just plug everything in and forget about it with the lithium charging from car battery when available and solar when not, or both simultaneously if possible.

My Vehicle has an AGM as the Starter battery but I have a choice of 2x or 3x 115Ah Deep cycle batteries, They will run my fridge for weeks but although that all sounds very well if you run them down to 50% it can take up to 18 hours using a 35A AC wall Charger, And that means staying in one spot for a long time running a Generator,

My Best investment was to buy the Dometic PLB-40 Lithium Pack because it can run the fridge during the night and I can plug a Solar Panel directly in to it to charge it or I can plug it in to the Cigar Socket and it will charge pretty quickly, Although the PLB is not cheap it does away with the need for Duel Battery systems and DC to DC Chargers because it has one built in and when using Solar you don't need a Charge Controller when using solar panels up to 150w which is about 7.5/8Ah.

I love the PLB's because they are a simple fix when it comes to keeping it simple and they are 100% portable, I bought 2 of them which has kind of made my Deep Cycle batteries redundant and I only need them for heavy Draw situations like running heaters in Winter,

Hope that helps.

 

[67cj5]

Medium on the ARB Fridge is 11.4v which it shuts off at

View attachment 612862
This is a batteries state of charge for a given voltage:

So 11.4v cutoff on your starter battery is draining it down BELOW 10% SOC, again I'm stoked your managing to crawl back out of the woods doing stupid **** like that.. but I know for a fact my vehicle will not even try to crank over at 11.4v.. not to mention the severe abuse this is doing to the cells and those batteries wont last.

Yep I agree, A Couple of things "People" Need to know about these Cut Off's,

If you set is to Hi @ 11.8v The Fridge will keep Running when the Battery is reading well below 11.8v IE 11.62v and when the fridge finishes it RUN Cycle the Battery Voltage will return back up to 11.9 to 12+v as it rests during it's OFF Cycle and each time it starts it will keep doing it's Run and Off Cycles until it's rest voltage has reached below 11.8 and by this time The batteries Running Voltages could be as low as 11.3 to 11.5 Volts Maybe even lower,

Run it down that far Is Ok Once maybe 2 or 3 times But do it any more than that and even a Deep Cycle Battery will be Damaged and it's usable life will be cut in Half or Worse,

These Battery Cut Offs are Nothing more than a ONE TIME Safety Barrier, NOT a LIMIT that you can use on a Daily Bases Each Day Every Day,

Every One here needs to always make sure that their battery voltage never drops below 50% and with some Deep Cycle Batteries can go as low as 70%, Any Fridge users Goal should be a maximum of 50% and the more batteries you have and the bigger they are the harder and longer it takes to replace that Charge which in most cases leads to many people never getting their batteries to their full capacity.

My Deep Cycle have been off Charge for over 16 hours and their Voltage is reading 13.406v, Using Deep Cycle batteries they will build up Calcium if you slowly discharge them and charge them to the Normal 14.4v using a normal charger which is why I use a normal charger and Once they have reached that point I hook up the 26A NOCO Smart Charger which Pulses the Voltage up to 16v Once it has done it's thing burning off the Calcium build up within the batteries, This is why my batteries hold such high Voltage for such a long time, Then once it has finished it's pulsing I will run the Repair Mode and when that has finished I will RE Run it's Charge Mode and then leave them to sit, this also adds up to 200 more CCA to the Batteries Rated 800cca because they are Duel Purpose Deep Cycle Batteries.

This Higher Stored Voltage will run my fridge for over 48 hours before my Batteries Stored Voltage reaches 12.720v,