Newbie question: Deep cycle to run ARB Fridge+

woytovich

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LandLocked93

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Is your point that I've been around for a long time, believe in science and don't know much about deep cycle batteries?
lol just figured you'd had to deal with power sources off and on (no pun) over your tenure.
 

woytovich

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lol just figured you'd had to deal with power sources off and on (no pun) over your tenure.
Just starting batteries... and lately struggling with/worrying about running the fridge off of the 2003 Yukon XLs starting battery.
 

woytovich

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LandLocked93

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Just starting batteries... and lately struggling with/worrying about running the fridge off of the 2003 Yukon XLs starting battery.
Ok...what do you offer in trade?



lol
One option would be running what's there on a typical outing.
See how often (if at all) you have to crank the truck to charge the batt to run the fridge without killing the start capability.

edit:this all manual of course. But once you see what you have, you'll figure out what best you need.
 
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I am doubtful that a 100ah non-lithium battery will last 3-4 days, outside of winter. On warm nights (lows around 60) my 55ah agm will drop from 13.0 at sunset to 12.5 by morning. That's 1/2 of my "usable" capacity, or 1/4 of yours in a 12 hour period.

I know you don't have a designated expo rig, but I'd strongly consider buying a panel and controller that you would use on your future rig and propping it up/lay on the ground at camp. You'll have zero power issues then, and when you get your future expo rig you'll already have the parts.

I'll stop kicking the dead horse now
 

woytovich

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I'm running a test now. 15 hours in. ARB running at 34 degrees, I've opened the lid 4 times so far for about 20-30 seconds each time to simulate some random usage. There are 3 one quart bottles of water in the fridge. I ran it up to temp on AC before I started with the battery. It's in the house at about 68 degrees.
According to the "gauge" lights on the National Luna battery box I'm still at 100%. At some point I'll put a meter on the battery.
 

woytovich

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I am doubtful that a 100ah non-lithium battery will last 3-4 days, outside of winter. On warm nights (lows around 60) my 55ah agm will drop from 13.0 at sunset to 12.5 by morning. That's 1/2 of my "usable" capacity, or 1/4 of yours in a 12 hour period.

I know you don't have a designated expo rig, but I'd strongly consider buying a panel and controller that you would use on your future rig and propping it up/lay on the ground at camp. You'll have zero power issues then, and when you get your future expo rig you'll already have the parts.

I'll stop kicking the dead horse now
Not kicking a dead horse at all. I have considered a suitcase system for easy portability. We'll see how things work out this season - I'm not going to be out in the wild so much that I can't run the truck if need be.
 

e9999

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I think there may be some misunderstanding out there as to whether the effect of the fridge contents is affecting things a lot.
In principle, if the fridge is NOT opened, and it has reached dynamic steady-state, whether it's empty or not should not make any significant difference in run time off the battery, yet I see that mentioned a lot. Of course, it does make a big difference as to how long it takes to reach that steady-state, but that is a different story.
Now, if you open the fridge and replace the cold air inside with hot air then yes, in principle it being full means less hot air in so working less hard to bring the air temp back down. But the air mass has comparatively little heat content so again, probably not a huge effect.
 

woytovich

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12.45 on a voltmeter at 21.5 hours. Fridge opened 6 times - pulled all 3 bottles in and out a couple of times. National Luna still reports 100% (weird or expected?)
 
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I think there may be some misunderstanding out there as to whether the effect of the fridge contents is affecting things a lot.
In principle, if the fridge is NOT opened, and it has reached dynamic steady-state, whether it's empty or not should not make any significant difference in run time off the battery, yet I see that mentioned a lot. Of course, it does make a big difference as to how long it takes to reach that steady-state, but that is a different story.
Now, if you open the fridge and replace the cold air inside with hot air then yes, in principle it being full means less hot air in so working less hard to bring the air temp back down. But the air mass has comparatively little heat content so again, probably not a huge effect.
Agree if not opened much. Just from personal experience I hear my fridge run more if not full verse near empty.

on a side note I just picked up a NL60 dual. Will be interesting to see how it compares to my Engel 45 on power consumption. Won’t have much of an opinion until the end of summer. I’ve got it test running now on 110AC and it definitely puts out more heat than my Engel.
 
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sdnative

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I think there may be some misunderstanding out there as to whether the effect of the fridge contents is affecting things a lot.
In principle, if the fridge is NOT opened, and it has reached dynamic steady-state, whether it's empty or not should not make any significant difference in run time off the battery, yet I see that mentioned a lot. Of course, it does make a big difference as to how long it takes to reach that steady-state, but that is a different story.
Now, if you open the fridge and replace the cold air inside with hot air then yes, in principle it being full means less hot air in so working less hard to bring the air temp back down. But the air mass has comparatively little heat content so again, probably not a huge effect.

The fridge and its contents are a thermodynamic system. The amount of energy required to change the temperature is related to the contents heat capacity. Liquids and solids have higher heat capacity than air. If there is a temperature difference between the inside and outside of the fridge, there will be some heat transfer through the walls of the fridge, how much depends on the insulation. Higher heat capacity will reduce the amount of temperature change for a given amount of heat transfer.

Now, objects with a higher heat capacity will take longer to reach set temperature (same concept as above in reverse).
 

e9999

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One difference you should see is that the compressor on/off cycle will be faster with an empty fridge vs a full one. Because the average heat capacity of the contents will be lower in the former case and conversely there is more thermal inertia in the latter. However, on average over time, the energy consumption should be similar (barring odd effects of compressor temperature on efficiency and the like) regardless of the frequency of cycling, because in first approximation the only thing that matters is the average temperature inside vs the outside one as far as the actual heat transfer is concerned. And the energy used by the compressor is directly related to that rate of heat ingress. Again all that only for a closed fridge in quasi steady-state, of course. If you're really interested in this, a cheap Watt / energy meter will keep track of the energy consumption and give you numbers. I have bought decent ones for less than $30.

But anyway, this is academic. In practice, I always try to keep the fridge as full as possible. Not for less battery use, but simply because it is safer in case of a problem with the fridge, as in it will take longer to warm up with the compressor not working if it's full than if not, so I have more time to deal with the situation before the food goes bad. For that matter, I always start a trip with a bunch of frozen bottles of water in there if there is room. Not that it's that likely that the fridge will go bust, but I have seen the odd inadvertent cord disconnect.


A big effect is the ambient temperature. If you're running your fridge at 34F inside and the ambient is at 68F, that is only 34F difference. If the outside of the fridge were to be 102F, say, or a difference of 68F (double the former), the heat transfer will be twice as much and the compressor should run twice as long in first approximation, everything else the same, and use about double the energy. Unfortunately, whereas for most of us it is not too common to experience 102F outside the truck, it is not that unlikely at all to see such high temperatures inside if the sun is beating on the truck and the A/C is not going.
 

woytovich

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12.32 on the meter 36 hours in. The National Luna led reads 12.5, guess I should try a different volt meter to verify.

PXL_20220327_152718257.jpeg
 
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e9999

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digital voltmeters are typically very accurate, even the cheapo ones. The LED bars OTOH, not so much usually. The little wattmeters I mentioned earlier also typically have a voltage display, that is convenient for monitoring. Keep in mind that when the compressor is going on DC, there will likely be a significant voltage drop between the battery and the fridge if the distances are not very short or if the cables are thin, because you likely will be pulling a few amps.
You will also find charts online showing the relationship between voltage and charge level. Unfortunately, they are kind of all over the place from what I recall. And that is complicated by the fact that those should really refer to a rested battery, not one being used.

(What are those 2 ports referred to on the pic?)
 

woytovich

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digital voltmeters are typically very accurate, even the cheapo ones. The LED bars OTOH, not so much usually. The little wattmeters I mentioned earlier also typically have a voltage display, that is convenient for monitoring. Keep in mind that when the compressor is going on DC, there will likely be a significant voltage drop between the battery and the fridge if the distances are not very short or if the cables are thin, because you likely will be pulling a few amps.
You will also find charts online showing the relationship between voltage and charge level. Unfortunately, they are kind of all over the place from what I recall. And that is complicated by the fact that those should really refer to a rested battery, not one being used.

(What are those 2 ports referred to on the pic?)
The two ports are both cigarette lighter type.... One is the hella type which is a smaller and the cigar is a regular cigarette lighter. I'm plugged into the cigarette lighter port for the ARB fridge.
I'm taking my readings when the fridge has been off for a few minutes. And I turn off power to the fridge for a moment when I read with the digital voltmeter.
 

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