Newbie question: Deep cycle to run ARB Fridge+

woytovich

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So I guess I'm getting to around 50% on the battery. That's just about 2 full days, inside at about 68 degrees F, opening the fridge 10 or so times, 3 quarts of water in the fridge with 2 of them removed at about the 36 hour mark.
Far from scientific but I'm quite happy knowing I can eek out 2 full days without a lot of drama (at 68 ambient). Given that I generally do run the truck for a few minutes each day and as long as I'm hooked up to a good DC-DC charger I should be fine for my expected use - for now.
I'm going to repeat this with my Engel later this week to see if I notice any difference.
 
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Easy math, averaging 1ah.

I just looked at the pic of the charger - says it peaks at 2.7amps. It would take 18.5hrs to top off those 50ah. Simultaneously the fridge is consuming 1ah, so really charge is 1.7ah, which is 26.7hrs.

Maybe I'm misreading the charger decal, just wanted to mention. That'd be a lot of idling if you're out there for 4 days.
 
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I have a Victron SmartShunt on the negative side of my aux battery and I find that its very valuable in tracking how many amp-hours I've consumed. The app on my phone connects to the shunt via bluetooth. It shows me the battery voltage, current flow (in amps), power (in watts, either as a - number for power leaving the battery or a + number for the battery receiving a charge), and how many ah's my devices have consumed. Since its measuring all current in and out of the battery it can account for charging and discharging at the same time to give an accurate number of consumed ah's.

Its a tad spendy but gives me much more info about my battery's state of charge than based on voltage alone.
 

woytovich

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Easy math, averaging 1ah.

I just looked at the pic of the charger - says it peaks at 2.7amps. It would take 18.5hrs to top off those 50ah. Simultaneously the fridge is consuming 1ah, so really charge is 1.7ah, which is 26.7hrs.

Maybe I'm misreading the charger decal, just wanted to mention. That'd be a lot of idling if you're out there for 4 days.
I'll be using a 20a CTEK dc to DC charger in the truck.
 

e9999

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it certainly seems to be a good idea to limit the DoD for the AGM to 50% to be safe, but my impression is that the AGMs are more forgiving of deep discharge than the flooded ones. I would not worry too much about getting a bit below 50% charge once in a while. I've even seen sites claiming it's fine to go down to 80% discharge with the AGMs deep cycles.
 

woytovich

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Fully recharged with a 4 amp AC charger in about 14 hours.
Initial voltage right after charging: 13.09. I'll remeasure again later to see where it settles.
 
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e9999

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mine settles right around 13V when fully charged with the standard FLA protocol after a few hours of rest at typical room temperature (70-80F). It is noticeably higher resting voltage than the FLA ones.
(Keep in mind that the AGM ideally wants a bit higher voltage than FLA when absorption charging, though, you may want to use a charger that allows for that. I don't always bother TBH.)
 

woytovich

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Ok, 24 hours in with the Engel MR040 I'm at 12.51v
I get the general feeling that it cycles on and off more often than the ARB but stays running for a shorter period of time. I don't have any actual stats to back this up though.
 

e9999

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^ Aside from differences in insulation and size, that could also depend on how much the control scheme allows for departure from the set point. Some are sloppier than others.
 

woytovich

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48 hours in with the Engel: 12.28v (arguably around 40% discharged)

End of test. I'm going to call that just about the same as the ARB given that I didn't use a separate thermometer to "set" intended internal temperature. I relied on the reading of the ARB and a small mercury thermometer in the Engel to try to get them the same. I should have thought about that ahead of time...

Bottom line is I can probably expect to get 48 hours out of either fridge with paying attention to contents management, limiting "open" time, getting a transit bag or making some similar insulation cover and keeping them out of any overly hot environment (read: sun). That solves the "problem" for me in the short term.
 
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e9999

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Well 2 days on a 100Ah battery is respectable and you didn't bring it down all the way either. Not very hot outside, though, so will be significantly less when it is. But seems "normal" overall.

IMO, it's a good idea to get a wireless thermometer with a little portable display that has an adjustable alarm. Good to keep track of things and avoid disasters, to set the desired temperature inside (at best the fridge built-in display shows the wall temperature) and will also show what the air temp range is while cycling if you're curious about such things. Those are very inexpensive and may save the day on a trip.
 
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I've used a dual probe Bluetooth thermometer by ThermoPro before, my wife bought it to use for the smoker, although the tiny battery doesn't last more than 4 hours when unplugged. It has a min/max alarm you can set. Personally, I don't sweat it, just wanted to test display accuracy.

Amazon product

Getting everything cold at home on 120V/turning the temp below freezing while driving will give you some extra time too. It takes a full 2 days to freeze waterbottles in my dometic set at 6 degrees FYI, so you can crank that temp down for a 4 hour drive without fear of freezing veggies or exploding beer. Then you get a few hours of zero consumption as the temp slowly returns to 34/whatever you set it at.

One other thing is inline battery monitor with a shunt. There are some decent ones to be had for under $60. My Dometic has one built it, not sure about Engel or ARB. It tracks your battery voltage and will shut off power once it drops below a threshold you set. May not be your thing but thought I'd mention.

Happy camping
 

e9999

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I would suggest to get an emitter and receiver that run on AAs or bigger. Package size does not matter that much for this application, but not having to worry about the battery for a long time is great. I have an old RadioShack, the AA batteries (2 ea) last many months and will do fine even at 0F. That's fantastic. Don't think that smaller batteries will do as well. I prefer not to have wires or have to use the phone.
 
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I have a Victron SmartShunt on the negative side of my aux battery and I find that its very valuable in tracking how many amp-hours I've consumed. The app on my phone connects to the shunt via bluetooth. It shows me the battery voltage, current flow (in amps), power (in watts, either as a - number for power leaving the battery or a + number for the battery receiving a charge), and how many ah's my devices have consumed. Since its measuring all current in and out of the battery it can account for charging and discharging at the same time to give an accurate number of consumed ah's.

Its a tad spendy but gives me much more info about my battery's state of charge than based on voltage alone.
Got a question. I have been looking at the BMV-712, what is the difference with that vs just a smartshunt? I see a lot of reports that the bluetooth range on the smartshunt is quit short but the BMV is better. Thanks
 

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My experience with several Victron MPPT Blue and Smart controllers: The Smart controllers, with built in Bluetooth, have about a 10' +/- range. Whereas the Blue controller with separate BT dongle has about a 25-30' range. From the nose box of our trailer (steel) where the Victron Blue controller is installed with separate BT dongle, I can get steady & reliable communication from the cab of our Chevy Silverado HD2500. Whereas when I had the previously installed Smart controller...no bueno.
 
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Got a question. I have been looking at the BMV-712, what is the difference with that vs just a smartshunt? I see a lot of reports that the bluetooth range on the smartshunt is quit short but the BMV is better. Thanks
Believe the BMV-712 is going to have its own display and bluetooth. The smartshunt is only read via the app. The bluetooth range on the smartshunt is not that great to be honest but I put most of that to the fact that its installed under a metal hood. I usually have to get within about 5 feet of it to get it to connect.
 
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from first hand experience, you will be disappointed trying to get 3 days off battery alone( even 2 ) on a fridge unless its 60*F, in the shade and never opened. The expensive fridges will buy some time as they are more efficient. IMO get a minimum of 60 watts solar, 2 good agm batteries, and you could run for 5 days given proper conditions, I have learned over the years that pre-cooling on 110, packing full, keeping shaded, adding frozen water bottles will prolong the time I can not have to run engine to charge. at 45 watts on 2 agm's, separated to preserve starting capability of solar my system will go 4 days. Now as to low voltage cutoff, which will ruin your food while your sleeping, I have found that even tho it shows 13.2 volts, when fridge cuts on the voltage reading drops to 11.4 and the low voltage may cut it off, what I find with the solar is it keeps system at 13+ volts but the drop in voltage when fridge cuts on gets worse as the days go by, I will add more solar to fix this but as is I have to run engine for an hour or so after 4 + days. A better fridge would also solve this problem as I currently have a cheap one that is less efficient, I did this on purpose so if the system design will support this fridge it will definitely support a good fridge for 5+ days. There are plenty of 120 watt solar set ups that would allow all kinds of goodies to operate if I upgraded my solar from 45 to 120. FWIW I currently have an Aspenora 42 quart, had an OG Engel 45 quart, and will get an arb after I save up. Don't ask what battery, I pretty much hate them all.
 

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