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  1. #21
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    Default Re: How long will fridge on battery last in various scenarios

    One other thing to mention when it comes to meat. We have fund that vacuum packing meat really makes a difference. You get far less freezer burn and if the meat defrosts it stays fresher for longer. We have all of our camping meat vacuum packed.
    Lusted for a Landy but the Pajero was sexier and bigger in the right departments, just like my Missus.

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  3. #22
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    Smile Re: How long will fridge on battery last in various scenarios

    Kaydee you have to set targets..........

    For me the turning point was when I took my multimeter with and could see exactly what was happening, now I was not guessing any more. Now days those small voltmeters are cheap and can be fitted anywhere, you can use a switch for multiple batteries etc.

    Better than the voltmeter would be this project - https://www.4x4community.co.za/forum...attery-monitor

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  5. #23
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Gifmonster View Post
    Okay so the setup is- Paj 2005 3.8v6

    Dometic 40 l fridge freezer 12v/220v

    Second battery in national luna box with national luna solonoid sytem -Deep cycle battery 12 volt 102 amp

    We measured what we could and the fridges seems to draw between 2.5 amp and 3 amps per hour. So in theory the battery when full should sustain the fridge 102/2=51 then 50/2.5=20 hours ?

    Are these calculations correct?


    So what we are thinking, charge battery full, put it on to charge while driving (maintenance or top up) then while driving run fridge of starter battery and only when stopping run fridge off second battery?
    (then solar panel to top up second battery when standing for more than 20 hours (one day), What type and size panel etc and regulator?)

    Or would this not make a difference and the fridge can be plugged in to the second battery when driving and and receiving charge from the first?

    If any assumptions or calculation are extremely wrong , please point out and help us figure it out?
    Keep in mind that the fridge will cycle on and off.

    If set to -10 it will cool down to -12 and stop and wait till it reaches -8 then the compressor will start again. The on/off cycle will depend on how long it takes between the two levels. High ambient temps and opening the fridge or placing warm goods into the fridge will shorten the time between cycling.

    I tested my 60l fridge at zero degrees with 32-degree amb. temp. with a 105ah DC battery and it lasted 48 hours before it was 50% depleted.

    Do this test at -15 degrees at 40-degree ambient temp and it will probably last 24 hours.

    an 80-watt panel will give you 4 amp. ( 100w/5amps 120w/6amps) That's in perfect conditions.

    Work on 5 hours a day for solar calculations.

    Fit the biggest batteries and solar panels that you can manage!
    Last edited by DC Polokwane; 2018/10/17 at 09:31 AM.
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  6. #24
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Pieter de Waal View Post
    Plan for the worst scenario you think you will encounter, add 50 % and then out there be aware of what is happening and have some sympathy. Do not open the fridge 32 times

    Read the article in SA4x4 August
    Itís even easier than that. No calculations and guesses. Worst case scenario is fringe running 24/7.

    Very easy to get in warmer places where night time temps are in the 30's.

    KZN North Coast, Summer, add thirsty people because of the heat. Bingo.

    In fact Jozini dam February, fridge running 24/7, cant get the temp down to negative temps.
    Cheers

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  8. #25
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Paul Dold View Post
    On solar power one doesn't usually achieve the rating - conditions vary.

    Obviously the more panels the better. While some forum members seem to manage with relatively low amounts of solar for me a good rule of thumb is 160W.

    When temps really heat up like Kgalagadi or Richtersveld the ambient temp has a huge impact on fridge and battery. Batteries don't seem to be as efficient at high temperatures.
    Agree and neither does solar panels and charger controllers. Panels loose efficiency and controllers cut out.
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  9. #26
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by HobieDave View Post
    Kaydee you have to set targets..........

    For me the turning point was when I took my multimeter with and could see exactly what was happening, now I was not guessing any more. Now days those small voltmeters are cheap and can be fitted anywhere, you can use a switch for multiple batteries etc.

    Better than the voltmeter would be this project - https://www.4x4community.co.za/forum...attery-monitor
    Hi, Iím battling to understand the logic of running the fridge on the main batteryrather than the aux when driving.

    Yes theoretically there could be some gains/advantages, but for all practical purposes and reasonably configured systems, the overall system performance improvement would be so small as to be not worth the effort and cost and complication, and in fact probably not even measurable. (Effective performance/efficiency, not actual voltdrops)
    Cheers

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    A V6 and an inline 4

    The frogs are starting to notice that the water is getting warm but it is already too hot to do anything about it.....

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  11. #27
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Paul Dold View Post
    Gifmonster - Twotracks - great web site!
    Enjoying the read!
    Thank you very much Paul!!! I need to go sit and write some more!!!
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  12. #28
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Fluffy View Post
    Hi, Iím battling to understand the logic of running the fridge on the main batteryrather than the aux when driving.

    Yes theoretically there could be some gains/advantages, but for all practical purposes and reasonably configured systems, the overall system performance improvement would be so small as to be not worth the effort and cost and complication, and in fact probably not even measurable. (Effective performance/efficiency, not actual voltdrops)
    I was just thinking the alternator can handle the batteries and firdge?

    Wwas thinking maybe the fridge will draw more from the aux battery that the front/main battery can replace through the solonoid?
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  14. #29
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    Default Re: How long will fridge on battery last in various scenarios

    With a lot of alternators producing 120amp even the 30year old alternators of 55amp will have no sweat.
    Last edited by ekkekan; 2018/10/17 at 10:49 AM.

  15. #30
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by HobieDave View Post
    Kaydee you have to set targets..........

    For me the turning point was when I took my multimeter with and could see exactly what was happening, now I was not guessing any more. Now days those small voltmeters are cheap and can be fitted anywhere, you can use a switch for multiple batteries etc.

    Better than the voltmeter would be this project - https://www.4x4community.co.za/forum...attery-monitor
    Both my battery packs equipped with Volt/Ammeters. They work very well. After every charge I reset them and monitor.

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  17. #31
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    Default Re: How long will fridge on battery last in various scenarios

    Fluffy can keep me right on this, but my understanding is that demand is demand. If I feed a main from the alternator and the main in turn feeds an aux that has a load, the demand will remain a constant.

    If the fridge demands 3 amps this will be drawn from the aux which in turn will draw from the main which in turn will demand from the alternator (bucket and hosepipe theory), you may experience some minimal losses due to resistance in the wires, but if your wiring is up to scratch, these will be minimal.

    I see this with my setup on the semi flex solar panel. The fridge can be running, the battery can be full and the PWM controller still dumps volts. (red flashing light, green light solid) I use Deltec 105 high cycle because I am happy to stay in the 13.8 volt range. A deep cycle will require 14.4 and a DC_DC set up.

    Full battery supplying 3 amps to fridge, solar panel supplying 5 amps to a full battery. I don't have one but I suspect an MPPT would do even better and would be more suitable for a bigger fridge with a higher amp draw.
    Lusted for a Landy but the Pajero was sexier and bigger in the right departments, just like my Missus.

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  19. #32
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    Default Re: How long will fridge on battery last in various scenarios

    The time a fridge runs out of 24 hour various a lot, depending various factors, but in places like the Kalahari and Koakoveld in summer it is about 20 hours out of the 24 hours, with good management of the fridge.
    Last edited by JLK; 2018/10/17 at 11:17 AM.
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Stranger View Post
    One other thing to mention when it comes to meat. We have fund that vacuum packing meat really makes a difference. You get far less freezer burn and if the meat defrosts it stays fresher for longer. We have all of our camping meat vacuum packed.
    GREAT Advice ..its what we do too

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  22. #34
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Paul Dold View Post
    Have always set the fridge at -5C but having just come back from Kgalagadi have adopted -2C.
    This avoids the compressor running flat out non-stop in a hot car when temps are 35C+
    The fridge usually achieves a temp about 1 degree below the setting.

    I agree with really freezing everything at -18C before you leave home.
    Agree with you Paul ..But our Freezer stays in the trailer tent back at camp working off the solar panels and is not in the vehicle so when we unplug at night in Lion territory the minus 18 gets the freezer through the night ..When I plug in the following day it has fallen to about -2 to -3 about but is soon back to -18 while we are out

  23. #35
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    Default Re: How long will fridge on battery last in various scenarios

    If all installations were done correctly then there wouldn't be much difference.

    Measuring the current in to the aux and the current drawn by fridges etc especially with a dc dc it's sometimes very low so I prefer the main battery and alternator to supply the power while the dc dc does the best it can, that way there is more power going in to the aux batteries.

    Heat here compounds the problem as the alternator should reduce its output and the dc dc as well.

  24. #36
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by HobieDave View Post
    If all installations were done correctly then there wouldn't be much difference.

    Measuring the current in to the aux and the current drawn by fridges etc especially with a dc dc it's sometimes very low so I prefer the main battery and alternator to supply the power while the dc dc does the best it can, that way there is more power going in to the aux batteries.

    Heat here compounds the problem as the alternator should reduce its output and the dc dc as well.
    No, no, no, no, did I mention NO.

    Instead of getting complicated, let me rather just say NO.
    Cheers

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    The frogs are starting to notice that the water is getting warm but it is already too hot to do anything about it.....

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  26. #37
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    Default Re: How long will fridge on battery last in various scenarios

    Let me rather just say WHY Fluff??
    Merit before Race - anything else IS Racism.
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  28. #38
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    Default Re: How long will fridge on battery last in various scenarios

    Quote Originally Posted by Capt Chaos View Post
    Let me rather just say WHY Fluff??
    Ja please help us out here oom Fluffy?
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  29. #39
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    Default Re: How long will fridge on battery last in various scenarios

    If the fridge draws let's say 5 amp then you will lose 5 amps either way. On a solenoid system by connecting it to the starter battery, you are only jumping the queue. No measurable difference.

    Maybe with a DC/DC charger, there might be a difference because the alternator has more amps available? By not taxing the DC/DC charger it should operate at full but limited (20amps) potential while the alternator has ample spare amps available to power the fridge?

    But there are a lot of variables .....
    Last edited by DC Polokwane; 2018/10/17 at 02:38 PM.
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  31. #40
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    Default Re: How long will fridge on battery last in various scenarios

    My 2 fully portable packs. Both Solar capable and one with DC-DC 30A charger.
    Both V/A meters.
    Served me well the past 4 years.
    Attached Images Attached Images  

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