Outer Limits 4x4 Board

Hey guys. How long should i be getting out of my battery running just my fridge. I have two calicum n70 size marine battery's isolated with a piranna dual battery system. The problem i have is my 40lt fridge (compressor type) will not last 24 hours before it cuts you on low voltage. Does this sound normal? I have checked for voltage drop and fixed it up so i have less than .3A from the battery at the front to the fridge in the back. Also have a 120A alt. in the GQ. Thanks

did you check voltage drop across the accessory outlet when the fridge was unplugged or turned on? could still be voltage drop under load. what size wire did you use? are both batteries charged and in good condition? really need to know how much your fridge draws before we can do any calcs.

I get more than that out of 1 n70 battery

Are you draining one N70, or both to run the fridge?

At what voltage does the cut-out operate?

What make & model fridge?

IIRC, an N70 isn't a particularly big battery - I would guess somewhere in the 40 - 50Ah range.

Depending on your fridge, where it sits and how you use it, it could easily be drawing more than 20Ah a day - or half of one battery's capacity.

If the cut-out is set to trigger around 50% SOC you could easily hit this mark inside 24 hours (if you're only drawing from one battery.)

If you're discharging every day, and only charging a few hours a day, you won't be fully charging your battery every day - if you're not starting at 100% charge each day your battery will reach cut-out sooner.

So, although less than 24 hours sucks, it's not necessarily an indication of a fault.

it is drawing off only 1 battery. i checked the voltage drop at full load. the battery the fridge runs off is only 3 months old so should be good. not sure what the cut out is will have to check that. i dont know the make/ model of the fridge. it has a little computer fan for the condensor but it runs all the time. i think i might disconnect that to try and reduce current draw. i tried to measure the current draw but my cheap little multimeter had to much voltage drop across it and the fridge would not start up. and i dont have access to a dc clamp meter.

disconnecting the fan will reduce heat transfer therefore efficiency. it probably wont cool properly. make sure when you are checking for amps you change the lead configuration on your meter (leave black lead in COM and change red lead to amps) and make sure it is set to read amps - generally it will be a 10 amp setting. do this at the battery - its easier and you are checking the total drain on the battery. disconnect the earth lead from the battery and connect the meter in series. this will indicate the combined current draw of everything, not just the fridge - this way you can check if anything else is discharging the battery too.
id say if it is a cheap no-name fridge this could be playing a big part in the quality and efficiency of the unit.

yeah, i changed the leads when i measured the amps. and the battery did not have any current draw when the car is turned off and the fridge is not running. I am a refrigeration mechanic by trade so if i disconnect the cond. fan i will be watching to make sure the head pressure does not get to high. i am guessing the fridge just draws alot of current and the battery does not last. would stepping up to a deep cycle battery make much difference?

well then youd know more about its effects than me, i hate refrigeration

i tried to measure the current draw but my cheap little multimeter had to much voltage drop across it and the fridge would not start up.

sorry i mis interpreted this, i thought you were trying to measure amps with it set to volts
have you tested the meter? blown fuse? iv never come across one that had too much resistance to take a measurement like that, but good to know for future reference.

id focus on finding a meter that wont have that much voltage drop across it. before you spend any money guessing and trying different things id get the fridge going and find out how much its drawing first. throwing a deep cycle battery in wont make too much difference in way of a/hrs but it will handle being discharged and charged back up alot better so this would probably be advisable anyway. but like i said, i'd find out what your dealing with first so you buy something suitable.

thanks mate. i think i will get my hands on a better meter and find out the current draw and go from there.