Outer Limits 4x4 Board

(tried this in the auto electrical section with no luck, hoping for a larger audience here)

I have a question about running my Waeco fridge. I have a second (30Ah) "thumper" battery which I have tested will keep the fridge going overnight (with the fridge set to the second step @5C)

Now I understand that there are many types of battery isolator out there, to cut the main (start) battery out of the circuit when the engine is stopped. So the main battery is not drained (at all) allowing the car to start. I had one in the previous Patrols.

My question is - do I need an isolator with my Waeco which has a "battery saver" switch on the back, which can be set to low (10.4v) medium (11v) and high (12v) I expect the battery saver is there to save the battery from deep-discharge (thus killing it) but will the high setting still allow the car to start if it gets down to 12V?

With an isolator, I cant use any of the starter battery energy for the fridge (thus extending the capacity of the thumper)

Any advice much appreciated...

i use my 40l waeco on the medium setting every day in my D40 navara and it starts fine so i dont think you will have any problems as i only have the standard starting battery installed.

Brad

i would set it up with an isolater and not use the battery saver. if you use a deep cycle with an isolated starter you can run the secondary flat and it wont matter.

I think it may come down to how easy your car starts.
We did trip through the NT with a 50ltr waeco and ran the fridge with the switch on the low setting. The fridge cut out a few times, meaning the battery was at 10.4 and the car still started fine. That was in a Subaru Outback, diesel may need a bit more charge though.

the battery saver measures the voltage inside the fridge. that means after the voltage drop across the wiring between the fridge and the battery.
if you battery was really at 10.4V it won't start anything, it's dead.

so if you used starter motor cable to wire up your fridge ( big thick wire ) then you will get a lot less voltage drop between the fridge and the battery. with a 10.4V cutout at the fridge, you battery would be down to a fairly low voltage. ( i'm guessing, but well under 12V ) This isn't good.

if you've used smaller sized cable then the voltage drop will be greater and your battery voltage will be greater when the fridge cuts out.

some isolaters even allow you to draw some power from the main battery before they isolate it. sort of a combination of isolating and cut out.

so the answer to your question is, it depends

if you are around civilisation and can cope with possibly needing a jump start and/or a new battery then no problem. if you're going bush then i'd be looking at an isolater and second battery.
i use an isolater, dual batteries and the fridge cutout set to medium