Battery cut-out voltage

[brianvicki]

I have a 62amp agm battery in the Jeep for running a fridge etc., what is the best voltage for cut-out
the fridge has 3 setting, I def don’t like low….

level	cut-out comp off	Cut -in comp on
low	9.6	10.6
medium	11.1	12.1
High	11.8	12.8

 

[Swaggie]

High as a minimum.

62 amphr battery won’t give you much time especially if it’s not lithium…
Lead acid don’t like being run down all the time, my deep cycle doesn’t go below 50%.
you’ll need a inline monitor to see how many amps the compressor uses over 24hrs

I’d also suggest a 200-250 watt solar panel otherwise you’ll need to keep the motor going on the second day most likely if your not driving around.

 

[Colly18]

I guess I'm about to learn something here? But I've no idea what your 'Cut-in comp on' setting is about. I'm assuming comp means 'compressor' and, in which case, it should operate in any situation where the fridge temperature is above what you have the fridge temperature set for.
At the medium cut-off setting of 11.1 volts the battery is effectively flat (is my understanding). So I'd opt for the high setting, + make sure your second/agm battery is isolated from the vehicle main starting battery. Having said that much depends on the accuracy of the fridge electronics. You could play around with testing the medium setting and monitoring what is happening with a multimeter.

 

[Colly18]

High as a minimum.

62 amphr battery won’t give you much time especially if it’s not lithium…
Lead acid don’t like being run down all the time, my deep cycle doesn’t go below 50%.
you’ll need a inline monitor to see how many amps the compressor uses over 24hrs

I’d also suggest a 200-250 watt solar panel otherwise you’ll need to keep the motor going on the second day most likely if your not driving around.

With solar panel charging of the second battery (in my experience) a lot depends on the ambient temperature and number of times you are opening and closing the fridge, + it depends on what size and power draw car fridge you have. In many mild climate situations a decent 60 watt solar panel will keep things running well with many car fridges. But in hot conditions and constant fridge use, as Swaggie suggests, you will need double or triple the capacity to keep things running OK. A few variables to consider!?

 

[Triton14]

Your AGM shouldn't go below 50% discharge which is 12.05V otherwise you will shorten it life if you do it constantly.
So if your amp consumption outstrips your battery capacity then you need to larger in Ah capacity

 

[red hilux]

I guess I'm about to learn something here? But I've no idea what your 'Cut-in comp on' setting is about. I'm assuming comp means 'compressor' and, in which case, it should operate in any situation where the fridge temperature is above what you have the fridge temperature set for.

Cut out comp off is the voltage when the fridge says the battery is flat

cut in comp on is the voltage the fridge will now restart as it thinks it’s now charged

 

[McGinnis]

High. Cutting out at 11.1v, the battery is already well into degradation territory. I don't really like the built-in battery savers on fridges, though I understand why they're there - for those that like to plug and play. They tend to cut out too low even on high, and cut back on too low.

You're likely to run into issues if you don't run appropriate cable gauges also - voltage drop from your battery (depending on where it is) may well mean the fridge is never getting appropriate voltage for a 'high' setting once under load.

Make sure your cable runs are appropriately sized, use the length of the entire circuit (return, not just TO the device) to calculate the appropriate gauge, and test voltage at the fridge side while it's under appropriate load - not just with a multimeter on the end and nothing else.

 

[brianvicki]

High. Cutting out at 11.1v, the battery is already well into degradation territory. I don't really like the built-in battery savers on fridges, though I understand why they're there - for those that like to plug and play. They tend to cut out too low even on high, and cut back on too low.

You're likely to run into issues if you don't run appropriate cable gauges also - voltage drop from your battery (depending on where it is) may well mean the fridge is never getting appropriate voltage for a 'high' setting once under load.

Make sure your cable runs are appropriately sized, use the length of the entire circuit (return, not just TO the device) to calculate the appropriate gauge, and test voltage at the fridge side while it's under appropriate load - not just with a multimeter on the end and nothing else.

Fridge is right next to the battery and I use use 25amp or thereabouts cable

 

[red hilux]

If you’re going solar panel route. Buy the most biggest panel you can fit. An example, a 120w solar panel won’t deliver 120w power. There are a lot of losses.
You want to be sure you’re pumping much as possible, more so if your a camper that may not be driving as much

 

[brianvicki]

What is the most suitable voltage for cut-out….. the current high setting is 12.4… medium is too,low, so low looking at a battery cut-out with Anderson plugs and set the voltage myself

 

[McGinnis]

It depends on the battery, but typically for an AGM, I'd say ~12.0v or a little lower. That'll being you to roughly 50% state of charge. Check the details of your particular battery though as they do vary.

Also note you're better off being conservative - minimising deep discharges will prolong the life of the battery, and also keep in mind any voltage readings taken while the battery is active are not necessarily super accurate - only after a battery has 'rested' for some time will it's voltage stabilise. This effect is lesser when the battery is under load, though, than when it is under charge so may not be a big deal.

 

[McGinnis]

Maybe too much information for a simple task, but if you do want to monitor your battery properly, get a shunt-based monitor like the Victron BMV712 or something. It will measure current in and current out to advise you more accurately of your battery's state of charge.

I don't know if any SoC monitors have relay outputs to cut off supply, but it'd be nice if there was something like that around.

 

[Triton14]

50% state of charge is 12.05V so I would set the cut out to not be below this otherwise you will shorten you batteries life if done constantly.

This is why so many people are going Lithium, can be taken to a much lower state of charge(80-90%) and half the weight.

 

[boobook]

The cut out voltage is not a tool to manage the fridge and battery. It's a last resort protection so you don't totally destroy your battery every time you use the fridge.

Set it to high if your battery is also the starter, and medium otherwise. Low is for emergency over ride use but at the expense of your batteries long term life. However you will find that you want be able to rely on the fridge without it cutting out after a few hours.

Then get a bigger battery and a means to keep it charged. Like 160w plus of solar.

 

[CTL]

I don't know if any SoC monitors have relay outputs to cut off supply, but it'd be nice if there was something like that around.

The Enerdrive ePro Plus has relay outputs.

 

[brianvicki]

Thanks for the input, this subject gets interesting, when you look at various products on the market.
e.g https://www.projecta.com.au/battery-maintenance-tools/battery-discharge-protector
this product cuts out @ 11.6v….

 

[Robbo63]

I agree with Boobook 120AH for my accessories and fridge set on medium 150 solar panel mounted on the roof even my starter battery is a big stop start 900cca and the fridge will flatten it in 2 days with no driving.
better to have bigger and not need it.

 

[McGinnis]

50% state of charge is 12.05V so I would set the cut out to not be below this otherwise you will shorten you batteries life if done constantly.
View attachment 72731

This is why so many people are going Lithium, can be taken to a much lower state of charge(80-90%) and half the weight.

The voltage at 50% depth varies from battery to battery - some manufacturers put it as low as 11.90v.

But totally agree, just get a lithium. Lighter, cheaper in the long run but with higher upfront costs, and so much better.

 

[Triton14]

some manufacturers put it as low as 11.90v.

And like I said many battery manufacturers overstate their batteries Ah capacity, 12.05v is 12.05v.
Thats the one stable in the equation.

 

[TimNWVic]

Maybe too much information for a simple task, but if you do want to monitor your battery properly, get a shunt-based monitor like the Victron BMV712 or something. It will measure current in and current out to advise you more accurately of your battery's state of charge.

I don't know if any SoC monitors have relay outputs to cut off supply, but it'd be nice if there was something like that around.

The BMV712 has a configurable relay trigger to turn things off. Would need to control a separate high current relay with it though.