Low voltage protector

[Hadenough]

I am fitting a low voltage cut out to my fridge. I have sourced one with presets. 9.5 to 12v for disconnect and 11.5 to 13v for reconnect. Is 12v too low for disconnect? Up to now I have never let the bank go below 12.5 before manually switching off the fridge.

 

[MagicIsland]

I suppose it depends on your battery banks, if your using the same battery for engine starting then 12v cut out is far too low, however if you have another bank for leisure use then its not too far off. My compressor as a built in cut out at 12.3v , under weekend use only conditions my 2 * 110 amp leisure batteries can power the fridge none stop no problem and recover with 5 days of MPPT solar charge. If we are on the boat for 4 days or more without shore power then we see the LVP cutting in, I also notice the water pump running on when the taps are used, when I check the battery voltage it's around 11.8-12v at this point it will take a shore power battery charge to bring the batteries back up to 100% charge. So again may depend on your recharge options.

 

[Hadenough]

I have two banks, 284AH domestic and 142AH engine. I charge from 180W of solar (recent) and can use a 50A charger from a 4.5kw genny even at anchor. I have been in the habit of running the genny for an hour when the bank dropped to 12.5V. (Which I will still do as the solar season changes).
Currently the solar pretty much keeps up with the fridge at the (sunny) moment but I had, before the solar, been in the habit of switching the fridge off overnight in case it ran the domestic bank too low while there is no monitoring. I don't think I need to do that any more as the bank is usually sitting at around 12.9V when we go to bed and the solar starts charging at sunrise. I am fitting the protector to remove any risk.
After all that waffle I suppose my question is what voltage is too low for the disconnect given that the preset on the unit I am looking at is 12V, I have it in my head from somewhere that 12.2V is effectively a dead battery

 

[lw395]

Don't forget to allow a bit for voltage drop in the wiring.
Beyond that, it mostly a matter of preference, and weighing up spoilt food/warm beer against shortening the life of your batteries.

 

[vyv_cox]

The instantaneous voltage when the fridge is running is far lower than the battery voltage with no draw. When my fridge is running the voltage is, for example, 12.3, whereas as soon as it stops it is 12.6, rising to 12.7 in a few minutes. Your 12.0 is perfectly safe, I think mine, although never used, is far lower, something like 11.0.

 

[lw395]

The instantaneous voltage when the fridge is running is far lower than the battery voltage with no draw. When my fridge is running the voltage is, for example, 12.3, whereas as soon as it stops it is 12.6, rising to 12.7 in a few minutes. Your 12.0 is perfectly safe, I think mine, although never used, is far lower, something like 11.0.

Because of this, you need to make sure that there is enough 'hysteresis' i.e. when it shuts off due to the volts falling, it does not switch back on two minutes later when the volts have risen a bit. Only to instantly switch off again.

 

[Hadenough]

Thanks both that's what I was after. That means that the protector I am looking at has enough range for me to experiment with settings. I'll get it ordered.

 

[nigelmercier]

Are you sure it doesn't already have one? I'm pretty sure that all Danfoss controllers have, but they default to 10.5V unless adjusted with an external resistor.

 

[Hadenough]

Are you sure it doesn't already have one? I'm pretty sure that all Danfoss controllers have, but they default to 10.5V unless adjusted with an external resistor.

Thanks but it is a 1986 model Engel and manual makes no mention of one. Our old boat had a Danfoss with a 10.5 default which did for the old service battery in less than a season. Hence my nervousness about the appropriate disconnect voltage.