Battery saver for fridge

[Elemental]

Does anyone know of a voltage sensing unit that can detect a charging voltage and automatically turn the power supply to a fridge on, and turn it off again when the charging ceases? The current boat has two, large fridges and I'd like to defend the service batteries from drain during long, offshore passages. I'm not looking for a unit that detects a discharged battery (partial or otherwise) I want to disable the fridge even if the battery is fully charged and only run it when the shore power is connected, or when the engine is running. Basically, it's for when we forget to turn off the freezer when we go sailing.
The previous boat had a device from (now defunct) JWMarine called a FridgeMate which did exactly that. I can likely run up something using a voltage sensor and micro-controller but if there's a device out there ...

 

[PaulRainbow]

Hi Mark. A quick Google search turns up :Amazon.co.uk

Others: adjustable battery protector - Google Suche

 

[Buck Turgidson]

Does anyone know of a voltage sensing unit that can detect a charging voltage and automatically turn the power supply to a fridge on, and turn it off again when the charging ceases? The current boat has two, large fridges and I'd like to defend the service batteries from drain during long, offshore passages. I'm not looking for a unit that detects a discharged battery (partial or otherwise) I want to disable the fridge even if the battery is fully charged and only run it when the shore power is connected, or when the engine is running. Basically, it's for when we forget to turn off the freezer when we go sailing.
The previous boat had a device from (now defunct) JWMarine called a FridgeMate which did exactly that. I can likely run up something using a voltage sensor and micro-controller but if there's a device out there ...

Just google battery Isolator and find one with a cut out voltage below the float voltage of your charger. I just did that and found several with cutout at 12.8v which would serve your purpose . No link unless you want to buy from Switzerland

 

[superheat6k]

This Sontay relay can be adjusted to switch its signal relay on at a preset level, which can then operate a power relay to your fridge.

https://son04-live-0559e086fe33459f92ce8a277429-ab9e917.divio-media.org/specs/IO-A-RM_wzW2klL.pdf

 

[LiftyK]

I have a FridgeMate sitting at home. I used it before switching from a cool box to a compressor fridge. If you’re interested please send me a message. I’d rather see it used than wasted so happy to part with it for a nominal sum.

 

[roaringgirl]

If your freezer goes on and off with charge voltage, don't you risk poisoning yourself?

 

[Refueler]

Does anyone know of a voltage sensing unit that can detect a charging voltage and automatically turn the power supply to a fridge on, and turn it off again when the charging ceases? The current boat has two, large fridges and I'd like to defend the service batteries from drain during long, offshore passages. I'm not looking for a unit that detects a discharged battery (partial or otherwise) I want to disable the fridge even if the battery is fully charged and only run it when the shore power is connected, or when the engine is running. Basically, it's for when we forget to turn off the freezer when we go sailing.
The previous boat had a device from (now defunct) JWMarine called a FridgeMate which did exactly that. I can likely run up something using a voltage sensor and micro-controller but if there's a device out there ...

Because my Coolbox was power hungry - I fitted a car headlight relay .... any reasonable relay will do that can handle up to 10A

Basically when 12V is applied to the relay - it connects the box. Remove the 12v and it disconnects the box.

At present it is using the alternator .... once engine starts and alternator kicks in ... box works. Stop engine and box cuts out. Uses a cigarette lighter plug - as supplied - which I can unplug and put to an always on when shore power available. With my new Vevor Fridge box - I will add a switch to save that plug change.

Cheap .. easy to do ... works.

OK - it lacks the battery saver setting ... but at least I know I will not be dragging battery down.

Online stores like Banggood have many cut-out items that can do this job ...

 

[PaulRainbow]

If your freezer goes on and off with charge voltage, don't you risk poisoning yourself?

The OP does not mention freezers Roger, just two large fridges.

Edit, my mistake, he did mention a freezer

 

[PaulRainbow]

Because my Coolbox was power hungry - I fitted a car headlight relay .... any reasonable relay will do that can handle up to 10A

Basically when 12V is applied to the relay - it connects the box. Remove the 12v and it disconnects the box.

At present it is using the alternator .... once engine starts and alternator kicks in ... box works. Stop engine and box cuts out. Uses a cigarette lighter plug - as supplied - which I can unplug and put to an always on when shore power available. With my new Vevor Fridge box - I will add a switch to save that plug change.

Cheap .. easy to do ... works.

OK - it lacks the battery saver setting ... but at least I know I will not be dragging battery down.

Online stores like Banggood have many cut-out items that can do this job ...

The device in post #2 does the job properly, has a 10a rating and costs less than a tenner, why would the OP want to mess around with headlamp relays ?

What about when charging comes from solar or shore power ?

By the way, no need for heavy current relays to control a fridge, just interrupt the thermostat connection.

 

[Elemental]

The OP does not mention freezers Roger, just two large fridges.

Actually Paul, I think I did mention the word "freezer" in the original post because it can be used as one, but we don't use it that way so the issue doesn't arise.

 

[PaulRainbow]

Actually Paul, I think I did mention the word "freezer" in the original post because it can be used as one, but we don't use it that way so the issue doesn't arise.

Ah, missed that Mark

 

[Refueler]

The device in post #2 does the job properly, has a 10a rating and costs less than a tenner, why would the OP want to mess around with headlamp relays ?

What about when charging comes from solar or shore power ?

By the way, no need for heavy current relays to control a fridge, just interrupt the thermostat connection.

That's interesting .... because if you go back in time .. I linked to same item many moons ago .... if I remember rightly about 2 years ago ?

In fact I linked to two items based on same tech : A charge controller and the second being the Battery Saver item you have linked to.

I had actually forgotten about them ... I have a bagful of them from Banggood at about 2 quid each.

Reason I have the relay - is that I fitted it many years ago before such cheap chinese controllers were available, I bought it over counter without any waiting. Never got round to swapping it out.

 

[Elemental]

By the way, no need for heavy current relays to control a fridge, just interrupt the thermostat connection.

I did think about doing it this way, but it means taking the fridge apart. Switching the power on and off will be easier to implement. The total current draw on both units seems to be about 7A so two of those you linked to should suffice.

 

[Refueler]

Just want to add one thought.

Any cut-in / cut-out switch whether solid state or not that is connected only to battery ... will have a standing current draw on the battery. Most are of course in mA ... so not a big deal. But some are higher and of course even small draw added to existing all adds up.

Its part of the reason I haven't got round to swapping out my car relay.

I have had times when my boat has had batterys drained even though moored at bottom of garden ... Gardener forgets to reconnect supply cable from house ... onboard items that have standing feed such as radio memory etc. have drained battery down to then not able to start engine. Luckily I have the second battery.

Just a comment to bear in mind.

 

[Elemental]

Just want to add one thought.

Any cut-in / cut-out switch whether solid state or not that is connected only to battery ... will have a standing current draw on the battery. Most are of course in mA ... so not a big deal. But some are higher and of course even small draw added to existing all adds up.

Its part of the reason I haven't got round to swapping out my car relay.

I have had times when my boat has had batterys drained even though moored at bottom of garden ... Gardener forgets to reconnect supply cable from house ... onboard items that have standing feed such as radio memory etc. have drained battery down to then not able to start engine. Luckily I have the second battery.

Just a comment to bear in mind.

I know. Our standing draw is currently around 500mA - enough to worry about after about a week or so. Also on the list are some solar panels to address that issue too...

 

[Refueler]

I know. Our standing draw is currently around 500mA - enough to worry about after about a week or so. Also on the list are some solar panels to address that issue too...

That's not so small an amount.

I have to admit that I am waiting for my boat to return from repairs - I then plan to build / fit a transom arch with solar .... that way I protect systems / batterys in case 'gardener' leaves boat unplugged again !