Low volt sensor for 12 volt cooler

Daydream believer

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I have a standard set up with domestic battery bank & a starter battery seperated with a cyrix battery combiner. Shore power triple stage charger plus charging from standard volvo engine alternator.
When I bought the boat I made the mistake of not having a fridge & the option of fitting one is now long since dead.
I have decided to fit a 12 volt cool box. It does not have a 240 volt option
I have wired it to the fridge wiring loom that was installed by the boat builder but never used. It is controlled from a switch on the switch panel
I have fitted a cigar socket & the cool box is fed from this socket.
The cool box has an on off switch. The cigar socket can be disconnected.The cool box will stay cool for 6-8 hours if the lid is not opened so will serve my purpose.

My problem is, that if I sail with the cool box turned on, I will flatten the domestic bank quickly, unless running the engine.
if in port & I leave the boat plugged to shore power with the cool box on & go out for the day & someone disconnects my power lead, or there is a power cut( quite possible) I will come back to a flat battery.
I want to be able to turn the box off without having to remember & leave maximum amps for the usual sailing electronics. I want it to turn on automatically when voltage exceeds 13 V ie when engine running or shore power charger on.
is there something that i can put into the line just before the cigar socket that senses the voltage & will disconnect/reconnect it at 13 V?
If there is something I do not want one that lets the batteries go down to 50% or less leaving batteries discharged first. I do not/will not have other means of charging, ie solar cells etc.
How do forumites manage fridges on their boats please?
I might add that i am not particularly competent with an understanding of electrics.
Thanks
 
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I fitted a common headlamp relay that triggers once alternator starts charging ... that way I cannot flatten battery.

Example : 12V 80A 40A Automotive 5Pin Car Headlight Starter Auto Relay Waterproof Common | eBay

If I want to run when engine is off - I have manual switch I can over-ride the relay.

You can find stand alone voltage cut-offs on Banggood and other similar stores to put in the manual switched line and most are user settable to the voltage you decide.

or this : 12V Battery Low Voltage Cut off Switch Controller Excessive Protection Module | eBay
 
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Also called a split charge relay such as Victron Cyrix-CT or Durite 0-727-33. Rather overkill for a fridge as rated at more than 100amps. A cheaper variety is sold by caravan suppliers such as Towsure (£9.95)
 
Also called a split charge relay such as Victron Cyrix-CT or Durite 0-727-33. Rather overkill for a fridge as rated at more than 100amps. A cheaper variety is sold by caravan suppliers such as Towsure (£9.95)

Yes, a caravan split charge relay would be cheaper, although they often don't quote specific connect/disconnect voltages. The TEC3M is often seen.

Towbar electrics Charge relay TEC3M
 
I thought DB wanted both power from alternator and possibility to run from battery without draining battery past reasonable level ..

The relay and cut-off as I suggested giving both possibilities of power all come to less than the caravan relay - which only provides power when alternator is running.
 
And your cheaper suggestion? (Apart from a caravan relay which is linked in post 5).

12v relay ... $3 incl shipping

User settable voltage cut off .... $5 incl shipping.


See my previous post for links ... but they are available in highstreet shops ...

Lets say $1 for a switch to manually power up ..... total $9

As I said - cheaper than the relay only caravan job ... which in reality is no different to the relay I suggest ... is £9.95

How much for your VSR ?
 
12v relay ... $3 incl shipping

User settable voltage cut off .... $5 incl shipping.

Lets say $1 for a switch to manually power up ..... total $9

How much for your VSR ?

Well, the link in post 5 said £8.99 and it's completely automatic, no need for switches.

Remember, the requirement in the OP was specific - "I want to be able to turn the box off without having to remember & leave maximum amps for the usual sailing electronics. I want it to turn on automatically when voltage exceeds 13 V ie when engine running or shore power charger on. Is there something that i can put into the line just before the cigar socket that senses the voltage & will disconnect/reconnect it at 13 V?"
 
I have a standard set up........................
I have decided to fit a 12 volt cool box. It does not have a 240 volt option

My problem is, that if I sail with the cool box turned on, I will flatten the domestic bank quickly, unless running the engine.

I want to be able to turn the box off without having to remember & leave maximum amps for the usual sailing electronics. I want it to turn on automatically when voltage exceeds 13 V ie when engine running or shore power charger on.
is there something that i can put into the line just before the cigar socket that senses the voltage & will disconnect/reconnect it at 13 V?
If there is something I do not want one that lets the batteries go down to 50% or less leaving batteries discharged first. I do not/will not have other means of charging, ie solar cells etc.

I think you will find that the KEMO battery guard module, M148A, is just what you are looking for

Cheaper than a VSR and with an adjustable cut off voltage (10.4 to 13.3)

KEMO 148A Battery Guard but shop around you may find a better price
 
Well, the link in post 5 said £8.99 and it's completely automatic, no need for switches.

Remember, the requirement in the OP was specific - "I want to be able to turn the box off without having to remember & leave maximum amps for the usual sailing electronics. I want it to turn on automatically when voltage exceeds 13 V ie when engine running or shore power charger on. Is there something that i can put into the line just before the cigar socket that senses the voltage & will disconnect/reconnect it at 13 V?"

My relay does EXACTLY what he wants from engine ... it only powers when alternator cuts in ... powers off when alternator stops ...

As to price .... I took the price from post #4 ... because I was not going to click on your link ..... which STILL is more than my $9 all in ...

And for safety - I prefer to have a switch to be sure its OFF .. and no fault can do otherwise.
 
With either the Kemo or the tec there are several terminals. the kemo has an adjustable voltage which may be better as reading the reviews a customer has had a problem with switching on the tec. Also the tec has wierd wiring configuration I would have no idea what the writing on the terminals means.
Vic. With the Kemo is it just a case of putting the -ve & +ve in on 2 of the terminals & the same out on the other 2 tearminals . Or is it a bit more complicated with further wiring?
 
My relay does EXACTLY what he wants from engine ... it only powers when alternator cuts in ... powers off when alternator stops ...

As to price .... I took the price from post #4 ... because I was not going to click on your link ..... which STILL is more than my $9 all in ...

And for safety - I prefer to have a switch to be sure its OFF .. and no fault can do otherwise.

You perhaps haven't fully grasped the OP's requirement. He also wants something which automatically connects the fridge when the battery charger is connected to shorepower.
 
With either the Kemo or the tec there are several terminals. the kemo has an adjustable voltage which may be better as reading the reviews a customer has had a problem with switching on the tec. Also the tec has wierd wiring configuration I would have no idea what the writing on the terminals means.
Vic. With the Kemo is it just a case of putting the -ve & +ve in on 2 of the terminals & the same out on the other 2 tearminals . Or is it a bit more complicated with further wiring?
4 terminals
Positive ( with fuse) and negative in.
Positive and negative out

http://www.farnell.com/datasheets/1714756.pdf
 
With either the Kemo or the tec there are several terminals. the kemo has an adjustable voltage which may be better as reading the reviews a customer has had a problem with switching on the tec. Also the tec has wierd wiring configuration I would have no idea what the writing on the terminals means.
Vic. With the Kemo is it just a case of putting the -ve & +ve in on 2 of the terminals & the same out on the other 2 tearminals . Or is it a bit more complicated with further wiring?

The TEC3M is also adjustable for voltage, although as standard it connects at 13.5v and disconnects at 12.9v. You'd wire the fridge to terminal 2. Wire the positive feed to one of the 12v input terminals and the negative feed to both the Earth terminal and the fridge.

Screenshot 2020-02-18 at 21.16.19.png
 
I think it's still pricier than the TEC3M.

At what voltage does the TEC3M cut out ?
Is it adjustable? If so over what range.
At what voltage does in cut in again

I have not managed to find the full technical data which I would want to read before choosing it................ Got a link?
 
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