Low volt sensor for 12 volt cooler

Vics & PVB This is not a competition, so please do not try to score points I did not intend to promote ill feeling. I am just grateful for the help(y)
I will look at the 2 in the morning when i am less tired & order one or the other tomorrow.
But i will not tell you who won, to prevent cheering :LOL:

Thanks
 
Daydream believer said:
Vics & PVB This is not a competition, so please do not try to score points I did not intend to promote ill feeling. I am just grateful for the help(y)
I will look at the 2 in the morning when i am less tired & order one or the other tomorrow.
But i will not tell you who won, to prevent cheering :LOL:

Thanks
Click to expand...

;)
 
Daydream believer said:
Vics & PVB This is not a competition, so please do not try to score points I did not intend to promote ill feeling. I am just grateful for the help(y)
I will look at the 2 in the morning when i am less tired & order one or the other tomorrow.
But i will not tell you who won, to prevent cheering :LOL:

Thanks
Click to expand...

Sorry if you feel this is becoming a competition

I just don't believe that a VSR/ split charge relay has the right characteristics . They are designed to control the charging of a second battery. The KEMO device on the other hand is designed to disconnect a non essential load at a preselected voltage to avoid discharging the battery lower than you want.
A VSR typically disconnects at around 12.7 to 12.8 volts . (TEC3M ,12.9 volts) This will give you no scope to power your cool box from the battery because the relay will open almost as soon as charging stops. Assuming you have a decent sized domestic battery you should be able to run the coolbox from it for several hours without running it to anything like 50% discharged. Suppose you opted to stop at 20% discharged. The rested volts would be about 12.5 volts but the actual volts while on load would be somewhat lower. You could set the disconnect volts on the KEMO accordingly.

Pvb says that the TEC3M is adjustable but I cannot find any info on the range and so far pvb has not provided a link to any detailed technical information. Maybe the TEC3M will adjust sufficiently, maybe it won't. A figure somewhat less than 12.5 volts would be outside the range which I'd expect for a VSR.

If having no capability to run the cool-box with no shorepower or alternator charging suits you then by all means fit a VSR type of split charge relay. Perhaps the TEC3M will adjust to give you some such capability, but without some decent technical information you just don't know.
 
Going back to OP, starting the engine or mains charger, assuming the engine battery is okay, you will see a voltage of 13.6 volt, so a simple VSR will cut straight away. Once charge stops voltage will full and VSR will drop out isolating coolbox.

Brian
 
Daydream believer said:
That looks very easy to wire up but I am concerned that the cut OFF voltage can be set at 13 V. reading the note on ebay the cut off is much lower so battery wouold loose a lot of its amps before cut off-- Am I reading that right?
I did buy one of the relays you also suggested but then having done so I could not see how to use it or how to get voltage correct
Click to expand...

Hi DB ... if its the one I linked to - it should be capable of being adjusted from 9 to 15V ....

I have been meaning to fit one myself - that's why I have the link ... and if I did - of course I would meter the item on a first run to ensure I get setting right.

Of course PVB's single VSR if it can work in the battery feed to box is simpler ... than two items as I suggest.

I do not know the draw on your box ... but mine draws between 7 and 10A depending on ambient around ... and that was why I wanted alternator direct ... 10A needs reasonable cabling etc.

The relay operates on any voltage from about 10v up to 18v ... so it is not a shut off device ... That is why it is only controlling engine alternator power to the box. Once alternator starts charging - the relay clicks in ... alternator stops - relay clicks out.

I have a diagram of how to wire the relay somewhere ... will have to search through ...

But again - if you want to spend a bit more and simplify - - go the VSR route ... making sure of course the VSR is suitable rated shut off etc.
 
OK ... I hope this is the right one !!

relay-connectedcorrd-1.jpg

Basically the 'light' is the ignition LED and when alternator is not running has 12v passing through. It holds the contacts 30-87 open via solenoid 85-86. Once alternator starts charging - the voltage reverses on the 'light' and is zero at 85-86 ... the relay 30-87 contacts close and power is then fed to the box.
When alternator stops and voltage decays - the LED 'light ' is then on again .. feeds 12v to the solenoid opening 30-87 contacts... power is cut from box.

The LED light is of course wired to the exciter side of alternator to have that reversal of voltage.

The numbers are as per the terminals on the Land Rover Relay I used

NOTE : If anyone notes any connection error there - please post .. I know I had to alter something but it was years ago when I did it ...
 
All I did was to use an old mechanical tumble dryer timer switch installed in the system. Wind up for up to 2 hours or anything in between. Suitable for 10 amps or so. Also put a relay in the circuit that connected the unit up when the engine was running (ignition switch spare low amp connection for relay operation on/off circuit) so the coolbox ran all the time when engine running. Simple solutions
 
Refueler said:
OK ... I hope this is the right one !!

relay-connectedcorrd-1.jpg

Basically the 'light' is the ignition LED and when alternator is not running has 12v passing through. It holds the contacts 30-87 open via solenoid 85-86. Once alternator starts charging - the voltage reverses on the 'light' and is zero at 85-86 ... the relay 30-87 contacts close and power is then fed to the box.
When alternator stops and voltage decays - the LED 'light ' is then on again .. feeds 12v to the solenoid opening 30-87 contacts... power is cut from box.

The LED light is of course wired to the exciter side of alternator to have that reversal of voltage.

The numbers are as per the terminals on the Land Rover Relay I used

NOTE : If anyone notes any connection error there - please post .. I know I had to alter something but it was years ago when I did it ...
Click to expand...
With all due respect , that makes it so complicated.Plus I have a shore charger to consider.
I have 2 wires +ve & -ve . All I want to do is cut power when voltage drops below 13 V & switch it back on at 13.1 V. I do not want to run wires anywhere else. Just cut the 2 wires & insert a sensor. Why do I need to run wires back to the alternator & how will that tell when the shore charger is on?
 
johnlilley said:
All I did was to use an old mechanical tumble dryer timer switch installed in the system. Wind up for up to 2 hours or anything in between. Suitable for 10 amps or so. Also put a relay in the circuit that connected the unit up when the engine was running (ignition switch spare low amp connection for relay operation on/off circuit) so the coolbox ran all the time when engine running. Simple solutions
Click to expand...
So if the shore power is on & no engine running it only runs for 2 hours (or whatever) or not at all - is that what you are saying?
 
Daydream believer said:
With all due respect , that makes it so complicated.Plus I have a shore charger to consider.
I have 2 wires +ve & -ve . All I want to do is cut power when voltage drops below 13 V & switch it back on at 13.1 V. I do not want to run wires anywhere else. Just cut the 2 wires & insert a sensor. Why do I need to run wires back to the alternator & how will that tell when the shore charger is on?
Click to expand...


No worries....

In fact you don't need to run anything back to alternator if you have an ignition light ... that is your source for triggering the relay.

Your original post indicated you wanted power from engine or via battery subject to cut off.

For just the two wires ... then a voltage cut off as I linked to or a VSR will do it.

I would check carefully what amps your box pulls and I would be inclined to have a switch in the line unless you rely on the box plug ? Why ? The box could pull all or more than your charger puts out - then it will be dragging battery down anyway ... its also possible if your charger is a 'clever auto' unit - the fact box is now there could like the charger I used to have - cause charger to default off ...
I had to revert to an older dumb charger ...

I have the relay for the reason above ... my box takes up to 10A and I thought it better to get the power from alternator direct instead of from battery.
 
I have a mains/12V cool box. I always run it whilst still on mains or engine to get it as cool as possible. Then I use a cheap electronic thermometer (from Lidl or Aldi for about £5) to keep an eye on the temperature. The long lead means the display is under the sprayhood. When the temparature rises to 7C I turn the fridge back on until it drops to 3C. By doing this all day I use very little of the house batteries' capacity. They are constantly charged by a solar panel. Naturally as soon as I use the engine I turn the cool box on. I find this system simple and almost fool proof - unless the fool does not turn it off! The funny thing I have found is the coolbox I leave on overnight and it does not run continously, so it probably does not use as much power as I expect and never had flat batteries in the morning (2x 105Amp).
 
Concerto said:
I have a mains/12V cool box. I always run it whilst still on mains or engine to get it as cool as possible. Then I use a cheap electronic thermometer (from Lidl or Aldi for about £5) to keep an eye on the temperature. The long lead means the display is under the sprayhood. When the temparature rises to 7C I turn the fridge back on until it drops to 3C. By doing this all day I use very little of the house batteries' capacity. They are constantly charged by a solar panel. Naturally as soon as I use the engine I turn the cool box on. I find this system simple and almost fool proof - unless the fool does not turn it off! The funny thing I have found is the coolbox I leave on overnight and it does not run continously, so it probably does not use as much power as I expect and never had flat batteries in the morning (2x 105Amp).
Click to expand...


It does maje a big difference what type of box you have .... if you have the good Waeco box - it will vary its power draw depending on its internal temp ... but if you have the typical picnic coolbox as I have - it draws at minimum 7A and up to 10A ... with no stopping.

I have fitted a relay to avoid draining my battery too low due to its power consumption.

I too have a cheap Digi-thermometer ... the lead to the probe is thin enough - box lid can close on it without problem.
 
VicS said:
I just don't believe that a VSR/ split charge relay has the right characteristics . They are designed to control the charging of a second battery. The KEMO device on the other hand is designed to disconnect a non essential load at a preselected voltage to avoid discharging the battery lower than you want.
A VSR typically disconnects at around 12.7 to 12.8 volts . (TEC3M ,12.9 volts) This will give you no scope to power your cool box from the battery because the relay will open almost as soon as charging stops. Assuming you have a decent sized domestic battery you should be able to run the coolbox from it for several hours without running it to anything like 50% discharged.
Click to expand...

Read the OP again! He doesn't want to run the fridge off the battery, but only when either the engine's running or the mains charger is on. Some kind of VSR is ideal for this purpose, and the standard voltage settings will be perfect.
 
Refueler said:
No worries....

In fact you don't need to run anything back to alternator if you have an ignition light ... that is your source for triggering the relay.
I would be inclined to have a switch in the line unless you rely on the box plug ?
Click to expand...
Only 2 wires -No wires to ignition light- no ignition light anyway
Switched in 2 places as per my original post
 
Refueler said:
It does maje a big difference what type of box you have .... if you have the good Waeco box - it will vary its power draw depending on its internal temp ... but if you have the typical picnic coolbox as I have - it draws at minimum 7A and up to 10A ... with no stopping.

I have fitted a relay to avoid draining my battery too low due to its power consumption.

I too have a cheap Digi-thermometer ... the lead to the probe is thin enough - box lid can close on it without problem.
Click to expand...
I have a Waeco cool box, bought for that reason.
 
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