12V to caravan fridge

[Steam]

Is it normal for the 12 V light on my caravan fridge to go on and off at regular 15 second intervals whilst my car is idling ?

 

[birdman101]

Normally you will find it flashing is if the Smart Alternator has not cut in and charging. Switch your headlights on and see if it stays on and stops flashing. If it does this shows it is the voltage to low when the Alternator not charging. By putting the load of the lights on thus drawing more current activates the Alternator to work.

 

[RogerL]

It may be caused by a voltage sensing relay in the car's towing wiring which "chatters", ie alternates between on/off - often caused by wiring that's too thin for the loads involved.

A good auto electrician, not a towbar fitter, could resolve the issue by fitting heavy duty cable and a latching relay - but at significant cost.

 

[Steam]

Normally you will find it flashing is if the Smart Alternator has not cut in and charging. Switch your headlights on and see if it stays on and stops flashing. If it does this shows it is the voltage to low when the Alternator not charging. By putting the load of the lights on thus drawing more current activates the Alternator to work.

Ok thanks I will try this over the weekend. I tested the voltage output from the battery / alternator and it was 13.7 with the engine running and 12.4 with the engine off

 

[birdman101]

Alternator when charging should show 14.2 volts . When towing I plug a voltage gauge in cigar socket and this shows 14.2 volts and the fridge then operates. If for any reason the voltage reads lower then I know the fridge will not be running. I have towed for years with one of these plugged in.https://www.ebay.co.uk/itm/26619640...DG&stype=1&var=&widget_ver=artemis&media=MOREhttps://www.ebay.co.uk/itm/26429270...DG&stype=1&var=&widget_ver=artemis&media=MORE

 

[RogerL]

Alternator when charging should show 14.2 volts . When towing I plug a voltage gauge in cigar socket and this shows 14.2 volts and the fridge then operates. If for any reason the voltage reads lower then I know the fridge will not be running. I have towed for years with one of these plugged in.https://www.ebay.co.uk/itm/26619640...DG&stype=1&var=&widget_ver=artemis&media=MOREhttps://www.ebay.co.uk/itm/26429270...DG&stype=1&var=&widget_ver=artemis&media=MORE

That used to be true, but doesn't apply to cars with smart alternators, ie anything younger than about 20 years.

 

[birdman101]

That used to be true, but doesn't apply to cars with smart alternators, ie anything younger than about 20 years.

I am afraid you are incorrect. When a Smart Alternator is fully charging it will show 14.2 volts. Family been in motor trade all our lives and we do know motors, All my actual own cars have had Smart Alternators for last 20 years, and I tow between 9 and 10 months of the year.

 

[RogerL]

I am afraid you are incorrect. When a Smart Alternator is fully charging it will show 14.2 volts. Family been in motor trade all our lives and we do know motors, All my actual own cars have had Smart Alternators for last 20 years, and I tow between 9 and 10 months of the year.

Of course it'll show 14+V when charging - but it can also show 12v when it's in a non-charging mode, but with the engine running. - that's what makes it smart!.

 

[birdman101]

But if you read post the fridge will not run when the alternator is not charging as fridge relay will not cut in for the Element under 13.5 volts. Without the engine running a fully charged Battery will read 12.6 volts

 

[Steam]

Alternator when charging should show 14.2 volts . When towing I plug a voltage gauge in cigar socket and this shows 14.2 volts and the fridge then operates. If for any reason the voltage reads lower then I know the fridge will not be running. I have towed for years with one of these plugged in.https://www.ebay.co.uk/itm/26619640...DG&stype=1&var=&widget_ver=artemis&media=MOREhttps://www.ebay.co.uk/itm/26429270...DG&stype=1&var=&widget_ver=artemis&media=MORE

Thanks for the info based on your info I suspect my alternator is not giving the required voltage . I will be getting it checked out next week

 

[Steam]

But if you read post the fridge will not run when the alternator is not charging as fridge relay will not cut in for the Element under 13.5 volts. Without the engine running a fully charged Battery will read 12.6 volts

Well had my alternator tested and they said it’s fine running at 13.2 . Very occasionally it goes up to 14.1 . but obviously I can’t see what’s happening in the caravan when it goes up .

 

[birdman101]

Put your headlights on and see if I goes up to 14.2v. If it does then go in caravan with car still running. Fridge should then work. Then with fridge and headlights on get back in car and switch headlights off and fridge will still be going if voltage still shows 14.2 v. If this works you will have to get in habit of switching lights on each time before switching fridge on

 

[Steam]

Put your headlights on and see if I goes up to 14.2v. If it does then go in caravan with car still running. Fridge should then work. Then with fridge and headlights on get back in car and switch headlights off and fridge will still be going if voltage still shows 14.2 v. If this works you will have to get in habit of switching lights on each time before switching fridge on

Ok thanks will try this next week

 

[Steam]

Ok thanks will try this next week

Turned headlights on and voltage stays at 13.2 v so I guess it won’t activate the relay fully as like you said it needs 13.5 v . So maybe have to see an auto electrician

 

[RogerL]

Turned headlights on and voltage stays at 13.2 v so I guess it won’t activate the relay fully as like you said it needs 13.5 v . So maybe have to see an auto electrician

There's almost always some voltage drop between alternator and caravan fridge, made worse if the wiring is too marginal.

Anyway 13.5v sounds too low for an alternator which is charging the car battery - I'd expect 14.4 -14.8v.

 

[birdman101]

Myself and family have been involved in motor trade for years,all makes of cars , . and all when on full load you expect 14.2 volts. What car do you have and where are you measuring the car voltage. You need to go direct on Battery terminals. Without car running good Battery will be 12.6 volts. Then start car and put some load on such has main headlights and the expect 14.2 volts. If not there is a problem. If 14.2 volts, but at towbar with lights still on there is below around 13.8v then the wiring through the car is to thin. If 13.8 or lower by the time you have any further voltage drop when reaching the fridge it will not operate.
I don’t know your abilities ,but if you can do a test yourself if you do not see the required voltage,disconnect the Battery monitor and see if voltage rises. If it rises it may be the diagnostics needs plugging in and it may be the charging voltage is set to low.