Silly question time

[Steve1962]

Today’s silly question(s). If I plug my caravan in to mains at home, prior to travel, then use battery to maintain the fridge temp whilst driving:


1) is it the car or the caravan battery maintaining the fridge temp?


2) if car battery, when we make a number of stops (travelling quite a way), will it drain my car battery?





Whenever we’ve done this previously, the fridge isn’t remotely cool so what am I doing wrong?

Thanks
Steve

 

[otherclive]

When coupled to the car it’s the cars system providing power via the caravan 12v system. When car engine is turned off no power to the fridge. Modern cars smart alternators can be problematic. When stopped and engine switched off the caravan will not drain the car battery.

I would pre cool the fridge using home 240v prior to setting off, then fill fridge either cold/ frozen stuff and it would stay okay during a days driving.

 

[otherclive]

This PC article explains some of the issues concerning you.

https://forums.practicalcaravan.com/threads/cooling-fridge-question.61768/

 

[RogerL]

Assuming you've pre-cooled the fridge on mains for 24 hours it's the car's alternator output being used to keep the fridge cool. The car battery won't be used during stops as the fridge isn't powered then, unless you switch to gas.

Almost all modern cars have "smart" alternators which cut the charging output to reduce fuel and some aren't good at over-riding that when towing, even if fitted with the car maker's towing electrics.

 

[JTQ]

Can I just add*, my experience is the cooling you will achieve on route is at best marginal.

The reason why is that the voltage drop in the wires right through from the alternator to the fridge's element are almost certainly going to be significant, typically the car and caravan industry don't put in the thickness of cables it really needs for this task.

In respect to the car's wiring that is not surprising as it tends to be just a UK thing, so cars typically are not wired up adequately to do this heavy duty task. Low voltage to the fridge, lower cooling performance achieved.

Adding to the issue is that with smart alternators they try to limit the power being drained off the engine to drive the alternator, so when the car's battery is back charged the voltage from the smart charging system can back off, adding to the even lower voltage the fridge will get.

I suspect along with many I take the view anything is better than nothing but I am not convinced there is a great deal of benefit actually gained.

Edit* being typed so not then aware others had already made much the same point.
This fridge feature comes of more use in motorhomes where the better converts can wire it up for the job it needs to do.
I would also add that stocked with well cooled or even frozen stuff our fridges make pretty good cool boxes without the need to be powered. Five or six hour ferry crossings, where no powering happens have never presented us with an issue.

 

[Dustydog]

As all above plus the caravan leisure battery is not connected at any time to the 12v cooling.

 

[Sam Vimes]

Ooh ooh please Miss/Sir I know this one.

My Dometic Fridge senses the 12v level and if it's too low it doesn't work. With my Smart Alternator, the normal 12v varies from over 14v to just under 12v at the caravan connector. The fridge needs a hefty current to keep it cool and the voltage drop down the wires is significant enough to cause the fridge to 'switch off' when the Smart Alternator drops the voltage.

It puzzled me a first because we'd stop after a few miles from home to check if the caravan was still there 😁 and sometimes the fridge was on, other times it was off. I got the tow bar installers to check the wiring and you could see their test rig dropping out and in on the 12v as the Smart Alternator did it's thing.

Not all Smart Alternator systems are the same and may not exhibit the same issues. Equally not all fridges may be the same.

Don't get me started on charging the leisure battery when driving 🙄.

These days we turn the fridge on for 24hrs before setting off, disconnect the leisure battery and everything stays cold in the fridge anyway.

 

[Hutch]

As all the above-mentioned factors,
But when first at home, I use gas to chill the fridge down first( that way I know the fridge is working on gas) then I switch to mains for several hours , then Mrs fills the fridge with supplies. .

 

[Buckman]

Today’s silly question(s). If I plug my caravan in to mains at home, prior to travel, then use battery to maintain the fridge temp whilst driving:


1) is it the car or the caravan battery maintaining the fridge temp?


2) if car battery, when we make a number of stops (travelling quite a way), will it drain my car battery?





Whenever we’ve done this previously, the fridge isn’t remotely cool so what am I doing wrong?

Thanks
Steve

If you have a car with a Smart alternative that is probably the reason why the fridge never gets cold. A workaround is to turn on the car headlights.

 

[birdman101]

When towing I put a plug-in voltage meter in the 12 volt cigar lighter socket and that shows 14.2 volts with fridge on and Alternator charging. If this ever dropped the voltage I would know the fridge was off.

 

[Buckman]

When coupled to the car it’s the cars system providing power via the caravan 12v system. When car engine is turned off no power to the fridge. Modern cars smart alternators can be problematic. When stopped and engine switched off the caravan will not drain the car battery.

I would pre cool the fridge using home 240v prior to setting off, then fill fridge either cold/ frozen stuff and it would stay okay during a days driving.

Sent you a PM.

 

[Mr Plodd]

I have travelled, via ferry, to Spain having packed my fridge with pre-cooled food and a 2 litre bottle of frozen water. The contents were still cold and frozen food still frozen apart from the ready meal at the front of the ice compartment which we knew would defrost so scheduled that to be our first meal on arrival.
Caravan fridges on 12v are pretty much of a joke at the best if times. I have never even bothered to switch to 12v when travelling.
Others do the same so don't get stressed about it.

 

[Mr Plodd]

If you have a car with a Smart alternative that is probably the reason why the fridge never gets cold. A workaround is to turn on the car headlights.

Doesn't work if you have LED headlights, they don't draw enough current.

 

[Dustydog]

And no one is going to use their heated seats whilst it’s 30 deg + outside😎

 

[Buckman]

And no one is going to use their heated seats whilst it’s 30 deg + outside😎

Using the air con probably a better idea?

 

[IanB1485]

You can fit ( if its a real problem ) a voltage booster , this is basically a 12V D.C to 14.2V D.C converter and wire it into the fridge supply wires either in the car or caravan. this will boost the power to the fridge's 12V heater and ensure the fridge works at peak efficiency ( well as far as it can on 12V ). As it takes more current from the car's systems it will fool a smart alternator due to the increased load and the alternator will carry on working and it overcomes the voltage drop in the wires .Or you can , like most of us do pre-cool the fridge prior to a trip and then load it up with frozen food or as we do , pack pre-frozen freezer blocks around the food. (water has a huge thermal capacity compared with air) . domestic freezers run at about -20 Deg C ( three star) which will keep most frozen foods good for 3 months , as caravaners we usually don't require that longevity so even slightly frozen food will usually keep for the duration of the holiday. I also have an electric cool box which is also packed with pre-frozen freezer blocks.

 

[Mr Plodd]

Using the air con probably a better idea?

Aircon uses an engine driven compressor, so no additional electrical load, so unlikely to work.

 

[Tobes]

Aircon uses an engine driven compressor, so no additional electrical load, so unlikely to work.

I would turn on my cooled seat, which has an electric fan, but my AC runs from an electric pump motor, so I wouldn't need to, but I don't have an alternator, just a DC DC converter. I'll shut up...

 

[Dustydog]

Using the air con probably a better idea?

Mr Plodd beat me 😉

 

[Dustydog]

I would turn on my cooled seat, which has an electric fan, but my AC runs from an electric pump motor, so I wouldn't need to, but I don't have an alternator, just a DC DC converter. I'll shut up...

Could you use an inverter and go on 230v😉

 

[Tobes]

Could you use an inverter and go on 230v😉

Haha! With the right tow car (not mine) they have a 3pin 13A socket in the rear seat area. With the right extension lead out the boot and in through the front window, you could run the fridge via 230! (Note - don't do this - it's just a joke) (Also note, when on a non-hookup site you absolutely can do this via the V2L adapter!)

 

[Sam Vimes]

There are many implementations of smart alternator systems. Some are clever enough to know there's a load on the rear and stop the 'smart function' Others can be overridden by turning on lights or air con, or other electrical systems. None of those work for me.

Some cars can have the EMU modified when installing the tow bar wiring harness. Not mine.

I recall it was Sargent that recognised this as a problem and produced a DC-DC converter to get the volts back up to nominal for the on board caravan systems.

It may not be the Smart Alternator that's at the root of the problem. Some people have reported bad wiring in the caravan and towing harness where poor or insufficient 0V returns have been used resulting in larger than expected voltage drops.

 

[Sam Vimes]

I should have said Sterling Power not Sargent.

This video outlines the problem.

View: https://m.youtube.com/watch?v=JsMuXScOBWw

 

[Martin_E]

And no one is going to use their heated seats whilst it’s 30 deg + outside😎

I use my heated seat even when we have temperatures like today, it helps my back no end