Solar power to fridge issue

[Jayse134]

Just bought a motorhome with solar power already fitted with a controller but never connected to anything except the TV. What I wanted to do with the load leads was to connect to the 12V supply on top of the fridge to power that, as the 12v supply from the engine only works when the engine is running. however if I put the solar pos and neg leads to the fridge the caravan style distribution panel doesn't like it at all (either switched on or off) and clicks away. is there a simple solution to this or do I need to isolate leisure 12v from the solar 12v altogether for the fridge. I only want solar on the fridge when we are out and about during the day so the I want to continue with engine 12v when driving but solar for the few hours we may stop. obviously gas/240v when on on sight.

why are the simple things always the most difficult!

 

[ProfJohnL]

Hello Jayse,

Welcome to the forum.

I suspect your problem is more likely to be the solar panel is not powerful enough to run the fridge. Most fridges in caravans and motorhome have three way powering options to cool the fridge. the 12V cooling usually requires 8 to 10A of DC current (100 to 120W,) which the engine is very capable of providing, but a solar array would have to be able to provide that amount of current to make it work. The 12V cooling is only normally used when the engine is running such as driving to your holiday site,

Generally if you are sited "off grid" (no mains power) it is expected you would run the fridge on gas. Trying to run it on 12V will flatten your leisure battery in a matter of a few hours.

(Edit)P.S. A solar panel would not work overnight anyway.

 

[Buckman]

Prof is correct as ther is no ways a solar panel unless it is very large will power a fridge. Fridge is designed to work on 12v when it has a constant 12v and then it only maintains the temperature and does not cool down the fridge. On a hot sunny day probably no chance of cooling down the fridge below the ambient temperature. Why not use gas?

 

[RogerL]

Prof is correct as ther is no ways a solar panel unless it is very large will power a fridge. Fridge is designed to work on 1w2v when it has a constant 12v and then it only maintains the temperature and does not cool down the fridge. On a hot sunny day probably no chance of cooling down the fridge below the ambient temperature. Why not use gas?

Caravan fridges are usually rated at the same or similar power for 12v, 230V and LPG - but many car have wiring which cause voltage drop, reducing power.

 

[ProfJohnL]

Fridge is designed to work on 1w2v when it has a constant 12v and then it only maintains the temperature and does not cool down the fridge.

This above is not true, and it has been explained many times previously.

As Roger L states, the power of the 12V system is roughly the same as the 230V mains system and can provide a similar amount of cooling effect to the fridge. However the 12V system is only usually active when the caravan is being towed, and the windage around the fridge's ventilation slots can compromise the refrigeration effect. But if it's stationary the 12V system is still live it will provide similar cooling performance to mains or gas.

In fact the mains and gas systems are thermostatically controlled so it they tend to turn off/down when the fridge is cold enough, where as the 12V is not thermostatically controlled so in theory it could cool further than the mains, but because the engine is turned off soon after being towed its not its generally seen to cool the fridge further.

 

[Buckman]

This above is not true, and it has been explained many times previously.

As Roger L states, the power of the 12V system is roughly the same as the 230V mains system and can provide a similar amount of cooling effect to the fridge. However the 12V system is only usually active when the caravan is being towed, and the windage around the fridge's ventilation slots can compromise the refrigeration effect. But if it's stationary the 12V system is still live it will provide similar cooling performance to mains or gas.

In fact the mains and gas systems are thermostatically controlled so it they tend to turn off/down when the fridge is cold enough, where as the 12V is not thermostatically controlled so in theory it could cool further than the mains, but because the engine is turned off soon after being towed its not its generally seen to cool the fridge further.

So for these years my fridge has been faulty and the dealer has been wrong and talking nonsense?

 

[otherclive]

So for these years my fridge has been faulty and the dealer has been wrong and talking nonsense?

It wouldn’t be the first time a dealer has been found wanting.

 

[Buckman]

It wouldn’t be the first time a dealer has been found wanting.

Our fridge does not cool down on 12v, but does keep it at the same temperature for the duration of the trip whether 4 or 5 hours. Definitely will not freeze anything, but will keep frozen foods solid.
I thought it was the amp and not the 12v that counted towards it cooling and I am not sure what sort of amp a solar panel will generate.
I assume that the tech when they fitted the electrics for the towbar fitted the correct wiring for the fridge. We have not used the 12v for quite some time, but taking into account this thread, we will be doing so tomorrow on our trip up the M5.

 

[RogerL]

Our fridge does not cool down on 12v, but does keep it at the same temperature for the duration of the trip whether 4 or 5 hours. Definitely will not freeze anything, but will keep frozen foods solid.
I thought it was the amp and not the 12v that counted towards it cooling and I am not sure what sort of amp a solar panel will generate.
I assume that the tech when they fitted the electrics for the towbar fitted the correct wiring for the fridge. We have not used the 12v for quite some time, but taking into account this thread, we will be doing so tomorrow on our trip up the M5.

It generally takes 24 hours on 230V to bring a fridge down to temperature - it's not a like comparison to expect 12v to get down to the same temperature during a journey of a few hours - caravan fridges generally aren't designed to freeze food down from ambient, only maintain already frozen food.

Sadly, the technical ability of towbar fitters varies considerably, even among specialist towing businesses.

 

[Buckman]

It generally takes 24 hours on 230V to bring a fridge down to temperature - it's not a like comparison to expect 12v to get down to the same temperature during a journey of a few hours - caravan fridges generally aren't designed to freeze food down from ambient, only maintain already frozen food.

Sadly, the technical ability of towbar fitters varies considerably, even among specialist towing businesses.

Apologies for not making it clear. We cool down the fridge to maximum before a long journey i.e. travelling to port, trip to continent and then the drive to the site.

 

[Challenger]

So for these years my fridge has been faulty and the dealer has been wrong and talking nonsense?

No . You have been trying to use it in a way for which it was never designed. A fridge will use about 8 amps on 12 v. Can you find a solar panel that will supply that ? As mentioned previously, it would flatten a leisure battery in very short order !

 

[Buckman]

No . You have been trying to use it in a way for which it was never designed. A fridge will use about 8 amps on 12 v. Can you find a solar panel that will supply that ? As mentioned previously, it would flatten a leisure battery in very short order !

I was refering to the 12v when connected to the car. The OP wants to run the fridge only off solar panel which I doubt can happen.

 

[ProfJohnL]

Our fridge does not cool down on 12v, but does keep it at the same temperature for the duration of the trip whether 4 or 5 hours. Definitely will not freeze anything, but will keep frozen foods solid.
I thought it was the amp and not the 12v that counted towards it cooling and I am not sure what sort of amp a solar panel will generate.
I assume that the tech when they fitted the electrics for the towbar fitted the correct wiring for the fridge. We have not used the 12v for quite some time, but taking into account this thread, we will be doing so tomorrow on our trip up the M5.

Apologies for not making it clear. We cool down the fridge to maximum before a long journey i.e. travelling to port, trip to continent and then the drive to the site.

When fridges cool down the temperature initially falls quickly but the rate of change reduces as the temperature difference to the ambient increases, In fact the rate of change is an exponential pattern. In addition most fridges do have a limit to the temperature difference they can create due to the formulation of the refrigerant gas they use, so most fridge manufacturers will quote a maximum temperature difference relative to ambient.

If you have pre cooled the fridge before connecting the 12V supply, then even though the 12V systems may have some capacity to further cool the fridge, it may only be a few degrees cooler at best depending on the ambient conditions and it would take considerably longer to cool the last few degrees than it does to drop the first few degrees.

But as soon as the caravan is in motion the air flow around the fridge caused by towing aerodynamics will disturb the effectiveness of the cooling system and it may prevent any further temperature reduction. It's all very installation dependant, so some installation's may be better and some worse.

The combination of the exponential cooling curve, and motion air flow disturbance and the limited time of operation on 12V power (basically only whilst towing) may prevent the 12V operation from producing any significant additional cooling. But if the fridge were stationary and operated on 12V with an adequate 12V supply, it would demonstrate very similar performance to either mains or gas operation.