Fridge performance 12v vs 240v

demonboy

demonboy

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Can anyone tell me why both my fridges cut off at the desired temperature when on shore power but do not when on 12v? They've been like this since I've had the boat but never bothered to ask. They are standard Danfoss compressors and both thermostats have been replaced.
 
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1) The stats control the 240v power not the 12v power so on 12v they run non-stop?
2) Who ever fitted them didnot wore them up correctly
3) On 12v they do not get down to set temperature
 
cliff said:
1) The stats control the 240v power not the 12v power so on 12v they run non-stop?
2) Who ever fitted them didnot wore them up correctly
3) On 12v they do not get down to set temperature
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No, on 12v they DO get down to the set temperature, but then they continue to get colder. If I don't turn them off manually they freeze everything.

They run at 4amps each, batteries just 2m away. Cable is sufficient (guessing 10mm2?).
 
Thats weird. If they are like mine, then they are running on a nominal 12v circuit all the time and the only difference is that when you are on 240 v shore power, the battery charger is charging the batteries and raising the 12v circuit voltage to somewhere between 13.4v and 14.5 volts. I cannot see why a higher circuit voltage would stop the thermostats from working when you are saying the fridges clearly get down to temperature.

Initially I did wonder if your fridges had a dual 240v ac and 12v dc operation, but that would require two different compressor motors and would seem a daft way to do things. If indeed this is the way they operate then either there are two thermostats to each fridge with one not working or there is complicated circuitry to allow one thermostats to control both 240v and 12 v and that isnt working.

Try Danfoss.
 
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I don't doubt it's true but I cant understand the thinking that leads to not having thermostatic control when running off the battery.

My 12V only fridge certainly has thermostatic control. I can hear the fridge cut in and out. So thermostatic control on 12V DC is certainly possible. And it chills the wine/beer perfectly well.
 
nigelmercier said:
I assume that this is the case, from reading the OP. There is an adaptor box that provides 27V when there is mains present, or the battery feed if not.

Like this: http://www.dometic.com/enuk/Europe/...ystems/Adapters/Products/?productdataid=98915
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Then you've misunderstood, my apologies. It is a basic Danfoss 12v fridge. When plugged into shore-power it is still running off 12v. I can't see how a simple wiring error could cause this kind of behaviour, unless the wire to the thermostat is too thin, and only works with the help of a full charge coming from shore-power.

I find it curious that stuey_two says fridges in caravans behave in the same way. I think I need to contact Danfoss directly and ask this question.
 
So what you are saying is that when the battery voltage is high and under charge, the fridges switch on and off with the thermostat; but when the battery voltage is lower and not under charge, they keep running continuously and freeze the contents? This is counter-intuitive, so I'm at a loss to explain it. It would still be worth checking the connections on the control unit against the manual.

When you do contact Danfoss, don't mention shore-power, it confuses the issue.
 
nigelmercier said:
On shore power they run at 24V, well my similar model does.

Possibly your cables are not fat enough, and you are getting a voltage drop. What is the length and approx. cable size?
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Interestingly - if you look - you'll find ALL Danfoss units run on 230v ac. Those in boats have a (Danfoss-supplied) solid-state inverter which copes with 24 or 12v dc supply.

Your reply leads me to believe you have a 24 volt supply on your boat - in effect when on shore mains supply the units still work off the dc circuit, so you are quite right.

If both the OP's units have the Italian ASU-Isotherm control, what he's seeing is the supercool phase coming in as his charger gets the system volts above 13.5-13.8 volts. This means that the fan starts up and the thermostat cut off on the holding plate is lowered to -14C instead of 4C before the compressor cuts out.
 
charles_reed said:
Interestingly - if you look - you'll find ALL Danfoss units run on 230v ac....
Your reply leads me to believe you have a 24 volt supply on your boat ...
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I had figured that an inverter was involved, you don't happen to know the pinouts of the control box output? I've got one I salvaged from a faulty unit and I'd like to test it.

I do have 24V on my boat, but it is not connected to the fridge. The box I linked to in post #9 has two inputs (12V, 230V) and one output (12V/27V). If mains is present, it generates 27V, if not, it passes through the 12V. The control box on the fridge sorts it out.
 
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nigelmercier said:
Fixed link: http://www.novakool.com/support/documents/R134a_12-24V_DC_11-01_Cn46c702.pdf

I might help the OP, but there are several different models of control box.

Unfortunately it doesn't give the pinout of the output connector.
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I've got the Danfoss fitting instructions back on the boat and that gives both pin outputs and dip-switch settings - unfortunately the boat is 1883nm away on great-circle route...

Try this download site your unit is probably the 010N07**

http://www.secop.com/technical-literature/electronic-units-instruct.html
 
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Mr Reed is correct, all Danfoss run on 230 V and a solid state inverter.

It is that inverter that is responsible for the so difficult to get rid off interference on short wave radio´s.

No idea what causes Mr Demonboy´s problem, there is more.
A lot of modern equipment such as tablets take for ever to charge over an inverter.

12V to 230V, than in the tablets charger to 5 V again. Tablets charger gets extreme hot.
So the inverters 230 V is not perfect enough. Spiky.
 
stuey_two said:
Dometic fridges in caravans do this as well, thermostatic control when running on mains or gas but no control when using 12v.
It's a pita.
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Isn't that just on the absorption ones not compressor models? (Only absorption ones can run on gas!)
If I remember rightly, on mains you have about a 200W heater element and a 'stat, on 12V it's a 95W element and no stat., it's only intended for use when towing not static.

Not a comparison for demonboy's problem therefore.
 
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