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Power consumption of 12v fridge


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  • 3 years later...
On ‎16‎/‎05‎/‎2016 at 18:25, Alan de Enfield said:

 

No - your fridge uses 2x the amps that your TV uses, the difference is the time run.

If your fridge really is 90 watts then its drawing 7.5 amps

The TV at 45 watts is drawing 3.75 amps

 

The TV runs continuously, and uses 7.5Ah

The fridge switches on and off every 15 - 20 minutes. 20 minutes off, 20 minutes on, 20 minutes off, 20 minutes on so is only running about 1 hour in 3. so as an average is only 2.5Ah

 

 

I am really doubting the 300wH a day that the fridge data plate is quoting - this would be with the 220v compressor. We have no idea what the 12v compressor (if it is fitted with one) is drawing.

Alan, please help me out here. The data plate on my fridge says 120 watt / 220-240 volt. I'm running the fridge direct from my 24 volt battery bank. Does it mean the fridge draws 5 amps whenever the compressor is running?

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19 minutes ago, cutandpolished61 said:

Alan, please help me out here. The data plate on my fridge says 120 watt / 220-240 volt. I'm running the fridge direct from my 24 volt battery bank. Does it mean the fridge draws 5 amps whenever the compressor is running?

 

 

No, it means the people who converted your fridge to 24Vdc didn't bother to remove the old, redundant and now-incorrect data plate.

 

You need to look at the manual for the 24Vdc compressor that's been fitted to convert it. Probably a Danfoss. Have a look at the data label on the compressor in particular to identify it, then google the manual for the compressor. This should tell you the current when running. 

 

 

 

Or, just turn the fridge ON and look at your ammeter!

 

 

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41 minutes ago, cutandpolished61 said:

Alan, please help me out here. The data plate on my fridge says 120 watt / 220-240 volt. I'm running the fridge direct from my 24 volt battery bank. Does it mean the fridge draws 5 amps whenever the compressor is running?

See if thsi helps.

 

I am looking in my Danfoss (the 12/24V compressor) manual and the current quoted at 24 volts is anything between 0.75 amps and 3.25 amps depending upon the RPM the motor is set to run to (jump lead on control box I think) and the temperature but I am not sure if that is cabinet temperature or ambient temperature. You can see that no one can answer your question with any certainty apart from ignore that label. Even if you measure the current you still have to guestimate how long per day the motor runs.

 

Across many boaters a consumption of between about 35 and 50 Ah per day seems about correct - again depending upon fridge setting and ambient premature - oh plus how well the boat's fridge cavity is ventilated.

 

 

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Sad I know …………...

 

I have actually timed the duration of my fridge on / off.

It runs approximately 1/3 of the time (during the day, and presumably less at night) 

It will vary tremendously depending on the temperature setting, the ambient temperature, how much 'stuff' is in the freezer / ice box, and the number of times you open the door.

 

Mine use between 30Ah and 35Ah

 

I have the Waeco CR80 which is quoted as 40W average.

 

 

Screenshot (127).png

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1 hour ago, cutandpolished61 said:

Alan, please help me out here. The data plate on my fridge says 120 watt / 220-240 volt. I'm running the fridge direct from my 24 volt battery bank. Does it mean the fridge draws 5 amps whenever the compressor is running?

Could cutandpolished mean that he is running his 240V fridge direct from his 24 V batteries via his inverter? In which case he may well be running at 5A. My 240V fridge takes circa 4A with the compressor running.

I agree, the way to see how much current is using is to look at the battery monitor.

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23 minutes ago, Alan de Enfield said:

Sad I know …………...

 

I have actually timed the duration of my fridge on / off.

It runs approximately 1/3 of the time (during the day, and presumably less at night) 

It will vary tremendously depending on the temperature setting, the ambient temperature, how much 'stuff' is in the freezer / ice box, and the number of times you open the door.

 

Mine use between 30Ah and 35Ah

 

 

I timed my 240 volt fridge as well, I just connect an hour counter across the compressor motor. But I didn't do it under test conditions, ie. the fridge was in use. I did publish them before as I tried fitting extra insulation and a fan at the back. I came to the conclusion that the thermostat is not actually a stat at all but a timer, because as I improved things the fridge got colder.

This is what I posted before :-

 

I have been running another set of tests on our 240 volt fridge. The fridge runs via a Mastervolt Mass Sine 24/1500 and all current readings are take from a Sterling Battery Management unit.

The inverter + Fridge + fans =3.5 amps
The Inverter + Fridge = 3.4 amps
The Inverter = 0.4 amps           

I have connected a RS hour meter across the refrigerator compressor to record compressor run hours.
The refrigerator is a LEC Elan and sits under a worktop with 25mm air gap each side and 50mm between the top of the refrigerator and the underside of the work top. The air space behind the refrigerator is well over the recommended space as the hull side slopes from the floor to the gunwale.
There are ventilation holes drilled in the floor behind and below the fridge. Also there are 4 computer fans mounted in the floor connected in series parallel that when running blow cool air from under the floor up the condenser. All readings were taken with the fridge in normal use.

 

The fridge thermostat was set at 3 and had been running for a couple of days to allow things to stabilise before readings were taken at 1700 hrs each day. The thermometer inside the fridge was reading at the top of the acceptable range.

At the end of the first day with the fans off and the fridge running as normal the hour meter recorded 7.6 hrs in 24 hrs.
On the second day the fans were switch on and the reading at the end of 24 hrs was 7 hrs.
The next day the fans were switched off and the hours run were 7.1 This indicates to me that the fridge was adequately ventilated as
installed. That night I insulated the fridge on both sides and the top with sheets of 25mm close cell insulation foam covered on both sides with aluminium foil as used in the building trade. At this point things got interesting which I can't explain. The running hours were slightly less but the internal temperature of the fridge fell. Over the next 2 days I adjusted the thermostat setting to bring the internal temperature back to its original level. This resulted on it now being set at 1.5 as opposed to the original 3. I don't know why this happened as in my book the thermostat should keep the inside of the fridge at a constant temperature. I suspect it is a timer and not a stat.

Once this had settled down I started recording readings again which run between 6.3 and 5.7 hours per day

 

Date        Time        meter reading   hours run     
11/8/06 1700hrs       1170.2
12/8/06 1700 hrs       1177.8                7.6
Fan on
13/8/06 1700hrs         1184.7               6.9
Fan off
14/8/06 1700hrs           1191.8              7.1
Insulation added and fans on
15/8/06 1700hrs          1198.5              6.7
reduced stat setting
16/8/06 1700hrs        1205.0              6.5
17/8/06 1700 hrs       1211.3               6.7
18/8/06 1700hrs         1217.0             5.7
19/8/06 1700hrs         1223.6            6.6
20/8/06 1700hrs          1230.0           6.4
21/8/06 1700hrs           1235.5           5.5
22/8/06 1700hrs             1241.2           5.7

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2 minutes ago, ditchcrawler said:

I timed my 240 volt fridge as well, I just connect an hour counter across the compressor motor. But I didn't do it under test conditions, ie. the fridge was in use. I did publish them before as I tried fitting extra insulation and a fan at the back. I came to the conclusion that the thermostat is not actually a stat at all but a timer, because as I improved things the fridge got colder.

This is what I posted before :-

 

I have been running another set of tests on our 240 volt fridge. The fridge runs via a Mastervolt Mass Sine 24/1500 and all current readings are take from a Sterling Battery Management unit.

The inverter + Fridge + fans =3.5 amps
The Inverter + Fridge = 3.4 amps
The Inverter = 0.4 amps           

I have connected a RS hour meter across the refrigerator compressor to record compressor run hours.
The refrigerator is a LEC Elan and sits under a worktop with 25mm air gap each side and 50mm between the top of the refrigerator and the underside of the work top. The air space behind the refrigerator is well over the recommended space as the hull side slopes from the floor to the gunwale.
There are ventilation holes drilled in the floor behind and below the fridge. Also there are 4 computer fans mounted in the floor connected in series parallel that when running blow cool air from under the floor up the condenser. All readings were taken with the fridge in normal use.

 

The fridge thermostat was set at 3 and had been running for a couple of days to allow things to stabilise before readings were taken at 1700 hrs each day. The thermometer inside the fridge was reading at the top of the acceptable range.

At the end of the first day with the fans off and the fridge running as normal the hour meter recorded 7.6 hrs in 24 hrs.
On the second day the fans were switch on and the reading at the end of 24 hrs was 7 hrs.
The next day the fans were switched off and the hours run were 7.1 This indicates to me that the fridge was adequately ventilated as
installed. That night I insulated the fridge on both sides and the top with sheets of 25mm close cell insulation foam covered on both sides with aluminium foil as used in the building trade. At this point things got interesting which I can't explain. The running hours were slightly less but the internal temperature of the fridge fell. Over the next 2 days I adjusted the thermostat setting to bring the internal temperature back to its original level. This resulted on it now being set at 1.5 as opposed to the original 3. I don't know why this happened as in my book the thermostat should keep the inside of the fridge at a constant temperature. I suspect it is a timer and not a stat.

Once this had settled down I started recording readings again which run between 6.3 and 5.7 hours per day

 

Date        Time        meter reading   hours run     
11/8/06 1700hrs       1170.2
12/8/06 1700 hrs       1177.8                7.6
Fan on
13/8/06 1700hrs         1184.7               6.9
Fan off
14/8/06 1700hrs           1191.8              7.1
Insulation added and fans on
15/8/06 1700hrs          1198.5              6.7
reduced stat setting
16/8/06 1700hrs        1205.0              6.5
17/8/06 1700 hrs       1211.3               6.7
18/8/06 1700hrs         1217.0             5.7
19/8/06 1700hrs         1223.6            6.6
20/8/06 1700hrs          1230.0           6.4
21/8/06 1700hrs           1235.5           5.5
22/8/06 1700hrs             1241.2           5.7

 

 

Blimey mate, all cutandpolished asked was the current his compressor draws!

 

 

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Just now, Mike the Boilerman said:

 

My method was quicker. Look at the ammeter. 

 

 

 

It certainly is quicker (if you want an instantaneous figure) but, is it as accurate when looking at Ah over 24 hours ?

An ammeter won't give you run-time.

 

I'm sure that the OP realises the difference between Amps and Ah, and the need to put Ah, and not Amps, back in the battery(s)

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Just now, Alan de Enfield said:

It certainly is quicker (if you want an instantaneous figure) but, is it as accurate when looking at Ah over 24 hours ?

An ammeter won't give you run-time.

 

I'm sure that the OP realises the difference between Amps and Ah, and the need to put Ah, and not Amps, back in the battery(s)

 

I'm sure he does too, which is why he didn't ask that question.

 

He wants to know the current specifically "whenever the compressor is running", to quote him.

 

 

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9 minutes ago, Mike the Boilerman said:

 

My method was quicker. Look at the ammeter. 

 

 

 

Talk about over-complicating things!

 

 

The reason for the readings was to try make it more economical to run, I reduced the run time by 2 hrs a day. I only posted it to show that Alan was not the only one sad enough to time his fridge.

Also with 240 volt fridges the power consumption in a year is not a real in use figure a bit like the MPG of a car, its just a comparison number taken under test conditions. 12/24 fridge manufacturers don't use that system and can say what they like.

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5 hours ago, ditchcrawler said:

I timed my 240 volt fridge as well, I just connect an hour counter across the compressor motor. But I didn't do it under test conditions, ie. the fridge was in use. I did publish them before as I tried fitting extra insulation and a fan at the back. I came to the conclusion that the thermostat is not actually a stat at all but a timer, because as I improved things the fridge got colder.

This is what I posted before :-

 

I have been running another set of tests on our 240 volt fridge. The fridge runs via a Mastervolt Mass Sine 24/1500 and all current readings are take from a Sterling Battery Management unit.

The inverter + Fridge + fans =3.5 amps
The Inverter + Fridge = 3.4 amps
The Inverter = 0.4 amps           

I have connected a RS hour meter across the refrigerator compressor to record compressor run hours.
The refrigerator is a LEC Elan and sits under a worktop with 25mm air gap each side and 50mm between the top of the refrigerator and the underside of the work top. The air space behind the refrigerator is well over the recommended space as the hull side slopes from the floor to the gunwale.
There are ventilation holes drilled in the floor behind and below the fridge. Also there are 4 computer fans mounted in the floor connected in series parallel that when running blow cool air from under the floor up the condenser. All readings were taken with the fridge in normal use.

 

The fridge thermostat was set at 3 and had been running for a couple of days to allow things to stabilise before readings were taken at 1700 hrs each day. The thermometer inside the fridge was reading at the top of the acceptable range.

At the end of the first day with the fans off and the fridge running as normal the hour meter recorded 7.6 hrs in 24 hrs.
On the second day the fans were switch on and the reading at the end of 24 hrs was 7 hrs.
The next day the fans were switched off and the hours run were 7.1 This indicates to me that the fridge was adequately ventilated as
installed. That night I insulated the fridge on both sides and the top with sheets of 25mm close cell insulation foam covered on both sides with aluminium foil as used in the building trade. At this point things got interesting which I can't explain. The running hours were slightly less but the internal temperature of the fridge fell. Over the next 2 days I adjusted the thermostat setting to bring the internal temperature back to its original level. This resulted on it now being set at 1.5 as opposed to the original 3. I don't know why this happened as in my book the thermostat should keep the inside of the fridge at a constant temperature. I suspect it is a timer and not a stat.

Once this had settled down I started recording readings again which run between 6.3 and 5.7 hours per day

 

Date        Time        meter reading   hours run     
11/8/06 1700hrs       1170.2
12/8/06 1700 hrs       1177.8                7.6
Fan on
13/8/06 1700hrs         1184.7               6.9
Fan off
14/8/06 1700hrs           1191.8              7.1
Insulation added and fans on
15/8/06 1700hrs          1198.5              6.7
reduced stat setting
16/8/06 1700hrs        1205.0              6.5
17/8/06 1700 hrs       1211.3               6.7
18/8/06 1700hrs         1217.0             5.7
19/8/06 1700hrs         1223.6            6.6
20/8/06 1700hrs          1230.0           6.4
21/8/06 1700hrs           1235.5           5.5
22/8/06 1700hrs             1241.2           5.7

Just an explanation about fridge thermostats ...

 

There is a lot of thermal mass in the fridge cooling system, so if it had a straight thermostat that was on until the set temperature was reached, once this happened the compressor would stop but the fridge cooling system / evaporator etc would still be full of very cold fluid. The fridge internal temperature would continue to fall, stuff would freeze etc. Eventually the coolant would have all evaporated and temperature would start to rise. Everything including the ice box (if you have one) would warm up until the cut-in temperature was reached. The compressor would then run but it takes a while for the coolant to cool down, in the mean time the fridge temperature would continue to rise, before the whole cycle repeating.

 

In other words, if it was a straight thermostat there would be huge temperature fluctuations. Therefore the thermostat has an element of duty cycle control mixed with cabinet temperature and the knob setting, in order to maintain a fairly constant cabinet temperature. The downside is that, as you discovered, the absolute temperature regulation isn’t very good.

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23 minutes ago, nicknorman said:

Just an explanation about fridge thermostats ...

 

There is a lot of thermal mass in the fridge cooling system, so if it had a straight thermostat that was on until the set temperature was reached, once this happened the compressor would stop but the fridge cooling system / evaporator etc would still be full of very cold fluid. The fridge internal temperature would continue to fall, stuff would freeze etc. Eventually the coolant would have all evaporated and temperature would start to rise. Everything including the ice box (if you have one) would warm up until the cut-in temperature was reached. The compressor would then run but it takes a while for the coolant to cool down, in the mean time the fridge temperature would continue to rise, before the whole cycle repeating.

 

In other words, if it was a straight thermostat there would be huge temperature fluctuations. Therefore the thermostat has an element of duty cycle control mixed with cabinet temperature and the knob setting, in order to maintain a fairly constant cabinet temperature. The downside is that, as you discovered, the absolute temperature regulation isn’t very good.

I havent found a capillary yet

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51 minutes ago, ditchcrawler said:

I havent found a capillary yet

I don’t think ours (shoreline) has a visible capillary but there must be a restriction in the circuit. Our fridge is one of those slightly weird ones that doesn’t have a visible radiator at the back, as I understand it the radiator is built into the fridge sides, so probably the capillary or other restriction / expansion device is hidden in there as well

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Every fridge thermostat I ever sold back in the day, had a capillary. Exactly what temperature it measured I'm not sure. I don't think it monitored the cabinet temperature, more likely the condenser temperature. This would then stop the wide hysteresis in the cabinet that monitoring the cabinet temperature would cause as described above.

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1 minute ago, Ex Brummie said:

Every fridge thermostat I ever sold back in the day, had a capillary. Exactly what temperature it measured I'm not sure. I don't think it monitored the cabinet temperature, more likely the condenser temperature. This would then stop the wide hysteresis in the cabinet that monitoring the cabinet temperature would cause as described above.

Just like all the ones I fitted over the years, clipped to the Condenser

 

Fridge Thermostat | eSpares

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Ah sorry you meant the temperature sensor. Some modern fridges use electronic temperature sensing. Certainly the Siemens fridge in my rental flat, which I had to fix recently, has an electronic thermostat with no capillary.

Edited by nicknorman
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