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LEC 240V fridge power consumption with inverter / power audit


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I'm going to attempt to do a power audit so I know what I need to be prepared for after summer (currently 720W solar is covering my needs, but notice things get a little low after a few cloudy days).

 

The boat currently has a 240V LEC under counter fridge freezer, model T50084W. Unknown age, looks to be a good few years old, but seems to work well. I want to assess how much power this uses if left on 24 hours a day, with the inverter. Then I can figure out if I'm better going with a 12V fridge, a newer 240V (not sure if you can get more efficient than A+ forn undercounter fridge/freezers?), or if the current setup is fine.

 

I have a Victron Phoenix 12/800 inverter, plus 1 x starter battery and 2 x Deka Unigy HR7500ET lesiure batteries (750W?? Can't tell capacity)

 

I can't tell from the spec sheet below how many watts the fridge uses or how to work out how many watts per hour (so I can then work out the amp hour draw).

 

I also am not sure how much draw from the battery the inverter uses being on 24/7... Does this model inverter have a 'sleep' mode whereby it turns itself off when no/low power is being drawn (eg, if fridge compressor is not running)? ⁉️

 

 

1076588192_Screenshot2021-06-30at15_09_22.png.e8c763eafa4780841fa5c3eb9b6080c8.png

Edited by thingsweregood
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Manufacturer's energy consumption data is based on a particular type of usage. Yours will almost certainly be different. It varies with the temperature setting you use, how full you keep the fridge and how often you open the door, whether it is a larder fridge or has an ice box, as well as the ambient (cabin) temperature and how well ventilated the coils on the back of the fridge are. So rather than trying to fathom something out from the data it might be better to rely on those boaters who have measured their fridge consumption. This has been covered in previous threads, although you will have to dig around for it.

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3 minutes ago, David Mack said:

Manufacturer's energy consumption data is based on a particular type of usage. Yours will almost certainly be different. It varies with the temperature setting you use, how full you keep the fridge and how often you open the door, whether it is a larder fridge or has an ice box, as well as the ambient (cabin) temperature and how well ventilated the coils on the back of the fridge are. So rather than trying to fathom something out from the data it might be better to rely on those boaters who have measured their fridge consumption. This has been covered in previous threads, although you will have to dig around for it.

Cool, will do some digging.

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3 minutes ago, nbfiresprite said:

168kws divided by 365 = 460.27 watts per day

 

10 watts per amp = 46 amps per day

 

1.91 amps per hour at 12 volts

Your units are all over the place!!

 

Assuming that annual figure of 168 is in KWh (the standard domestic electricity 'unit'), then the daily average use is 460 Watt hours, which over 24 hours equates to an average power consumption of 460/24 or about 20 Watts, which will draw something like 2 Amps average current from a 12V battery. But for a power audit you need the daily consumption in Ah, which is about 46 Ah. 

 

But as I said above this assumes that the manufacturers figures and your use pattern are typical. 

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3 minutes ago, David Mack said:

Your units are all over the place!!

 

Assuming that annual figure of 168 is in KWh (the standard domestic electricity 'unit'), then the daily average use is 460 Watt hours, which over 24 hours equates to an average power consumption of 460/24 or about 20 Watts, which will draw something like 2 Amps average current from a 12V battery. But for a power audit you need the daily consumption in Ah, which is about 46 Ah. 

 

But as I said above this assumes that the manufacturers figures and your use pattern are typical. 

So assuming 'typical' use and roughly accurate manufacturer figures, I should take 46 Ah as the figure to enter on my power audit?

 

I also FINALLY managed to find the brand name/model number of my batteries on the unit (those 68kg guys are hard to move in a small space!): I've got 2 x Deka Unigy HR7500ET. I can't tell what the Ah/capacity of these would be?

 

IMG_2709.JPG.765f12a5d86192a1df5dbdb53db8a397.JPG

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50 minutes ago, thingsweregood said:

I'm going to attempt to do a power audit so I know what I need to be prepared for after summer (currently 720W solar is covering my needs, but notice things get a little low after a few cloudy days).

 

 

2-ways of measuring :

 

1) Get an ammeter (amp counter) between the batteries and the inverter, this will count all the amps used by the inverter, and will include what it uses to make 230v AND what it uses to power itself.

 

2) Get a mains plug in watt counter, connect it between your fridge and the 3-pin socket and it'll, count the actual watts used IN YOUR application over (say) 24 hours. You can do the same for every 230v appliance.

 

An absolutely wonderful tool, you will sit for hours watching it count the Wh used by everything you can find to plug in. You'll wonder what you did before you got one.

Measure the fridge on a cold day, and then for interest measure the fridge on a hot day - hours of entertainment for all the family.

 

Power Consumption Meter UK Plug in Electricity Energy Monitor Watt Kwh Analyzer | eBay

 

Image 3 - Power Consumption Meter UK Plug in Electricity Energy Monitor Watt Kwh Analyzer

Edited by Alan de Enfield
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25 minutes ago, Alan de Enfield said:

An absolutely wonderful tool, you will sit for hours watching it count the Wh used by everything you can find to plug in. You'll wonder what you did before you got one.

Measure the fridge on a cold day, and then for interest measure the fridge on a hot day - hours of entertainment for all the family.

 

Power Consumption Meter UK Plug in Electricity Energy Monitor Watt Kwh Analyzer | eBay

 

Image 3 - Power Consumption Meter UK Plug in Electricity Energy Monitor Watt Kwh Analyzer

 

I've got one of these (different make/model) but haven't used it for years and it seems to have died. It's it the internal battery that's gone? I can't seem to get it apart.

Edited by blackrose
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3 minutes ago, blackrose said:

 

I've got one of these (different make/model) but haven't used it for years and it seems to have died. It's it the internal battery that's gone? I can't seem to get it apart.

Sonic screwdriver needed, about 2lbs.  One tap.

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12 minutes ago, Tracy D'arth said:

Sonic screwdriver needed, about 2lbs.  One tap.

 

The screws came out easily enough with a standard cross head screwdriver, but it doesn't seem to want to come apart.

 

Edit, pulled it apart. There is no internal battery I can see. Chucked it in the bin.

Edited by blackrose
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1 hour ago, thingsweregood said:

So assuming 'typical' use and roughly accurate manufacturer figures, I should take 46 Ah as the figure to enter on my power audit?

 

I also FINALLY managed to find the brand name/model number of my batteries on the unit (those 68kg guys are hard to move in a small space!): I've got 2 x Deka Unigy HR7500ET. I can't tell what the Ah/capacity of these would be?

 

IMG_2709.JPG.765f12a5d86192a1df5dbdb53db8a397.JPG

 

I may well be wrong, but the 750 watts per cell @ 15min to 1.67 volts per cell makes me suspect they are neither deep cycle or starting batteries.

 

A Google on the part number you gives shows they are AGM construction for Uninterruptible Power Supply use, so maybe not ideal for a boat. The data sheet here https://www.sure-power.com/wp-content/uploads/2014/07/Deka-Unigy High Rate Series HR7500ET.pdf

only gives discharge data over 60 minutes, not the 12 hours or so for overnight.

 

Hopefully someone who understand this type of battery will give you better info.

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2 hours ago, thingsweregood said:

I also FINALLY managed to find the brand name/model number of my batteries on the unit (those 68kg guys are hard to move in a small space!): I've got 2 x Deka Unigy HR7500ET. I can't tell what the Ah/capacity of these would be?

 

 

To a certain extent (depending on construction) weight is proportional to capacity,

My batteries weigh 55kg - 58kg and depending on supplier are rated at 200Ah to 230Ah

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The most energy efficient 230V undercounter fridge with a freezer compartment is the Liebherr TP 1764

 

https://www.sust-it.net/energy-saving/undercounter-fridges

 

Running cost per year is quoted as 99kWh/year (118l+18l) compared to your 168kWh (62l+28l), assuming this is measured on the same basis (the LEC data sheet is not clear) -- the LEC fridge is smaller but the freezer is bigger.

Edited by IanD
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I have just converted an  undercounter freezer that is at least ten years old to be a larder fridge using an external stat.

I measured its use at 200Wh a day  or 73kWh a year way more efficient than a normal fridge?

I'm sure with a newer more efficient freezer  you could get that figure down to 50kwh a year.

I am surprised more boaters don't go down this route.

Edited by Loddon
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5 minutes ago, Loddon said:

I have just converted an  undercounter freezer that is at least ten years old to be a larder fridge using an external stat.

I measured its use at 200Wh a day  or 73kWh a year way more efficient than a normal fridge?

I'm sure with a newer more efficient freezer  you could get that figure down to 50kwh a year.

I am surprised more boaters don't go down this route.

Presumably the converted freezer is more efficient because it has better insulation? But the downside I suspect is that the thicker insulation means less available storage volume inside the “fridge”. Bearing in mind there are 2 conflicting precious commodities on a boat - storage space and electrical energy - it will be a matter of where the best compromise lies.

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Found my results the formating may be crap

 

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 work top 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
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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A fridge thermostat isn’t a straightforward thermostat, it includes an element of “run time” as well. This is because there is too much thermal lag. eg if the compressor is running, then the fridge hits the right internal temperature and the compressor turns off, the system is still full of cold refrigerant which continues to evaporate and cool, and the cooling plate is still very cold. So after the desired temperature is reached and the compressor turns off, the fridge temperature will continue to fall, potentially freezing the contents. Ditto when the temperature does eventually rise to trigger the thermostat to cut in, it takes a while for the refrigerant to be pumped and start to cool the cooling plate, in the meantime the temperature continues to rise. So there will be big fluctuations in temperature.

 

By adding a “run time” component to the thermostat - or in fact measuring a combination of the fridge internal temperature and the coolant temperature (which is much colder) - the fluctuations are smoothed out. But it means that if you improve the insulation, the relationship between average coolant temperature and internal temperature changes, and so the internal temperature will decrease.

 

Also worth mentioning that plenty of modern fridges don't have a radiator at the back, they just have a plastic sheet. The radiator is built into the sides under the metal. So if you insulate the sides, the fridge can’t dump the heat! So your technique should only be used on a fridge with a visible radiator at the back.

 

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40 minutes ago, nicknorman said:

fridge thermostat isn’t a straightforward thermostat, it includes an element of “run time” as well. This is because there is too much thermal lag. eg if the compressor is running, then the fridge hits the right internal temperature and the compressor turns off, the system is still full of cold refrigerant which continues to evaporate and cool, and the cooling plate is still very cold. So after the desired temperature is reached and the compressor turns off, the fridge temperature will continue to fall, potentially freezing the contents. Ditto when the temperature does eventually rise to trigger the thermostat to cut in, it takes a while for the refrigerant to be pumped and start to cool the cooling plate, in the meantime the temperature continues to rise. So there will be big fluctuations in temperature.

Yes I think it caught me to start with ?

Temp on stat set at 3deg (ideal fridge temp?) Overnight a glass of water in the fridge had an ice skin on it. Temp set to 4.5deg  no ice skin and temp remains between 3 and 5.5 deg.

Yes the insulation is thicker but that's partly what makes it more efficient.

If I needed to reduce my consumption it would be in the boat already.

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5 hours ago, Alan de Enfield said:

 

 

2-ways of measuring :

 

1) Get an ammeter (amp counter) between the batteries and the inverter, this will count all the amps used by the inverter, and will include what it uses to make 230v AND what it uses to power itself.

 

 

An ammeter measures amps. 

 

You would also need a clock to measure ampere-hours.  Or an ampere-hour counter - which is a combined clock and ammeter

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12 hours ago, ditchcrawler said:

Found my results the formating may be crap

 

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 work top 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
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

 

So in the initial run, the inverter + fridge consumed 3.4 Amps and ran for 7.6 hours in 24. So the daily power consumption was 26 Ah.

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9 hours ago, David Mack said:

So in the initial run, the inverter + fridge consumed 3.4 Amps and ran for 7.6 hours in 24. So the daily power consumption was 26 Ah.

But that was at 24 volts

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