Keeping Up Posted September 2, 2016 Report Posted September 2, 2016 My new Waeco fridge manual gives an "average power consumption 40w" Item number CR-0080E Capacity: 78 litres Freezer compartment: 8 litres Average power consumption: 40 W Weight: 23 kg Now 40w at 12,5 volts = 3.2 amps. The fridge actually runs approximately 20 minutes per hour (1/3 of an hour) Or - to put it another way 1.1Ah over 1 hour, or 26.4Ah over 24 hours. I think you may be wrong. When they say the average power consumption is 40 watts, they probably mean that the average current consumption at 12v is 3.2 amps, so in 24 hours you would be using 76.8 ampere-hours. The motor will be taking more than 3.2 amps when running.
boathunter Posted September 2, 2016 Report Posted September 2, 2016 When I read the threads it is almost always clear that the questioners do in fact understand, but are simply using the wrong terms. Then under the barrage of ah amps per hour nit picking, they give up and buy some more batteries. They may be technically wrong, but you do know what they mean. I do and I'm far from an electrical whiz. 1
nicknorman Posted September 2, 2016 Report Posted September 2, 2016 I think you may be wrong. When they say the average power consumption is 40 watts, they probably mean that the average current consumption at 12v is 3.2 amps, so in 24 hours you would be using 76.8 ampere-hours. The motor will be taking more than 3.2 amps when running. It is very confusing - why can't manufacturers quote their products' energy consumption unambiguously? But in this case I would have thought that 77AH per day was too high for a modern fridge to be correct, 26AH is more likely.
Alan de Enfield Posted September 2, 2016 Report Posted September 2, 2016 I think you may be wrong. When they say the average power consumption is 40 watts, they probably mean that the average current consumption at 12v is 3.2 amps, so in 24 hours you would be using 76.8 ampere-hours. The motor will be taking more than 3.2 amps when running. It is very confusing - why can't manufacturers quote their products' energy consumption unambiguously? But in this case I would have thought that 77AH per day was too high for a modern fridge to be correct, 26AH is more likely. Hmmm - hadn't thought about that - is the 'average' the average over 1 hour, 12 hours, 24 hours, 1 week, or 1 month ? The rating on my old 'Electrolux 3-way' was 65 watts, and, I can easily accept that over 20 years development that fridges have improved. I agree - why can there not be a 'standard' measurement as there is with domestic fridges / freezers. This is the spec for my 220v Freezer - it is fairly straightforward & understandable. "Energy consumption: 153kWh per year based on standard test results for 24 hours" 153,000 Wh per annum = 420Wh per day = 34Ah per day (via the inverter I work on 48Ah per day)
MtB Posted September 2, 2016 Report Posted September 2, 2016 (edited) Hmmm - hadn't thought about that - is the 'average' the average over 1 hour, 12 hours, 24 hours, 1 week, or 1 month ? The rating on my old 'Electrolux 3-way' was 65 watts, and, I can easily accept that over 20 years development that fridges have improved. I agree - why can there not be a 'standard' measurement as there is with domestic fridges / freezers. This is the spec for my 220v Freezer - it is fairly straightforward & understandable. "Energy consumption: 153kWh per year based on standard test results for 24 hours" 153,000 Wh per annum = 420Wh per day = 34Ah per day (via the inverter I work on 48Ah per day) Firstly to Terry, I had no intention of appearing condescending. It was intended as a pointer to the OP to do some research because he clearly has a gap in his understanding. Secondly when I read someone write "Amps per hour", the context usually suggests to me they mean just "Amps". It never occurred to me the OP might have meant AH as boathunter says I must have known he meant. I didn't, and I was not nit-picking. In fact I still don't think that's what he meant - perhaps he could clarify please. My and boathunter's continuing disagreement about what the OP meant illustrates WHY the nit-picking is necessary. Now on to fridges...! Fridges need TWO specifications: 1) Energy consumption over say, 24hrs as suggested above is needed for the user to do his energy audit and size the batteries, charger etc when designing a system. 2) The actual current in Amps (not Amps per hour!) drawn by the fridge whilst it is running in order to calculate the size of the cables feeding it. Usually only the first is quoted by manufacturers and it leads to us having to guess the cable sizes required. Edited September 2, 2016 by Mike the Boilerman
Alan de Enfield Posted September 2, 2016 Report Posted September 2, 2016 There is also a third variable to consider - Distance. (So that Volt drop can be taken into account). Waeco produce a graph of cable size against distance which is useful - but remember that the distance is actually 2x the 'real' distance. See page 9 Waeco CR 80 manual.pdf So, by default they are actually telling you what size of cable you need to use, and the energy consumption. Happy ?
WotEver Posted September 2, 2016 Report Posted September 2, 2016 I think you may be wrong. When they say the average power consumption is 40 watts, they probably mean that the average current consumption at 12v is 3.2 amps, so in 24 hours you would be using 76.8 ampere-hours. The motor will be taking more than 3.2 amps when running. That's exactly what I thought when I read Alan's post. Although that probably isn't the case... They may be technically wrong, but you do know what they mean. I do and I'm far from an electrical whiz. Do we? I'm not at all confident of that. Just look at the posts since - he 'may' have meant 2Ah or he may have meant 2A. Only he can clarify that.
WotEver Posted September 2, 2016 Report Posted September 2, 2016 There is also a third variable to consider - Distance. (So that Volt drop can be taken into account). Waeco produce a graph of cable size against distance which is useful - but remember that the distance is actually 2x the 'real' distance. See page 9 Waeco CR 80 manual.pdf So, by default they are actually telling you what size of cable you need to use, and the energy consumption. Happy ? It's interesting to note that the Waeco graph shows similar (but one size up) to the generic Shoreline advice of 1mm2 per metre distance. So Shoreline would say 10mm2 for 10 metres but the graph shows 12mm2.
boathunter Posted September 2, 2016 Report Posted September 2, 2016 That's exactly what I thought when I read Alan's post. Although that probably isn't the case... Do we? I'm not at all confident of that. Just look at the posts since - he 'may' have meant 2Ah or he may have meant 2A. Only he can clarify that. If the term amps per hour is used, I think it causes more confusion to you guys who properly understand the correct terms, than it does among us dabblers. That was my point. MikeTB reads it as amps, choosing to ignore the time element, I see it as ah. 2 amps for an hour is 2ah is it not?
WotEver Posted September 2, 2016 Report Posted September 2, 2016 (edited) 2 amps for an hour is 2ah is it not?If it draws 2A constantly and is switched on for an hour then yes, it has consumed 2Ah. If it has a maximum demand of 2A and a 50% duty cycle and is on for an hour then it has consumed 1Ah. If it has a maximum demand of 4A and has a 50% duty cycle then it would have consumed 2Ah but would require thicker cables. So, did he mean that it has a constant demand of 2A, or an average demand of 2A, or something else? Why was an hour even mentioned? If it's only on for an hour each day then there's a reason for mentioning the hour, otherwise it shouldn't even feature. This is why it's important - we don't really know what he meant. We can guess, sure, but we could guess wrong. Look at the confusion regarding Alan's fridge. If the correct terminology is used then there's no need for guesses. Tony Edited September 2, 2016 by WotEver 2
Tony Brooks Posted September 2, 2016 Report Posted September 2, 2016 If the term amps per hour is used, I think it causes more confusion to you guys who properly understand the correct terms, than it does among us dabblers. That was my point. MikeTB reads it as amps, choosing to ignore the time element, I see it as ah. 2 amps for an hour is 2ah is it not? ONLY if the 2 amps is running for one hour as I explained. From memory there was no mention of "how long" the 2 amps per hour was being supplied. In the context of potentially undercharging or over discharging of batteries that is all important. I read it as a figure that was not usable so did not respond.
boathunter Posted September 2, 2016 Report Posted September 2, 2016 ONLY if the 2 amps is running for one hour as I explained. From memory there was no mention of "how long" the 2 amps per hour was being supplied. In the context of potentially undercharging or over discharging of batteries that is all important. I read it as a figure that was not usable so did not respond. I do see what you mean, I was just presenting the view from the other side. I enjoy battery threads where massive consumption and continual under charging is baffling the would-be battery custodian. I've walked in these shoes myself, luckily with one cheap battery at a time as I can reduce one to 50% capacity in couple of weekends.
Murflynn Posted September 2, 2016 Report Posted September 2, 2016 Hmmm - hadn't thought about that - is the 'average' the average over 1 hour, 12 hours, 24 hours, 1 week, or 1 month ? it makes no difference. it could be the average over a century (assuming the appliance will last that long). I thought that understanding what AVERAGE means is something you learn at primary school.
Machpoint005 Posted September 2, 2016 Report Posted September 2, 2016 If it draws 2A constantly and is switched on for an hour then yes, it has consumed 2Ah. If it has a maximum demand of 2A and a 50% duty cycle and is on for an hour then it has consumed 1Ah. If it has a maximum demand of 4A and has a 50% duty cycle then it would have consumed 2Ah but would require thicker cables. So, did he mean that it has a constant demand of 2A, or an average demand of 2A, or something else? Why was an hour even mentioned? If it's only on for an hour each day then there's a reason for mentioning the hour, otherwise it shouldn't even feature. This is why it's important - we don't really know what he meant. We can guess, sure, but we could guess wrong. Look at the confusion regarding Alan's fridge. If the correct terminology is used then there's no need for guesses. Tony Exactly. Have a greenie. it makes no difference. it could be the average over a century (assuming the appliance will last that long). I thought that understanding what AVERAGE means is something you learn at primary school. Linear average, at least, but let's not go all statistical.
Paul C Posted September 2, 2016 Report Posted September 2, 2016 it makes no difference. it could be the average over a century (assuming the appliance will last that long). I thought that understanding what AVERAGE means is something you learn at primary school. Its a fair enough point because the average over a day could quite conceivably be different for summer and winter use. The average over a year, which is on first appearance what the annual kWh figures would suggest, although I suspect they don't actually take a year to evaluate and use some assumptions, such as ambient temperature (which may be different on a boat).
Alan de Enfield Posted September 2, 2016 Report Posted September 2, 2016 (edited) it makes no difference. it could be the average over a century (assuming the appliance will last that long). I thought that understanding what AVERAGE means is something you learn at primary school. Ah - but is it a 40 w average power consumption over a day (suggesting 1.667Wh per hour), or is it 40 w average over 1 hour (suggesting 40Wh per hour) ? The 'book' does not say it uses 40w of power, it says that on average (over some unspecified period) it uses 40w. At some point during the unspecified period it will be using more than 40w, and at other times less than 40w. As a comparison an 80w light bulb would average 40Wh per hour if it was in use for 50% of the time. Edited September 2, 2016 by Alan de Enfield
Murflynn Posted September 2, 2016 Report Posted September 2, 2016 Ah - but is it a 40 w average power consumption over a day (suggesting 1.667Wh per hour), or is it 40 w average over 1 hour (suggesting 40Wh per hour) ? The 'book' does not say it uses 40w of power, it says that on average (over some unspecified period) it uses 40w. At some point during the unspecified period it will be using more than 40w, and at other times less than 40w. As a comparison an 80w light bulb would average 40Wh per hour if it was in use for 50% of the time. you just don't get it, do you? 40w average power consumption (over any period you like to nominate) equates to 40Wh per hour. of course the running power may be 80w and it may have a typical duty cycle of 50:50 giving an average of 40w. simples.
nicknorman Posted September 2, 2016 Report Posted September 2, 2016 So the question is, is the average of 40 watts the average over many hours, or the average whilst the motor is running - since of course the startup current will be higher than the running current, and the running current will increase a bit as the pressure in the coolant circuit increases.
Keeping Up Posted September 2, 2016 Report Posted September 2, 2016 I reckon the manufacturers of the less efficient fridges have a vested interest in quoting misleading figures so that their fridges look more efficient than the others. Of cuorse that then propmpts the other manufacturers to come up with a different set of misleading figures (using made-up units if necessary) to make theirs look more efficient again. And so it goes on ... It seems that there are lies, damn lies, statistics, and manufacturers figures
MtB Posted September 2, 2016 Report Posted September 2, 2016 Exactly. Have a greenie. Linear average, at least, but let's not go all statistical. it makes no difference. it could be the average over a century (assuming the appliance will last that long). I thought that understanding what AVERAGE means is something you learn at primary school. Yes, this. I learned about mean, median and mode averages at skool. Which of those did you mean? (See what I did there?!) Now Machpoint005 introduces a fourth type, linear average. Wossat then?
Terryb Posted September 2, 2016 Report Posted September 2, 2016 When I read the threads it is almost always clear that the questioners do in fact understand, but are simply using the wrong terms. Then under the barrage of ah amps per hour nit picking, they give up and buy some more batteries. They may be technically wrong, but you do know what they mean. I do and I'm far from an electrical whiz. GREENY
WotEver Posted September 2, 2016 Report Posted September 2, 2016 So the question is, is the average of 40 watts the average over many hours, or the average whilst the motor is running - since of course the startup current will be higher than the running current, and the running current will increase a bit as the pressure in the coolant circuit increases. I suspect it's the latter as 40W average (in the true meaning of the word) would be a pretty inefficient fridge, somewhere in the region of 76Ah per day at 12V. Or maybe it's the former... Why oh why can't we be given 'real' figures.
MtB Posted September 2, 2016 Report Posted September 2, 2016 I suspect it's the latter as 40W average (in the true meaning of the word) would be a pretty inefficient fridge, somewhere in the region of 76Ah per day at 12V. Or maybe it's the former... Why oh why can't we be given 'real' figures. I'm coming to the conclusion that people like boathunter, Terryb, phil_ambrose actually enjoy using non-existent units, simply so they can say "you knew what we meant".
WotEver Posted September 2, 2016 Report Posted September 2, 2016 I roared with laughter when I saw Terryb's 'greenie' post above
boathunter Posted September 2, 2016 Report Posted September 2, 2016 1.19ah/h at 5°C in fridge, 25°C ambient. 2.0ah/h at 5°C in fridge, 32°C ambient Weaco crx80 Mine consumes about 25ah in 24 hours, it's cooler than 25°C on average so the numbers tally.
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