Calculate power requirements for Shoreline Fridge

[Johny London]

Ok, I don't mean to pick on anyone but a few things that confuse me are...

 

Bengo: "The fridge itself uses about 2 Amps, only when the compressor is running, and it will typically run  30-60% of the time."

So that would equate to about 0.6-1.2amps per hour, quite low!

 

 

Neil2: "We have a Shoreline, I turn it up when we're running and down to "2" when moored and it seems to draw around 2 amps for about 20 minutes an hour."

It's open to interpretation but I took that to mean the fridge was drawing 2amps while running, equating to around 15amps a day. Dr Bob agrees with me and sais "2amps for 20 mins an hour is circa 16Ahr per 24 hours. Sounds very low."

 

Dor: "Our normal sized Shoreline fridge, with a 4* freezer compartment, uses 3.0 amps when the compressor is running."

That sounds very low for a running fridge/freezer, but good luck to ya. Interestingly MTBM confirms this!? And AndrewIC! Is there some disparity going on between models or is this fridge vs fridge freezer in some cases?

 

Ivan&Alice: "Thanks for all the figures. I'm working on the fridge running 1/3 of the time (8 hours per day) drawing an average of 6A, resulting in a 48Ah consumption per day."

If it's drawing an average of 6a, then it would be (6x24) = 150a per day

 

To top it all off, just look at the variation in these figures...

 

@Alan de Enfield - 45Ah
@BEngo - 50Ah
@Keeping Up - 35Ah (with bilge fans)
@Neil2 - 16Ah
@dor - 30Ah (3A*(25/60)*24h)
@Mike the Boilerman - 36Ah

 

Apologies for being such a pedant, but the figures we are getting seem to be all over the place, not helped by people expressing them differently.

 

A thought occurs - could it be that those who are using very little power, don't have their fridges very cold? Surely it is meaningless without knowing the temperature we are achieving? Setting no 2 doesn't mean too much.
 

 

[dor]

3 minutes ago, Johny London said:

Ok, I don't mean to pick on anyone but a few things that confuse me are...

 

Bengo: "The fridge itself uses about 2 Amps, only when the compressor is running, and it will typically run  30-60% of the time."

So that would equate to about 0.6-1.2amps per hour, quite low!

 

 

Neil2: "We have a Shoreline, I turn it up when we're running and down to "2" when moored and it seems to draw around 2 amps for about 20 minutes an hour."

It's open to interpretation but I took that to mean the fridge was drawing 2amps while running, equating to around 15amps a day. Dr Bob agrees with me and sais "2amps for 20 mins an hour is circa 16Ahr per 24 hours. Sounds very low."

 

Dor: "Our normal sized Shoreline fridge, with a 4* freezer compartment, uses 3.0 amps when the compressor is running."

That sounds very low for a running fridge/freezer, but good luck to ya. Interestingly MTBM confirms this!? And AndrewIC! Is there some disparity going on between models or is this fridge vs fridge freezer in some cases?

 

Ivan&Alice: "Thanks for all the figures. I'm working on the fridge running 1/3 of the time (8 hours per day) drawing an average of 6A, resulting in a 48Ah consumption per day."

If it's drawing an average of 6a, then it would be (6x24) = 150a per day

 

To top it all off, just look at the variation in these figures...

 

@Alan de Enfield - 45Ah
@BEngo - 50Ah
@Keeping Up - 35Ah (with bilge fans)
@Neil2 - 16Ah
@dor - 30Ah (3A*(25/60)*24h)
@Mike the Boilerman - 36Ah

 

Apologies for being such a pedant, but the figures we are getting seem to be all over the place, not helped by people expressing them differently.

 

A thought occurs - could it be that those who are using very little power, don't have their fridges very cold? Surely it is meaningless without knowing the temperature we are achieving? Setting no 2 doesn't mean too much.
 

 

I would not have said my fridge draws 3.0 amps when running if it was not the case.

I have a Blue Sea ammeter which I think is pretty accurate, especially as it agrees with other meters.

 I qualified my setting of ‘2’ by saying it was enough to turn the frozen milk yellow, I.e. it is pretty cold!

Shoreline seem to use whatever cabinets they can get a good deal on at the time,   which might explain the variation in currents reported.

[WotEver]

38 minutes ago, Johny London said:

a few things that confuse me are...

 

Bengo: "The fridge itself uses about 2 Amps, only when the compressor is running, and it will typically run  30-60% of the time."

So that would equate to about 0.6-1.2amps per hour, quite low!

Not really that low. 24 hours at 1.2Ah per hour equates to 28.8Ah daily. Close to the 30Ah suggested by some. 

[WotEver]

33 minutes ago, dor said:

Thanks for all the figures. I'm working on the fridge running 1/3 of the time (8 hours per day) drawing an average of 6A, resulting in a 48Ah consumption per day."

If it's drawing an average of 6a, then it would be (6x24) = 150a per day

No. It draws 6A when it’s running. It’s running for a third of the time.

 

So to calculate the daily consumption we take a third of 24hours = 8. Multiply that by the current when it’s running (6) gives us 8x6=48Ah per day. (Or you could take a third of the current (2) and multiply that by 24.  Same difference). 

[Dr Bob]

7 hours ago, Johny London said:

In the hot weather I find that mine runs quite a lot though the consumption does seem to be a couple amps an hour on average and I have it set to three or four on the stat. It's typically 7c inside.

 

7°C is quite high.

4°C or less is the recommended level by most and is what we have always tried to achieve. In hot weather though it can be difficult to get the temp by the fridge door that low (away from the cold zone at the back). Having an interior temp 10°C higher than normal (ie 30 rather than 20C) does put a strain and we see 5-6°C by the door but <4°C at the back on our typical setting.

[WotEver]

Basically 12V fridges use between about 30Ah to 50Ah per day. Whereabouts on that scale any particular fridge will lay depends upon how cold you run it, how often you open the door, how long you keep the door open, which compressor you have, how well insulated the cabinet is, how good the ventilation around the cooling fins is, how ‘full’ the fridge is, and the ambient temperature of the boat. 

 

52 minutes ago, Johny London said:

look at the variation in these figures...

Yup. See above for an explanation. 

Edited August 11, 2019 by WotEver
Added a bit

[Alan de Enfield]

2 hours ago, Johny London said:

To top it all off, just look at the variation in these figures...

 

@Alan de Enfield - 45Ah
@BEngo - 50Ah
@Keeping Up - 35Ah (with bilge fans)
@Neil2 - 16Ah
@dor - 30Ah (3A*(25/60)*24h)
@Mike the Boilerman - 36Ah

 

I said my old (not very efficient) fridge was about 45Ah.

I said my new (high priced, good insulation) fridge was 29-30Ah

 

The majority of respondees are around the 30-35Ah mark.

[MtB]

2 hours ago, Johny London said:

So that would equate to about 0.6-1.2amps per hour, quite low!

 

You were doing so well, but here we are back to meaningless twaddle. 

 

 

[Johny London]

12 hours ago, Mike the Boilerman said:

 

You were doing so well, but here we are back to meaningless twaddle. 

 

 

I knew someone would get me on the old a/h's. 

 

So should I have said 0.6-1.2a/h per hour??? In which case I've added to the already confusing array of ways the figures are being expressed.

 

It seems that the fridges are roughly falling into two categories, around 30a/h a day and high 40's. I'm still unclear who has fridge freezers and who has just fridges.

So - the compressors are capable of variable running speeds? (I thought I read this further back but cannot find it now). I thought they were either on or off. The former being the case would account for the wide variance of figures. The later being the case it makes no difference what insulation, temperature setting or fridge/freezer configuration (assuming all the compressors are the same one... the Danfoss BD35F , are they?). They would just draw what they draw, when running. 

[MtB]

2 minutes ago, Johny London said:

So should I have said 0.6-1.2a/h per hour???

 

No, one Amp drawn for one hour is an AmpHour, not an Amp per Hour. 

 

The forward slash you keep putting in means "per". Leave it out and I think you'll be fine!

 

"Per" means "divided by", so as you can hopefully now see, putting in those extraneous forward slashes completely changes the meaning of what you are writing.

 

 

 

[Chewbacka]

2 hours ago, Johny London said:

I knew someone would get me on the old a/h's. 

 

So should I have said 0.6-1.2a/h per hour??? In which case I've added to the already confusing array of ways the figures are being expressed.

 

It seems that the fridges are roughly falling into two categories, around 30a/h a day and high 40's. I'm still unclear who has fridge freezers and who has just fridges.

So - the compressors are capable of variable running speeds? (I thought I read this further back but cannot find it now). I thought they were either on or off. The former being the case would account for the wide variance of figures. The later being the case it makes no difference what insulation, temperature setting or fridge/freezer configuration (assuming all the compressors are the same one... the Danfoss BD35F , are they?). They would just draw what they draw, when running. 

It is actually current (Amps) multiplied by time (Hours) so written a Ah.  You could also have amp seconds or amp minutes which nobody uses.

 

Fridge compressors run at a fixed speed, at a (reasonably) constant current, but they do not run continuously, so two different people can have quite different Ah figures for the same fridge.

[MtB]

23 minutes ago, Chewbacka said:

It is actually current (Amps) multiplied by time (Hours) so written a Ah.

 

And to expand on this, although the "x" symbol means "multiplied by", it is a mathematical convention to leave it out with algebra and dimensions, so two units stated next to each other means "multiplied by". "AH" = "A x H" = "A multiplied by H". All three mean the same thing. 

 

Similarly "A/H" means "A divided by H", which actually means the rate at which an increasing current is rising, or a decreasing current is falling. 

 

 

 

 

 

[WotEver]

8 hours ago, Johny London said:

So - the compressors are capable of variable running speeds? (I thought I read this further back but cannot find it now). I thought they were either on or off. The former being the case would account for the wide variance of figures. The later being the case it makes no difference what insulation, temperature setting or fridge/freezer configuration (assuming all the compressors are the same one... the Danfoss BD35F , are they?). They would just draw what they draw, when running. 

No, it is the latter. And yes, they just draw what they draw when running. The huge daily variables come from how long and how often they are running, as I explained in post #56.