Calculate power requirements for Shoreline Fridge

[jetzi]

I realise this is a "how long is a piece of string" question, but I need some figures to work with.

 

I'm trying to re-audit my power requirements and I have a Shoreline RR47A 12V fridge with Danfoss BD35F compressor. I've been through the user manual and the only thing I can see regarding power usage is that it requires a 15A fuse. I'm sure that during normal usage it can't be using this much? I've seen

 

I realise as well that power consumption during warm and cold weather will be different, and it will also be different depending on how much we open the fridge and how much we use it. We tend to keep the fridge fairly full and we open it perhaps 8 or 9 times a day, and the freezer perhaps twice a day. There is a fair amount of space behind the fridge for the heat exchanger to work but it is rather boxed in.

 

Some minimum / average / maximum values would be really useful for summer/winter - what should I work with?

 

The fridge is located a good 15m (one way) cable run from the battery bank. I'm not sure what the cable thickness is but they are thicker than the others - around 6-7mm in diameter including the insulation. I'd also like to calculate whether the cables I have are sufficient.

 

Any help much appreciated!

[Alan de Enfield]

Work on 45Ah per day.

 

6mm2 cable (not 6mm OD) will give you 3.58% drop over 15 metres.

The maximum normally accepted is 3-4 % so it heading towards the top end.

 

(I use 8.5mm2 on mine)

Edited August 2, 2019 by Alan de Enfield

[BEngo]

The 15 A fuse is there to deal with the large inrush current when the compressor starts up.The fridge itself uses about 2 Amps, only when the compressor is running, and it will typically run  30-60% of the time.   Much depends on the ambient temperature and the installation.  Clean condenser grids at the back, good ventilation, and a computer fan or two blowing bilge air up at the back helps a lot.  Fans need to connected to the fan terminal on the control unit connector and then they will switch automatically.

 

I work on 50Ah every day for a margin of underperformance.

 

 Cables need to be sized for the initial inrush current and the voltage drop that produces. The acceptable limits of voltage are in the BD35 instructions.  Bigger is better as far as cables go and for a 30m (electrical round trip) total cable run I would go for 10mm2.  That is the aea of the copper, not the diameter of the cable.  Your present set of cables at 6mm outside diameter may well be adequate though.   What is the diameter of the copper bit?

If the fridge starts OK,  even when the batteries are fairly low and the engine is off,  I would leave well alone.

 

N

 

[Keeping Up]

With a couple of computer fans blowing cold air up from the bilge, I reckon ours consumed about 35 Ah per day.

[Alan de Enfield]

11 minutes ago, Keeping Up said:

With a couple of computer fans blowing cold air up from the bilge, I reckon ours consumed about 35 Ah per day.

My Waeco is 29-30Ah per day running about 25% of the time.

 

Our previous Shoreline was 45Ah per day.

[WotEver]

1 hour ago, ivan&alice said:

The fridge is located a good 15m (one way) cable run from the battery bank. I'm not sure what the cable thickness is but they are thicker than the others - around 6-7mm in diameter including the insulation.

Shoreline mandate 1mm² per metre run, so you should be using 15mm² cable. 16mm² is the closest you’re likely to get and that has an OD of about 8.5mm. 

[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.  On that setting we find it keeps everything really cold, in fact colder than our fridge at home on it's maximum setting. 

 

As we never use the ice box I removed the lid - don't know if that makes any difference..?  

[Bobbybass]

We have 6 of those blue freezer.blocks. When cruising we put them in the ice section so that they freeze without consuming battery power. After we moor up..we move three into the regular fridge. They act as a buffer when the door is opened.  Before going to bed we take the warm blocks out completely and put the still frozen  blocks from the ice tray into the regular fridge. They buffer the fridge during the night. Once we start the engine next day...all blocks go back into the ice tray.

[Dr Bob]

18 hours ago, Neil2 said:

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.  On that setting we find it keeps everything really cold, in fact colder than our fridge at home on it's maximum setting.

2amps for 20 mins an hour is circa 16Ahr per 24 hours. Sounds very low.

Our 240V fridge uses circa 4.5A when the compressor is running....similar numbers to what Alan is claiming above ie 30Ahr per day at 25% cycle. Alan's must be taking circa 4-5A with the compressor running as well.

21 hours ago, BEngo said:

The 15 A fuse is there to deal with the large inrush current when the compressor starts up.The fridge itself uses about 2 Amps, only when the compressor is running, and it will typically run  30-60% of the time.   Much depends on the ambient temperature and the installation.  Clean condenser grids at the back, good ventilation, and a computer fan or two blowing bilge air up at the back helps a lot.  Fans need to connected to the fan terminal on the control unit connector and then they will switch automatically.

 

I work on 50Ah every day for a margin of underperformance.

 

These numbers seem strange. 2A for 40-50% cycle is 24Ahrs per 24 hours. I would think the most efficient fridges use circa 25Ahrs per day and this one cant be if the compressor is running half the time?.....can it? If your 50Ahr every day estimate is nearer then either your 2A or 24Ahr is way off.

 

Everything I have read on here is that you are likely to get most optimum performance from a 240V fridge and ours is pretty good with a cycle of 25% ( 50 mins of compressor then 2 1/2 hours of standby......when ice free after a defrost). I reckon on around 25Ahrs per day on ours. Are these 2A compressor figures correct?

[Alan de Enfield]

6 minutes ago, Dr Bob said:

....similar numbers to what Alan is claiming above ie 30Ahr per day at 25% cycle. Alan's must be taking circa 4-5A with the compressor running as well.

Yes - I am working on about 4.5 amps for 15 minute in the hour so calling it roughly 5Ah per 4 hours or 30Ah per 24 hours.

All depends on ambient temperature and number of door openings.

[Chewbacka]

7 minutes ago, Alan de Enfield said:

Yes - I am working on about 4.5 amps for 15 minute in the hour so calling it roughly 5Ah per 4 hours or 30Ah per 24 hours.

All depends on ambient temperature and number of door openings.

Door openings and how full the fridge is.  If empty lots of cold air falls out and is replaced by warm air that needs cooling.  So keep your fridge full to reduce power consumption.

Edited August 3, 2019 by Chewbacka

[Bobbybass]

27 minutes ago, Chewbacka said:

Door openings and how full the fridge is.  If empty lots of cold air falls out and is replaced by warm air that needs cooling.  So keep your fridge full to reduce power consumption.

Did you read my section above...about our use of blue freezer-bag blocks?. Even in the hot with door opening ..it was rare the compressor ran for any period.

[Onewheeler]

1 hour ago, Dr Bob said:

2amps for 20 mins an hour is circa 16Ahr per 24 hours. Sounds very low.

Our 240V fridge uses circa 4.5A when the compressor is running....similar numbers to what Alan is claiming above ie 30Ahr per day at 25% cycle. Alan's must be taking circa 4-5A with the compressor running as well.

These numbers seem strange. 2A for 40-50% cycle is 24Ahrs per 24 hours. I would think the most efficient fridges use circa 25Ahrs per day and this one cant be if the compressor is running half the time?.....can it? If your 50Ahr every day estimate is nearer then either your 2A or 24Ahr is way off

Sounds about right. Our domestic A+ 230V fridge in a boat in mid France consumes 14 W average in conditions hotter than usual in the UK. About 65 W when the compressor is running.

[dor]

Our normal sized Shoreline fridge, with a 4* freezer compartment, uses 3.0 amps when the compressor is running.  During the day, when ambient temperature is warmer and the door is being regularly opened, it runs about 25 minutes in the hour.  Overnight it is on for less than 20 minutes per hour.  Setting is just below 2, which keeps the freezer section cold enough to keep frozen milk yellow.

Edited August 3, 2019 by dor

[Alan de Enfield]

2 minutes ago, dor said:

Shoreline fridge, with a 4* freezer compartment, uses 3.0 volts when the compressor is running. 

I think you need to get some charge in your batteries ………………………...

[cuthound]

9 minutes ago, Alan de Enfield said:

I think you need to get some charge in your batteries ………………………...

 

Or feed it with much larger cables than speaker cable ?

Edited August 3, 2019 by cuthound
Clarification

[Alan de Enfield]

15 minutes ago, dor said:

Setting is just below 2, which keeps the freezer section cold enough to keep frozen milk yellow.

Are you sure it is Milk ?

 

"Never eat / drink the yellow-snow"

[dor]

ok, I've updated the error!

 

yes yellow milk;  once milk is frozen below about -12 it takes on a yellow hue.  This only applies to full cream milk.

[jetzi]

23 hours ago, BEngo said:

Cables need to be sized for the initial inrush current and the voltage drop that produces. The acceptable limits of voltage are in the BD35 instructions.  Bigger is better as far as cables go and for a 30m (electrical round trip) total cable run I would go for 10mm2.  That is the aea of the copper, not the diameter of the cable.  Your present set of cables at 6mm outside diameter may well be adequate though.   What is the diameter of the copper bit?

If the fridge starts OK,  even when the batteries are fairly low and the engine is off,  I would leave well alone.

I don't know what the diameter of the copper bit is and it is hard to tell without calipers and stripping the wire.

 

The fridge starts and works fine so the wiring seems adequate. I'm more trying to figure out what the usage would be, thinking that if I could work out the average current draw on the fridge I could get an accurate number.

 

23 hours ago, Keeping Up said:

With a couple of computer fans blowing cold air up from the bilge, I reckon ours consumed about 35 Ah per day.

What if you detached the condenser coils and put them in the bilge? If you wanted to go really extreme what about putting them in a skin tank on the outside of the hull? Seems like this could be more effective than fans?

 

23 hours ago, WotEver said:

Shoreline mandate 1mm² per metre run, so you should be using 15mm² cable. 16mm² is the closest you’re likely to get and that has an OD of about 8.5mm. 

That seems like a heck of a lot. I calculate that 16mm^2 over a 15m run can handle 20A with a voltage drop of less than 5%. But I suppose this is to handle the peak power draw when the compressor starts up?

If I ever do replace the cables though I will put in 16mm^2 to make sure that I'm not losing any power since the fridge is a big consumer.

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. Of course I will do everything I can to reduce this, but I just want this as a bit-worse-than-average figure to go on when calculating my generation requirements.

That seem in line with what everyone expects?

[MtB]

2 minutes ago, ivan&alice said:

I'm more trying to figure out what the usage would be, thinking that if I could work out the average current draw on the fridge I could get an accurate number.

 

My 12V Shoreline fridge with the same compressor is drawing 2.9A right now (I just measured it with the clamp meter), so power consumption is 34.8W when running. 

 

I'd say it runs about 50% of the time so energy consumption is 1.5AH per hour, or 36AH per day. 

 

[Alan de Enfield]

8 minutes ago, ivan&alice said:

That seem in line with what everyone expects?

I did suggest (in post #2) to work on 45Ah per day to give a bit of safety-margin.

[Neil2]

22 minutes ago, Dr Bob said:

2amps for 20 mins an hour is circa 16Ahr per 24 hours. Sounds very low.

Our 240V fridge uses circa 4.5A when the compressor is running....similar numbers to what Alan is claiming above ie 30Ahr per day at 25% cycle. Alan's must be taking circa 4-5A with the compressor running as well.

These numbers seem strange. 2A for 40-50% cycle is 24Ahrs per 24 hours. I would think the most efficient fridges use circa 25Ahrs per day and this one cant be if the compressor is running half the time?.....can it? If your 50Ahr every day estimate is nearer then either your 2A or 24Ahr is way off.

 

Everything I have read on here is that you are likely to get most optimum performance from a 240V fridge and ours is pretty good with a cycle of 25% ( 50 mins of compressor then 2 1/2 hours of standby......when ice free after a defrost). I reckon on around 25Ahrs per day on ours. Are these 2A compressor figures correct?

I agree the numbers do look too low, but that's what the ammeter on the boat says, and I've checked it against other appliances.  I should emphasise that this is after cruising all day with the fridge turned up full and remember I don't have a lid on the ice box.  So when we are moored everything is already really cold and I assume the fridge is hardly having to work at all with the compressor spinning at the lowest rpm.  

[jetzi]

9 minutes ago, Mike the Boilerman said:

My 12V Shoreline fridge with the same compressor is drawing 2.9A right now (I just measured it with the clamp meter), so power consumption is 34.8W when running. 

 

I'd say it runs about 50% of the time so energy consumption is 1.5AH per hour, or 36AH per day.

Thanks for checking! I will measure mine and see if it is around the same. If I add an amp for buffer and increas the running time to 50% it still comes out to 48Ah / day.

 

7 minutes ago, Alan de Enfield said:

I did suggest (in post #2) to work on 45Ah per day to give a bit of safety-margin. 

Yes, I know! I just wanted to hear from a few others. To summarise this is what everyone reckons is a good figure to use per day:

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

[WotEver]

54 minutes ago, ivan&alice said:

That seems like a heck of a lot. I calculate that 16mm^2 over a 15m run can handle 20A with a voltage drop of less than 5%. But I suppose this is to handle the peak power draw when the compressor starts up?

Exactly so. They’re not my figures, they’re Shoreline’s. It’s so that when the batteries are a bit tired and the fridge starts up it doesn’t give up and bleep ‘low voltage’ at you. 

[Tony Brooks]

27 minutes ago, WotEver said:

Exactly so. They’re not my figures, they’re Shoreline’s. It’s so that when the batteries are a bit tired and the fridge starts up it doesn’t give up and bleep ‘low voltage’ at you. 

And Danfoss the compressor makers figures. It really is not worth skimping on cable size for a fridge. However I think there is another company making 12V DC fridge compressors but I doubt the consumption will be any less and may be a bit more.