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12v/240v fridge


Polly Graff

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Hi - I know very little about narrowboat electrics and what little I do know, I got from this forum. I want to fit a 12v fridge in my boat with the option to run off shorepower when its available. I have been advised not to go through the fuse box but to wire it direct from the batteries. This will involve around a 6-7metre cable run each way - so positve 6/7m to the fridge, negative 6/7m back again. I am planning to use 6mm cable and to include an in line fuse (I believe 10 amp is recommended? - not certain about that) and an in line switch. So - thats the theory ,, however, I am unc;lear exactly where and how to connect the cables to the 12v supply. I have three leisure batteries and a starter battery. Under the engine cover there are two battery isolators. I have no idea what they isolate - one is quite a substantial job with what looks like a stainless steel lever (the bit you pull out to isolate) and the other is more like the standard red plastic job. They are both newly fitted by a highly reputable outfit. I have a suspicion that connecting the cables direct to the leisure batteries is inadvisable - though not sure about that either. But logic dictates that I should be connecting the fridge cables somewhere on the fridge side of one or other (or possibly both) of the battery islolators. So - is that right and, if so, how do you go about connecting the cables? Any advice would be gratefully received. Also, how does the shore power part work on these fridges. Is there just a separate 13amp cable with a plug you can just plug into a socket when shore power is available  ...  or is it more complicated than that?

Thanks in advance PG

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1 minute ago, Polly Graff said:

Also, how does the shore power part work on these fridges.

 

Basically, it doesn't. You have to choose between either a 12Vdc fridge or a 230Vac mains fridge.  To run a 12V fridge from the mains on your mooring, just connect up a battery charger to the mains supply and the batteries. 

 

There are fridges available that run on both but they are a disaster as far as wrecking your batteries are concerned as they suck so much power, and are best avoided.

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1 hour ago, Polly Graff said:

Hi - I know very little about narrowboat electrics and what little I do know, I got from this forum. I want to fit a 12v fridge in my boat with the option to run off shorepower when its available. I have been advised not to go through the fuse box but to wire it direct from the batteries. This will involve around a 6-7metre cable run each way - so positve 6/7m to the fridge, negative 6/7m back again. I am planning to use 6mm cable and to include an in line fuse (I believe 10 amp is recommended? - not certain about that) and an in line switch. So - thats the theory ,, however, I am unc;lear exactly where and how to connect the cables to the 12v supply. I have three leisure batteries and a starter battery. Under the engine cover there are two battery isolators. I have no idea what they isolate - one is quite a substantial job with what looks like a stainless steel lever (the bit you pull out to isolate) and the other is more like the standard red plastic job. They are both newly fitted by a highly reputable outfit. I have a suspicion that connecting the cables direct to the leisure batteries is inadvisable - though not sure about that either. But logic dictates that I should be connecting the fridge cables somewhere on the fridge side of one or other (or possibly both) of the battery islolators. So - is that right and, if so, how do you go about connecting the cables? Any advice would be gratefully received. Also, how does the shore power part work on these fridges. Is there just a separate 13amp cable with a plug you can just plug into a socket when shore power is available  ...  or is it more complicated than that?

Thanks in advance PG

 

Edited by Tracy D'arth
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5 minutes ago, Tracy D'arth said:

Because you know so little that you thing a 13a plug is the way to connect 240v shore power to your boat please get a professional to do your electrics….

 

on my boat it is as simple as having a cable with a 13A plug that plugs into the shore power supply, (or generator). How do you do it?

 

Getting a professional to connect the other end of the cable to the shore power inlet on the boat seems a bit over the top, (to me).

 

5 minutes ago, Tracy D'arth said:

 

You must not connect the 12v fridge to the batteries directly, they must be fed via the cabin battery isolator.


I believe the OP suggested that this would be the logical way….. he also said that he “had been told” to connect directly to the batteries, and was checking here because it didn’t seem logical.

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1 hour ago, Tracy D'arth said:

Because you know so little that you thing a 13a plug is the way to connect 240v shore power to your boat please get a professional to do your electrics.

 

You must not connect the 12v fridge to the batteries directly, they must be fed via the cabin battery isolator.

 

Must admit this is something that has always confused me - I have had two boats where the fridge was connected direct to the battery (both passed BSI) and IIRC the instructions for last fridge I installed actually stated that the unit must be connected direct. 

 

In the days when boats were typically fitted out without electric fridges, I guess retro fitting was easier by simply wiring to the battery rather  than to the isolator, but provided there is a fuse near to the battery does it really matter?     

Edited by Neil2
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The Boat Safety Scheme requires that all electrical appliances should be connected via the battery isolator, unless one of the listed exemptions (which don't include fridges) applies or the manufacturers instructions say it should be connected to the batteries directly. So unless your fridge manufacturer specifies a direct connection then the fridge should be connected to the non-battery side of the isolator.

In practice I can't see any reason why the fridge can't be connected to a suitably rated fuse on the main fuse board - the cables from there to the isolator to the battery should already be sized for the maximum current the boat's combined appliances can draw.

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1 hour ago, David Mack said:

In practice I can't see any reason why the fridge can't be connected to a suitably rated fuse on the main fuse board - the cables from there to the isolator to the battery should already be sized for the maximum current the boat's combined appliances can draw.

 

Dangerous word, 'should'..!

 

But even so, it really can't be that difficult to connect to the switched side of the battery isolator if there is no spare fuse in the fuseboard or if the cables to the fuseboard are too small. 

 

 

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3 hours ago, Polly Graff said:

I have been advised not to go through the fuse box but to wire it direct from the batteries.

 

Who advised you to do that? I don't know much about 12v fridges as mine runs either from shore power or gas, but I'd have thought that like any other 12v appliances as long as all the cable cross sectional areas are sufficient to prevent excessive voltage drop then connecting the fridge via the boats fuse board would be fine. What's the advantage of connecting the fridge direct to the batteries?

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LOL - I may be ignorant but not completely intellectually defict! I do know that shore power doesn't come to the boat via a 13amp plug!!! What I meant was this:- on my boat, there is a shore power inlet (blue, round thing) - but that feeds a 13 amp socket on which someone in the past has helpfully written 'shoreline'. Plugging a 13amp plug into that socket then feeds what I like to think of as a 13amp ring main (i.e., lots of 13amp sockets up and down the boat). Next to the socket marked 'shoreline', there is another which the same person from the past has labelled 'inverter'. If you plug the above mentioned plug into the socket marked 'inverter', the inverter then feeds the 'ring main'. Since you can't plug the plug into two sockets at once, there is no risk of having the shoreline and the inverter feeding the 13amp plugs at the same time. So what I meant is, if you have a two way fridge which can work off either 12v or 240/230v, is it just a case of plugging it into a 13amp socket (which is being fed from the shoreline when the system is plugged into the 'shoreline' plug.

 

Moving on from that, MtB is saying that 12v/240v fridges should be avoided because they wreck batteries. Is this a generally held view? I have read about absorption fridges and that they are not good for batteries but I was talking about a 12v/240v compressor fridge. I have seen a couple of these advertised. Is the general view that it would be better to get a straightforward 12v fridge and a battery charger to harness the shoreline to keep the batteries charged, rather than one of these. My boat does not have a battery charger at the moment.

 

Lastly, the general consensus sxeems to be that the 12v should be connected to the fridge side of the battery isolator. How would one do that (i.e, the practicalities)?, is 6mm cabling okay for a 6 - 7m cable run and should I use a 10amp fuse or something bigger/smaller?

 

Thanks all,

PG

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38 minutes ago, MtB said:

 

Dangerous word, 'should'..!

 

But even so, it really can't be that difficult to connect to the switched side of the battery isolator if there is no spare fuse in the fuseboard or if the cables to the fuseboard are too small. 

 

 

 

Maybe this is why the manufacturers insist that their fridges are connected direct, to avoid any possibility of overloading, however remote.

 

And as David says, this requirement would override any Boat Safety regs.

 

Thinking about the two boats I had, the connections to the battery isolator were away from the batteries and on the other side of a steel bulkhead - I think it was a simple case of being easier to connect to the battery terminals.

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8 minutes ago, Polly Graff said:

LOL - I may be ignorant but not completely intellectually defict! I do know that shore power doesn't come to the boat via a 13amp plug!!!

 

The trouble is, we don't know how much you know. And from some of your questions, it is best we err on the safe side.

 

Nor did we know how your boat is wired until you told us. There is a staggering spectrum of ways it has been done on boats out there,  ranging from very well to appallingly dangerous.

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What you need is a mobiltronic MPS-35. 
 

https://www.dometic.com/en-gb/outdoor/uk/products/food-and-beverage/portable-coolboxes/coolbox-accessories/dometic-coolpower-mps-35-_-256409

 

 

Automatically converts 240v to 24v when 240v is available…when 240v is disconnected the fridge then runs on 12 or 24v….most of not all fridges with a danfoss BD-35 compressor will run on 12 or 24v. 

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I have never seen a 12  DC/240 V  Compressor fridge.  Are you sure you are not misreading an advert for a 12/24 V  DC  fridge? There are several if these  usually a house fridge cabinet with a Danfoss/ SECOP  BD35 compressor with a clever electronic package.  They will actually work off about 11V DC up to 16V or 22 V DC up to something like 30V.  But not AC at all.

N

 

N

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3 minutes ago, BEngo said:

I have never seen a 12  DC/240 V  Compressor fridge.  Are you sure you are not misreading an advert for a 12/24 V  DC  fridge? There are several if these  usually a house fridge cabinet with a Danfoss/ SECOP  BD35 compressor with a clever electronic package.  They will actually work off about 11V DC up to 16V or 22 V DC up to something like 30V.  But not AC at all.

N

 

N

Dometic did make one that had a built in converter which had a dc and ac input. I think they were a special order. 
 

My original Engel fridge also had a 240v ac & 12v dc connection as standard. They had a very odd compressor tho….I think modern Engels use a BD35….was a well built fridge! 

Edited by frangar
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Thanks very much everybody. I think I must have dreamed the 12v/240v combination so will put it out of my mind. Its an old boat and I wouldn't be convinced the cables to the fuse box would be up to the job. So - I'll opt for a straightforward 12v fridge which I will connect to the non-battery side of the leisure batteries isolator - once I've found out how that is done! Any suggestions would be gratefully received.

PG

39 minutes ago, MtB said:

 

The trouble is, we don't know how much you know. And from some of your questions, it is best we err on the safe side.

 

Nor did we know how your boat is wired until you told us. There is a staggering spectrum of ways it has been done on boats out there,  ranging from very well to appallingly dangerous.

Yes - I entirely get that - and I found the idea of plugging my boat into a 13amp socket genuinely amusing - so no offence taken or intended. The thing is, you can't learn anything in life without asking questions - and when you first start learning, some of the questions probably will be pretty stupid!

Regards, PG

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1 hour ago, Polly Graff said:

LOL - I may be ignorant but not completely intellectually defict! I do know that shore power doesn't come to the boat via a 13amp plug!!!

 

Oh it does sometimes. I lived on a garden end mooring on the Thames for 3 years where I took shore power from a 13 amp socket/plug. 

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Polly Graff, for what it’s worth I have a 2 way Engel fridge, they do exist, and it works well. If I’m travelling and putting in the engine hours, then on 12v it’s fine. Of course it’ll drain your batteries, like anything else would if you don’t put some charge back. 
 

How to wire one up, I ain’t got the foggiest.


I can plug the boat into shore power and simply plug the fridge in at the wall but for some reason I currently have it plugged into an extension lead which is then plugged in to the shore socket (don’t ask why)

 

 

 

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Polly.

 

To wire your fridge up you will need

Enough cable in the positive colour of your choice to go from the fridge to the battery isolator and allow for the fridge to be pulled out.  Cable size to suit length.  I think 10mm sq  cross section area would be OK.

Ditto for the negative cable in a different colour.

Two crimp on ring terminals to fit the cable and with the hole in the ring the right size for the isolator stud, and the battery negative terminal or busbar.  Usually these are 10mm for the isolator and 8mm for the battery terminal.  YMMV, so check first.

 

A switch with cable sockets to fit your chosen positive cable.

Two terminals for the fridge end of the cables.  Usually  6MM female push on type,  sized to suit your cables.

 

Crimping tool(s) for the various terminals.  Cheap crappy ones are no good and make bad joints with voltage drop so make sure you have good ones.

 

A multimeter or a 12V  test lamp.

 

Doing the job.

Mount the switch in a suitable position.

Run the positive  cables from the fridge to the switch and then to the battery isolator.  Cut the positive cable at the switch.   Run the negative cable from the fridge to the battery or bus bar.  Observe the BSS rules on support, separation from 240V, gas pipes etc.  This may not be the easiest part of the job.

 

Set the switch to OFF.

Connect the positive cable to the switch in and out  terminals.

Fit the terminals  to the fridge end but don't  connect yet.  Fit the terminals to the other end, crimp and connect positive to the battery isolator, negative to the battery negative or busbar.  Leave them somewhere safe- well apart, not touching anything metal,  not likely to be disturbed.

 

At the fridge end using a multimeter or test lamp check there is 12V or more at the cable ends and that the switch works.  Switch OFF.

 

Connect the positive cable to the positive terminal of the fridge.  Ditto the negative cable.

 

Put fridge in its final location keeping the spare cable out of the way of 'stuff'.

 

Switch ON.  The fridge should start up and the light inside should work.  If it is a Danfoss unit there is a short delay between switching on and the motor running.  If it does not run consult the Danfoss book and the flashing LED to see what might be awry.

 

More realistically, I think you would be better with a professional. Tell us where your boat is and someone may be able to reccomend an electrician.

 

N

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On 22/08/2021 at 16:55, Polly Graff said:

LOL - I may be ignorant but not completely intellectually defict! I do know that shore power doesn't come to the boat via a 13amp plug!!!

Shore power in the marina where I moor is from bog standard 13A sockets in a small box.

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