Continuing fridge issues

[Boater Sam]

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v. If the inverter cannot get its output to the required voltage, it will not start the compressor but will draw current. Insufficien copper problem, get some 10 mm sq cables in but testing it next to a charged battery with some decent size cable is a good idea.

[MtB]

4 minutes ago, Boater Sam said:

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v.

 

Really? Now that IS interesting! 

Is it a 240Vac compressor then? If so, it looks to me as though an el cheapo 240Vac fridge must be dead easily converted to 12v. Have we been had for the last 20 years?

[WotEver]

46 minutes ago, Flyboy said:

Not necessarily so, you would still get a voltage drop if the compressor was siezed. The stall current will be quite high.

As suggested in posts 3 & 6, with an alternative suggestion in post 8. 

The cabling needs updating anyway so once that’s done we’ll know if the fridge has a problem. In the mean time if OP really wants to drag a battery out of the bank into the galley and rig up a temporary supply then I’m not going to stop him. It just seems a bit pointless. 

30 minutes ago, Boater Sam said:

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v.

How do you know this? It’s not previously been mentioned. 

[Flyboy]

On 06/04/2018 at 09:28, colmac said:

Thanks all. First point, the fridge doesn't have a temperature "knob" it's an all singing dancing modern one with a series of LED's to set the temperature. The voltage drop between the batteries and fridge is due, I presume ,to a voltage drop due to the length of cable twixt the two,12m.  I think a call to the manufacturers is the answer, only had the fridge for 3 weeks.Cheers all.

If you have an isolation switch (which you should have) near to the fridge it may be contributing to the voltage drop.. You need a decent 20amp or larger  DC switch. I seen several fridges with problems caused by a totally inadequate 5amp AC domestic light switches being used. I would not recommend a fridge to be powered from the DC panel as the switches are normally inadequate. It should be connected directly to the main bus bar via a 20-30 amp fuse.

[Boater Sam]

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v. If the inverter cannot get its output to the required voltage, it will not start the compressor but will draw current. Insufficien copper problem, get some 10 mm sq cables in but testing it next to a charged battery with some decent size cable is a good idea.

Torn a number apart.

My current thinking is to use an efficient 240v AC domestic fridge, build into it a dedicated inverter big enough to start the compressor properly, say 1000w, and wire the fridge stat into the inverter on/off circuit, shorting out the original wires to the stat. That way the inverter only comes on when the fridge needs it, no standing losses.

[WotEver]

9 minutes ago, Boater Sam said:

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v.

That’s not what Danfoss say. They specifically refer to a D.C. compressor and also refer to a 230V to 12V conversion within the electronics box. 

http://files.danfoss.com/TechnicalInfo/Dila/06/bd_compressors_04-2007_pk100c802.pdf

[Alan de Enfield]

14 minutes ago, Boater Sam said:

My current thinking is to use an efficient 240v AC domestic fridge, build into it a dedicated inverter big enough to start the compressor properly, say 1000w, and wire the fridge stat into the inverter on/off circuit, shorting out the original wires to the stat. That way the inverter only comes on when the fridge needs it, no standing losses.

 

Surely having a fridge with its own dedicated inverter 'built-in' will mean that you will need long lengths of 'big' cables running from the batteries to the inverter - isn't one of the benefits of 230v that you can have the inverter close to the batteries (short length of 'fat cable') and run 'small' cables to the 230v fridge ?

Edited April 7, 2018 by Alan de Enfield

[Boater Sam]

Correct, but then you have to leave the main inverter running constantly, wasting power all the time, if you are not on a shore line. Surely that is the problem running a mains fridge on a boat.

[Tony Brooks]

30 minutes ago, WotEver said:

That’s not what Danfoss say. They specifically refer to a D.C. compressor and also refer to a 230V to 12V conversion within the electronics box. 

http://files.danfoss.com/TechnicalInfo/Dila/06/bd_compressors_04-2007_pk100c802.pdf

Yes and if you read and think about what they say it seems the motor is more of a stepper motor than a normal 12V motor. I think it has a permanent magnet rotor. How would that work with an AC supply? (rhetorical question to cast some doubt on some of the advice that has been given).

It would help if the OP gave make & model of the fridge in this topic (unless I have missed it).

[Alan de Enfield]

3 minutes ago, Boater Sam said:

Surely that is the problem running a mains fridge on a boat.

But it is not a problem if you have an electrical system designed to do so.

We have 230v AC fridges / freezers on both our boats running off the inverters, we have a fridge running via an inverter in our Horse Trailer (with 1x 110Ah battery) - we don't have any issues / problems as the 'system' is designed to work with a fridge / freezer

If you are trying to shoehorn a 230v Fridge into an existing marginal electrical system then, yes, you may have problems.

We may be boating but we don't intend to live in a cave, we design our equipment around our lives, not our lives around the equipment.

[OldGoat]

I did a lot of 'research' on this topic some years ago and am under the impression that the inverter option was dropped - the document above is dated 2007 and I've seen no reference to it since...

[WotEver]

19 minutes ago, Tony Brooks said:

It would help if the OP gave make & model of the fridge in this topic (unless I have missed it).

Yes it would, and no you haven’t missed it. 

13 minutes ago, OldGoat said:

I did a lot of 'research' on this topic some years ago and am under the impression that the inverter option was dropped - the document above is dated 2007 and I've seen no reference to it since...

So can you point to any document that supports Boater Sam’s assertion that 12V Danfoss Compressors are actually mains compressors with an inverter?

[WotEver]

If you wanted to power a 230V fridge with a dedicated inverter then you’d have the inverter close to the batteries and run a small signal cable from the fridge to turn the inverter on and off. (If you could find a suitable fridge). Alternatively you could leave the fridge stat set to maximum and purchase a separate stat to control the inverter. 

[OldGoat]

8 minutes ago, WotEver said:

Yes it would, and no you haven’t missed it. 

So can you point to any document that supports Boater Sam’s assertion that 12V Danfoss Compressors are actually mains compressors with an inverter?

No I can't !

if you delve through the large PDF in a previous post, you'll see that one of the power options was 240V  - but that was an add-on to the standard 12/24v controller. I have a dim recollection that the term 'inverter' was incorrect (translation from the Danish?), more likely a digital power supply - similar to a PC power pack; they can be quite small and fit into the Danfoss control unit. The BD35 and 50 have always been low voltage units.  

[Boater Sam]

I never said the compresor was a mains voltage one, I'm not making any further comments as I am being misunderstood and the replies will be confusing and false for the OP.

[WotEver]

19 minutes ago, Boater Sam said:

I never said the compresor was a mains voltage one,

So what did you mean by this then?

1 hour ago, Boater Sam said:

The fridge even though its 12v does have its own inverter inside, the compressor is not 12v.

 

29 minutes ago, OldGoat said:

if you delve through the large PDF in a previous post, you'll see that one of the power options was 240V  - but that was an add-on to the standard 12/24v controller.

Yes, exactly as I said when I wrote...

1 hour ago, WotEver said:

They specifically refer to a D.C. compressor and also refer to a 230V to 12V conversion within the electronics box.

 

[Neil Smith]

I converted a mains fridge freezer to 12v by buying a 12v dc compressor and fitting it, the motor clearly states 12v dc on its label so no need for an inverter.

Neil

[WotEver]

4 minutes ago, Neil Smith said:

I converted a mains fridge freezer to 12v by buying a 12v dc compressor and fitting it, the motor clearly states 12v dc on its label so no need for an inverter.

Neil

Absolutely Neil. I honestly don’t know why folk say such silly things.   

[Tony Brooks]

If I am correct in my belief the motors have permanent magnet rotors then naturally the battery DC will need to be "chopped up" and directed to the correct set of stator windings but that is not an inverter, its an electronic driver device just as you have on stepper motors. I suspect the driver is what Mr Sam is calling an inverter.

One thing is for sure and that is if you compare the size of the electronic control unit on a fridge and the cheapest, smallest inverter the fridge unit will be around 1/3 the size of the inverter and with a much smaller heat sink if it has one at all. To my mind that says it is not an inverter.

14 hours ago, OldGoat said:

if you delve through the large PDF in a previous post, you'll see that one of the power options was 240V  - but that was an add-on to the standard 12/24v controller. I have a dim recollection that the term 'inverter' was incorrect (translation from the Danish?), more likely a digital power supply - similar to a PC power pack; they can be quite small and fit into the Danfoss control unit. The BD35 and 50 have always been low voltage units.  

That is what I believe the case to be and I think Shoreline still sell an optional mains to 12V DC power pack for use when the boat is on shore power but its a separate box.

[Neil Smith]

Yes tony, that would just be a step down 240-12v transformer of suitable size to cope with the fridge motor, I was thinking about it myself but figured that if I am on mains the battery charger and solar would cope.

Neil

[Tony Brooks]

11 minutes ago, Neil Smith said:

Yes tony, that would just be a step down 240-12v transformer of suitable size to cope with the fridge motor, I was thinking about it myself but figured that if I am on mains the battery charger and solar would cope.

Neil

The battery charger bit is why I have never understood why Shoreline ever tried to sell the product unless it was intended for non-boating applications.