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Puffling

What makes a 12v fridge twice the price?

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As anyone looking to replace their fridge must know, a 12v boat/caravan fridge is not cheap. In fact under 500 pounds seems like a brilliant deal from what I have seen.

My question I am posing to the more knowledgeable members (electrical engineers, possibly), is why is the fact that a 12v motor is used in place of a 240v motor a reason to double the price? Is there a sound design point requiring more to be spent on the electrics, or is it the often witnessed If it has leisure or marine before the model number, bung another 50% on the price ?

 

Apologies if the topic has already been dealt with, a search revealed nothing recent.

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50 million mains fridges are cheaper to produce than one thousand 12 volt fridges if you get what I mean.

  • Greenie 2

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I suspect it's a matter of quantity / economies of scale.  As more units are produced, the unit price will reduce. 

Edited by Scholar Gypsy

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“Because they can” In part, I suspect.

 

But it is also due to the efficiencies of volume. The market for a main fridge is massive, that for a 12v fridge is by contrast, tiny. I’m pretty sure the 12v fridge suppliers buy a mains one, rip out the mains compressor, and install a 12v one, all done by hand.

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At least one manufacturer buys them complete as mains fridges, then you pay for the labour cost of removing the 240v motor and disposing of it as well as fitting all the 12v bits.

  • Greenie 1

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1 minute ago, Keeping Up said:

At least one manufacturer buys them complete as mains fridges, then you pay for the labour cost of removing the 240v motor and disposing of it as well as fitting all the 12v bits.

I had a hunch this might be what happens.

 

So if I can find a suitable 12V DC motor secondhand (they usually have a long life as long as the brushes are replaced), I come out of it with a cheaper 12v fridge plus a free 240 volt AC motor.

7 minutes ago, nicknorman said:

“Because they can” In part, I suspect.

 

But it is also due to the efficiencies of volume. The market for a main fridge is massive, that for a 12v fridge is by contrast, tiny. I’m pretty sure the 12v fridge suppliers buy a mains one, rip out the mains compressor, and install a 12v one, all done by hand.

I see a business opportunity here, don't you?

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15 minutes ago, Puffling said:

why is the fact that a 12v motor is used in place of a 240v motor a reason to double the price? 

Because it's not "in place of", it's "in addition to".

 

Take a cheap 240V fridge, add in the price of removing the 240V compressor motor and fitting a 12V motor in its place, and then selling it to a much smaller market, and the result is not surprising.

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Just now, Puffling said:

I had a hunch this might be what happens.

 

So if I can find a suitable 12V DC motor secondhand (they usually have a long life as long as the brushes are replaced), I come out of it with a cheaper 12v fridge plus a free 240 volt AC motor.

The control board that they fit is relatively complex too. Supposedly to reduce battery consumption as well as make it tolerant of variations in battery voltage. Whether or not that is necessary is debatable.

 

Cheaper than a 12v fridge could be a mains fridge plus an inverter. This gives you the advantage that if it fails while you are travelling, a quick trip to the nearest electrical store provides a quick cheap replacement.

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4 minutes ago, Puffling said:

 

I see a business opportunity here, don't you?

No.

If it was that easy it would already be done.

 

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5 minutes ago, Puffling said:

I had a hunch this might be what happens.

 

So if I can find a suitable 12V DC motor secondhand (they usually have a long life as long as the brushes are replaced), I come out of it with a cheaper 12v fridge plus a free 240 volt AC motor.

I see a business opportunity here, don't you?

 

No - because its not a simple 12V motor, if it was the current demand would likely to be far more.  The "motors" and compressors are sealed units so there is no way you will connect a standard 12v motor to  the works. The motors are much more like stepper motors so need an elaborate electronic control box. Even if you find a second hand unit complete with control box you then need to equipment and skill to re-gas it while complying with environmental regulations.

 

Buy and efficient inverter, an A++ mains fridge, and plenty of solar charging

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8 minutes ago, Puffling said:

I had a hunch this might be what happens.

 

So if I can find a suitable 12V DC motor secondhand (they usually have a long life as long as the brushes are replaced), I come out of it with a cheaper 12v fridge plus a free 240 volt AC motor.

I see a business opportunity here, don't you?

I think one of the smaller 12 volt fridge companies already does this, you take them your chosen 240v fridge and they convert it to 12 volts. The 12v compressor is an expensive and well made unit, and the conversion needs a bit of equipment and expertise, so if you set up a company doing the conversion your prices will likely turn out just the same.

 

.................Dave

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22 minutes ago, Puffling said:

My question I am posing to the more knowledgeable members (electrical engineers, possibly), is why is the fact that a 12v motor is used in place of a 240v motor a reason to double the price? Is there a sound design point requiring more to be spent on the electrics, or is it the often witnessed If it has leisure or marine before the model number, bung another 50% on the price ?

 

The 240v motors are ac only induction motors built into the compressor unit and sealed into the gas system. You would need either a ac motor or controlled by an electronic converter(shoreline) or what is a built in inverter. Both are costlly. A cheaper option is to find a high quality, efficient sine wave inverter and use a domestic fridge.

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1 minute ago, Mike Adams said:

. A cheaper option is to find a high quality, efficient sine wave inverter and use a domestic fridge.

That is what we did. The fridge in question is now sitting in our kitchen here.

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1 minute ago, Tony Brooks said:

 

No - because its not a simple 12V motor, if it was the current demand would likely to be far more.  The "motors" and compressors are sealed units so there is no way you will connect a standard 12v motor to  the works. The motors are much more like stepper motors so need an elaborate electronic control box. Even if you find a second hand unit complete with control box you then need to equipment and skill to re-gas it while complying with environmental regulations.

 

Buy and efficient inverter, an A++ mains fridge, and plenty of solar charging

Thanks, Tony. I was originally going into this thinking that running through an inverter to get mains would be terribly inefficient. But a quick check shows that inverters become more efficient when heavily loaded. I've seen figures of 95% conversion efficiency mentioned, admittedly in domestic solar systems.

 

So by using a 240v mains fridge with some eutectic system for reducing the cycling time of the motor (fancy way of saying a slim tank of water-glycol mixture in the freezer compartment) running through an inverter, we are probably looking at a cost saving in the hardware and little power loss. Would you agree?

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6 minutes ago, Puffling said:

I had a hunch this might be what happens.

 

So if I can find a suitable 12V DC motor secondhand (they usually have a long life as long as the brushes are replaced), I come out of it with a cheaper 12v fridge plus a free 240 volt AC motor.

I see a business opportunity here, don't you?

If you can convince enough people that your brand on Amazon  'FRIDGEYWIDGEYFOODGOSQUIDGY' does it's job like the big players do then you might sell a few, but I doubt you'd make much profit. 

 

I had a 12v fridge with the boat when I bought it, developed a startup error after 3 years (if it was the original fridge then it did OK at 16 years old). Replaced with £120 Bush 240v one, haven't noticed any difference in power consumption and seems pretty efficient. 

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Just now, Puffling said:

Thanks, Tony. I was originally going into this thinking that running through an inverter to get mains would be terribly inefficient. But a quick check shows that inverters become more efficient when heavily loaded. I've seen figures of 95% conversion efficiency mentioned, admittedly in domestic solar systems.

 

So by using a 240v mains fridge with some eutectic system for reducing the cycling time of the motor (fancy way of saying a slim tank of water-glycol mixture in the freezer compartment) running through an inverter, we are probably looking at a cost saving in the hardware and little power loss. Would you agree?

 

Yes or no depending upon the fridge and inverter you choose. As you seem to want cheap I fear a low efficiency fridge and an Ebay special far eastern inefficient inverter and no amount of filling the freezer compartment will sort that combination out. I repeat - an efficient inverter and A++ or A+ fridge. Just make sure that the fridge can wake the inverter up if it has dropped into low current mode.

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1 minute ago, Rumsky said:

If you can convince enough people that your brand on Amazon  'FRIDGEYWIDGEYFOODGOSQUIDGY' does it's job like the big players do then you might sell a few, but I doubt you'd make much profit. 

 

I had a 12v fridge with the boat when I bought it, developed a startup error after 3 years (if it was the original fridge then it did OK at 16 years old). Replaced with £120 Bush 240v one, haven't noticed any difference in power consumption and seems pretty efficient. 

Sounds like the perfect fridge to fit aboard Boaty McBoatface 😛

 

Good to hear your switch to 240v was without any serious power consumption difference.

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Just now, Puffling said:

Good to hear your switch to 240v was without any serious power consumption difference.

Not just his. There are numerous threads on here that demonstrate the same. 

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1 minute ago, Puffling said:

Good to hear your switch to 240v was without any serious power consumption difference.

I have a 12v fridge and a 220v Freezer powered via an inverter.

 

The fridge uses ~30Ah per day

The freezer uses ~40Ah per day (but generally freezers 'take; a bit more than fridges anyway).

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3 minutes ago, Puffling said:

Thanks, Tony. I was originally going into this thinking that running through an inverter to get mains would be terribly inefficient. But a quick check shows that inverters become more efficient when heavily loaded. I've seen figures of 95% conversion efficiency mentioned, admittedly in domestic solar systems.

 

So by using a 240v mains fridge with some eutectic system for reducing the cycling time of the motor (fancy way of saying a slim tank of water-glycol mixture in the freezer compartment) running through an inverter, we are probably looking at a cost saving in the hardware and little power loss. Would you agree?

Danfoss make the 12v motor compressors and the electronic switching module to drive them. They are a Danish company and Denmark is a very expensive country to make stuff in, like Morco stoves the price reflects this. Its not a simple DC brush motor but a sequentially powered multiple winding induction  motor like a stepping motor.

 

If you buy a mains fridge that has a good old fashioned mechanical clicky thermostat you could install a dedicated pure sign inverter, around 1000 Watts, in the back of the fridge and use the fridge stat to switch the inverter on and off with a bit of wiring alteration to both. That way you have no standing inverter losses to drain the batteries.

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2 minutes ago, Tony Brooks said:

 

Yes or no depending upon the fridge and inverter you choose. As you seem to want cheap I fear a low efficiency fridge and an Ebay special far eastern inefficient inverter and no amount of filling the freezer compartment will sort that combination out. I repeat - an efficient inverter and A++ or A+ fridge. Just make sure that the fridge can wake the inverter up if it has dropped into low current mode.

I like to go cheap, but not when it's big environmental stuff involved. Definitely planning to seek out an A+ fridge at the least if I go with this option.

 

I've had quite a few cheapo eBay electronic deals (mainly LED power supplies) mainly because I couldn't be ar$ed to construct my own (I'm an electronics engineer). They usually work well enough, until they don't. But for an inverter I'd definitely build my own, rather than buy.

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3 minutes ago, Tracy D'arth said:

Danfoss make the 12v motor compressors and the electronic switching module to drive them. They are a Danish company and Denmark is a very expensive country to make stuff in, like Morco stoves the price reflects this. Its not a simple DC brush motor but a sequentially powered multiple winding induction  motor like a stepping motor.

 

If you buy a mains fridge that has a good old fashioned mechanical clicky thermostat you could install a dedicated pure sign inverter, around 1000 Watts, in the back of the fridge and use the fridge stat to switch the inverter on and off with a bit of wiring alteration to both. That way you have no standing inverter losses to drain the batteries.

Good info Tracy. Danfoss are a highly regarded company.

 

But I think I'd want to consolidate my inverter function in one unit if I did use mains refrigeration. For reasons of overall efficiency, plus having it "in the back of the fridge" would be a very unfriendly place (heat, switching pulses) for a piece of electronic gear.

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2 minutes ago, Puffling said:

Good info Tracy. Danfoss are a highly regarded company.

 

But I think I'd want to consolidate my inverter function in one unit if I did use mains refrigeration. For reasons of overall efficiency, plus having it "in the back of the fridge" would be a very unfriendly place (heat, switching pulses) for a piece of electronic gear.

It works fine, done a few over the years .Inverters are switching devices. Other pulses don't bother them one bit. Its pretty cool at the bottom of a fridge, the heat off the condenser rises drawing cold air in over the compressor.

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Some years ago a friend of mine who had a refrigeration / aircon business looked into converting a 230v fridge to 12v for me. Even at the best trade prices he could get the costs would have been more than buying one off the shelf.

 

There was no question of labour charges.

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