Running a 12 volt computer fan and a boats 12volt system?

There are about a zillion different models of 'computer fan' covering varying amounts of cheap, quiet, powerful, reliable etc.
I think you'd be unlucky to find a 12V one that blew up at 14.5V, but you never know!
Most of them these days seem to have some electronics in to control the speed, not a simple motor.
Probably best not to expect it to last forever though.
 
Quote "This is the data sheet for the danfoss compressor which is the most common compressor used on mobile fridge/freezers

https://assets.danfoss.com/documents/DOC147286416541/DOC147286416541.pdf

It talks about a 12 Vdc fan to be used on both 12Vdc and 24Vdc supply systems.

There is some kind of supply voltage detection in the controller so I would not be concerned with using a 12Vdc fan driven by the fridge/freezer controller as the controller controls the voltage across the fan terminals" End Quote

Yes, I've just fitted a new Dometic fridge, there's a label on the compressor which says 12 or 24 volts, with a controller, so there's obviously some electricery in the controller to stabilize the voltage, but I'm not sure if it's stabilised to 12 or 24 volts. My guess is that the controller is using some sort or inverter technology, so it could easily be either 12 or 24 volts.
 
Ian_Edwards said:
Quote "This is the data sheet for the danfoss compressor which is the most common compressor used on mobile fridge/freezers

https://assets.danfoss.com/documents/DOC147286416541/DOC147286416541.pdf

It talks about a 12 Vdc fan to be used on both 12Vdc and 24Vdc supply systems.

There is some kind of supply voltage detection in the controller so I would not be concerned with using a 12Vdc fan driven by the fridge/freezer controller as the controller controls the voltage across the fan terminals" End Quote

Yes, I've just fitted a new Dometic fridge, there's a label on the compressor which says 12 or 24 volts, with a controller, so there's obviously some electricery in the controller to stabilize the voltage, but I'm not sure if it's stabilised to 12 or 24 volts. My guess is that the controller is using some sort or inverter technology, so it could easily be either 12 or 24 volts.
Click to expand...

But the datasheet says only use a 12VDC fan so It sounds like that if the compressor is used on 24 VDC the fan will be supplied with 12VDC
 
Neeves said:
... We found computer fans can be more noisy at the dead of night than you would think - but as we re-cycle the fans - we have spares (and of different sizes).

Jonathan
Click to expand...

True.
In the computor fan extractor above my bunk I added a 100 Ohm resistor to one side of the two pole switch that came with the fan. This drops 3 volts and reduces the speed and noise of the fan to as good as silent.
The compressor on the fridge is louder than the extra fan that I fitted there, though.
 
Hmm, the posts about thd advisability or not of hanging a computer fan off the switched side of the fridge controller has got me thinking.
My compressor runs permanently hot in summer. If I connect it to the 12v supply to the fridge from my main panel, I calculate that it will add about 5% to the approximately 40AH drawn from the batteries by the fridge each day. I'll take that hit. Well, my battery bank and solar panels will. I hope that doing this will reduce the temperature that the compressor is operating at and save a bit of energy in return. Or perhaps extend the life of the compressor. Its 40 year old predessor died within 2 years of Mediterranean temperatures! ?
 
By putting a fan on the compressor will not reduce the energy used as the energy is being drawn anyway.

What it will do is reduce the temperature of the compressor and help to extend its life.

On second thoughts it your fridge is air cooled it could reduce the cycle time as will more insulation.
 
If you did need to provide a true 12v supply, what would be the best way of doing that? I'm finding that I can't charge either my or SWMBO'S phones using a car charger, and have had to use an inverter and a 240v charger instead. I presume the phones, which are both fairly new, are quite voltage sensitive, as they automatically shut down when plugged in to the car charger.
(Sorry for thread drift...)
 
Kelpie said:
If you did need to provide a true 12v supply, what would be the best way of doing that? I'm finding that I can't charge either my or SWMBO'S phones using a car charger, and have had to use an inverter and a 240v charger instead. I presume the phones, which are both fairly new, are quite voltage sensitive, as they automatically shut down when plugged in to the car charger.
(Sorry for thread drift...)
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I’d check that the car charger is cable of delivering enough amps to charge the phone(s). Some new phones need more than an older 12v charger can provide.
 
Rogershaw said:
By putting a fan on the compressor will not reduce the energy used as the energy is being drawn anyway.
..
Click to expand...
That's not true.
The fridge is a heat pump, which will run more efficiently the lower the sink temperature, as well as having less work to do.
 
Cooling compressor by any amount will reduce the total needed to rejected by the condenser, amount will be very small but still there. Air flow over the condenser is the priority though and somewhere for this heat to be removed too and not just moved around the inside of the cupboard area. The often used back of packet calculation is 3% power reduction for each 1 degree temp drop
 
Just to explain a DC motor does not draw current in a linear rate dependent on voltage as will say a light bulb. In the case of a DC motor with brushes the motor can be spun and works as a generator. This means that even as it spins under it's own power it is also generating a voltage internally which opposes the supply voltage. So the faster a motor spins the less current it draws becuae of this back EMF. So if you hit the motor with a higher voltage than designed for the motor will spin faster and yes will daw more current but not very much more compared to the increase in voltage. However the faster a fan runs the greater the air movement in an exponential way. So there will be more load on the motor at higher speeds.
Next problem is that many small fans are described as brushless ie using transistor switches in stead of commutator so I don't know if the above applies.
So if OP has any doubts or wants to reduce current slow the fan he can fit silican diodes in series aprox .7 volt drop each diode or use an adjustable buck regulator. ol'will
 
TernVI said:
That's not true.
The fridge is a heat pump, which will run more efficiently the lower the sink temperature, as well as having less work to do.
Click to expand...

thinwater said:
Nope. Read up on the thermodynamics of heat pumps. Efficiency depends on the high/low temperature differential; the narrower the spread, the more efficient. This is fundamental.
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You are correct but what you are talking about with a heat pump is the condenser temperature not the compressor temperature.

I have a water cooled condenser on both my fridge and freezer for the most efficient heat pump cycle. Any fan on the compressed will not lower the power consumption in my case the outside water temperature will by reducing the duty cycle of the compressor.
 
There are, obviously, computer fans and computer fans

I don't recall, as I am at home, what our fridge draws when it is cycled 'on' 4 amps? - Computer fans that I encounter draw fractions of an amp. I have a spare 80mm square one in front of me now, it draws 0.13 amp and 2 x 60mm fans which draw 55 and 65 mA each (all 3 are 12v). If a computer fan draws so much that it exceeds Danfoss' limits its simply too big (and must have come from a massive computer). I do know that the Danfoss fans are larger (again - the ones I see) and must be about 100mm square. The fans we have installed come from old 'domestic' computers (and in fact are probably much larger than used now (as my laptop now has no fan) and we use them as a supplement to the Danfoss fan and are not intended to replace it - in any way. I know you can buy 'computer fans' from retail outlets - but I doubt anyone will have the bigger versions in a conventional home computer. All our fans have been re-birthed (from domestic computers) - it would not cross my consciousness to go and buy one.

Jonathan
 
The way to measure the efficiency of a fridge/freezer is to measure the duty cycle.

I took 2 hour meters to measure the power on time and the compressor on time. Divide one by the other gives the duty cycle.

The lower the duty cycle the less power will be used

35917669402_8439099475_b.jpg


The red button resets both hour meters at the same time.
 
Neeves said:
There are, obviously, computer fans and computer fans

I don't recall, as I am at home, what our fridge draws when it is cycled 'on' 4 amps? - Computer fans that I encounter draw fractions of an amp. I have a spare 80mm square one in front of me now, it draws 0.13 amp and 2 x 60mm fans which draw 55 and 65 mA each (all 3 are 12v). If a computer fan draws so much that it exceeds Danfoss' limits its simply too big (and must have come from a massive computer). I do know that the Danfoss fans are larger (again - the ones I see) and must be about 100mm square. The fans we have installed come from old 'domestic' computers (and in fact are probably much larger than used now (as my laptop now has no fan) and we use them as a supplement to the Danfoss fan and are not intended to replace it - in any way. I know you can buy 'computer fans' from retail outlets - but I doubt anyone will have the bigger versions in a conventional home computer. All our fans have been re-birthed (from domestic computers) - it would not cross my consciousness to go and buy one.

Jonathan
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My 'home' computer has a big psu fan which has never run at full power. I think it's quite watty if it ever got turned to 100%.

I've fitted 100mm fans in equipment which draw 3A at full chat. The kind of thing that's intended to suck a lot of air through a filter.
They look pretty much the same, but cost more.
 
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