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

Ian_Edwards

Ian_Edwards

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I need to add some extra cooling to a freezer, I'm looking at at a 120mm 12 volt computer fan, but both my alternator and battery charger will charge at around 14.5volts (I can't remember the exact figure) on bulk charge.
Do computer fans survive running at 14 volts+ ?
The fan I'm looking at is one of these or similar:
link
https://www.amazon.co.uk/upHere-Com...ed-search-10&pf_rd_t=BROWSE&pf_rd_i=430516031
Anyone with any experience of running a computer fan at 20% or more over the rated voltage?
 
It'll still depend on getting a fresh supply of cool air from somewhere rather than just moving the existing air around the compressor. I had the same problem with an air-cooled compressor in a cockpit locker. I replaced it with a keel cooler which transformed the fridge and uses far less power.
 
You'll be fine. Computer fan on the compressor and a tiny fan in the fridge, a couple of computer fans in extractors in the deckhead, all regularly handle up to 14.3v from the chargers and have done for years.
So do the cheapo LEDs that I fitted 8 years ago except in one recently installed fitting. I reckon these warnings we get about charging voltages damaging our 12v fittings might be somewhat overstated. I was always intending to fit a voltage stabiliser but experience has taught me it isn't needed.
 
Catalina36 said:
It'll still depend on getting a fresh supply of cool air from somewhere rather than just moving the existing air around the compressor. I had the same problem with an air-cooled compressor in a cockpit locker. I replaced it with a keel cooler which transformed the fridge and uses far less power.
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I'm with you on that.
Last year my 40 year old air cooled Dometic system died and I replaced it like for like. I wish I'd bitten the bullet and gone for keel cooled. That said, we're liveaboards in the Med and the fridge and our 200w solar/450AH batteries manage fine for up to 2 weeks on the hook. But the heads, where the compressor is installed, gets like the Black Hole of Calcutta! ?
 
differentroads said:
I'm with you on that.
Last year my 40 year old air cooled Dometic system died and I replaced it like for like. I wish I'd bitten the bullet and gone for keel cooled. That said, we're liveaboards in the Med and the fridge and our 200w solar/450AH batteries manage fine for up to 2 weeks on the hook. But the heads, where the compressor is installed, gets like the Black Hole of Calcutta! ?
Click to expand...
One of the things I did do right was put ventilation in from the bilge to the compressor location. The woodwork around the compressor is currently 32 degrees, the bilge 26 degrees. Still hot but the sea is around that temperature so I can't do any better.
 
Ian_Edwards said:
Thanks all for the prompt reassurance, I'm using it at the top of the locker to extract hot air into the cabin, the cool air will get in through the bilge.
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I did the same. I also fitted a small discrete switch for when I didn't need that level of cooling in cooler climes.
 
I'm going to run this one using a small relay to switch on at the same time the compressor is running, I don't really want to parallel it up on the same supply as the fan already on the compressor.
 
We wired ours in the same circuit as the existing fan, so they all come on at the same time. We have the space and draw air from the bow locker and that ducting has a fan on it which draws air from the bow and blows it over the compressor etc, we have another fan that pulls the warmed air and vents it into the engine bay. We also have a separate deep freeze, under the galley sole, which uses much of the same ducting. We reasoned when at anchor the bow locker would have the coolest air.

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
 
Ian_Edwards said:
I'm going to run this one using a small relay to switch on at the same time the compressor is running, I don't really want to parallel it up on the same supply as the fan already on the compressor.
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Computer fans take so little current that there's no problem simply wiring it into the compressor fan's supply. I did this last century when I fitted a new fridge in my parents' ageing motor cruiser. It worked fine for many years.
 
They last a reasonable length of time despite the over voltage issue and are not expensive to replace, just make sure they are adequately fused.

As an alternative there are inexpensive circuits that will reduce the voltage. Often a larger diameter fan running at a lower voltage than specified (for example 9v for a 12v fan) will be quieter, consume less power but move more air than a small fan operating at a higher speed. You can even add add a thermostat so the fan only runs as needed.

However, while this offers some advantages, projects like this can become complex and time consuming, so unless you have an interest in electronics the KISS approach of a 12v fan directly wired is good solution. Replace when it fails which is likely to many years.
 
noelex said:
Often a larger diameter fan running at a lower voltage than specified (for example 9v for a 12v fan) will be quieter, consume less power but move more air than a small fan operating at a higher speed.
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Yes, that's very true. The engine compartment fan in my boat is a 24v inline unit running on 12v, so is certainly quiet (although as it only runs when the engine's running, that's a bit subjective!)
 
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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
 
Rogershaw said:
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
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True, a warning though, if you exceed the. Whatever amp which is the Danfoss limit, fridge compressor won't start. Got the t-shirt. Easy to do with an old bigish comp fan and a second similar one.

Boat 24V, 2fans on each fridge, all fine now, but got the warning leds on both so I know what's going on!

V
 
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