Noisy bilge blowers, why don't they make two sped models?

blampied

blampied

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I'm looking for a slow quiet 12v bilge blower fan.
We live on our 10 meter motor boat and would like to have a quiet blower running in the engine bay almost continuously to keep the boat smelling fresh and engine smells from percolating up into the living areas.
We have solar panels that most of the day provide a wasted excess of 12v power, the regulator has a take off that is live anytime the regulator has more power than it requires for battery charging. (That's most of daylight hours)

The banshee racket that Bilge blowers make may be insignificant while the engines are running, but when tied up in port are very obtrusive. We don't need to move huge quantities of air just a continious gentle suck would be sufficient.

We are a 12v boat and I was initially thinking of using a 24v blower assuming it would run at half speed with only 12v, however an electrician friend has pointed out that 12v through a 24v fan would eventually cause it to overheat.

It's a shame no manufactures supply two speed fans so they can be turned down.
what are my options for a slow quiet 12v ducted fan?
 
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Yes I would agree that for long term running to ventilate the boat a computer type fan would be best quietest and least current.
Fans have a characteristic that a small reduction in fan speed gives a large reduction in air moved. Sadly quantity of air moved air moved also relates to amount of noise made. You could try a speed control type voltage reducer on your engine fan just to see how this relationship of sound level to air moved works in practice. But really I would suggest you stick with the existing engine room fan for when the engine is running and for a period after then use a small computer fan to get air moving through the boat.
No a fan motor will not (usually) overheat on reduced voltage. The current will reduce and so power dissipated will be a quarter in theory except that at a lower speed the motor will draw more current so power (heat ) will be less but not a much less as you might expect.
To explain all electric motors (but more obviously with permanent magnet field motors) if driven by an outside rotation will act as a generator producing a voltage (and current) Now when a motor is running because it is powered internally it still generates a voltage and this voltage opposes the original powering voltage. Hence a motor with no load rotates faster but draws less current. More load slower rotation more current. Hence at initial start your starter motor draws a large current which reduces dramatically as rotation (cranking) speed increases.
Hence your electricians assertion that a 24v fan on 12v will draw more current so get hot. Well perhaps if air flow is so small as to not cool the motor enough but essentially less power dissipated so not likely to overheat. Some maybe more than others. olewill
 
I fitted a computer fan to the fridge in Mrs OH's motorhome, as it struggled on hot days (abroad!). I shopped for a super quiet model as some can be quite noisy. It works 100% - the fridge stays cold even on the hottest Mediterranean days with full sun on the fridge side of the van, yet we often dont know whether its running, and I have more than once had to check that its still working!
 
Thank you all for the advise.
I like that a 24v fan that I was originally thinking about is unlikely to overheat significantly on 12v, this looks like the simplest solution to what I'm trying to achieve
 
Warning !

I once fitted a quite expensive at the time solar powered extractor vent - closeable in heavy weather - above my fuel locker; I grilled the salesman ( At the Earl's Court Boatshow so a while ago ) and he promised me hand on heart it was ' spark - safe '.

The thing conked out after 12.0001 months, pretty much the same as the makers; I gave it to my ace electrician chum ( who knows the score and has sailed a lot with me ) to fix, he turned up ashen faced, " forget explosion-safe, this thing's more like a spark generator ! "

So it's a matter of wonder I'm not in orbit right now, peering through and tapping on the window of the ISS from the outside.

I have checked and no current solar extractor fan I'm aware of is spark-safe.
 
blampied said:
Thank you all for the advise.
I like that a 24v fan that I was originally thinking about is unlikely to overheat significantly on 12v, this looks like the simplest solution to what I'm trying to achieve
Click to expand...

Just to add that my Bavaria's engine room fan is a 24v version, running on 12v. It's quiet, and works fine.
 
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