OT - an electronics question please
Submitted: Monday, Oct 27, 2008 at 12:43
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Mikee5 (Logan QLD)
I have fitted a computer fan in the fridge cavity of my caravan, it is wired via a relay to switch on and off with the fridge (Vitrifrigo 12v), all good so far, now SWMBO wants the fan speed variable so that it can be slowed at night (too noisy). My thoughts are a wire wound potentiometer, and I guess it must be able to carry the max fan power of 3 watts. Am I on the right track? Dick Smith on line have a budle of these but all different ohms, and now I am getting beyond my knowlwedge. Can anyone point me in the right direction please. Also these things have three tabs, which wire goes on which?
Reply By: MrBitchi (QLD) - Monday, Oct 27, 2008 at 12:49
Monday, Oct 27, 2008 at 12:49
Why not just put in a switch to switch it off at night?
AnswerID:
332114
Follow Up By: Mikee5 (Logan QLD) - Monday, Oct 27, 2008 at 13:20
Monday, Oct 27, 2008 at 13:20
Hi
John,
Yes a switch would be the thing, however SWMBO wants the fan running but slower, so I am going to give it a try.
Cheers, Mike.
FollowupID:
599955
Reply By: Robin Miller - Monday, Oct 27, 2008 at 13:04
Monday, Oct 27, 2008 at 13:04
Hi there Mike
One of those will do, as you say make sure its 3w or more.
A value of 100 ohms will give you a fair bit of control as fans
resistance probably around 50 ohms.
You could go higher say up to 200ohm, but I wouldn't go much further as you risk having the fan stall out if batts volts drop.
Wire from the centre tap to one of the outside ones.
The resistance of those things changes at different rates as you rotate them depending on type.
Usually its best to go for one with a "Linear" taper.
E.G. Dick Smith R6907 or R6909
AnswerID:
332121
Follow Up By: Mikee5 (Logan QLD) - Monday, Oct 27, 2008 at 13:26
Monday, Oct 27, 2008 at 13:26
Hi Robin,
Thank you for helping me out. I was browsing these before I posted but had no clue as to what suited. I will buy one today and try it at the weekend.
Cheers, Mike.
FollowupID:
599958
Follow Up By: Robin Miller - Monday, Oct 27, 2008 at 13:32
Monday, Oct 27, 2008 at 13:32
Its a bit of an educated guess Mike but R6907 will probably cut minimum speed to half and R6909 to a third.
FollowupID:
599960
Reply By: Member - Alan H (QLD) - Monday, Oct 27, 2008 at 13:10
Monday, Oct 27, 2008 at 13:10
As stated I believe a switch would do the the trick. The idea of having the fan is to assist airflow in the heat of the day. It should be able to cope with the night.
To get real fancy, could put a light sensor on the switch so that it will automatically startup during the day. (also a different alarm clock to stop sleepins)
Alan
AnswerID:
332124
Follow Up By: Member - Graham H (QLD) - Monday, Oct 27, 2008 at 13:25
Monday, Oct 27, 2008 at 13:25
Easiest solution is buy a better quality fan that is quieter and put it on a rubber mount.
Its probably vibration causing the noise rather than the fan.
FollowupID:
599957
Reply By: austastar - Monday, Oct 27, 2008 at 14:45
Monday, Oct 27, 2008 at 14:45
Put a
second fan in, and wire it so that you can run in series or parallel with the other.
Best of both worlds
AnswerID:
332139
Reply By: RoyHarvey - Monday, Oct 27, 2008 at 16:46
Reply By: Boobook2 - Monday, Oct 27, 2008 at 19:39
Monday, Oct 27, 2008 at 19:39
I would put a thremostat in series with the fan. One that triggers on at say 30 DEgrees and off at 25.
If it is cold eg over night then the fan will be off. If it gets hot then the fan works.
You can even put a 40 degree one near the cooling fins on a gas fridge and it will turn on when the fridge gets hot.
Bacuase you open it less over night it will be cooler and hence less noise.
I saw a variable thermostat at a car parts place for a davis craig engine fan recently, that would be perfect.
AnswerID:
332188
Reply By: The Geriatric Gypsies - Tuesday, Oct 28, 2008 at 09:31
Tuesday, Oct 28, 2008 at 09:31
goodday mikees
are you having trouble with heat with the vitrifrigo as we have never had a problem with the waeco it was only ever the 3 way fridges because of the heat produced while operating or is it a 3way
steve
AnswerID:
332298
Follow Up By: Mikee5 (Logan QLD) - Tuesday, Oct 28, 2008 at 13:24
Tuesday, Oct 28, 2008 at 13:24
Hi Steve,
No and yes. The fridge (12v only) works fine but when we go off road, I block off the two caravan wall vents to keep the dust out. This means that the fridge gets less air and the internal temp rises, this fan is to suck the air out of the cabinet and into the van when the vents are blocked. Also to run it overnight to save pulling off the dust covers each night.
Mike
FollowupID:
600170
Reply By: NeilT - Tuesday, Oct 28, 2008 at 12:28
Tuesday, Oct 28, 2008 at 12:28
Don't even worry about electronics. You don't need them if you have the quietest fan in the world:
Nexus Case Fans
This site has a very large range - most are almost as quiet as the Nexus.
AnswerID:
332320
Follow Up By: Mikee5 (Logan QLD) - Tuesday, Oct 28, 2008 at 13:29
Tuesday, Oct 28, 2008 at 13:29
Hi Neil,
I have already bought and fitted the fan. It is an IP55 rated fan (dustproof motor). If/when it wears out I will look more into these quiet ones, although they don't seem to have the IP55 rating. Thanks.
Mike.
FollowupID:
600171
Follow Up By: NeilT - Tuesday, Oct 28, 2008 at 14:35
Tuesday, Oct 28, 2008 at 14:35
Mike - from what I can work out the IP55 rating is for an enclosure - not a motor. IP55 seems to mean it's dustproof as
well as " Protected against water jets" - very handy in rain. I'm thinking that when the time comes you keep the enclosure that the fan is currently in and then install a super quiet fan (i.e. Nexus)
FollowupID:
600177