In article 457c195f.0@entanet,
Skeggy wrote:
I want to set up a rack of 3 small fans (as a gadget to put under a
radiator on a cold day). I've got 3 Sharkoon 1000 PC fans, 12v 1.44 Watt
each. I want to power the rack from a normal plug-in mains adapter. I've
got a 12V DC / 800mA adapter available but I'm not quite sure if this
will be OK.

So delving way way back to my schooldays I think I dimly remember that:

W = VA so as W=1.44 and V=12, current will be 0.12 or 120mA for each
fan. V = iR so if V = 12 and i = 0.12 then R is 200, so resistance of
each fan is 200 Ohm.

So I'm thinking I'd be OK to wire up the 3 fans in parallel, current 3 x
120 = 360mA, resistance 66 Ohm?

You ain't half complicating things. ;-) Watts is V x A so 12 x 0.8, in the
case of your adaptor, gives 9.6 watts maximum output.

3 x 1.44 for the fans gives 4.32 watts so OK.


Also, I don't know if the 12/800mA adapter I've got is regulated, or if
this matters. It has a symbol on it like a segmented orange (a bit like
'Panaorama' logo) and also a square within a square if that helps.

With the load being approx half the maximum of the supply you're fine
either way. (An unregulated supply delivers rather more volts than its
nominal if very lightly loaded)

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Dave Plowman London SW
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