# I'm confused, Fan wiring !

• posted on February 17, 2007, 10:29 pm

Got a 12V fan from Screwfix with the transformer.
It states in the instructions to wire the fan up with 1.5mm cable from the transformer to the fan. The wires from the choc block inside are about 0.5mm so why use 1.5mm
Fan spec is 12V x 50Hz @ 20VA
12V / 20VA = 0.6Amp
Or am I missing something. ?
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the_constructor

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• posted on February 17, 2007, 10:51 pm
On Sat, 17 Feb 2007 22:29:51 -0000, "the_constructor"

Possible voltage drop depending on the length of run

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• posted on February 17, 2007, 11:22 pm
On Sat, 17 Feb 2007 22:29:51 -0000, "the_constructor"

Volt drop. The short wires on the transformer won't drop much voltage but run to the fan from a couple of metres away with with the same size conductors will.
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Regards,
Stuart.

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• posted on February 17, 2007, 11:23 pm
the_constructor wrote:

A physics lesson, perhaps - you divide volt amps by volts to get amps. Even so, it is only a couple of amps at most. A 10 ft* run of 0.5mm2 would only drop half a volt - hardly a problem. (* 20 ft of wire)
Got the web page for the instruction manual?
The ones I have seen have only specified the mains wiring cable sizes - so that particular manual may have lost something in translation..
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Sue

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• posted on February 18, 2007, 1:07 am
the_constructor wrote:

As others have said, voltage drop is an issue on 12V systems since losing as little a 1V will make a big difference as a percentage of the nominal voltage.
As a general note you also need to keep in mind that with AC motor devices (especially those likely to use an induction motor such as a fan), their maximum current draw will tend to be higher than you would expect based just on the real power consumption of the motor since they will present a reactive load to the supply.
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Cheers,

John.

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• posted on February 18, 2007, 8:21 am
On Sun, 18 Feb 2007 01:07:39 +0000, John Rumm
|!the_constructor wrote: |! |!> Got a 12V fan from Screwfix with the transformer. |!> |!> It states in the instructions to wire the fan up with 1.5mm cable from the |!> transformer to the fan. The wires from the choc block inside are about 0.5mm |!> so why use 1.5mm |!>
|!> |!> 12V / 20VA = 0.6Amp |!> |!> Or am I missing something. ? |! |!As others have said, voltage drop is an issue on 12V systems since |!losing as little a 1V will make a big difference as a percentage of the |!nominal voltage.
Agreed, in my caravan which is all 12V, voltage drop is a *problem* I have had to increase the size of the 3m long wires to the 3 amp TV.
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Dave Fawthrop <dave hyphenologist co uk>
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