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Re: MOT testing
Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
I hate to spoil the party but things get worse:
On 27 May 2002, at 14:54, Tesla list wrote:
> Original poster: "Alexander Rice by way of Terry Fritz
> >Original poster: "Tim J by way of Terry
> Fritz <twftesla-at-qwest-dot-net>"
> >The best way to measure a MOT is by
> feeding 120V or 240V (depending on MOT)
> >into the secondary. The primary should be
> around 5 to 6 Volts output. Then
> >you take 120V or measured mains voltage
> and divide by primary Volts.
> >120 V
> >_____ = 20:1 transformer or 2400 VAC
> >6 V
> that is fine to measure turn ratio
> >......then once your done that step use
> the mA current setting to measure
> >output current on the primary. This will
> tell you what sort of drawing rate
> >the transformer has.
> um, no actually it will just blow the
> fuse, if a transformer transforms voltage
> in the ratio 1:20 then it transforms
> current in the ratio 20:1 . since you are
> operating the device in reverse you have
> 120/20 = 6v but at (guessing 13A
> 'secondary' current) 13*20 = 260A which
> will do _bad things_ to your meter!
While those measurements might give you some idea of the reflected
load current you might see in the primary of a normal transformer
they take no account of the very high magnetizing (idling) current
drawn by a MOT while it is doing nothing other than being connected
to the mains.