An Engineer in Wonderland – Motor treasure
I have been having great fun messing about with motors.
A friend of mine has a new lathe.
Actually, it is an old lathe, a Mark 1 Master from Colchester.
It weighs half a tonne (or half a ton as it is of such vintage?) and replaces an even more magnificent Colchester Triumph which literally weighs a tonne and was just a little too big for the workshop.
Anyway, a previous owner replaced the three-phase motor with a single-phase one of the same power – 2.2kW (3hp).
The mechanical installation was fine, but the electrical installation was a little haphazard.
Now, I only know a little bit about motors, and take my hat off to those that know a lot, so I have been doing plenty of reading.
And I came across this marvellous book which not only has the straightforward stuff, but includes practical information that must have taken years to accumulate, and possibly then only through experience rather than theory.
For example, how do you tell the amount of ‘slip’ – the difference between synchronous speed and actual speed – of an induction motor.
Simple it seems – just take a look at the diagram below, which I hope Brooks Motors will forgive me for reproducing.
It turns out that end-to-end, an induction motor shaft carries an ac voltage waveform whose frequency is proportional to the slip rate.
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