On 2 Nov, 09:56, (Andrew Gabriel) wrote:
In article ,
* * * * robgraham writes:

I have an older Ikea quad spotlight system in my workshop for lighting
over the wood turning lathe. *It uses a toroidal transfomer. *I was
checking out a portable infra red heater which has a 700w/350w switch
- when switched to the lower setting, the transformer in the light
hummed noticeably. *Any ideas why ?

My guess is:

a) You have significant voltage drop in your workshop with the
heater on (do the lights dim when the heater comes on?), and
b) the heater has only one element, and for the low power setting,
it is using either phase control or half-wave rectifier to generate
the low power setting.

These two mean the mains sine wave fed to the toroidal transfomer
is distorted, and mains toroidal transformers can get a bit
unhappy when that happens and start drawing a strange current
waveform. In theory, this can cause the transformer to overheat,
but I doubt the effect in your case would be bad enough for that.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Thanks Andrew - there is certainly a longish run to the workshop but a
700W heater - it's one of those ones with a bulb like thing and a
hyperbolic reflector - is hardly going to load anything significantly,
and this is at the half power setting.

I didn't realise that toroidal transformers were that sensitive. I
did guess it was a non-sinusoidal supply problem but I was surprised
that a 30A+ supply would be affected by a 'dirty' 1.5A load, and
further the lights and power are on separate mcbs on the local split
distribution CU

The 2kw fan heater makes no difference to the lights - the 3kw
circular saw does on start up.

Rob