Curious hum from light transformer
 

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 ?

Rob

Curious hum from light transformer
 

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]

Curious hum from light transformer
 

On Nov 2, 9:56*am, (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.

non-sine load.


NT

Curious hum from light transformer
 

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

Curious hum from light transformer
 

In article ,
robgraham writes:
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.

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.

Well, this might not be the correct explanation, but it was
all I could think of. It would be interesting to know how
the 350W switch works. It's probably really a 'dirty' 3A load.
If the 2kw fan heater doesn't cause any dimming of the lights
when you switch it on, I'm rather stumped.

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

Curious hum from light transformer
 

In message , Andrew Gabriel
writes

snip

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.

Well, this might not be the correct explanation, but it was
all I could think of. It would be interesting to know how
the 350W switch works. It's probably really a 'dirty' 3A load.
If the 2kw fan heater doesn't cause any dimming of the lights
when you switch it on, I'm rather stumped.

A friend with an American camper van (mobile home:-) complained of
something similar.

In his case the toroidal step up transformer seemed to be affected by
the current load when the microwave cooker was in use. The most
noticeable effect was serious smoke from the diesel generator.

regards


--
Tim Lamb

Curious hum from light transformer
 

On Nov 2, 9:22*pm, robgraham wrote:

I didn't realise that toroidal transformers were that sensitive. *I
did guess it was a non-sinusoidal supply problem

unlikely

but I was surprised
that a 30A+ supply would be affected by a 'dirty' 1.5A load,

it won't be to any significant extent. Look at the load side of the
transformer.


NT

Curious hum from light transformer
 

On 3 Nov, 09:25, NT wrote:
On Nov 2, 9:22*pm, robgraham wrote:

I didn't realise that toroidal transformers were that sensitive. *I
did guess it was a non-sinusoidal supply problem

unlikely

but I was surprised
that a 30A+ supply would be affected by a 'dirty' 1.5A load,

it won't be to any significant extent. Look at the load side of the
transformer.

NT

NT - can you explain what you mean by that - it's 100W transformer
feeding 4 off 20W GU something-or-other bulbs. Is it possible it's
the bulb filaments 'singing' ?
Rob

Curious hum from light transformer
 

In article ,
Tim Lamb writes:

A friend with an American camper van (mobile home:-) complained of
something similar.

In his case the toroidal step up transformer seemed to be affected by
the current load when the microwave cooker was in use. The most
noticeable effect was serious smoke from the diesel generator.

The current waveform drawn by a microwave I looked at
had the strangest shape I've seen from any device.
Probably not a very high power factor, but I didn't
measure it.

Microwave ovens often only half-wave rectify the EHT
for the magnatron. They use an oversized EI lamination
mains transformer which will cope with this without
saturating on the DC component, but a tordoidal transformer
won't handle significant DC loads because of absolutely no
air gaps in the core. He probably managed to saturate the
core, which will cause excess current and overheating
of the primary winding, and maybe overloading whatever
was suppling it.

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