LED lights failing

[SUNRAY]

Referring to notes from 2012 re a panel fault of devices 'dropping out' and 'breakers tripping':


24V 750VA Park (PES) transformer, primary MCB 6C,
With no sec load I had to operate the pri MCB 4 times before it held in. referring to MI’s - changed to16D.
Pri voltage 243V, OFF LOAD pri current 0.45A (approx 100VA)
OFF LOAD Sec voltage 27.7V

4.8A – 25.6V
7.2A – 25.5V
9.7A – 25.5V
12.7A – 25.5V
17.3A – 25.5V
22.8A – 25.5V
26.2A – 25.5V
31.0A – 25.5V
34.6A – 25.5V
38.6A – 25.5V
42.1A – 25.5V
46.2A – 25.4V

Ie the regulation from 25% to 135% is pretty much flat according to a meter with a 0.1V resolution.
However they are quite inefficient as seen by the offload current which does improve with load.

 

[JohnW2]

It is simply a transformer designed for control panel use.

BAS has already made most of the points I was going to make/ask in response to that, so I will wait and see how you respond to his responses!

Kind Regards, John

 

[SUNRAY]

A control panel is just a type of enclosure, and, per se, has absolutely no electrical properties, except possibly EMI screening.

Er no...
A control panel is a panel that controls, it may be built into an enclosure which may be metal and provides screening or it may be in a plastic box to provide waterproofing, it may be armoured or intrinsically safe etc. It may not be in any sort of enclosure if you go back in time...

I'm not going to go into great detail of what control panels do or how they perform their functions as there is an endless variety, needless to say most of them have a transformer of some sort to power the panel which may be anything from 1VA upwards, biggest I've provided is 3KVA but they do go bigger. and yes they are designed differently to a 'regular' transformer.

 

[JohnW2]

I wouldn't classify either BAS or myself as being unduly dim, but think we are both struggling to understand all this, given that no-one has really provided much of an answer to what seemed to be a very simple question.

What aspects of whatever these control panels are controlling, in whatever fashion they are doing that controlling, dictate that they require 'special' transformers in them?

Kind Regards, John

 

[SUNRAY]

The simple fact is 'control' transformers are made to a different standard to say an amplifier mains transformer which in turn is different to a bell transformer, I don't know the absolute ins and outs of each design, as I leave that to others to design and build, but I do understand that they are different.
As mentioned previously one of the common differences is they mostly seem to weld the laminations together which goes against the theory that I learnt many years ago.

 

[JohnW2]

The simple fact is 'control' transformers are made to a different standard to say an amplifier mains transformer which in turn is different to a bell transformer, I don't know the absolute ins and outs of each design, as I leave that to others to design and build, but I do understand that they are different.

I have no problem with that as a concept, but I don't think I'm going to be any the wiser about 'control transformers' unless/until someone is able to explain to me what aspects of whatever 'control transformers' are controlling and/or the mechanism whereby they achieve that control, dictate the need for a different type of transformer than one which is used for other purposes.

Maybe Mr Google can help me - watch this space!

Kind Regards, John

 

[bernardgreen]

Control transformers supply the power to the control circuits on a machine. Circuits such as the Top_Start buttons and power contactor coil. Emergency Stop circuits, opening and closing valves etc etc. The term "control" comes ( I believe ) from the days when electrical controls were finally added to mechanical machines to bring all the controls to a central control instead of having valves and levers spread all around the machine.

The control transformer has to have good regulation ( as already mentioned ) to prevent the secondary voltage dropping as the output current increases.. There is no regulation as such. In all transformers the secondary voltage drops as the load current increases due to the resistance if the secondary winding creating a voltage opposing the magnetically induced voltage. In a control transformer this opposing voltage is minimised by having a very low resistance secondary winding which requires large cross section winding wire or tape ( Tape can result in smaller diameter transformers. ). The secondary winding can carry many times the maximum load current before the opposing voltage (and hence the reduction in output voltage) becomes significant

A normal transformer that is required to supply a known load current is designed ( or selected ) by taking account of the opposing voltage at the design current by adding it to the required on load output voltage and using this result as the off load voltage for the transformer secondary. The wire used in the the secondary winding need only carry the load current without over heating.