Cable length with lighting inverters

[ericmark]

With 50Hz cable lengths and use of coiled coil bulbs is unlikely to cause a problem the resonant length would be huge.

However with lighting inverters the frequency can be quite high and I wonder about cable lengths? With the old tordinal transformer I would use 4mm twin core to power 4 lamps around the room from one central unit my only worry was volt drop.

However I have not seen any information about cable lengths with inverters and at such high frequency one would expect just like a CB radio the voltage standing wave ratio would be critical and if wrong would cause over heating and premature failure. Also of course if the cable is not matched it could transmit and cause EMC problems.

Does that mean with inverters when powering 4 lamps there is a maximum cable length irrespective of volt drop?

Is this the reason we hear so many complaints about lighting inverters having a short life when compared with a tordinal transformer?

 

[Aragorn84]

I've noticed on HF fluro ballasts theres often a maximum cable length printed on them, and its usually only just long enough to get the cables into an average fitting. The ballast running my fishtank lights is a bit overlength on one side simply due to the remote placement of the ballasts in relation to the tubes.

Not sure if the switching PSU's have any similar limits though, arent they essentially outputting DC?

 

[JohnW2]

However I have not seen any information about cable lengths with inverters and at such high frequency one would expect just like a CB radio the voltage standing wave ratio would be critical and if wrong would cause over heating and premature failure. Also of course if the cable is not matched it could transmit and cause EMC problems.?

AC-AC SMPSs ('electronic transformers') for ELV lighting often do come with a stated maximum output cable length - often 2m or 4m.

It's surprisingly rare for even detailed specifications for these things to indicate what the output frequency is. I've found one (Osram Haotronic Professional) which does indicate the 'operating frequency' (which I assume translates to output frequency) as 40 kHz and that specifies the maximum output cable length as 2m. I can but presume that relates to EMC considerations since, with a wavelength of about 7,500 metres, I would not have expected standing waves (or 'skin effect' at that frequency) to be a significant issue.

Kind Regards, John

 

[bernardgreen]

The output lead length and type of cable can affect the function of some electronic transformers. Most it is the poor quality ones. those designed to be minimum manufacturing cost, whose function can be affected.

Those that have a smoothed DC output ( a capacitor on the output ) will not be affected by the capacitance between pos and neg wires in the lead and fitting. Those designed such that the output is high frequency chopped DC will be affected to some extent. How muchh depends on the design.

Any capacitance on an output which is chopped DC appears as a transient short circuit until the capacitance is charged evry time the DC is chopped on or off. Although extremely short duration the repetative transient shorts from a long length of lead may damage the output devices and reduce their life time.

 

[winston1]

The output lead length and type of cable can affect the function of some electronic transformers.

Not transformers please. They are switch mode power supplies.

 

[stillp]

From the IEC's International Electrotechnical Dictionary (IEC 60050):
IEV ref 151-13-42

en transformer
electric energy converter without moving parts that changes voltages and currents associated with electric energy without change of frequency

 

[EFLImpudence]

Yes, transform is just a word meaning Makes a marked change in the form, nature, or appearance of [something]

Therefore a transformer is something which does that by whatever means.

It is not limited to wire-wound or even electrical devices.

 

[JohnW2]

Yes, transform is just a word meaning Makes a marked change in the form, nature, or appearance of [something] Therefore a transformer is something which does that by whatever means. It is not limited to wire-wound or even electrical devices.

That's certainly a view, but the IEC definition which stillp posted requires that there be no change in frequency - and I don't think you'll find any of the sort of switched-mode electronic devices we're talking about which would satisfy that criterion. I imagine that such could only be achieved by going to DC and then converting it back to 50Hz AC (frequency synched to the input) - something which would presumably only be done if output frequency were crucial.

I also wonder whether resistors, capacitors and inductors would be regarded as satisfying the IEC definition of 'transformer', since they certainly have the ability to 'change voltages and currents associated with electric energy'. Indeed, a resistor could even do it with DC.

Kind Regards, John

 

[winston1]

From the IEC's International Electrotechnical Dictionary (IEC 60050):
IEV ref 151-13-42

en transformer
electric energy converter without moving parts that changes voltages and currents associated with electric energy without change of frequency

1:1 isolation transformers don't change voltage or current so the IEC is wrong.

From Wikipedia:

A transformer is an electrical device that transfers energy between two circuits through electromagnetic induction. A transformer may be used as a safe and efficient voltage converter to change the AC voltage at its input to a higher or lower voltage at its output. Other uses include current conversion, isolation with or without changing voltage and impedance conversion.

 

[stillp]

1:1 isolation transformers don't change voltage or current so the IEC is wrong.

That's debatable. The whole point of an isolation transformenr is to change the reference point of a voltage, but in the usual sense of "voltage" meaning only the potential difference between the two terminals of either the primary or of the secondary, then you're right.

I'm please that all transformers are safe and efficient, thank you Wikipedia.

 

[Monkeh]

From the IEC's International Electrotechnical Dictionary (IEC 60050):
IEV ref 151-13-42

en transformer
electric energy converter without moving parts that changes voltages and currents associated with electric energy without change of frequency

Well, unfortunately, a frequency change does occur with electronic drivers.

 

[JohnW2]

Well, unfortunately, a frequency change does occur with electronic drivers.

Indeed.

... the IEC definition which stillp posted requires that there be no change in frequency - and I don't think you'll find any of the sort of switched-mode electronic devices we're talking about which would satisfy that criterion. ....

Kind Regards, John

 

[EFLImpudence]

1:1 isolation transformers don't change voltage or current

Does that mean they aren't transformers, then?

It's just a word..

If something transforms something else then it is a transformer.
What does a rectifier put right?

 

[JohnW2]

1:1 isolation transformers don't change voltage or current

Does that mean they aren't transformers, then?

As even stillp, who presented us with the definition, has agreed that a 1:1 transformer is on the borderline of satisfying/not satisfying the IEC definition.

It's just a word.. If something transforms something else then it is a transformer.

You can't really generalise (about 'transformation') to that extent, else an awful lot of things would be called 'transformers' - e.g. most/all lamps, heaters, engines, machines etc. etc., for a start !!

What does a rectifier put right?

That is different. All dictionaries have the two, totally different, meanings (and most also have a third, relating to a chemical purification process).

As you should know, I'm largely with you on this issue. If not only for historic reasons (but also for present-day clarity/precision) I'm as unhappy/uncomfortable as winston1 about calling a SMPS 'a transformer' (just as I'm uncomfortable about electricians' "continuity measurements" !!) - but, unlike him, I have no great problem with their being called 'electronic transformers', just as I'm happy with 'electronic tape measures' and 'electronic cigarettes' etc.

Kind Regards, John

 

[ericmark]

I have no great problem with their being called 'electronic transformers', just as I'm happy with 'electronic tape measures' and 'electronic cigarettes' etc.

Kind Regards, John

I think you have hit the nail on the head. As long as the name differentiates between an inductive transformer and another device then not so bad.

However well before the lighting manufacturer started making switch mode high frequency devices to power 12 volt lights the welding machine manufactures started to produce the inverter which replaced the welding transformer giving far better control with a better feel and much lighter.

Since the name "Inverter" has already been used to describe these devices I see little point in using another name for basic same device.

Be it to raise or lower the voltage the electronic device to replace the transformer as been called an inverter. Often used with DC input to raise the voltage. In the old days it was called a rotary converter we also had the synchronous vibrator with transformer to raise voltage in the old days.

Although they contain a switch mode power supply in theroy there is no need for an inverter to contain any voltage or current control other than afforded by the transformer action. So rectify to DC feed a capacitor then turn to AC at high frequency then use a high frequency transformer is all that is required. And yes Electronic Transformer would describe this being basic the same as using the synchronous vibrator with transformer but using electronics rather than mechanical means to get the AC.

Where the current or voltage is regulated I would have called them drivers (current) or power supplies (voltage).

So where voltage is controlled one would expect the word "Regulated" so "Electronic Regulated Transformer" would be an acceptable description but it is rather a mouth full would not "Inverter" be better?

My thanks to point out the 2 or 4 meter limit also the frequency at 40 kHz amateur radio starts at 136 kHz so unlikely to cause interference. Some of the HF fluorescent units go into the Ghz range so very different.