Cheap transformer?

[Joseph_Pestell]

5 hours ago, kevinlms said:

What you need to know is that these transformers are designed for a specific purpose - that of providing a power source for quartz halogen lights and so they are optimised for that. This means that they are designed to put out a constant supply for 50 Watt lights.

 

You could use them for other functions, with a similar load characteristics, but they would be unsuitable for loads significantly less than 50 Watts, because as others have stated, the voltage will float much higher.

 

Sorry, but it is not 'being negative' to inform you why they won't work. Nor should it be considered as wrong to tell you that no transformer will work on DC. It's a fact of physics.

 

Agreed, good information is not negative. It is the way that some people convey that information that gives a rather negative impression.

[BoD]

5 hours ago, kevinlms said:

. Nor should it be considered as wrong to tell you that no transformer will work on DC. It's a fact of physics.

Might this not be simply a case of people using the wrong terminology?*  When we were young the whole controller that came with our train set was called ‘the transformer’. Just google train set or model railway transformers and it still happens today.  Some manufacturers don’t help either.

 

For many the power supply unit of whatever type is just the transformer.  This is not acceptable for those who are ‘into’ electronics, professionally or otherwise, but for the majority of laypersons it does the job.  Out of interest, and not being up to date with these things, is there a single device that can change the  DC voltage and what is it called?

 

* If I were Churchill I might call it a terminological inexactitude.

[KeithMacdonald]

28 minutes ago, BoD said:

 Out of interest, and not being up to date with these things, is there a single device that can change the  DC voltage and what is it called?

 

Yes, a DC-DC converter.

 

A few decades ago, I built one myself to bring 24V truck voltage (in a very old truck) down to 12V regulated for a 12V stereo radio.

 

Nowadays, much easier to buy one off the shelf from people like RS Components 

https://uk.rs-online.com/web/c/power-supplies-transformers/dc-dc-converters/

or Farnell UK

https://uk.farnell.com/c/power-line-protection/power-supplies/dc-dc-converters

[cliff park]

A device to change DC to a different DC is called an inverter. It normally works along the lines of an oscillator to chop up the DC voltage, feed that through a transformer ( Chopped up dc looks a lot like AC, albeit square wave) then rectify the resultant AC to produce DC, then smooth it and voila. Another way is to use the DC to turn a motor, and use this to drive an alternator, push the resultant AC through a transformer, then rectify............etc. These techniques are really for high power DC to DC, especially the second one. Of course with modern miniature electronics the whole thing can be much smaller, but the same principles still apply 

[jpendle]

27 minutes ago, BoD said:

Might this not be simply a case of people using the wrong terminology?*  When we were young the whole controller that came with our train set was called ‘the transformer’. Just google train set or model railway transformers and it still happens today.  Some manufacturers don’t help either.

 

For many the power supply unit of whatever type is just the transformer.  This is not acceptable for those who are ‘into’ electronics, professionally or otherwise, but for the majority of laypersons it does the job.  Out of interest, and not being up to date with these things, is there a single device that can change the  DC voltage and what is it called?

 

* If I were Churchill I might call it a terminological inexactitude.

 

It absolutely is a case of people using the wrong terminology, which in and of itself is not a big deal.

 

When I call the 2 leading wheels on a 2-6-0 loco, a bogie, I'm just using the wrong terminology, and nobody gets hurt.

 

BUT when talking about an electrical device which can be connected to the mains in your house then the terminology becomes more important, because you can get hurt messing with domestic mains voltages.

 

BTW there are many devices that will change a DC voltage, but for the purposes of powering things up, then the device is typically called a voltage regulator, and it converts higher voltages to lower voltages, e.g 12VDC to 5VDC, or 5VDC to 3.3VDC , etc.

 

And just for the record, a transformer that converts 240VAC to 24VAC, can be wired backwards to convert 24VAC to 240VAC, which is why you don't want to wire one of these backwards and then plug it in. A power supply that you plug in and which generates between 0VDC and 12VDC (i.e. a model train controller) doesn't do anything if wired backwards, except maybe go up in a puff of smoke .

 

Regards,

 

John P

[jpendle]

1 minute ago, cliff park said:

A device to change DC to a different DC is called an inverter. It normally works along the lines of an oscillator to chop up the DC voltage, feed that through a transformer ( Chopped up dc looks a lot like AC, albeit square wave) then rectify the resultant AC to produce DC, then smooth it and voila. Another way is to use the DC to turn a motor, and use this to drive an alternator, push the resultant AC through a transformer, then rectify............etc. These techniques are really for high power DC to DC, especially the second one. Of course with modern miniature electronics the whole thing can be much smaller, but the same principles still apply 

Sorry, but an inverter converts DC to AC, not DC to DC. For example inverters are used on solar panels to convert the DC voltage back to mains AC so that your house mains supply can be run from them.

 

Regards,

 

John P

[Nearholmer]

I was typing that!

 

JPendle is absolutely right. I'm afraid that the loose use of the word 'inverter' to mean 'any sort of converter' leads to just the same sort of confusion as does  using 'transformer' to mean 'controller'.

[Crosland]

13 hours ago, KeithMacdonald said:

 

Yes, a DC-DC converter.

 

If stepping down, all you need is a regulator, subject to a few details of the actual application.

[Crosland]

13 hours ago, cliff park said:

A device to change DC to a different DC is called an inverter. 

 

An inverter converts DC to AC.

 

 

[kevinlms]

15 hours ago, jpendle said:

 

except maybe go up in a puff of smoke .

 

Regards,

 

John P

Ah now we're getting somewhere. A 2nd reference to a puff of smoke tonight!

 

[ELTEL]

Just a thought the opening page states a output of 11.6 v which I think is totally inadequate to fire solenoid point motors (ok for  stall type point motors)

 

I believe most point manufacturers state 16v to 24v for point motors.

 

Just a thought.

 

Terry 

[AndyID]

On 20/12/2019 at 11:21, Joseph_Pestell said:

I have been pulling apart a bar that has halogen lamps.

 

Each lamp has it's own transformer rated at 11.6V and maximum 4.9A. The label does not say whether AC or DC but I am assuming the former. On the face of it, great for running the point motors, accessories, etc on a layout. Anyone tried this?

 

Halogens usually replaced these days as so energy-inefficient. So there should be lots of these transformers about.

 

Hi Joseph,

 

11.6V at 4.9A is 57VA (volt/amperes). A 57VA transformer weighs about a kilogram. If the one you are looking at weighs a lot less than that it's not simply a transformer (although it might say it's a transformer on the case) and it's going to be some sort of electronic power supply - probably switched-mode. Hopefully it does actually have a small high-frequency transformer in it to isolate the potentially lethal input voltage from the output connections but I wouldn't use it until I had convinced myself it does.

 

Filament bulbs (including halogens) are basically resistors and they'll tolerate all sorts of strange input voltage waveforms that could be completely incompatible with other devices. The output might actually be high frequency AC. Without knowing a lot more about it I'd recommend you don't use it to power anything other than 12 volt filament bulbs.

 

Cheers!

Andy

 

 

[RobjUK]

7 hours ago, AndyID said:

(although it might say it's a transformer on the case)

 

That's hit the nail on the head - the manufacturers started labelling electronic power supplies for low voltage lights as "electronic transformers" or just transformers... Presumably to avoid confusing resellers or sparkies who a not familiar with electronics terminology.

 

In a very loose sense it is accurate as it does transform [as in change] one voltage to another - but in electrical engineering or electronics terminology a transformer is strictly a wound electromagnetic component.

 

Flick through this video to see the guts of a typical halogen "electronic transformer" and compare to the actual transformer and switched mode PSU photos below. [Done as links it does not hog the thread space].

 

The halogen lamp PSU is rather simpler than a DC output PSU, as it does not need the rectifiers and smoothing caps.

 

https://www.youtube.com/watch?v=LnbAGZjFnew

 

https://media.rs-online.com/t_large/F0504329-01.jpg

 

https://i.ytimg.com/vi/B19rB_FR5Mk/maxresdefault.jpg

[Joseph_Pestell]

On 24/12/2019 at 05:14, AndyID said:

 

Hi Joseph,

 

11.6V at 4.9A is 57VA (volt/amperes). A 57VA transformer weighs about a kilogram. If the one you are looking at weighs a lot less than that it's not simply a transformer (although it might say it's a transformer on the case) and it's going to be some sort of electronic power supply - probably switched-mode. Hopefully it does actually have a small high-frequency transformer in it to isolate the potentially lethal input voltage from the output connections but I wouldn't use it until I had convinced myself it does.

 

Filament bulbs (including halogens) are basically resistors and they'll tolerate all sorts of strange input voltage waveforms that could be completely incompatible with other devices. The output might actually be high frequency AC. Without knowing a lot more about it I'd recommend you don't use it to power anything other than 12 volt filament bulbs.

 

Cheers!

Andy

 

 

 

Weight (or rather the lack of it) is what led me to ask the question in the first place. My past experience of transformers is that they generate a lot of heat and I could not see how that heat would be dissipated in such a lightweight item.

On 22/12/2019 at 12:19, ELTEL said:

Just a thought the opening page states a output of 11.6 v which I think is totally inadequate to fire solenoid point motors (ok for  stall type point motors)

 

I believe most point manufacturers state 16v to 24v for point motors.

 

Just a thought.

 

Terry 

 

I have experimented a lot with voltage and solenoid point motors. Especially with Peco points and their spring, 8v DC can give a very satisfactory operation where the motor does the first bit and then the spring takes over. Gives a good representation of a point controlled by a local signal box with point rodding.

 

 

[Junctionmad]

It goes to illustrate a significant point that unless you have a good understanding of the principles backed by some practical industry experience ,re-tasking old , often un-labelled equipment , can be a trap for the unwary. 
 

the best advice is to stay with branded kit unless you know what you are doing , assumptions can wreck your kit or hurt u 

[nicam49]

But also, if the tranny 'looks' like a bog standard iron-cored jobbie, it might just be an auto transformer... which means the output won't be isolated from the mains.... potentially shocking! (pun intended) 

Edited December 25, 2019 by nicam49
Afterthought

[Sol]

13 hours ago, nicam49 said:

But also, if the tranny 'looks' like a bog standard iron-cored jobbie, it might just be an auto transformer... which means the output won't be isolated from the mains.... potentially shocking! (pun intended) 

 

But that can be found by using a multimeter in ohms mode.... making sure input side is not connected to output side... and if the tranny is not labelled input / output, using it as a door stop...

[Junctionmad]

In electronics professionally for 30 years. Never heard a transformer called a “ tranny “ , a “ traffo “ yes. 

[Free At Last]

Only ever heard them being called a 'tranny' in the years I spent in construction.

[AndyID]

7 hours ago, Free At Last said:

Only ever heard them being called a 'tranny' in the years I spent in construction.

 

What have you been doing since then?

[WIMorrison]

A tranny was a van in my parlance

[Free At Last]

5 hours ago, AndyID said:

 

What have you been doing since then?

All sorts of things, thanks.

How about you?

Edited January 5, 2020 by Free At Last