Using an electronic transformer for a model tram motor?

[Tractorfan]

Hi,
A good friend has asked me to make a speed controller for the 12 volt DC motor in his model tram which will run on just a few metres of track.
I've found a simple, two transistor speed controller, and am thinking about powering it with an electronic transformer intended for halogen lamps. It is a high frequency AC device, and I'm pondering how to rectify & smooth it with bits from my junk-box. Would I need special diodes for the HF? or would IN4002s be OK at that frequency (maybe around 15Khz?)?
If not, I could use the 'traditional' 12 volt transformer from a scrap halogen desk lamp instead.
Thanks.
Pete.

[Al (astral highway)]

Hello,

That seems a lot of effort for a simple 12VDC supply; how about any old Walwart 12V supply?

If you want to go the other route, 15KHz is far too high to be a suitable frequency for the 1N400X series to deal with, they're general purpose rectifier diodes more suited for mains frequency. You could use Schottky diodes, instead.

[Refugee]

UF400X diodes are what you need.
I looked into model control some years ago and came to the conclusion that the current the motor takes can be used to control absolute speed and provide a speed indicator on the controller.
The motor produces a current waveform that can be measured.

[broadgage]

Standard rectifier diodes wont work with the very high frequency AC from an electronic transformer.

I would use copper iron transformer, or possibly an electronic transformer with DC output.
DC units are readily available as some types of 12 volt LED lamp require or prefer a DC supply.

[russell_w_b]

Best of luck... Here's what the output of an electronic transformer meant for powering halogen lamps looks like.

http://www.vintage-radio.net/forum/s...1&postcount=42

[Tractorfan]

Hi and thanks for your speedy replies,
I had a sneaky feeling that 1N4002 might not be suitable but wasn't certain .
I could use a wall wart, but seeing as I had a box full of electronic transformers and few wall warts of any use (or with European pins instead of UK ones, which is where the project is destined), I wanted to use what was to hand.
Not to worry, I have a halogen desk lamp that I can rob the iron/copper transformer from.
Thanks again,
Pete.

[thermionic]

Not to worry, I have a halogen desk lamp that I can rob the iron/copper transformer from.

Good call...! Trying to rectify the output from a halogen transformer is fraught with problems. In addition to the points above, they won't output any voltage until they are loaded. Therefore, you would need to introduce a load on the AC output, before rectification...

SimonT.

[winston_1]

There is no such thing as an electronic transformer, it is a made up term by manufacturers or distributers who don't know what a transformer is. (A device which changes voltage or current by magnetic induction, [or doesn't in the case of isolation transformers]).

Electronic halogen lamp drivers are a (poor) form of switch mode power supply which need a minimum load to work. No way can you rectify and smooth the output as you desire.

[Tractorfan]

Hi,
I realise that it's not a 'transformer' per se, but I used the term to differentiate it from a 'proper' transformer. Indeed, it's a 'driver'.
Cheers, Pete.