Electrical (but not Stag) question.

[Tdm]

Humour me while I ask a question relating to my other hobby - model railways.
A controller I purchased recently in the U.K. proved to be "duff", and a replacement has gone missing in a black hole somewhere.

I am therefore attempting to make my own but my knowledge of electrics is somewhat limited.
What item do I need that I can make or readily buy over here (in Tenerife) that will turn a 16/17 volt supply to one with a range (via knob or slider) from 0 to 12 volts. See attached diagram.
I need to know what "electrical" item I need between points "B" and "D" that will allow me to feed the track from 0 to 12 volts in either direction (ie. forwards or reverse movement of engine). I have an adaptor that converts 220/240 volts to 16/17 volts and just need something between that and the track that outputs 0 to 12 volts in forward or reverse. What is it called that varies the voltage (a regulator?) then I know what to ask for in a local electricians, ideally one with a knob or a slider control on it.

Thank you in advance - although this question does not relate directly to Stags, I am using some spare (no longer required) Stag parts of mine on the model railway I am building - for example cam buckets make ideal model oil refinery storage tanks, and exhaust brackets front and back ends of a "Nissan" hut ("n" scale).

[Kevin Garrod]

It's called a rheostat (you could pinch it off the Stag!) or potentiometer.

[GDPR]

Rheostat needs to be wire wound or it won't be able to shunt the current at low voltage.

I thought that the modern controllers are switching supplies that control the motor current by switching the power on and off very quickly, varying the on/off interval ratio to do it...

Or use your transformery thingy and an old Scalextric controller to shunt the current

[Stagdad]

Terry I think you need to search for a pwm (Pulse Width Modulation)controller of the correct values,peanuts on ebay,thats what Russ was descibing ie power on and off quickly

Cheers Steve

[GDPR]

That's what I was looking to say... cheers Steve

[V Mad]

A rheostat, almost a forgotten piece of kit. Simple but wasteful of power for that job.

These days of microelectronics, as Steve says, you can buy a controller that uses fast (PWM) switching to vary the (average) voltage. Cost around £4.00 + free post from Hong Kong.

I bought one for controlling a DC car heater motor. It produces an output from near zero to about 10 volts from a DC supply of 14.4 V.

Search 'DC motor speed controller' on the bay.

[Mike Stevens]

Hi Terry,

A simple rheostat (or variable resistor) is OK but doesn't really control the voltage, it just puts a variable resistance in the current path to the motor.

As stated, you want a regulator with a variable output. That can be either switched mode (on/off with varying ratio between on/off) or linear, (just reduce the voltage in a controlled fashion to what you want it to be). The latter is easy to make, plenty of bits around, the former is more efficient (loses less power) but that's probably not relevant at this power level.

Something you can buy of t'internet that does the job is simplest. If you get stuck, I'll be happy to help if you want!

Cheers,
Mike.

[Tdm]

Thanks for the replies Guys, now I know what to look for, will search one out.

[wilf]

Just one thing, we have all assumed that the output from your adaptor/transformer is actually DC - is it?

[Tdm]

Just one thing, we have all assumed that the output from your adaptor/transformer is actually DC - is it?

Yes Wilf - it is.
The only real problem with ordering things from the U.K., America, and other places is - sometimes they arrive and sometimes they don't
and can take a while to get here. Also Tenerife Customs sometimes put an Import surcharge on the item which is more than the actual
purchase price (remember the Canaries are outside the EU as regards Tax and VAT).
Always a bit hit and miss here with the post and whether you have to pay extra or not.