Model Forum / General / Railroads / August 2009

Take a look at the Gaugemaster 'Combi' it's a Hornby style  wall-mount
transformer and separate controller, but these are much better quality, and
not much more expensive than the Hornby transet efforts.

John.

The reason the ones you mention are poor at low speeds, is that they
are simple variable resistance units.

Which means that when you turn the knob you increase both current and
voltage.

But it takes more current to start than to keep it running, and the
voltage controls the speed.

So that by the time you have reached enough current you already have a
fairly high voltage, so the engine runs away like a scalded cat.

Modern electronic controllers use a voltage regulator chip, so you get
full current at all voltages.

You can also get good control from a single transistor and a variable
resistor. Obviously it needs a transformer, a rectifier and a
smoothing capacitor as well. A friend of my father's made one for us
when I was a boy. So if you know somebody who is an electronics nerd
(not a computer nerd) he might be able to help. There are books and
magazines on model railway electronics which give circuits like this,
including the exact components.

It's the sort of thing Tandy (Radio Shack) shops were perfect for.

Alternatively, before the days of this kind of controller, they used
variable transformers. Hammant and Morgan used to make one called the
Safety Minor - I had one more than 40 years ago. They used the same
system in the later versions of their Powermaster.

You might be able to get one of these at a swapmeet or on ebay. They
are still very good but out of fashion.

These worked by sliding a wiper along the secondary winding of a
transformer. So there wasn't a resistor involved to reduce current.

I believe they stressed the safety part because traditional variacs
were auto-transformers having just one winding and weren't really safe
enough for model railway use.

My O-gauge club (Kingston, in up-state New York) uses very ancient
variable transformer controllers which give excellent low speed
performance. It's a no-name setup built by a member decades ago and
used on club night ever since.

If you see a Hammant and Morgan Powermaster for sale, make sure it's
the variable transformer not the earlier resistance kind. But beware,
unless the seller actually used it he might not know.

Build your own ?  The circuit diagram for one of the Gaugemasters is around
publically somewhere and is pretty trivial to make.

Or there is the "cool crawler" which is a US design which can be found if
you search the internet.  I've made one, needs only vero board and a
multi-meter to check continuity as you build it. Its a nice controller for
OO and probably most N RTR stuff.  I built a version with a base unit which
remembers the last setting of the handset if the handset is unplugged and
moved to another position on the layout, and the handsets were built with
both a speed control and an "inertia" knob to give some acceleration and
braking delay, probably cost under £20.

Both need about 16v AC which an old H&M will give on its auxillary output.

- Nigel

I'd recommend a Gaugemaster Combi as John mentioned or if you are on
a really tight budget, buy one of those controllers that Bachmann/Farish
supply with their train sets as they are suprisingly good. You can buy
them for about £10-15 on Ebay.

Fred X