why wont this work

Ive searched and searched and have not seen this question or and answer. I want a hand held controller dc not dcc. I have a pulse throttle. but I don't like how it makes the motor hum and buzz I was told this is just the nature of the beast.
My question why cant I just connect a potentiometer to my controller. Crank it up and use the pot to control what goes to the track seems to be the same as what the regular controller/power pack is doing.
Thanks
Dick

Hi there Dick,

I may be wrong but I think  the arm on the potentiometer only deflects as a result of the voltage passing through it. It doesn't actually have the ability to " control" the voltage as such. It's deflection only measures.

A controller on the other hand is not much more than a variable resistor. As the knob is turned ( increasing or decreasing the resistance value ) the " resistance " to  holding back or allowing power to flow is increased or decreased allowing more or less power to be delivered to the track.

I've maybe not the best at explaining these things but I'm sure that someone else will be able to elaborate a bit better.

I hope I've been of some use

Cheers

Toto

potentiometer was probably the wrong name I thought all power control knob things were potentiometers.

I've maybe misunderstood Dick. I thought you were referring to the likes of a analogue voltage or ammeter type instrument.

I'll crawl back in my hole………..apologies

Toto

Dick, pulse controllers do make old motors hum - the nature of the process but designed to give finer control of the loco moving - the older style of controllers like H&M even had a half wave switch to give some control.
Perhaps adding a non-electrolytic capacitor across the controller output would tend to smooth it better.


Just found this for reading
http://www.instructables.com/id/Simple-controllers-for-DC-motors-inc-PWM-inertia/

With DC controllers, all knobs are potentiometers but with transistorised units, the pot does not have to be a heavy duty as it drives the transistors, not like the older  wire wound units of Hornby/Tri-ang/ H&M.  A variable resistor/potentiometer by its nature drops voltage & the amount it drops depends on the current drawn by the motor so two different motors may have a different speed at the same setting of the knob.

thanks for the replies. but what I really want is something  I can buy as I don't understand schematics at all

In that case go to
The Model Shop for Big Imaginations | Gaugemaster

select Gaugemaster Controls

or
Gaugemaster Multi scale Analogue controllers Products from Hattons Model Railways

or

http://www.morleycontrollers.com/Details.asp?ProductID=62

thanks sol. Im assuming the ones with feedback are the pulse ones.

Dick

Dick,
        I can recommend Morley Controllers.  No connection with the company, etc.  Each controller comes with TWO handheld controllers and a built-in CDU for changing turnouts (is that switches in the USA?)  The prices are very competitive compared to other makes.
 
Terry

I don't know for sure Dick but normally feedback is the gaps between pulses.

Almost right Sol. The motor becomes a generator every time the brushes pass a segment on the armature. The controller sends the pulses and gets a return. The pulses from the controller are getting a longer 'on' period the further you turn the knob up, this is pulse width modulation (pwm) You get full volts at the motor all the time, but in pulses, so the shorter the pulses, the slower it turns which is why you get better low speed control. When you turn the knob up, the pulses get longer, ipso fatso the loco goes faster. When the loco gets loaded up like coming to a rise in the track or a curve the controller sense that the motor is slowing because of the shorter return pulse and compensates for it. I don't know if I explained that all that well but hope you can understand my ramblings.

Edited to say, sorry I didn't realise how old the topic was. :roll:

I realize this is an old topic however I recently got a new and somewhat expensive atlas gp38. It runs silently at a snails pace on my basic dc powerpack. I hooked up my PWM throttle and it hums and buzzes as bad as my 30 year old blue box athearn. So Pulse is not for me. I still cant find a simple dc hand held throttle without pulse.

Dick

Dick ,I thought new Atlas would have 5 pole skewed wound motors & so PWM would be OK  but I have used these types years ago and found them perfect
http://jjhobbiesonline.com/store/catalog/product_info.php?cPath=25_46&products_id=77

Would a drawing of an actual simple hand held throttle help showing an exploded view?  I am getting on top of the paper work I have been lumbered with so when it is clear I could get started.
Cheers
Trevor

that would be great thanks

HI Dick and everyone else,
This was a while in coming … It is only a first stage as I intend to do a photo essay on making a throttle but it will get the ball rolling
This is shown on the inside of what we call a jiffy box and from the connection points of the items you put in. In some cases the relative are a bit exaggerated and certainly the colours in the wires are. We will be making a few of these for the club I am in so I hope to photograph as I do one or two,
Let me know what you think,
Regards from Oz

Trevor

Thanks Trevor That looks like what Im after. When I get a chance to study it Ill be in touch
Dick

I assume this would be using a 12 volt DC supply - I don't see a rectifier in the circuit.

Shaun.

Shaun, at the bottom of the drawing, it has
Red and Black are your positive & negatives wires in
so that means it is a DC input.

Gotcha. I missed that on the bottom!
The ones that we build are the same as Trevors, but as we are using 15 volt transformers, we build in a four diode circuit to give us DC.

Thought it was worth mentioning.

Shaun.