Potentiometers

Madman

Madman

Registered
25 Oct 2009
12,922
99
Pennsylvania, USA
How can I wire a potentiometer into a motor circuit ? Let's say I have a 12 VDC battery, controlling a motor. Is there a way to wire the potentiometer into the circuit without getting into electronics ?
 
-bbbb

-bbbb

Registered
21 Dec 2017
189
23
Idaho
It's merely a variable resistor. You can wire it how you would wire any resistor, except since it has 3 terminals, it's like two resistors sharing a leg in the middle, and the resistance of each of those resistors changes depending on how you adjust it. You don't have to use all three terminals, but make sure you use the middle terminal so that the adjustments will work.
 
John S

John S

Registered
5 Nov 2017
599
85
Exeter, Devon, UK
Using a potentiometer as a rheostat for simple motor control.

125571_6765b143461a924d2849dbad568bc801.png



The add wire, if the wiper ever loses contact with the resistive strip inside the potentiometer, this connection ensures the circuit does not completely open, that there will still be a resistive path to the motor. Old potentiometers tend to suffer from intermittent losses of contact between the wiper and the resistive strip, and if a circuit cannot tolerate the complete loss of continuity (infinite resistance) created by this condition, that “extra” wire provides a measure of protection by maintaining circuit continuity.

Should add this an extremely inefficient method of motor control, surplus voltage is wasted as heat.

If you could elucidate further, an off the shelf, ready made unit, may serve your purpose better.............


This is an improvement, minimum electronics required!

125580_0277a998bc0e209556cc9c1999fcaf12.jpg


Off the shelf solutions....
Add DPDT switch for reversing
125581_618516ff20b83e8fbd26beb5b6182b81.jpg



The following two, used on many numerous occasions, just need to add a DPDT switch for reversing.
The second one listed is in daily use as part of the control system on the two analogue display layouts, running 24/7 365 days a year.



Then there is this mega jobbie....

Several of these have been built, including the option for Linear Control, out for testing with G Scalers around the South West, can be found via this thread post #1218.


Possible (subject to feedback) could be the control system of choice for the Analogue Layout at the Exeter Garden Rail Show in October this year.

Electronic trickery, Bluetooth and WiFi versions are also out and about for testing.........................
 
Last edited:
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
22,785
275
Tamworth, Staffs.
Not a fan of this idea..

There is a reason tram resistor packs are on the roof, and no-one has asked what voltage battery, and what the motor current is going to be?
'Rheostats' tend to be large, and wire-wound, for a reason.

By the time you have sourced, and paid, for a wire-wound, decent wattage potentiometer, you could get a Chinese speed controller for less.
 
Rhinochugger

Rhinochugger

Retired Oik
27 Oct 2009
24,524
314
North West Norfolk
Not a fan of this idea..

There is a reason tram resistor packs are on the roof, and no-one has asked what voltage battery, and what the motor current is going to be?
'Rheostats' tend to be large, and wire-wound, for a reason.

By the time you have sourced, and paid, for a wire-wound, decent wattage potentiometer, you could get a Chinese speed controller for less.
IP Engineering use a simple pot controller, and I never managed to make 'em work, usually for the questions you just asked :oops::oops:

The theory's fine, but .................... :emo::emo:
 
Madman

Madman

Registered
25 Oct 2009
12,922
99
Pennsylvania, USA
Using a potentiometer as a rheostat for simple motor control.

View attachment 253204


The add wire, if the wiper ever loses contact with the resistive strip inside the potentiometer, this connection ensures the circuit does not completely open, that there will still be a resistive path to the motor. Old potentiometers tend to suffer from intermittent losses of contact between the wiper and the resistive strip, and if a circuit cannot tolerate the complete loss of continuity (infinite resistance) created by this condition, that “extra” wire provides a measure of protection by maintaining circuit continuity.

Should add this an extremely inefficient method of motor control, surplus voltage is wasted as heat.

If you could elucidate further, an off the shelf, ready made unit, may serve your purpose better.............


This is an improvement, minimum electronics required!

View attachment 253208

Off the shelf solutions....
Add DPDT switch for reversing
View attachment 253209


The following two, used on many numerous occasions, just need to add a DPDT switch for reversing.
The second one listed is in daily use as part of the control system on the two analogue display layouts, running 24/7 365 days a year.



Then there is this mega jobbie....

Several of these have been built, including the option for Linear Control, out for testing with G Scalers around the South West, can be found via this thread post #1218.


Possible (subject to feedback) could be the control system of choice for the Analogue Layout at the Exeter Garden Rail Show in October this year.

Electronic trickery, Bluetooth and WiFi versions are also out and about for testing.........................
I've been messing with building my own circuitry for a Playmobil Atlas crane loco. I usually use G Scale Graphics Railboss to operate my motive power, but at $200.00 plus, I thought I'd go on the cheap with this project.

I have the largest motor speed control you pictured and was trying to find a place for it, along with a receiver and battery. I thought of placing it on the roof and building a shroud to cover it, but it detracts from the appearance a bit too much. Thank you for showing one of the smaller motor speed controls. I will definitely get a hold of one for this project.
 
Greg Elmassian

Greg Elmassian

Registered
8 Mar 2014
2,669
120
San Diego
www.elmassian.com
Thanks Phil, I was hoping someone would speak up about figuring the wattage needed of the pot to handle a motor.

1 amp at 12 volts is 12 watts.... most of the pots that are about 1" in diameter are only 2 watts, sometimes 5 watts, i.e. you could literally burn one up on a small motor with very little voltage.

Greg
 
Fred2179G

Fred2179G

Registered
20 Apr 2017
233
7
USA
I thought of placing it on the roof and building a shroud to cover it,
I have one of those little speed controllers from china, and it works great. The shaft is disguised as the smoke stack/chimney. The central 'radiator' (?) is sitting on a DPDT slide switch for direction changes.
 

Attachments

PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
22,785
275
Tamworth, Staffs.
Is that an 'International Rescue' logo, I see on the side of that loco? :think::nerd::think:
 
Fred2179G

Fred2179G

Registered
20 Apr 2017
233
7
USA
Is that an 'International Rescue' logo, I see on the side of that loco? :think::nerd::think:
I dunno - is it? There is a small IR on it. It came from the UK so you might know better than me.
 

Attachments

PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
22,785
275
Tamworth, Staffs.
Oh yus!


From 50 seconds in..
:nerd::rock::rock:

(sad, isn't it?) :rolleyes::blush:
 
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
22,785
275
Tamworth, Staffs.
Whoever built it.. Must have used it as a 'Thunderbird'? :giggle::giggle:

Thunderbird = Loco's manned at various places, to go drag a failed unit to safety..
 
John S

John S

Registered
5 Nov 2017
599
85
Exeter, Devon, UK
I dunno - is it? There is a small IR on it. It came from the UK so you might know better than me.
Refreshing to hear of another satisfied user of "off the shelf China made items".

With reference to IR.........

125991_26fcc0e8b034eaf5d0c017ece924dc65.jpg
 
Fred2179G

Fred2179G

Registered
20 Apr 2017
233
7
USA
:D:inlove:>:):rofl::rofl::rofl: