Potentiometers

[bigjack]

I've converted one of my Stainz (the other is to be done as well, along with a Bachmann tram) to batteryu power. The one problem I'm having is, where can I get the right potentiometer from?

 

[Doug]

A potentiometer able to cope with the current rating for the Stainz will be quite big. You need to go with a simple speed controller. Somewhere in the GSC archives is a circuit - over to you Neil ...

 

[Neil Robinson]

Are you sure that you just want a potentiometer rather than a more sophisticated speed control circuit?
If so please post details of battery voltage, motor voltage range required for the speeds you have in mind and also the current you expect the motor to take.

 

[bigjack]

Are you sure that you just want a potentiometer rather than a more sophisticated speed control circuit?
If so please post details of battery voltage, motor voltage range required for the speeds you have in mind and also the current you expect the motor to take.

Neil, I'm open to suggestions. The loco is fitted with 8 X 2500mAh batteries, it runs quite nicely asit is. would just be nice to slow it down a little if I wanted to.

 

[Neil Robinson]

A potentiometer able to cope with the current rating for the Stainz will be quite big. You need to go with a simple speed controller. Somewhere in the GSC archives is a circuit - over to you Neil ...

Maybe it was on GSM.
I found the following in my files, I've not checked if Maplins still stock the bits.
For battery operation IC2 won't be needed but will give protection against incorrect battery connection. You'll need to fit the DPDT reversing switch after C3.

 

[Del Tapparo]

Potentiometers and linear voltage regulators like the one shown above are very inefficient. Meaning that they consume a lot of your battery power without getting it to the motor! Lots of heat, and much shorter run times on your battery pack.

The G-Scale Graphics "http://1stclass.mylargescale.com/DelTapparo/Simple_Critter.htm < Link To Simple Critter Control" is an efficient 5 amp PWM motor driver that fits in the space of a potentiometer. We have a range of controls from simple to complex.

 

[Neil Robinson]

it runs quite nicely asit is. would just be nice to slow it down a little if I wanted to.

In which case you could always add a few diodes in series for a slower speed and use a switch to short them out for top speed.

 

[Gizzy]

Are you sure that you just want a potentiometer rather than a more sophisticated speed control circuit?
If so please post details of battery voltage, motor voltage range required for the speeds you have in mind and also the current you expect the motor to take.

Neil, I'm open to suggestions. The loco is fitted with 8 X 2500mAh batteries, it runs quite nicely asit is. would just be nice to slow it down a little if I wanted to.

I guess your batteries are 1.2 Volts each Steve? Therefore 8 * 1.2 = 9.6 Volts

A Diode drops the voltage by 0.2 or 0.6 Volt depending on whether it is a Germanium or Silicon type, so if you want to reduce your speed using Neil's suggestion to about half (4.8 V) then you need 8 diodes in series....

(Edited to correct my errors as pointed out by Greg later.)

 

[bigjack]

Over the weekend I wired the batteries direct to the motor, wired this way the loco ran for over 4 hours.

Tonight I striped the loco, removed the digital chip, skates and bullets. Then rewired the loco via the original circuit board so the the lights and sound would work. Now testing the loco so that I can see how long it will run with sound and lights working. It's been 1/2 hr so far, I'll let you know the end result

 

[bigjack]

3 1/2 hrs running with sound and lights working

 

[gregh]

A Diode drops the voltage by 1.2 or 1.6 Volt depending on whether it is a Silicon or Germanium type, so if you want to reduce your speed using Neil's suggestion to about half (4.8 V) then you need 4 diodes in series....

Sorry, you've got wrong values there.

Silcon diodes drop about 0.7V. So you need 2 in series to reduce the effect of one battery cell. Forget Gemanium diodes - no such thing in power diodes.

 

[Gizzy]

A Diode drops the voltage by 1.2 or 1.6 Volt depending on whether it is a Silicon or Germanium type, so if you want to reduce your speed using Neil's suggestion to about half (4.8 V) then you need 4 diodes in series....

Sorry, you've got wrong values there.

Silcon diodes drop about 0.7V. So you need 2 in series to reduce the effect of one battery cell. Forget Gemanium diodes - no such thing in power diodes.

I stand corrected Greg. A silicon diode drops 0.6 volts, not 1.6. (Ge are 0.2).

I should really have refered to a reference book instead of relying on my addled memory!

So Bigjack will need 8 x 1.6 Si diodes to reduce the voltage from his 9.6V battery to half voltage.

However, from his other later posts, he seems to be doing just fine....

(N.B. I have edited my previous post to correct the mistake I made as pointed out by Greg.)