# Train too fast

Discussion in 'HO Scale Model Trains' started by CN_Pete, Nov 24, 2006.

1. ### CN_PeteMember

Have a question,
I am building my own track cleaner car and am using an old tyco drive.
The motor runs too fast for what i am looking for.
Has anyone found a way of reducing the voltage to the motor while the throttle is at
full speed.
I want the motor to run at 6 to 8 volts while the track volatage is set at 12 volts.

Is this possible.

Thanke
2. ### LongIslandTomMember

This is not one of those old notorious pancake motor drive Tycos, is it?

Pancake motor drives have a very high gear ratio, because the motor armature is directly geared to the truck axles without much reduction. That means there is very high starting resistance-- You usually have to crank up the power to relatively high levels for it to start moving, resulting in high starting speeds.

I wouldn't use a pancake motor drive loco for track cleaning. Grab an old Athearn blue-box loco instead. They are also cheap, but much better at slow speeds because it has a much better motor and reduction gear mechanism.
3. ### FiatFanMember

The only way to do what you want (motor running at 6-8v while track is at 12v) is to use a resistor to reduce the voltage to the motor. I don't have the electrical knowldege to tell you what size. Perhaps some of our more knowledgeable members could jump in here.

Tom
4. ### msowsunMember

You would need fairly large resistors I think.

Another way is to build a transistorized voltage regulator circuit.

A low tech way to reduce voltage is to use diodes. Each diode in a series will drop the voltage by .7 volts without increasing the current or making any heat.

You will need at least at least 16 diodes. 8 in series for forward direction and and 8 in series for reverse direction would give you a voltage drop of about 5.6 volts. (.7 x 8 = 5.6)
12 - 5.6 = 6.4 at the motor.

I am curious as to why you need to have 6-8 Volts while the track is at 12V. Can you explain what you have planned? Does the track cleaner use 2 motors?
5. ### CN_PeteMember

I have built a transfer box which has a seperate motor to drive 2 scrub pads which clean the track. So when the drive motor is moving it along, the brushers spin fast.
6. ### msowsunMember

If you only install the diodes for one direction, you could use half as many.

Then when you operate in reverse, the scrub pad motor would automatically be turned off. (diodes only allow current to pass in one direction)