View Full Version : Speed limiting in DC

1st Nov 2012, 08:34 AM
I'm trying to come up with a cost effective solution to limit the max speed on my DC controller(s).

when my kids are using the layout it would serve as a prevention to allowing the train from going too fast, which when they often intend to slow or turn off they turn the dial in the wrong direction and accelerate.

My other plan would be for a possible around the tree layout if time and money will allow.

my first reaction would be to put a small screw into the controller creating a physical restriction. This of course would restrict me of power too if I need it.

Any one have a better way/suggestion?

1st Nov 2012, 08:41 AM
You could add a DPDT switch and a voltage regulator. When the kids are using it flip the switch so it goes through the voltage regulator, otherwise in Normal operation the voltage regulator is by passed.

1st Nov 2012, 09:50 AM
Ive heard of people using resistors in line with motors before.

1st Nov 2012, 10:25 AM
Hmm... the screw would be a pretty easy option, and could be removed when you want to run them.

I'd think about a current limit circuit that would either cap the current on the rails or, maybe better (behaviorally) a circuit breaker or fuse type setup. That way, you can train (think Pavlov) the kids to keep the power below the limits, else the trains stop... A breaker would be best, since you can easily reset it in case of an accident, or say "whoops, sorry...." in the less accidental cases...

1st Nov 2012, 04:52 PM
Just use a variable resistor/pot/rheostat in the line coming from your power supply to the track. It would work just like the current throttle but (in theory) if you set it at half, then only half of what the powerpack is sending out will get to the track. Turn it down for the kids and back up for you....as the kids get more responsible, you can turn it down less and less. But it would always be there for visitors/other kids/ect. Radioshack has a bunch of options for less than $4 each. Just be sure to get one that will handle the wattage (volts X amps = watts)

1st Nov 2012, 06:08 PM
I like the screw idea most of all. It's simple, cheap, easily removed and you probably have one handy.

But if you want a more complicated solution a key switch that kicks in a diode voltage reduction circuit. Depending on whether you put it before or after the direction switch. a single diode will drop the voltage .7v when placed in a circuit. Each successive on will reduce the voltage even more. Six in a line will reduce the voltage from 12 to 8. If you place the diodes after the direction switch a second set of matching pointed in the opposite direction is needed to maintain he train traveling in both directions. You might cheat and put more diodes in the reverse direction. You could just hardwire the diodes and have a jumper that will bypass them for your use.

Diodes have the advantage over resistors as they don't convert the excess electricity into heat.

1st Nov 2012, 06:34 PM
If you're going to make it complicated, I'd figure out a way so that when they went beyond, say.. 1/2 throttle, the controller handle becomes electrified.
It goes along with TD's behavior modification suggestion, but will be much more fun for you to watch. :eek: