"keep alive" for a DC motor to keep it spin during momentary power outages

Thread Starter

meehow

Joined Jun 3, 2021
8
The application is for an electric model train (HO) which operates on 0V - 16V DC power supply.
Locomotives often suffer from momentary power outages when crossing points, turnouts etc.
Some are equipped with a mechanical flywheel which keeps momentum for an inch or two which may be enough.
Many low end locomotives does not have any "keep alive" equipment and requires a push when they get stuck.
There are available off-the-shelf solutions but they are not affordable.

Would a capacitor serve a purpose?
Would it not limit the current to the DC motor while charging? PSU is capable of 1000ma @ 12V.
How to size it? The DC motor typically draws 250ma @ 12V.
What will happen when a power outage occurs? It will keep the motor running and then what?
I know, that I know very little about electronic!
Please help :)
 

KeithWalker

Joined Jul 10, 2017
1,789
Add some extra weight to the locomotives to give them a little more momentum. Regularly clean the wheels and power contacts on the locomotives and keep the rails clean and minimize any gaps in them. The insulated frogs in the turnouts and cross-overs are the biggest problem so spend a little extra and get good quality ones.
 

Thread Starter

meehow

Joined Jun 3, 2021
8
The voltage to the motor reverses, no?
You could try the largest electrolytic cap you can squeeze in but they are uni-polar.
Yes, so the cap would pop on reversed polarity. Not desirable.
Perhaps it can be protected by a diode?
Add a second cap for the other direction and separate them with diodes?
Any chance?
 

Thread Starter

meehow

Joined Jun 3, 2021
8
Can you run wires to the next carriage and install pickup wheels on it so power comes from more than one place on the rails?
That is doable for a DMU train! or a steam loco with a permanent coal wagon.
Not for any other locomotive where the wagons and coaches need to be switched.
 

djsfantasi

Joined Apr 11, 2010
7,700
There are two main ways to power a model train. DC is Direct Current; DCC is Digital Command Control. A capacitor across the power leads is almost a necessity with DCC. Thus, on DCC manufacturers sites and model railroad supply stores, there are capacitors for sale specifically for this purpose. Different caps are used for different engines because the space available to mount them differs by engine model. Maybe even manufacturer.

I’d suggest joining the model train forum and asking there.
 

djsfantasi

Joined Apr 11, 2010
7,700
Add some extra weight to the locomotives to give them a little more momentum. Regularly clean the wheels and power contacts on the locomotives and keep the rails clean and minimize any gaps in them. The insulated frogs in the turnouts and cross-overs are the biggest problem so spend a little extra and get good quality ones.
All good comments. Some turnouts come with metal frogs insulated from the rails. Extra contacts on the turnout machine can match frog/rail polarity eliminating any dead zones.
 

djsfantasi

Joined Apr 11, 2010
7,700
Ok. What about all the wheels on the loco?
Another good approach often taken. However, it may be difficult depending on the plastic shell. And the sizes of the pickups (phosphor bronze) are tiny and difficult to mount. Particularly when the trucks are not designed for extra pickups.
 
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