you should google this. Here's one site

you can, but it's not recommended.

DCC is an alternating voltage that carriers messages to each decoder. The carrier can be modified to result in an average DC voltage that can drive one DC locomotive. But when not running, the alternating voltage can generate heat in the DC motor that can damage it.

 

Not really recommended. Depending upon the DC Loco, it may be easy to install a decoder. What is the DC loco and does it have the DCC plug in it? Unless your attached to the loc for personal reasons, you might just want to replace it with a DCC unit or at least a DCC ready unit that you can just plug a decoder in.

 

If you absolutely have to stick with DC, you will need to ensure your DCC command station is set to DC operations. The Digitrax system can toggle DC on or off. Not sure how other systems do that.
To operate your DC loco on the DCC system, dial up 00 on your throttle. This will actually skew the sine wave to one side of center or the other. You can still run DCC locos while doing this but you may see a bit of change in their actual performance.
As mentioned before though, a decoder is pretty cheap compared to replacing a burned or damaged motor or even the shell of your loco if you let it get to hot.
Remember, go cheap, be disappointed. You usually end up paying much more in the end.

 

Also, DCC isn't magic; it won't make a silk purse out of a sow's ear.

That is to say, if the mechanism is old or in poor condition, and the loco is jerky or slow, it won't be any different using a decoder in it and using a DCC system to control it. Some people get the sense that DCC is about improved performance. Not so! It means more realistic performance, but only in operations. If the loco is in bad shape and behaves poorly in DC, it won't improve with the addition of a decoder.

If the loco has strong sentimental value and you'd rather not place it on the Permanent RIP track (that means "repair in place", not the other RIP...although same diff if you never use it again), consider re-gearing/and/or re-motoring it.

 

You would be better off adding a decoder to your
loco so it can run on your DCC layout.

Some locos are equipped so you can simply plug
in a decoder, if not you would have to wire
the motor & lights to install a decoder. In either
case, the cost for a non sound decoder is around 20.00
or less.

Keep the DC power pack to power turnouts, lights
and other accessories.

Don

 

If you go the route of adding a decoder to the DC loco, there is one big caveat you have to watch for -- The motor cannot be grounded to the frame! If your motor only has a single wire going to it then you have to figure out a way to isolate the motor from the frame, and this is usually more easily accomplished by installing a more modern motor rather than trying to salvage the original one.

The reason for this is that if the motor is grounded to the frame, that almost certainly means that one set of driver wheels is also electrically connected to the frame. With DCC you are picking up an AC signal from the rails, but then there is completely separate wiring that controls the direction of the motor. If the motor and the wheels are connected together then there is a good chance it will burn out the DCC controller that you just installed. Newer can-style motors have the outer housing insulated from the motor terminals, so those can be attached directly to the frame even if the wheels are also connected. Hope that makes sense?

 

Some DCC engines have decoders that can be set to run on DC or DCC. Usually it is on by default. Blackstone HOn3 engines with Sountraxx decoders work this way