RAILforum: Power Packs Provide Too Much Voltage

This is topic Power Packs Provide Too Much Voltage in forum Model Railroading at RAILforum.

To visit this topic, use this URL:
http://www.railforum.com/cgi-bin/ultimatebb.cgi/topic/3/82.html

Posted by Konstantin (Member # 18) on :

I like to run trains slowly. Power packs all seem to give too many volts. I typically use a top voltage of about 5 volts, which tends to equal about 45 scale miles per hour.

Is there a way to drop the voltage without dropping the amperage? I can put in a resitor, but that also limits the amps. I would like to be able to use more range of the throttle on the power pack.

I know that MRC makes a programable power pack, but I have tried it and it is not very good quality.

Thank you
Dean

------------------
Elias Valley Railroad (N-scale)
www.geocities.com/evrr

Posted by roseforest (Member # 135) on :

Let me start out by saying that all power packs are different. Even packs that are identical are going to operate slightly different. On the whole I guess when you turn the speed control (rheostat) to increase the voltage to the track you won't get 1 volt, then 2, then 3, etc. but it will start out at 4-7 volts and go up from there.

What you might try is putting some diodes in series together, that is end to end with all of them oriented the same direction. Each diode will eliminate 7/10ths of a volt. So if you put 7 of them in series (7 times .7 volts = 4.9 volts) you would have to turn on your power pack to at least 5 volts before you realized any voltage at the track. If for instance the variable voltage range of your power pack was 0-16 volts D.C., at the track you would really only get 0-11 volts D.C. This might give you the full throttle movement you are looking for.

Common diodes to look for at your local Radio Shack, etc. would be designated 1N4000 or 1N4001 which would carry at least 1 amp of current which should be enough for n-scale equipment. Diodes are directional in regards to current flow, that is why they have to oriented in the same direction. Each diode has a stripe around the diode near one end. That is the negative end. They need to be connected negative to positive for as many diodes you decide to use then connected in line with one of the wires going to the track. Also, since you will probably want to reverse the power to the track you will have to make an identical set with an identical number of diodes connected across the first set of diodes in the opposite direction.

I hope this helps you. If you need more information email me at rhdavis1@gte.net and I'll see what I can do.

Rex Davis - Sylmar, CA

[This message has been edited by roseforest (edited 11-17-2000).]