Thanks for the info.. I had read on different sites and never got it in terms that mean much, you guys were great
Perfect example, Ive got a Genesis F3A and F3B that start at a slightly different voltage., so you could adjust the CV2 on one of the locos to have them start at the same time.
[Edit - Sorry, Randy, you posted as I was composing my response.]
A perfectly reasonable question. The reason you can/should set CV2 is that not all drives, nor their fit/assembly, are equal. Some drives take a bit more power to get them to start turning than others. I have some engines that won't do a thing until I have a speed step of 10 showing on the throttle....what's up with that!? Well, what's up is the mechanism needs more voltage than speed step 10 can provide. I have to go to 11 or 12 to get the wheels to just begin to rotate.
So, if you don't get the slightest creep at speed step one on any locomotive, you input a 'higher' value to CV2 until that speed step of one shows you some signs of life. It may be 1 or it may be about 45, as it is for my P2K tiny SW8. Many of my newest engines, no matter what sound and motive decoders they have, are perfectly fine with a value of "0".
So, to your last question, you don't really assign the voltage, at least not directly or consciously. What you do is programme the decoder to assign the necessary start voltage, but you do this incrementally by upping the actual value one digit at a time until speed step "1" shows the drivers rotating.
By the way, I have observed that a cold locomotive set to run on speed step "1" will start of quite a bit more smartly once it has been in use and is warmed up some. Or, conversely, if you decide to set up CV2 on a nicely warmed engine, don't be dismayed to find that speed step "1" doesn't achieve a darned thing next time you go to move that engine when it hasn't been used for a while...hours or days.
-Crandell
The number you put in CV2 for starting voltage, or CV5 for top speed, or CV6 for mid-point voltage, isn't a voltage number, it's a percentage or just an arbitrary value. The only thing you can say about it is the higher the number, the greater the voltage, but a value of 5 does not mean 5 volts.
Some locos just won't go until you crank the throttle halfway up. So the entire range of speed control is in just half of the throttle range. If instead you bump up CV2 so the loco starts on speed step 1, you have the entire range of the throttle to use. Another reason to adjust CV2,5 and 6 would eb to speed match two locos you want ot MU together.
With decoders that have BEMF, CV2 becomes less important, but CV 5 will still restrict the top speed, and CV 6 will adjust the mid point speed.
Another reason to adjust all three is to have a switcher than runs slowly but if you crank the throttle all the way you can hustle it around the layout. Or make a road loco that takes a long time to get up to speed, so instead of a straight line between stop and full, it increases slowly to the mid point and then goes up faster. Or the opposite for a commuter train loco, so it gets up and moves out of the station, so you would set the mid point above exactly halfway so the speed increases rapidly from the start point.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Just starting this DCC stuff. got 2 engines now , Question.. Why do you want to program the starting and top end voltage.. The default for starting is "0". why do you want it different?? I guess the top end is to limit how fast it will go. And what do you set these at,, and how do you decide what voltage to set them
Thanks Bunchs